Troubleshooting A Hard Brake Pedal

Here’s a scary scenario we all dread as drivers. You’re cruising down the highway, wind flowing through your hair and “Born to be Wild” pumping from the stereo. Up ahead traffic begins to slow and you gently tap the brakes. To your horror, nothing happens! The pedal is stiff as a plank of wood. You have to practically stand on the brake to slow the vehicle down, but it does so eventually. Phew!

Let’s take a closer look at diagnosing the most frequent causes and solutions related to a hard brake pedal.

Vacuum Pressure

Vacuum – or really lack of vacuum pressure – is the most common cause of a hard brake pedal, and therefore the first thing to look at when a hard pedal is present. Any brake booster (whether from Master Power or any other supplier) needs a vacuum source to operate. In gasoline-powered cars, the engine provides a partial vacuum suitable for the brakes’ power booster. The booster requires 18” of vacuum to operate at full efficiency. Without the proper vacuum level, a brake booster will get a progressively harder pedal and eventually end up at a point where you feel like you are pushing against a wall. Your brake system’s booster works by a series of diaphragms inside the booster and air on both sides of the diaphragm. An improper amount of vacuum creates a scenario where the diaphragms can’t move the pushrod into the master cylinder. When this happens, the pedal gets harder.

If sufficient vacuum isn’t being supplied within the booster, you may have to consider installing an electric vacuum pump, or canister depending on how far below 18-inches the vacuum pressure has dropped. An external vacuum pump is basically an electric motor built to provide vacuum to the booster that your engine can’t provide. It plumbs into the brake system using a vacuum hose going from the booster directly to the pump. This completely removes the engine from the equation and provides the proper vacuum level to the system.

Before jumping directly to a vacuum pump though, there are a couple of quick and simple things that should be investigated. You should look at things like the hose supplying the booster from the engine. The most common problem we see is a person will be using a 3/8” fuel hose. Fuel hose is designed to resist expansion but won’t resist sucking closed like vacuum hose will. The proper hose to ask for is 11/32” vacuum hose. If you are running a fuel hose, when the engine is running and pulling vacuum on the booster, there is a good chance that the hose is sucking shut. If it is sucking shut, there is no chance of a vacuum being pulled on the unit. An obstruction in the hose could also be limiting vacuum contributing to the brake problem, so be sure to check this area thoroughly.

Another quick check would be the location of the vacuum source within the engine and the fittings used to install the vacuum hose. We have seem many instances where people will use a port that is way too small, not allowing the engine to pull the proper vacuum through the fittings. Make sure you are using a port in the intake manifold that is no smaller than a 3/8” NPT.

If all of those things check out within the system, another thing to look at is the actual size of the vacuum booster. Not enough assist within the booster can definitely cause a problem. A brake booster must be properly sized to the automobile that it is installed on. If the booster isn’t of the proper size, proper assist can’t be provided and the pedal will become hard due to the fact that the system is tapped out. At this point, the pedal becomes hard as the booster has done all it can but the vehicle still needs more. This can be the scariest of all scenarios when driving a vehicle.

The vacuum present in the booster is the first, and most obvious problem to consider. Brake boosters require a minimum 18-inch vacuum to operate optimally. The further you dip below this the harder the brake pedal becomes. Following our advice above should set you on the right path, but as always, we are here to get you the right equipment if you need it.

Valving Issues

Another culprit responsible for a hard pedal could be the combination valve, and in particular the Pressure Differential Valve within that valve. This valve is there for safety reasons but can cause headaches if things aren’t working properly.

The Pressure Differential Valve is designed to move should pressure drop on the front side of the valve versus the rear side and vice versa. When this happens, fluid coming from the master cylinder basically hits a wall.

Because the brake fluid can’t be compressed, the pedal becomes rock hard. You still can generate moderate pressure on the “good” side of the valve therefore allowing the car to be driven in a limp home scenario.

This condition is what is commonly known as and referred to as a tripped valve. If your pressure differential valve has been “tripped” it must then be re-centered by equalizing pressure on both sides of the valve. This is accomplished by getting the valve to move the proper direction and therefore putting the valve back in the center. Of course, the problem that caused the valve to “trip” must also be corrected at this time. If your vehicle has OEM disk brakes it is highly likely that it also utilizes some form of valving within the brake system. In this case, the same valve that operates the warning light on your dash – the pressure differential switch – could be the problem creating a hard brake pedal. Follow our plan above to on the right path, but as always, be cautious and employ a professional if you are unsure. Properly operating brakes are essential for safety. We are always here to get you the right equipment or additional help if you need it.

Pedal Ratio

Previously in this series, we addressed a hard brake caused by a tripped pressure differential valve, as well as insufficient vacuum pressure creating a too-hard brake pedal. Here we take up pedal ratio – essentially the relationship between your brake pedal length and where it pivots – an issue that comes to light with some regularity when drivers experience a hard brake.

Pedal ratio is overlooked by most people as a potential root cause of a stiff pedal. This is less of a problem with later muscle cars and more of a problem in earlier street rods when the booster/master is mounted under the vehicle. However, pedal ratio can be as big a problem in either case, so it must be considered as a potential cause for a hard brake pedal.

