Disappearing brake fluid.

[toddundy]

Hello, I recently found a 91 XL two door 4WD. The last time it was on the road was 2001. All it took to get it running again was a new fuel pump. It’s in remarkably good condition and I’ve done all the regular tuneup stuff. The problem that has me completely confused by right now is the brakes. I installed new rotors and pads up front and new shoes in the rear, everything went in like it should. After bleeding the brakes I topped it up with Dot 3. Everything feels good going down the road but after it sits for about a week the dash has rear anti-lock warning on as well as the parking brake lights lit. If I top off the fluid again everything‘s fine for another week or so. I’ve pulled off all four wheels looking for leaking brake fluid and nothing. Where it’s parked there is no sign of fluids on the ground. After it sits for more than a few days it always needs the brake fluid topped up and I have no idea where the fluid is going. Any ideas would be much appreciated.

 

[Gary Crist]

The master cylinder may be leaking into the brake booster. The seals in
the master can be damaged when bleeding brakes. Over time a ridge of
crud as well as wear in the bore of the master builds up. If depressed to far
when bleeding, one may damage the seals or "o"rings.

If it is the master, remember to bleed it first before installation.

 

[imp]

The master cylinder may be leaking into the brake booster. The seals in
the master can be damaged when bleeding brakes. Over time a ridge of
crud as well as wear in the bore of the master builds up. If depressed to far
when bleeding, one may damage the seals or "o"rings.

If it is the master, remember to bleed it first before installation.

The brake booster utilizes vacuum. Vacuum will suck in fluid accumulating and burn it up in the engine. No visible leaks.......no wonder!

 

[toddundy]

Thanks for the feedback. As soon as it gets above 20°F I’ll be working on the master cylinder.

 

[1sicbronconut]

Pull the vacuum supply hose out of the booster and use something like a long zip tie to put in there to see if there is any fluid in it.

 

[imp]

Pull the vacuum supply hose out of the booster and use something like a long zip tie to put in there to see if there is any fluid in it.

If the engine vacuum is gobbling brake fluid via the brake booster, the inside of the hose removed from it will be wet with fluid. It SHOULD be dry.

 

[Centaurious]

If the brake booster is full enough to have the big vacuum line suck brake fluid into the engine you will smoke up the area like an old mosquito fogger. it's like you pushed the smokescreen button in a James Bond car. Yes I have seen this on a Ranchero.

 

[imp]

If the brake booster is full enough to have the big vacuum line suck brake fluid into the engine you will smoke up the area like an old mosquito fogger. it's like you pushed the smokescreen button in a James Bond car. Yes I have seen this on a Ranchero.

Yeah, like anything burning oil that's not supposed to. We're thinking of the unobtrusive small crack in a diaphragm which allows only small amounts of fluid leakage.

 

[MakinJeepsWeep!]

If its not the booster you can check the frame and the junction on top of rear axle, ive soon fluid pool in crazy places and have enough time to disperse and dry before it really leaves a mark any where on the ground.