WHERE DID THE FLUID GO?
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Whatever you do on a vehicle, wear approved safety glasses, because everything you do regarding the repair of a vehicle can potentially cause damage to your eyes. That includes work you do repairing parts on or off the vehicle. I have a sign on my garage wall that says “Safety First”.
Just food for thought, I’ve experienced this condition with older (70’s) brake booster vehicles. I’ve found the rear compartment of a dual chamber master being drained empty (front chamber stays full) due to the booster vacuum drawing the brake fluid out and into the booster. However to fill a booster with enough brake fluid to get drawn into the intake to cause smoke would require several bottles full of fluid to have been added without checking why..! If the master in question is a single chamber this could still happen, but only if it also has a vacuum booster attached.
These questions are several years past. I doubt my reply would be of any use to the fellow
Wear safety glasses when do this Inspection.
These old chevys love to leak at wheel cylinders
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.
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.
1991 ignition replacement on jeep yj
What’s the purpose of the residual pressure in the brake systems ? I’ve heard many opposite things ; “you don’t need it”, “ it keeps the brakes lightly applied so less pedal travel when brakes applied” , “ it’s needed to allow the brakes to release”
The thought of vacumb drawing off the brake fluid is fascinating , firewall mounted remote reservoirs now are common in the kits and would easily hide a little leakage .
I put front disk kits on a lot of old 4 drum cars .they’re ms always mysterious problems, and as many expert opinions !Ive added vacumb pumps to the old slow idle inline 6’s I put the “easy to install “kits in , because of suspected low volume of vacumb production seemed like it might be a problem . That worked really well on a “cammy” v8 ,but seems to only add mystery problems to the slow ticking 6’s . My biggest issue is a mushy indeterminant pedal with weaker than original brakes, that stay lightly applied and get hot
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
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
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.
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.
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.
We have seen some older makes of master cylinders that did not use a diaphragm between the atmosphere and the fluid reservoir. Although it is often a small vent hole making it difficult for the fluid to ever evaporate the real issue with these systems is fluid contamination. By nature Glycol-ether (DOT 3, 4, and 5.1) brake fluids are hygroscopic<https://en.wikipedia.org/wiki/Hygroscopy> (water absorbing), which means they absorb moisture from the atmosphere under normal humidity levels. Brake fluid by itself is not compressible, however as it absorbs moisture, the water in the fluid is compressible, leading to a spongy feeling brake pedal. If you have a system like this I recommend flushing your brake system annually.
I am surprised, by your claim that your fluid evaporated, although over the years others have claimed the same… years ago we tested this assertion and placed an open bottle brake fluid on the bench of our shop, after more than a year, no noticeable drop in fluid level was detected.
I suspect there was/is a leak in the system on your Mercedes, somewhere, that remains undiscovered. I know we’ve had a few over the years that have eluded us, only to discover them later. If you still have this car I strongly suggest getting it on a lift and having someone pressurize the system several times as you explore for leaks… A small leak can quickly become a loss of braking under the right circumstances.
Thanks for your comment and wrench safe!
Your statement that water is compressible I believe is incorrect. Air in the lines is what causes the brakes to be spongy.
The very best thing you could do for your safety is convert to a dual master cylinder set up.
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.