My brakes went out....but only for a few minutes

[Heffenoche]

So here's the story. I'm driving my 85 FJ60 going down a big hill and my brakes go almost to the floor but I get some braking. When I go to pull over I pump the brakes three time to get the peddle to full height and full stopping power however repeated attempts have the peddle going almost to the floor but do pump up. I check at all wheels and there are no leaks, I also check the master cylinder and the amount of break fluid has not changed. I assume it’s the brake booster. So I decide to limp it home.

Checking on the brakes once or twice shows no change, then about 5 minutes later I need to slow down and the brakes work as normal and continue to the rest of the way home. If I pump the brakes and hold, then start the engine the peddle drops a tiny but which I think is correct. I then took it out for a short test drive and the brakes continue to work flawlessly.

Since the brakes are now working correctly I’m not sure the booster is bad as I originally suspected. With my limit brake knowledge I suspect that maybe the vacuum may have been blocks for a short period but is now open. What else should I check out before assuming everything is ok?

 

[fsusteve]

The booster assists with braking, if it goes the pedal is hard, the brakes just don't stop well. Sounds like air in the system, maybe it worked it's way out or the master's going bad.

 

[atomicpunk]

If your pedal goes to the floor, and there are no leaks from any line or hose, and the fluid level stays the same, it is probably your master cylinder. Try bleeding the brakes, and adjusting the rear brakes first.

 

[djanis99]

I'm an ASE certified tech. It sounds like your brake fluid got too hot and boiled. This is called brake fade and happens when going down mountains or racing (anytime you use your brakes a lot.

Cause: Brake fluid is hygroscopic meaning that it absorbs water from anywhere including the atmosphere. If you open a bottle of brake fluid it will absorb so much water after an hour or so it is no good same thing goes for your brake reservoir. You are supposed to flush your brake fluid every two years because it is assumed that after this time period that the brake fluid has absorbed enough water to make it no good. Flush you brake fluid!!

What happens to brake fluid when it absorbs water? It decreases the boiling point by about 100 degrees f. This decrease in boiling point will cause the brake fluid to boil easier under heavy braking (causing brake fade or a tremendous loss of braking power). The water in your brake fluid also wreaks havoc on the braking system especially newer models with ABS.

I hope that this answers your question or solves your problem

Dave 89fj62 chicago

 

[djanis99]

I forgot to explain that the reason that you lose braking power is that when the fluid boils it realeses air into the braking system. causing a "spongy" pedal

 

[vtcruiser60]

djanis99.....we are going to have a lot of use for you on this Board. Glad to have you.

 

[Heffenoche]

djanis99, I'm not sure if the boiling is my problem because the big hill I was going down was the first time I had used the brakes for a while and it went to the floor the first time I touched them (before that the road was flat). That said I still intend to change the brake fluid. Thanks for the advise.

 

[hj60]

djanis99, I'm not sure if the boiling is my problem because the big hill I was going down was the first time I had used the brakes for a while and it went to the floor the first time I touched them (before that the road was flat). That said I still intend to change the brake fluid. Thanks for the advise.

I'm not ASE certified (yet) but I am a mechanic.
If it's a steep enough hill, it can take seconds to boil a small quantity of brake fluid
at the calipers. And that's all it takes. The normally uncompressable fluid becomes a
highly compressable vapor and a 1/2" bubble at each caliper can be enough to
render your brakes useless. Worst part is they'll now be applied just enough to heat
up even more but not slow you down any, so more fluid can boil.

 

[Jman]

Whoa, now that's a good mini-lesson on brakes! Love this board.

 

[BigSur]

Well what's the answer to this brake question...

Sometimes when i brake and i mean sometimes (maybe 1 or 2 times a week) my brakes become super stiff and i only have to barely touch the brake pedal to stop but other times i gradually press down to stop. Why would my brakes turn into super brakes every once and awhile?

 

[fsusteve]

Well what's the answer to this brake question...

Sometimes when i brake and i mean sometimes (maybe 1 or 2 times a week) my brakes become super stiff and i only have to barely touch the brake pedal to stop but other times i gradually press down to stop. Why would my brakes turn into super brakes every once and awhile?

Mine are actually doing the same thing. I have adjusted them and the pushrod. They seem to do it after using them for a while, which could be explained by brake fade I think. Also could be my rubber hoses are stretching out some.