Pedal ratio refers to the relationship between the pedal’s pivot points and the length of the brake pedal. The pedal is used as a lever to apply motion to the booster (or directly to the master cylinder if your car does not have a power booster) based on the length of the pedal. If the pedal ratio is incorrect by as little as 1/4”, this can allow too little pushrod to move through to the booster. This, in turn prevents the booster from moving the piston into the master cylinder. The hard pedal you are feeling is actually the bottoming out of the pedal and its movement but leaving stroke within the master cylinder and therefore brake pressure at the wheels.

Correcting the pedal ratio can be sometimes difficult if it means moving the pedal pivot. The corrective action though can sometimes be as simple as relocating the connection point of the pushrod between the pedal and the booster. For reference, a power system should have a pedal ratio of 4:1 while a manual brake system should be 6:1.

Pedal ratio is not one of the more obvious causes of hard brake pedals. This is particularly true if the brackets and pedals are all factory installs. However, in cases where modifications have been made, this definitely may be an area worth looking into. Unfortunately during some brake modification processes, pedal ratio is not taken into consideration. After having new brake components installed you will need to reconfigure the pedal ratio to ensure optimum braking performance. Use the tips above or consult a professional mechanic.

Something Else

If it’s not related to the “top 3 reasons” behind a hard brake pedal, there are several additional possible problem spots for you to examine and troubleshoot. A thorough inspection of the whole system should help you identify any such underlying issue.

In a rear drum brake car, a possible area of concern can be your wheel cylinders. As we mentioned before in the article on valving, the wheel cylinders can similarly create a pressure differential problem. If a wheel cylinder is not moving or is frozen, the hydraulic brake fluid reaches that same wall. When that occurs, the pedal won’t move any further because it is not able to compress fluid. This can be a simple repair if that is the case.

It is also important to look at how much brake fluid is in the system and make sure it is not overfilled. If the fluid can’t return completely to the master cylinder, you could have a scenario where the system is hydraulically locked.

As with most complex systems, there any number of things that can go wrong in the brake system of a power booster equipped vehicle. Start by analyzing the most likely scenarios and problem spots first. More often than not, a hard-to-push brake pedal is directly associated with the power booster, master cylinder or pivot point ratio of your brake pedal.

Through a process of elimination you can likely spot the cause of the hard brake pedal, and then take steps to fix it. If you are unsure of the correct action to take, engage a professional mechanic.

Article Courtesy of: Master Power Brakes
Discussion
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92 Responses to “Troubleshooting A Hard Brake Pedal”
  1. Ted

    63 Corvair New master cylinder,new fluid,new wheel cylinders. When driving brake pedal becomes hard and brakes lock. I have to relieve pressure at the master cylinder to move it again? What is the problem?

    Reply
    • Iriya Lee

      The ’63 Corvair is a fun car, and if my sources are correct, the braking system is fairly simple… there is no proportioning valve, rather just a splitter that directs fluid to the front and rear brakes and a single reservoir master cylinder, and power brakes were not available in ’63, (please correct me if I am wrong in this description of your setup, as even my sources aren’t always 100% accurate, as mid year option changes and retrofits sometimes change things in diagnosing a problem).

      Given what you have told me, I would start by replacing the drum brake return springs in the drums, as well as cleaning all brake shoe components and backing plates. I suspect that the springs have become weak and can not push back the shoes, or perhaps there is corrosion inside the backing plates that the shoes are hanging up on and preventing them from returning.

      Even though you stated you had a new master, I wouldn’t rule that out either, as there is a check valve in the Master that maintains 10-12 lbs of residual pressure in the system. It is possible the check valve is faulty and not permitting fluid to return to the master or holding too much residual pressure.

      I hope this helps, and don’t hesitate to let us know what you discover once you dig further into it.

      Wrench Safe, Mark

      Reply
    • Bob Ricewasser

      It sounds to me like your master cyl. pushrod is out of adjustment. There needs to be just a tad of clearance between the tip of the pushrod and the back of the master cylinder piston. Check your service manual for the specification and how to make a special tool to adjust this clearance. What is happening is the when the fluid gets hot, it starts to expand and the master cylinder piston cannot retract all the way, this pressurizing the brake hydraulic system and locking up the brakes.

      Reply
  2. Tae tha' dutchman

    It sound like my brakes are dragging. But once I push the brake it makes a grunt noise then stops the dragging sound. I mean as soon as I barley push the brakes it makes a grunt noise then stop dragging. But when I stop again it starts dragging. What is this?

    Reply
    • Customer Service

      I think you have already diagnosed the problem with your braking system. assuming your car has drum brakes…

      It sounds like the brake shoes are hanging up after braking, it could be weak return springs, rusty backing plates, etc…I would consider opening up the drums and replacing all of the brake hardware and cleaning up the backing plates, and ensure all components are operating properly.

