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A friend of mine has a 79. This weekend he tried to bleed his brakes. HE had a soft low pedal and could not get a drop of fluid out of the rear wheel bleeders. HE recently changed "one" of the rear brake hoses. Any ideas?
Thanks,
Anthony
Well, first of all I'd say that if I were changing the rear brake hoses, I'd change BOTH of them. I'd tell HIM that, too.
There are several possibilities for the bleeding problem that he's experiencing. One of them relates to the fact that the 78-82 Corvette brake distribution block and pressure sensing switch conatins a proportioning function (unlike ALL 67-77 blocks). Another possibility is that a kinked flexible or steel brake line has occurred.
In any event, the very first thing that I would recommend is for him to use a MityVac vacuum pump to apply a vacuum to the rear bleeder valves and see if fluid transfer through the system then occurs. If it does, and I expect it will, the problem is solved. If not, then he'll need to check out some other things. Alternatively, he can use one of the pressure bleeding devices available on the market instead of the MityVac. The results and effect should be about the same as far as establishing fluid transfer.
One pumps up the brakes and then holds down on the pedal even if it goes to the floor. They then say "Down" which tells the other person to crack open the bleeder and allow fluid and air to bleed off.
The bleeder person then closes off the bleeder and says "Up" which tells the person holding the pedal that they can release the pedal and slowly pump more fluid into the lines and back and forth it goes until a solid stream of fluid leaves the bleeder.
Keep a watchful eye on the master cylinder so you don't run it dry or your going to have to possibly re- bleed it as well.
If this is what your already doing, then start back tracking along the system looking for possible kinked lines or as Joe stated proportioning valve block issues. Sometimes a well placed stone can flatten lines causing this issue too. Something to consider.
I agree with Joe, if one flex line is weak, then do both! It's cheap insurance. I think your friend should also look at the fronts as well as they usually take more of a beating and check up worse that the rears.
I have a '78 F-body that had not been driven for a bit. Went to flush the brake fluid and got zero from either rear wheel and it was the proportioning valve. This is a disc/drum setup, but my guess would be a similar proportioning valve/switch as a Y-body. I can not state this with verified data to back it up, but I have heard/read that replacement proportioning valves do not give the same front/rear bias as the original valves. I bought the replacement from a GM dealer and it did have a different external appearance. There is supposedly more front bias, but please keep in mind this was for an F-body.
Anthony, If all else fails, remove the bleeders and see if fluid will drip out of the caliper. I have found more than once that the bleeder can become clogged with rust or pieces of the bad brake hose.
Dan
Thanks for the responses. I don't think he has a Mighty Vac, so I'll recommend he take out the rear bleeders and see what happens. Hopefully clogged bleeders are the problem. This car has been sitting a while. If not, check for kinks in the steel lines, then onto the distribution block. In the meantime I'll tell him to replace "both" hoses.
Thanks again to everyone on this board. The responses/information gives me the little boost I need to try and tackle these problems myself. The advice I receive is indispensable.
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