Brakes won't hold when engine stalls

[STOUD]

I was midway up a hill climb last weekend when I stalled my Jeep. When the engine died I rolled all the way back down the hill even though I was pushing the brakes as hard as they would go. Once I flattened back out I was able to get it to stop. When the engine is running the brakes work well.

I assume the brakes should still hold pressure enough to stop when the engine dies?

Maybe unrelated but when it is really hot (95+) the front brakes lock up. It started when I was in Guam (2 years ago). I would just pull over a wait 30 mins and it would fix itself. I drove from San Clemente over to Temecula last year and as soon as I got over there the brakes locked up to the point that I could barely over power them to get off the road into a O'Reilly's parking lot. I replaced the calipers just to get home. I haven't had any issues since but I also haven't been back in hot weather.

 

[STOUD]

Can anyone with a manual confirm or deny that their brakes hold after stall?

 

[TJ4Jim]

Can anyone with a manual confirm or deny that their backs hold after stall?

Generally speaking there should not be any mechanical condition that causes a total brake failure except for a brake system hydraulic failure and then the E brake should be available as it is independent of the hydraulic system.

 

[mrblaine]

I was midway up a hill climb last weekend when I stalled my Jeep. When the engine died I rolled all the way back down the hill even though I was pushing the brakes as hard as they would go. Once I flattened back out I was able to get it to stop. When the engine is running the brakes work well.

I assume the brakes should still hold pressure enough to stop when the engine dies?

Maybe unrelated but when it is really hot (95+) the front brakes lock up. It started when I was in Guam (2 years ago). I would just pull over a wait 30 mins and it would fix itself. I drove from San Clemente over to Temecula last year and as soon as I got over there the brakes locked up to the point that I could barely over power them to get off the road into a O'Reilly's parking lot. I replaced the calipers just to get home. I haven't had any issues since but I also haven't been back in hot weather.

How did you bleed them in the parking lot?

 

[STOUD]

How did you bleed them in the parking lot?

When I replaced the calipers in the parking lot last year I had my daughter push the petal to the floor then close the screw. Repeat until no more sputtering and a smooth steady flow of fluid into a Gatorade bottle.

 

[mrblaine]

When I replaced the calipers in the parking lot last year I had my daughter push the petal to the floor then close the screw. Repeat until no more sputtering and a smooth steady flow of fluid into a Gatorade bottle.

If you are losing brakes with the motor off and not pumping them which bleeds off the vacuum, then you need to test for a bad check valve at the booster. Start it, let it run a few moments and then shut it off. You should have enough vacuum for one full pedal application with assist. If not, find out why.

 

[NskLJ]

I have seen a booster push rod too long causing the calipers to lock when hot but not your problem of not wanting to hold on a hill.

 

[mrblaine]

I have seen a booster push rod too long causing the calipers to lock when hot but not your problem of not wanting to hold on a hill.

Yes, but as you know, that will present at any drive length of more than a few blocks. If the fluid can't get into the reservoir through the master bore, then the heat from the rotor moving through the pads or after a few brake uses will cause the fluid to expand. If it can't get into the reservoir, then it pushes the pistons against the pads, create more heat, self applies harder, etc.

If that were the problem, it would have happened with the new pads.

 

[NskLJ]

You are correct, without seeeing the brake system hard to tell why it would not hold. Even without booster assistance you should be able to hold the vehicle. Maybe some parts store brand “ceramic pads”

 

[mrblaine]

Even without booster assistance you should be able to hold the vehicle.

You are very optimistic about the TJ brake system.

Maybe some parts store brand “ceramic pads”

Possible, but we need to find out if he is maintaining vacuum because unassisted they really don't work very well.

 

[NskLJ]

You are very optimistic about the TJ brake system.

Possible, but we need to find out if he is maintaining vacuum because unassisted they really don't work very well.

Yes, I also forgot to look at his profile picture, looks like he has 33 or 35’s. Mine would not stop once I went to the 35’s until I put one of your kits on it.

 

[STOUD]

If you are losing brakes with the motor off and not pumping them which bleeds off the vacuum, then you need to test for a bad check valve at the booster. Start it, let it run a few moments and then shut it off. You should have enough vacuum for one full pedal application with assist. If not, find out why.

Vacuum held for one full pedal. About half for the second. Zero on the third.

I could have went into the black and just started pushing all the pedals on the hill trying to stop.

 

[mrblaine]

Vacuum held for one full pedal. About half for the second. Zero on the third.

I could have went into the black and just started pushing all the pedals on the hill trying to stop.

Booster and check are fine. Don't pump the pedal. Bleeds off any vacuum reserve and any assist that provides.

 

[alittleoff]

Can anyone with a manual confirm or deny that their brakes hold after stall?

Not in my TJ but in my old FJ-40, I can confirm that the brakes can hold that heavy pig on a hill.
What I didn't do was push the clutch pedal in. Instead, I pulled the E-brake out to hold me for a second and then shifted it into reverse. Then after that pucker scare, I let the E-brake off and kept my foot off of the clutch pedal while I cranked it over to start it and idle back down the hill.

You could find a bunny hill to test this on.

 

[Jezza]

If you lost brake assist immediately when the engine died it sounds like a faulty check valve or a leaking brake booster. Unless of course you were pumping the pedal when it died. In which case you usually only get a few good assists before the vacuum reserve is depleted. For what it's worth when I first went turbo the entire guts of the brake booster check valve shot out onto the ground. I'm not sure that it was put together very well.