      Reply
  3. Robert

    1962 Grand Prix with 8 lugs wheels requiring maintaining 4 wheel drum brakes. All brake parts, cylinders, springs, hold downs and shoes replaced new 2 years ago. Car came to me with 11 in stock type booster and later dual master cylinder and 10 lb residual valves on both front and rear brake lines. Problem, no matter what I do the rear brakes do almost all the braking plus the rear shoes will gradually drag the drums making the rear brakes much hotter while the front and luke warm. This happens mostly in stop and go traffic at slow to moderate speeds. After driving highway speeds without much braking , I can stop and check drum temps and both front & rear are cool. I feel the problem is the master cyl piston is not allowing the pressure to bleed off after repeated use as in traffic. I have tried adjusting the booster pushrod but to no avail. Can you provide any help? Thank you-Bob

    Reply
    • Customer Service

      You failed to mention if the proportioning valve has been replaced. That would be my first item to replace given the circumstances you have described. I would suggest a good quality adjustable proportioning valve place in the line going to your rear brakes. If you are still running the factory Non-adjustable Proportioning valve it is important to know they ‘DO’ fail over time, and often overlooked by many car enthusiasts.

      Reply
  4. Wayne LaTourette

    I have a 72 lemans,put new master cylinder and brake petal is very hard.I have a bleeder in rear passenger side that’s stripped and I can’t bleed.Also cylinder where pedal depresses master in,is different size than origional.I have no power brakes n drums all around.What’s my first move in solving my problem?

    Reply
    • Wayne LaTourette

      I also bench bled master and bled three wheel cylindrs when installed…

      Reply
    • Customer Service

      Hi Wayne. Sometimes in order to answer a question you need to ask more questions… Sorry about this, but I want to make sure you get the right answer.
      1. You stated the new master, makes the brakes very hard. Are you certain they are harder than they are supposed to be? As non-power brake cars have a firmer pedal feel than power brake cars. many people first driving a non-power brake car believe the pedal seems too hard.
      2. Replace the stripped bleeder. You need to be able to properly bleed the brake system. You can put a vise grip on the bleeder and remove it and purchase a new one at the auto parts store. If all else fails, replace the rear wheel cylinders as then you’ll have new bleeders.

      3. You stated: “Cylinder where pedal depresses master in, is different size than original”. Are you saying the brake pedal rod entering the back of the master cylinder is different in diameter? if that is the case you may have an incorrect master, as it may be for a power brake car. You may need to replace your master with the correct one.
      Sorry for all the questions, but I am certain we can track down the source of your trouble.

      Reply
  5. Robert Brown

    Another problem with hard brake pedal is when some unknowing person has added motor oil (or some other non-brake fluid) to the system. It damages the internal parts and they expand and fluid will not return to master cylinder.. (the voice of experience)

    Reply
  6. Jon

    I had this problem on a 1953 Dodge, the brakes seemed fine for the first 5 miles then the pedal came to the top and very hard, then the brakes shoes starting to drag and got very hot, they were smoking when I finally got home, I bleed the cylinders on each wheel, I took apart the master cylinder and could find no problem there, then I went for a trial ride and same thing happened hot dragging brakes, I noticed that the brake lights stayed on too, I got under the car and ran the pedal adjusting nut out about 1/2 inch. I then heard a noise like fluid squirting, the brake lights went off . The brakes have been fine after that small adjustment. I think the piston in the master cylinder was not retracting enough to allow the brake fluid to return to the master cylinder. I hope this info will help some of you, It was a real pain for me till now.

    Reply
    • Customer Service

      Hi, Roby. My apologies as I am a little unclear as to what problem you are running into…Do you want to upgrade your manual braking system to power brakes? If that is the case you’ll need a vacuum operated brake booster and a Power brake master cylinder. the hornets were offered with power brakes so parts should be easy to come by. Feel free to correct me if I went the wrong direction with your request.

      Reply
  7. Greg

    I recently replaced my brake calipers on my truck, while driving on the highway my truck began to vibrate , this happened before I replaced the calipers with new ones. My brake pedal got hard attempting to pull over.

    Reply
    • Customer Service

      Hi Greg. I am not 100% sure of the problem you are experiencing, so let’s see if I have this correct. You were driving your truck when it began to vibrate “at speed”. You decided to pull over to determine what was wrong and while slowing down you experienced a hard brake pedal. Since then you have replaced the front calipers, I imagine to resolve the hard brake pedal issue and not the vibration issue as that is probably related to something else. As this is a problem that occurred all at once, perhaps it is related to the vacuum system if your car is power brake equipped. Check all the lines to ensure they are all hooked up, also take an engine vacuum check to determine if there is enough vacuum to properly operate the power assist.

      Reply
  8. Sean Canterbury

    my mechanic did a vacuum test and only getting 12, what do you look to repair or replace to get 18? trying to figure out how to proceed, front disc and rear drums, 72 Buick Skylark, 350. any help would GREATLY BE APPRECIATED. thanks

    Reply
    • Customer Service

      Hi, Sean. I would start by checking my ignition timing. Late timing can create a low (8-15 steady) vacuum pressure condition. If the timing checks out okay, unfortunately you’d have to dig deeper. I would do a compression test to help determine the the condition of the rings and valve seat. A loose timing chain can also result in late valve timing and lower vacuum pressure.

      Reply
  9. Sean Canterbury

    sorry forgot to mention HARD BRAKE PEDAL is my issue. booster and master cyc has been replaced.

    Reply
  10. john harris

    87 grandnational ok the brakes are hard to push at first then it graps all of a sudden 5 second delay disconnect electric pump very hard all the time once driving all hard also no brake light could it be accumulator or electric pump

    Reply
    • Customer Service

      We agree with your initial assessment, and suspect it is likely an issue with the pump and/or accumulator.
      We are reaching out to a few industry brake professionals and will update our response should we discover anything new.

