WHERE DID THE FLUID GO?

QA-53Chevy-1

Q:

I have a 1953 Chevrolet pickup. Since I have not had much time or money to work on the old truck, it just sits in my backyard. Recently, I moved it, and when I tried to use my brakes, it seemed as if the master cylinder was dry. I know it is hot out here in Phoenix, AZ, but can this cause the brake system to go dry? Do you have any ideas on how to cure this problem without spending a lot of money? I’m on a tight budget. Andrew McLemore Phoenix, AZ

A:

The reason master cylinders go dry is a leak in the system. It’s a closed, sealed system, so brake fluid would have no way to evaporate from heat. A good course of action would be to fill the master cylinder with brake fluid, and then have someone slowly pump the brake pedal while you explore where it may be leaking. Common leak-prone areas include the back of the master cylinder or any of the four wheel cylinders. You’ll also want to check all of the brake lines as well. Often, the culprits here are the swaged flex lines near the front wheels, or the flex line to the rear axle. Once you know exactly where the leak is, you’ll have a better idea on what needs to be done to fix it. Here’s a note of caution though, protect your eyes when looking for brake fluid leaks! That stuff really hurts if it gets into your eye. If you don’t immediately flush it out it, it can even cause permanent damage. So, be careful, and good luck! Mark Simpson Managing Editor
Discussion
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11 Responses to “WHERE DID THE FLUID GO?”
  1. Sam Stevens

    A quick check of the area beneath the vehicle will likely help identify the general are before putting more fluid in.. Which will leak right back out or make repairs – once repaired have plenty of fluid on hand as you will need it when bleeding after repair. Brake Fluid cycled through the system is Contaminated and should not be collected for reuse… Especially in a vehicle of this age. Discard fluid bled from system in an appropriate manner. Along with safety glasses – protective rubber gloves are recommended.

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  2. Tom McHugh

    I don’t know about this truck but I have an old Mercedes and the master and clutch slave reservoirs are vented to the atmosphere. The fluid will evaporate. I’ve had it happen twice where the fluid level dropped and I pumped air into the system. There were no leaks. My car is a 67 but I have no idea if this was a common practice back then.

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  3. David

    If your car uses a brake servo [booster] The shaft seal into the vacuum chamber, if leaking can draw fluid into your manifold take-off. This then draws the fluid into the engine where it is burned. Check your manifold tube for signs of brake fluid.
    David

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  4. ken sefton

    i have a 1968 firebird with power brakes after driving for a while brake pedal get high and hard front brakes start to hold if i pump brakes it will go away for a while or when i stop and pump brake pedal i replaced the calipers and found a vacuum leak from the intake to the booster any ideas would high temperature brake fluid help

    Reply
    • Customer Service Techs

      Thanks for the question, Your brake issues are a little puzzling, although this may be a case where we need just a little more information from you to help determine what the cause is. However, here are our first thoughts… You mentioned that you’ve replaced the front calipers… Was this car originally a disc brake car (few ’68 Firebirds were), or has it been upgraded? Has the master cylinder been replaced?

      Disc brakes require only 2lbs of residual pressure in the brake lines, while drum brakes require 10-12lbs of residual pressure. The 2lbs of residual pressure is achieved simply by the weight of the fluid in the lines if your master cylinder is located high on the firewall (stock Firebird location). If your car has a drum brake master cylinder, there is a check valve in the master cylinder that maintains a minimum of 10-12lbs of pressure in the line. That is too much for disc brakes and would effectively engage the front brakes even with your foot off the pedal. If you can give us answers to the questions above, We think we can help you track it down.

      Unless you are planning to do very aggressive road course type driving events, or plan on towing heavy loads down steep grades, there is really no need for high-temp brake fluids. We honestly feel your braking issues are not associated to your brake fluid. Although heating of your brake fluid may occur from the failure of your system to fully release the front brakes.

      Thanks again for the question, we look forward to assisting you in narrowing down the source of your Firebird’s problem, as they are great cars to cruise in, and many of us have fond memories made behind the wheel of a late sixties F-body.

      Wrench Safe.

      Reply
  5. Diesel DAN

    I’ve read everyone’s comments below and as one that’s spent a considerable time under vehicles replacing brake parts , I can say yes its a closed system so it shouldn’t evaporate , well that is assuming its working proper in the first place , first were all assuming that’s 100% real brake fluid in that container we see there under the hood , well I can tell ya on barn finds that’s not allways true , why I can tell ya some “imaginative ” things ive found in a reservoir too be , like weed killer , kerosene , oil !! things like that , of course these are things that should not be there , but even weak brake fluid (brown color) is just as bad as these other things folks add in there and I didn’t read anyones ideas on brake lines , why folks allways think that stainless makes a great brake line i’ll never know , when in fact its weaker than steel , more prone to just snapping off and is a total pain to flare !! of course my fav !! is copper coated steel -yes I know they make plastic coated too !! the copper adds that rust resistance we all want and the steel is mighty tough !! but easy to flare ( I do em right on the vehicle too ) and i’ll tell you weather its a 69 mach one above your head or a 24 ton roll pan loader your not gonna want to spend too much time under there !! ohh yes one more thing about disappearing fluid worn out/leaking power brake boosters will draw a vacuum thru the master cylinder and draw the brake fluid all the way into the engine manifold , makes smoke !! I got to experience that !! last year on an ole Torino that had sat since 1977

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  6. Tom

    I think I read all the comments. If the reservoir was empty, and you can’t find a leak, then I think someone mentioned that it may be leaking into the booster. If you basically had no brakes, but the reservoir still had some fluid, it is possible to fail the internal MC seal. That will prevent a pressure build also. This happened to a car I had sitting in the garage for a few years. The internal seals were basically destroyed.

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  7. JOHN SNIGIER

    Often the fluid leaks out on these vehicles during periods of non-use because the fluid leaks past the lips of the piston cups of the wheel cylinders and/or the Master Cylinder when residual pressure is lost. Some hydraulic brake parts manufacturers make new cylinders and/or rebuild kits with special springs and expanders to keep the lips in contact with the bores. EIS Brake parts was a pioneer in this field. Look for parts/kits with cup expanders inside. Peeling back the dust boot on the cylinders will usually reveal where the leak is.

    Reply