Changed the brake fluid. No problem bleeding the rear brakes, but both fronts leave a string of really small bubbles in the line coming off the bleeder each time I press the pedal.

Could this be related to the fact that over about 1,000 miles the fluid level in the front reservoir drops about half way? There is no sign of a leak at either caliper or the master cylinder. I don't think fluid is getting into the booster but how can I be sure?

The braking performance hasn't changed since I bought the car but the slow disappearance of brake fluid has always been there so I have no way to know if the brakes are working up to par. They seem to stop very well. All ideas will be greatly appreciated.

 

I just finished the same job on my 94 and witnessed exactly the same symptom. I don't have the disappearing brake fluid problem but thought that I may have induced the bubble problem by opening the bleed screw to far and allowed air to pull in during the down stroke of the brake pedal (?) I really stayed on the front calipers for quite a while doing the bleed routine, until I had six straight strokes of the pedal without any bubbles. My brake system seems greatly improved. Can't offer much else. LOL.
:seeya

 

I would throughly check all joint connections on the brake lines. If you see a wet spot, there's your fix. If for some reason your brake master cylinder is leaking into the booster, you have to replace the master cylinder and possibly the booster too. If brake fluid accumulates in the booster, it may accelerate the wear of the diaphram. If it were my car and I found my master cylinder leaking into the booster, I would just go ahead and change them both just so I could avoid fussing with it in the (quite possibly near) future.

Make sure all your bleeder valves are tighten properly. Sometimes the seating area of the bleeder valves become galled which provents an air tight seal. Also inspect the brake pistons in the calipers for any signs of a wet spots. If thats the case, you can buy a seal set for rebuilding the calipers for just a few bucks.

Rule out the little things before you commit yourself to replacing the expensive parts. BTW, how are you bleeding the brake lines? Sometimes people have goofed bleeding the brake lines which led them to believe that they needed to make expensive repairs when infact they only to needed to correct their procedure for bleeding the brake system.

What ever your cars problem may be, I hope it's an easy fix for you.

 

My bleeding procedure is the good old fashioned method employing my teenaged son as pedal operator. I did the fronts the same way as the rears and there were no bubbles from the rear brakes. There are no wet spots around the calipers or lines. The fact that the same thing happens to both front brakes seems to point to the master cylinder. How can I tell if the master cylinder is leaking into the booster? Will fluid eventually come out somewhere or should I remove the master cylinder from the booster and try to see into the opening there?

BTW, thanks for the good wishes on the repairs!


[Modified by es, 9:48 PM 5/20/2002]

 

I would seperate the master cylinder from the booster and swab the back of the master cylinder with a clean sheet of paper towel. If there is any dampness, the paper towel will absorb the moisture. You won't have to unfasten any of the brake lines to separate the master cylinder from the booster and it's only a matter of of 2 nuts you have to undo from the studs on the booster. I'd say it's worth taking a look. BTW, if I had to make a guess what the problem would be, I'd say it was your master cylinder. If you need to buy any substancial parts, get a hold of 18carfan (Jeff Kopp). I can't say enough kind words about him, he's a true gentleman. He works for a Chevy Dealer out of the midwest (Supieror Chevorlet) and he can get you some great prices on Corvette parts. Stay away from aftermarket or rebuilt parts when dealing with master cylinders or boosters. It's not worth taking a chance on saving a few bucks on such critical system parts. Let us know what you find.

Oh, if fluid is pooling in the booster, it will stay in the booster unless of course you have a crack in the body of the unit.