      Wrench Safe!

      Reply
    • Customer Service

      We agree with your initial assessment, and suspect it is likely an issue with the pump and/or accumulator.

      We are reaching out to a few industry brake professionals and will update our response should we discover anything new.

      Wrench Safe!

      Reply
  11. Doug

    I have built a 1967 chevelle. It has willwood 4 piston calipers on all 4 corners. I have installed a vacuum pump in the car. It is T ed in the motor. I thought because I was not getting full pressure to the brakes I needed a bigger booster and master cylinder. So I bought a dual action booster and a master cylinder with a 1 1/8 pin. I have found that I have good pressure to the front but the rear when the car is up on blocks does not stop very well at all. When the car is idling in gear I have to really stand on the pedal to make them stop. When there is any throttle they do not stop at all. I have bled all the brakes at least 4 times and I’m at my wits end. Please help me.

    Reply
    • Customer Service

      Hi, Doug. Are you still running the factory distribution block?

      Considering you have converted the entire car to disk brake, that was my first thought.

      I would remove it, run the front brake lines direct. and put an adjustable proportioning valve on the line to the rear brakes.

      Reply
  12. Mike

    I recently purchased a 1964 Rambler. The brake pedal is very stiff and it is very hard to engage the e brake handle. Also pulls to the right under braking.

    Reply
  13. Phillip A Ogle

    I’ve got a 2007 Chevy Malibu LT V6 . When the temp is above 70 degrees F the Brake Pedal gets hard but the brakes apply normally. By applying the E-Brake & releasing it the Brake Pedal drops & isn’t hard. Or let the car set overnight. the pedal goes down.

    Reply
  14. Phillip A Ogle

    The other problem I have with the same vehicle. Is as long as the heater is not in use the the engine temp stays normal. But turn the blower motor on and the engine temp goes up & the recovery tank over flows.

    Reply
  15. Tommy

    I have a 2004 Kia optima.i recently replaced the master cylinder. Cause the brake pedal was locking up after 10 min. after replacing it. And bleeding it and the lines. Now after driving about 15-20 min. The pedal still getting stiff. But nothing like before. After sitting a few hours it becomes spongy . I tried pumping them before starting. The petal stiff. Then when it started it softens up. I’m lost.

    Reply
    • Customer Service

      Hello Tommy,

      I would check the power brake booster, and also inspect the vacuum lines to and from the booster. Although I am not entirely versed in 2004 Kia brake operation specifics.

      Thanks

      Becky
      CCRC Video Membership

      Reply
  16. rhonda

    i own a 1964 chevy pickup. replaced master cylinder, bled brakes, valves, all that stuff, and has been great since (in feb). Now , all the sudden, they are almost locking completely up while driving, and i am un-certain what further steps should be taken

    Reply
    • Customer Service

      Hello Rhonda,

      I hate to do this to you, but we need just a little more information about your braking system to accurately assist you.

      Do you have the stock braking system in your truck? If so, is it power or manual brakes?

      If you have changed or upgraded your braking system: What did you upgrade it to? Disc or drum? Does it have power brakes? What type of proportioning valve is in it? Where is your master cylinder located (on the firewall or beneath the cab)?

      Sorry for all the questions, and we’re looking forward to assisting you.

      Wrench Safe,
      Mark CCRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special offer for your first year membership. http://go.ClassicCarRestorationClub.com/C8414

      Reply
  17. Elliott Jones

    I have a 1975 cadillac coupe deville my brake pedal is hard doing the drive and when it is off. I replaced the booster, master cylinder and proportional valve. When driving for about twenty minutes the front brakes start smelling like their stuck and they also feel stuck. What could it be?

    Reply
    • Customer Service

      Hello Elliott,

      You have replaced many of the components that are likely candidates to create most hard brake pedal issues, but you have in your question identified the next area I would service.
      You mentioned the brake smell like they’re stuck; are they? I would drive the car a bit, then using a hand held infrared thermometer check the temperature of the wheel itself. If the brakes are dragging, the heat will be transferred from the brakes to the wheel. BE CAREFUL, they can get really hot! You can also jack the car up right away and see if the wheel spins freely.
      I would suspect the piston in the front caliper, may not be extracting enough, as collector cars sit for extended periods and the piston can become sticky as corrosion begins to develop in the brake caliper. Additionally I would check the slides on the caliper, these can be pins or slide pads (depending upon make) that allow the caliper to center itself, but can be affected by corrosion as well.
      One note of caution, Don’t assume you calipers are good, just because you had them redone two or three years ago and have only driven a few hundred miles since… I always say, as much can go wrong with a car sitting still as can go wrong being driven every day.

      Wrench Safe,
      Mark CCRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.

      http://go.classiccarrestorationclub.com/C8455

      Reply
      • Rick

        Just got a barn-find low mileage 60 Lincoln. Treadle-vac looked unrebuildable due to storage corrosion on the operating rod so I bought a small diameter booster and split reservoir master to upgrade. Split the lines to front and rear, new hoses and lines and new wheel cylinders. Got the lines bled. But the pedal barely slows the car even with the vacuum line plumbed directly to engine vacuum to make sure no leaks anywhere else. Very hard pedal and no boost. Unsafe to drive and out of ideas to try. Any help would be appreciated!

