Brakes failed on the trail

[Max.Powerzz]

I was driving a moderate trail with LOTS of small rocks jutting from the dirt. On a particularly long downhill I switched into low but had to use the brakes occasionally due to tight turns. After about 15 minutes my brakes nearly failed. The brakes started to get spongy and then I lost about 90% of braking power, I could floor it and it would barely slow down. This was scary since I had my wife and 3 year old daughter with me. I put it in 4-low (I was only in 2wd before) and took it really slow. The rims and hubs were extremely hot. After about 15 minutes of not using the brakes they came back.

Did the brakes just overheat? I thought disc brakes didn't overheat as much? Could it be the brake fluid? I just had the brakes totally redone about 7k miles ago.

 

[Felix]

Whoa, that sucks. Not going to weigh in on your braking issues, I'm just glad you and the family are okay!

 

[cruiser88]

How long have you been using the same fluid?

 

[Trapper50cal]

exact

This exact thing happened to me too, last Saturday. Mild dirt road with TONS of washboards, wasn't using the brakes much at all, then went to apply and had to pump them 3 or 4 times to engage, parked it at the campsite, turned it off. I was wondering if a pad had bumped out, thereby make the distance the piston had to travel a lot longer. Checked them and everything seemed fine and present. Next morning they were fine. I think the jostling might have let an air bubble into the resevoir or something. It has to be air based (I think) or the brakes wouldn't have self corrected. I'm just going to bleed them properly (furtherst first and so on) and double check adjustment. WEIRD

 

[Marc311]

Sounds like brake fade. That could happen from brake use (which both of you said you weren't using your brakes much) or a pad dragging. But I don't know how washboard or rocks would cause you to drag a pad.

The other thought would be all that jostling creating foam in the fluid or, if your resevoir was low, maybe the fluid sloshed around enough that some air got pumped in from the master cylinder. But if that happened, one would think the air would still be in there and your brakes would still be spongey. I guess that would lead me back to thinking temp/fade. Hmmmmm.

Not much help - just thinking out loud. I'll be going now.

 

[Trapper50cal]

Think about it though

If air got in the line as a result of jostling the resevoir, the air if large enough would want to rise back out into the res. and disipate, wouldn't it?

 

[lehiguy]

Guys, you both need to check your wheel bearings. Any play will allow the rotor to push the pads away, dramaticly increasing the amount of pedal travel required to engage the brakes. It will usually be manifest when you're off road and the wheels get a pushed around more then when you're on the pavement.

 

[Front Range 4x4]

Hard to know w/o being there but I experienced a very bad case of overheating (smoking!) brakes recently and it sure sounds the same as you stated. Mine was due to trying to stop my 62 and the guy pulling me down a mountain back to pavement after having fuel supply problems and not being able to drive it out.

 

[Trapper50cal]

Wheel bearings

All front wheels bearings just replaced during longfield/knuckle rebuild. Rears looked fine when I replaced 3rd member. Could the front hub nuts have loosened up a bit? wheel would shift back and forth top to bottom if that were the case wouldn't they? Plus brakes came back next morning, still in the woods and were fine throughout getting back to pavement. That's why I thought it wasn't mechanical.

 

[Max.Powerzz]

Whoa, that sucks. Not going to weigh in on your braking issues, I'm just glad you and the family are okay!

Hey, good to hear from you Felix! We love the mountains of UT but we sure do miss DC.

I tried not to ride the brakes too hard but I did use them, especially on the tight turns (with 300 foot drop-offs!). I wonder if I did just overheat them. I've got a buddy across the street who's more mechanically inclined than me, I'll check out the wheel bearing option. Wheel bearings were replaced and repacked about 7k miles ago with the brakes. Once I cooled them down my brakes also came back, similar to Trapper's.

 

[Dynosoar]

Most likely you have OLD brake fluid. Brake fluid is hydroscopic (it attracts and absorbs water). When you activate (use) the brakes the fluid gets hot, really hot +212 deg F this boils the water turning it into water vapor (steam). Water is not compressible, however, steam is. So brakes get hot water turns to water vapor you loose your brakeing water vapor cools and changes back to liquid you regain hydraulic power. This would account for the loss of brakes when hot and the return of hydraulic power when cooled. Brake fluid should be replaced (completely) every 2 years.

Dynosoar

 

[cruiser88]

Most likely you have OLD break fluid. Break fluid is hydroscopic (it attracts and absorbs water). When you activate (use) the breaks the fluid gets hot, really hot +212 deg F this boils the water turning it into water vapor (steam). Water is not compressible, however, steam is. So breaks get hot water turns to water vapor you loose your breaking water vapor cools and changes back to liquid you regain hydraulic power. This would account for the loss of breaks when hot and the return of hydraulic power when cooled. Break fluid should be replaced (completely) every 2 years.

Dynosoar

Thank you....

 

[ntsqd]

Most likely you have OLD break fluid. Break fluid is hydroscopic (it attracts and absorbs water). When you activate (use) the breaks the fluid gets hot, really hot +212 deg F this boils the water turning it into water vapor (steam). Water is not compressible, however, steam is. So breaks get hot water turns to water vapor you loose your breaking water vapor cools and changes back to liquid you regain hydraulic power. This would account for the loss of breaks when hot and the return of hydraulic power when cooled. Break fluid should be replaced (completely) every 2 years.

Dynosoar

The Gold Star answer right there, only I've been told every year.
Yah, I don't do it either......

 

[Trapper50cal]

yup

ditto

 

[cullmancruiser]

Changing brake fluid won't hurt. I experienced severe brake fade after I upgraded to 4Runner calipers and I had new fluid. My problem turned out to be the cheap pads I used to try to save some $$. After installing high performance pads from Axxis my brake fade went away and my overall stopping power improved dramatically. I can lock up my 33's with no problem.
Lesson learned! Don't skimp on brake pads!