
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.
What would cause a Brake pedal on my 1940 Ford slowly get hard and have no free play stuck on the top, can't push down and lock up the back brakes?
Im buying a 1969 ford f -250 w/ a 390 v8 & manual 4 spd transmission with a vramma gear , it has drum brakes front and rear , When i test drove it i hit the brakes at 35 mph and had to use all my strength just to slow the truck to a stop, the fluid is clean and full , no leaks in the wheel cylinders and no visible signs of brake fluid leaks from the power booster , Can i remove the power boost brake system all together? My last 69 f 250 only bad a master cylinder, nothing else , i
I have a stock 1950 Mercury. my problem started a couple of days ago. After driving a few minutes the right front brake starts to drag and the drum gets hot. after the car sits and cools down the drag is gone. Today the brake completely locked and the car wouldn't move. I had a brain storm and I got under the car and opened the bleed valve on that brake cylinder and once a little fluid seeped out the brake retracted and I was able to go home. What can cause this to happen on only one wheel?
1958 Austin a35 hard break pedal for but no breaks
1961 VW bus, no power ANYTHING. Master cylinder, all wheel cylinders, shoes all replaced. Braking is working normally, except, in an emergency situation, quickly stomping on the brake results in almost no pedal travel at all, and no braking at all. If l remove my foot from the pedal, and press again calmly, brakes operate normally again. Please help if you can, as this is quite scary and very dangerous. Thank you.
When stomping on gas pedal in drive, to take off vacuumed hose pops off brake booster. Put hose clamp on it thinking it would stop it, but this caused hose to pull free from intake. WHY is this happening
How to cut air into two? First, find a way to cut air into two. This is a very simple thing. If you just remove one of the two, the other one is just air. So, there is no difference. There is no weight. If you remove the lighter one, the other one is still heavier. It's not the weight that makes it the heavier. The reason why the light one is lighter is because it has less weight. It's actually the weight of the air. It has less weight than the other one. So, that's why the light one is lighter.
One should understand the benefits of car detailing services because it is cheaper but very effective for a good look at a car. Thus, for the same reason, there are some ways mentioned in this blog. All potential workers should read it.
Toyota Runx1,8. After removing the inlet manifold to get to remove and renew starter motor and after reconnecting all the vacuum pipes, the booster brake pedal became hard as a rock. Unable to operate the brakes. Please help to diagnose. Thank you.
I’m running a 3/4 cam with 11to1 pistol’s I’ve been told the cam is taking the vacuum is that the problem?