        Reply
          • Customer Service

            Hello Rick,

            shared your question with Mark C. at Master Power Brakes and he has offered these insights as well:

            Moving away from the factory Treadle-Vac is completely understandable. I don’t know how that particular system operated from a pedal versus Treadle-Vac standpoint. Basically, I don’t know what the factory ratio is. That said, that would be one of the first things I would check. A vacuum booster equipped vehicle should have a brake pedal ration of 4:1 (Here is a link for more understanding: http://www.mpbrakes.com/techtalk/how-to-series/correctly-calculating-pedal-ratio). If the ratio is wrong, the pedal may not be providing the appropriate stroke for the input being given to make anything happen.

            The next thing I would look at is kind of related to one another. The basic question here would be what size of brake booster is being utilized and how much engine vacuum is available? With the weight of the vehicle, I would recommend nothing smaller than an 8” Dual Diaphragm Booster. It is definitely understood that room can be the deciding factor as to what can be used but anything smaller is only promoting the hard brake pedal problem. The vacuum level needs to be 18”.

            I hope this helps and let us know if you have any additional questions.

            Wrench Safe,
            Mark CCRC Video Membership

      • Elliott Jones

        Thanks I replaced the calipers and all the hose and the same problem front brakes still locking up.

        Reply
        • Elliott Jones

          I replaced the rear drums shoes and hardware kit and wheel cylinders and now the rear as well as the front tires are locking up. When I release the screw on the proportional valve for the rear the tires free up. Can it be a faulty proportional valve.

          Reply
  18. angelo

    62 f100. new master cylinder installed. No leakage. All manual drum brakes. No booster. Hard brake pedal but NO fluid going to wheel cylinders even with bleeders completely removed on all 4 wheels. Can’t bleed. Any suggestions? Have bled many brakes in prior years on various vehicles. This truck has set for 3years before I recently purchased. Thank you.

    Reply
    • Customer Service

      Hello Angelo.

      Assuming you still have the original single reservoir master cylinder, I suspect there is either a clog in the line before the splitter or a clog in the splitter or your new master cylinder is faulty (it happens, even with new parts). I would start at the master and loosen the line fitting, put on safety goggles wrap a rag around the fitting and have someone press the brake pedal. If fluid is present and the pedal travels to the floor then the culprit is likely a clogged line. Then loosen the line at the splitter and repeat fluid check process then check the lines as they leave the splitter. We are only trying to discover the source of the obstruction at this point and not concerned with bleeding the system.

      At this point you should have a good idea of where the problem resides, clean and/or replace the affected component then proceed with bleeding the brake system.

      I recently encountered a similar problem on a 1968 Cutlass. The car had been converted to a dual reservoir master cylinder at some point and the owner complained about a lack of brakes, although the brake pedal was hard. We went to bleed the rear brakes and no fluid was present and even with the rear bleeders removed we still had a hard pedal. The Master Cylinder was only a year old, so we found it hard to believe it could be the source of the problem… but we removed the line from the master, held a rag over the open port (wearing safety goggles) and had someone press the brake pedal to determine if fluid was passing through the master. To our surprise we still had a firm pedal and only a drop or two of brake fluid came out of the port. We replaced the master cylinder then everything worked perfectly.

      Wrench Safe,
      Mark CCRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      http://go.ClassicCarRestorationClub.com/C8652

      Reply
  19. Barry

    Have a 1994 f350 4×4 with the 351 w motor purchased used. Had ford dealer look at it for overall repair assessment. New front end, new brakes all the way around. Front is disc, rear is drum. RABSII ABS. All new calipers and pads on front, new wheel cylinder on rear, springs, clips, shoes, drums turned. Still had low pedal, but a pumped up pedal without motor running would move upon starting engine. Two years later started losing brakes, pedal going to the floor, having to pump pedal to stop. Leaking seen on front of booster so remanufactured booster/master cylinder unit from NAPA via Cardone was installed by Ford dealer brakes were working but very disappointed I still had a low pedal, over the course of two months brake pedal got harder and harder to the point now afraid to drive it. I pump pedal, hold and start engine pedal does not move one bit. Pulled hose off booster put a vacuum gauge and get 12-13 inches. I am replacing hose, the hose on it now is a 11/32 marked hose, if it is not enough vacuum, why did I not have this issue with a hard pedal on the booster that got leaked into and had to be replaced. When the replacement M/C and booster was installed all new fluid was put in and rear brakes were inspected and adjusted per the service ticket. I think this engine may have a vacuum cylinder as part of the smog and general operating system. Is it possible the vacuum cylinder (tank) is bad? Any way to test the tank?

    Reply
    • Customer Service

      Hello Barry,

      I suspect the problem with your brakes is related to low vacuum pressure as it should be closer to 18/in.Hg. I would start by checking the vacuum system for leaks then run a diagnostic engine vacuum check. Here is a link to and article that should help.

      https://www.classiccarrestorationclub.com/article/engine-vacuum-troubleshooting/

      Wrench Safe,
      Mark CCRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.

      http://go.ClassicCarRestorationClub.com/C8826

      Reply
  20. Jeff weller

    1969 amc rambler scrambler power front disc drum rear. Replaced master cylinder and rebuilt brass proportioning valve. Still has hard break ped. Could the check valve be stuck on the power brake unit and if so where do i find one or do you know a place that would rebuild it as this only fits this car. Thanks for any help. Sincerely. Jeff.

