Boiling brake fluid?

[TylerEss]

Hi again, everybody. Just checking in with the latest crisis-of-the-day...

I totally rebuild the suspension and brakes on the convertible. The brakes work well, except every once in a while, they barely work at all! About once per week, the pedal will just sink to the floor (along with my heart!) and the car will barely slow down at all.

It just happened a few minutes ago, on the expressway. I babied the car home at about 15MPH and put it in the driveway. Came in to get a 3/8ths wrench in case I needed to work on the brakelines. When I got back outside to the car, the brakes are working fine again!

I can't keep this up; it's dangerous. Any suggestions as to what's happening?

Two leads:

One: junkyard prop valve might be flaky.

Two: I did have to run a new pass. rear brakeline under the fuel tank. It comes a little close to the exhaust, but it doesn't seem too close. I don't think it's any closer than the passenger front line comes to the turbocharger.

Any way to tell if maybe the brake fluid is boiling from being too close to the exhaust or turbo?

Eeeep!

[JDAWG]

well if it too close to the exhaust i guess it could, did a search and came up with 284* as a boiling point. More than likely though you have air in it some where, get a few pints and a buddy and bleed it and rebleed it as much as you can.

[looneytuner]

rebuilt master cylinder? Apply light pressure to the brake pedal and see if it sinks ever so slowly. Rebuilds have more tendency to do this under light brake pressure.

[turbovanman²]

Did you replace the MC, if yes and its a rebuilt, throw the piece of sh*t in the trash can and buy a NEW one. It should be illegal to sell rebuilt MC's. If its your original, its shot. Install a NEW one, be sure to bench bleed before you install it.

[TylerEss]

One thing I did find is that one of the fittings on the prop valve was weeping. If it can let fluid out, I'm sure it can let air in, too... When I bled that line, there was tons of air in it. Tightened that fitting so it's not weeping now. Maybe that'll help fix this.

Once I bleed it some more, I'll try the gentle pressure test.

I'll probably eventually replace the MC anyway (since I replaced everything else!), but right now I'm not so much with the employment. If the current MC is safe, I'd rather save the money. If its unsafe, I'd rather replace it than die!

Is there any way to test it for sure? It is the original MC.

[looneytuner]

The rebuilds go with no warning. New ones generally give you the sinking pedal.

[TylerEss]

Allright. This one is a "new" (original, but never rebuilt) and the pedal is as hard as the Rock of Gibraltar. With either gentle pressure or "as hard as I can push" it just stays put.

I think I'll keep the car in town for a few weeks, where at least I'm not likely to *die* from a brake failure. It seems like it should be safe now, but I won't take my chances on the freeway until it's proved itself with time. I'll buy a new MC as insurance when I can afford it.