    Reply
  21. Dulce

    Hi i have a 2000 lexus gs300 my car brake light from my dash board turn on , i drove it from 10 blocks so i can get home as soon as i got home the pedal got hard and it was hard for the the brakes to get its takes like 5 seconds of delay to stop can you tell me what the problem might be please and i check the breake fluid is full so what can it be?

    Reply
    • Customer Service

      Hello Dulce,

      Your 2000 Lexus GS300 falls outside of our areas of expertise here at the Classic Car Restoration Club, but brakes are darn important to the safety of yourself and others and strongly suggest having it towed to a trustworthy service provider or dealership where they’ll have the correct diagnosis equipment for your computer controlled brake system.

      Thanks,
      Mark CCRC Video Membership

      Reply
  22. Kenneth Williams

    I installed front disk brakes on my 1970 chevelle. I bleed all the air out .I have a hard petal with the engine off.But when I start the engine petal goes almost to the floor. I’m not able to lock up the brakes or even to a good stop.My vacuum is around 12lbs .Changed the combination valve no help.

    Reply
  23. greg

    I have a 2005 chevy Silverado 4×4 1500, I replaced pads, drums and rotors and I’m still experiencing the break pedal hard frequently, it also feels like pads are against the rotors while driving putting presume on rotor.

    Reply
    • Customer Service

      Hi Greg. You mentioned it felt like pads were dragging. Are they? It is possible either the caliper piston or the pin slides on the caliper are corroded or stuck. If you drive it a short distance are the wheels getting hot? If you jack it up and spin the wheels are the brakes dragging? If this is the case you may need to replace your calipers and mounting hardware.

      Wrench Safe, Mark-CCRC

      Reply
  24. Richard Duncan

    I have a 1957 Studebaker champion .I have drum brakes on the rear and have been built a disc brake conversion on the front from an 03 Malibu. Once completed the brake pedal gets solid after pumping a few times and will not release pressure unless I bleed it off. Any ideas would be helpful

    Reply
  25. Corey

    I put a new master cylinder&power booster on my 1967 cadilac deville when i try to bleed the brakes the master cylinder is not taken any fluid could it be a got a bad master cylinder from the auto part store.

    Reply
  26. philip

    so I have a 81 chevy c10 and when the brakes are cold they work perfect but when they heat up the become touchy like try to stop and the fronts lockk up easy.i did the front rotors calipers and bearings it helped but not 100 percent

    Reply
  27. James

    Hi I have a 1993 gts25t skyline and when I rev it up ( launch) then brake quickly afterwards my pedal goes rock hard and won’t brake until the revs come down then it’s back to normal..they work good when driving normal and it only happens when I rev??

    Reply
  28. David Griffin

    I have a 1966 Chevelle ss , when you apply the brakes it jerks to the right real bad unless you pump the brakes, and it seems like the brakes are dragging a little for about 5 seconds, the car has drum brakes , need some advice.

    Reply
  29. Larry Hopkins

    Hello, I hope you will be able to help me, I’m helping a friend with a hot rod (30 Ford Touring) I call it a Heinz 57. Anyway this car was working perfectly after a cleanup of some electrical issues my friend asked if I could help with an upgrade of the Master Cylinder. I removed the old cast iron one and he purchased an aluminum one I won’t say the name but it starts with W and ends with wood. It worked flawlessly and was good to go for almost nine months. Then W wood sent him a “recall” so he asked that I remove it so that he could send it to them for “rework” he received it back in a few weeks and then the reinstall of coarse lead to all new fluid and bleeding. Here finally is his (my) problem after the refit hardly any brakes and absolutely no panic skidding. You almost have to stand on the brakes to stop, you could never panic stop.
    No booster installed on this Heinz before or after.
    Residual valves installed 2lb. on the front Disc and 10 lb. on the rear drums, yes; they are installed the correct way (they worked for nine months) before this nightmare.
    A proportional valve was removed when the “reworked” M C was installed, I don’t know how this could have upset the braking on this vehicle but, I’m about to recommend to him to reinstall it. It was removed as it was explained to us that with the use of residual valves it was not needed, True or false?
    W wood has no answers. After they spent considerable time trying to help, they just said go back over everything, one by one. I have and spent much time trying to figure this out. Another friend of his took a shot at figuring it out to no avail. While somewhat vindicated I still feel some responsibility.
    The brake lever, linkage rod, and mounting are the same as when it worked flawlessly. My friend purchased a second MC (same one) thinking there was a problem with the rework still “no joy”.
    Please help us this is not how I intended to spend my retirement.
    Respectfully,
    Shade tree electrical guy.

    Reply
  30. Trent Degenstein

    I have a 1996 Buick skylark 2.4 l intermittent problem with the brake pedal being impossible to push and a growling noise coming from under the hood for about 20 seconds.then the brakes work normal

    Reply
  31. Tommy

    68 Camaro up graded to power brakes new dual diaphragm booster,master cylinder,portion valve located adjusting rod in lower hole in pedal installed vacuum electric pump due to low engine vacuum no air in system when pump comes on vacuum pull’s pedal down a little enough to apply the brakes I can pull pedal back up very easy to release brakes installed a new booster same result vacuum gauge reading 21 hg I have adjusted rod many times l would appreciate any advice thanks

    Reply
  32. Chapy

    Just finishe’d up a full frame up on a 70 cutlass yesterday brakes bled great threw rear we came across one bad caliper changed it this morning now I can’t get any fluid at all out the rear the front bleed fine still and the pedal hard as hell

    Reply
  33. Paul Johnston

    I have a 1954 Mercury Monarch with the treadle-vac brake system. I had the Master cylinder and Booster rebuilt. I installed the rebuilt unit and found that the brake pedal is hard to push down. Slowly it will push down and the brakes will stop the car. When I take my foot off of the brake pedal it will slowly come back up.
    The car has all new brake lines and cylinders. What could the problem be?

    Reply
    • Customer Service

      Hello Paul,

      The Treadle Vac system are relatively simple in design although they are very dependent on good vacuum.

      The symptoms you’ve described are common when there is a failure somewhere in the vacuum systems.

      I would start by connecting a vacuum gauge and running the motor with the vacuum line to the booster disconnected and plugged.

      You should have 16″ to 20″ of Hg on the gauge. Next I would connect the brake system and recheck my vacuum readings.

      If you see a drop in vacuum there is a leak in the system.

      It may be a leaky line, connection, leaky reserve tank, sticky check valve, or in a worse case scenario a leaking newly rebuilt booster (it does happen).

      Check all of the components and replace as needed.

      Wrench Safe,
      Mark CCRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      http://go.ClassicCarRestorationClub.com/C10766

      Reply
  34. Kevin M Fisher

    I have a 1964 Chevelle Ragtop. Just finisher replacing master cylinder which is just a single master no power. Also replaced all wheel cylinders, shoes and cut all drums. Bled system (pedal pumping bleed). Still have to press very hard to stop vehicle even at very low speed. Any thoughts?

    Reply
  35. Kevin M Fisher

    I have a 1964 Chevelle Ragtop. Just finished replacing master cylinder which is just a single master no power. Also replaced all wheel cylinders, shoes springs and cut all drums. Bled system (pedal pumping bleed). Still have to press very hard to stop vehicle even at very low speed. Any thoughts?

    Reply
  36. shadrack

    my Isuzu 2.8 , 2001 model brakes are stiffer when i apply the second pressure when in motion. what is the problem

    Reply
  37. steve gordon

    i have a 2002 jeep grand cherokee. i was driving all day around town with no problems. parked at work for 6 hours and went to leave, the brake pedal was stiff, almost seemed there was no way to stop. i couldnt push hard enough down on the pedal to stop. Not sure what this could be from just sitting 6 hours???

    Reply
  38. Jim Nichols

    ABS Electric High Power/ have a hard brake petal – works once in a while / works mechanically/ electric motor gets hot / It’s in a hot Rod and it sat all winter

    Reply
    • kevin

      1967 1100B International Travelall , 4wd Dana 44 closed knuckle ,small ball,front axle
      Is there a bolt on disc conversion kit available ?
      Also Dana 44 rear axle , Is there a disc conversion kit available ?

      Reply
      • Customer Service

        Hello Kevin,

        As you’re probably aware there just weren’t a lot of ’67 1100b International’s built and of course they are not well embraced by the aftermarket.

        One source I’ve used for disc brake conversion parts for these great trucks is I H Parts America ( http://www.ihpartsamerica.com )

        Best of luck with your project!

        Mark
        Classic Car Restoration Club Video Membership

        Reply
  39. Pete

    I have a hard brake pedal in my 76 TA – I replaced the booster check valve, confirmed 18in vacuum, rebuilt the master cylinder, replaced the brake booster and proportioning valve and replaced the rear brake cylinders. My only other item is to rebuild the front calipers – could this be the culprit? Any help you can provide would be excellent – thank you.

    Pete

    Reply
  40. Mark

    Installed a dual m/c with a 8″ booster on my 55 150, all new lines. The problem I’m having is when I bleed the back brakes, no air but when I bled the front brakes no fluid at all, loosened line at m/c pushed pedal and no fluid, can the push rod not be adjusted correctly?

    Reply
  41. Larry Nicholson

    I have a 1982 Mustang w/302 engine with front disk and rear drum and a master cylinder w/booster, I have a vacuum of 21 inches, I have bled these brakes over and over. With engine off I have a very good high hard brake petal, with engine on my brake petal drops over 2″ and is very good, brakes well, it is just too low a petal, What can cause this 2″ drop in petal height??

    Reply
    • Customer Service

      Hi Larry,

      With the car started the brake pedal should drop, this shows that your brake booster is working.

      2-inches drop does seem excessive, as about 1-inch drop would be expected.

      But you mentioned your brakes were still good.

      The most common reason for low brake pedal is air in the lines, and it sounds like you’ve bled the system.

      I will forward your question to some brake experts, and report back should I hear anything that will steer you in the right direction.

      Wrench Safe,

      Mark
      Classic Car Restoration Club Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      https://go.ClassicCarRestorationClub.com/C12307

      Reply
  42. Ray

    I have O2 Trailblazer the front brakes are dragging really hard in the brake pedal gets really hard to push I’ll pull the from the engine in a releases the air and it will release the brakes it doesn’t happen every time you drive it it takes time for the pressure to build up and then my brakes will drag real bad.

    Reply
  43. Charles

    I have a 1966 Ford Mustang that does not have a brake booster. Continued to brake hard after replacing the master cylinder and disc pads (Factory GT option came with front disc brakes)

    Reply
  44. Vincent Marchisotto

    I ran into this with my juice brake 73 C-65 Rollback years ago . After replacing the booster there was no improvement . Stumped a local shop . I finally took it to a truck repair shop . After they replaced everything in the system, the culprit was sludge buildup in the wheel cylinders ! Cost me $2,000. to find out . Simple & would have been a cheap fix . Since brake cylinders etc. are usually replaced on a resto job, Vehicles that sit for long periods of time/possibly with some moisture in the system could still create this problem . I’d recommend flushing the entire system as a precaution .Hope this helps someone .

    Reply
  45. Roger

    I have a 67 Impala SS with Manual brakes. Replaced all lines, wheel cylinders, and master cylinder. Now pedal is hard and will hardly stop car. Any ideas?

    Reply
  46. Dave

    I am working on a 55 Lincoln capri drum brakes with a vacuum booster that looks new as well as the master cyl. The problem is that when I push on the brake pedal the brakes don’t apply until you get the pedal about 1/3 of the way down then all the brakes slam on and lock all the wheels. The brakes release just fine. I have checked all wheel cylinders and springs everything seem fine. I got involved with after someone else did all the work.Any ideas?

    Reply
  47. Craig Handley

    my manual disc/drum brakes do not stop very well . Pedal will go almost to floor. The M,C was bench bled and the system was power bled. However the brake pedal ratio is 5.3. Everything is new and seems to meet specs. It is scary to stop.

    Reply
  48. Nurse manda

    Love this article! It’s great to be able to understand what the mechanic may be telling us tomorrow. Thanks!

    Reply
  49. Arni

    Why does my isuzu 2.8 1998 model give me brake faliar now the brakes is 100% tomorrow its gone than i must bleed it again.

    Reply
  50. Chester Carson

    Right rear wheel (brake) locks up during storage. Check valve? obstruction in brake line?

    Reply
  51. Ron

    My rear wheels one side is rubbing rear fender the other side is fine .leaf spring are fine axle fine all centered .could it be worn brake drum. Thank you Ron

    Reply
    • Customer Service

      Hello Ron,

      I don’t believe your issue is related to a worn brake drum, as I have had this problem on several cars, especially when fitting oversized tires.

      You failed to mention the year, make and model of the car you’re working on, but often our first suspect is to check that the car body itself if bolted centered on the frame.

      Often we need to loosen all of the body mounting bolts and using ratchet straps pull the body to one side or the other on the frame.

      Depending on the year of your car, many 30s and 40s cars rear leaf springs are narrow and fail to hold the rear axle perfectly centered while driving and cornering.

      If this is the case consider upgrading to wider springs or adding a pan-hard bar to keep the rear centered, and stop chewing up the tires.

      Wrench Safe,

      Mark
      Classic Car Restoration Club Video Membership

      Reply
  52. TOM

    I HAVE OLDER CLASSIC CAR. MY CAR HAS FRONT DICS BRAKES AND REAR DRUMS. REAR BRAKES WERE STICKING, REPLACED EVERY THING.THAN HAD TO REPLACE MASTER CYLINDER AND BOOSTER EVEN WITH CANISTER LOW VACUME BRAKES GET HRD AFTER THREE PUMPS.DONT KNOW WHAT TO DO DON’T WANT TO ADJUST ILDLE TOO HIGH .WITCH WOULD WORK. ????

    Reply
  53. Resa White

    My brakes get hard and rpm goes up and it act like it don’t want to pull. What is that? It don’t do it all the time. What’s going on. 2011 srx cadallic

    Reply
  54. Dana Whisler

    I have a 51 Ford truck with a 2003 crown vic. front brakes and 11″ drum brakes from a 76 Bronco. The brake booster is a corvette type. But the master cylinder and proportioning valve is from a 76 dodge truck. Because with front disc. and rear drums. It has a 1 1/8″ master cylinder. The one inch master cylinder would not produce a brake peddle at all. The booster passes all the standard test. It slides the back brakes on the dirt but not the front brakes and the peddle is hard. The drum brakes are all new, one caliper is new and the other works fine. Any help would be appreciated. Thanks

    Reply
  55. James

    My 1972 olds Cutlass, I replaced 350 engine w/ 455 & 400 trains. Repositioned proportioning valve under master cycl. New master/ Boster. I have the rear tires end off ground, and when putting in drive I can slow down rear tires, but can’t stop them compleatly even putting pressure on peddle. I am only may be pulling 15 lbs of vacuum from eldabrock intake. I have 1 1/8 th inch bore in master. I have done a lot to try and fix this problem. Can you help me troubleshoot this brake problem some ?Thank you

    Reply
  56. Philip

    Having a problem with 1971 AMC Hornet has factory power disc brakes. When applying the brakes it slow you down and you will stop, but if you had to make a panic stop it’s a problem. Replaced everything on braking system (booster,disc pads, turn rotors, wheel cylinders, new rear drums, brake lines, after proportioning valve) still have same problem. Where do I go next? Thanks

    Reply