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Old 08-14-2005, 10:56 PM
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1976 Corvette brake problems

I just purchased a 76 vette that has been sitting for about nine months and I am now trying to solve my brake problem. First thing I did was change the front pads and bleed the brakes. They seem to work just fine at first, however I didn't close the bleeder screws all the way so air got back into the system. I've tried bleeding them several times without much luck. I even pressed very hard on the pedal to reset the valve.

I installed speed bleeders and bled them again and again, no luck. I even used a power bleeder, which I must say is the best way to bleed any brake system. After bleeding the brakes I now have a hard pedal and when I press on the pedal I can hear a hissing sound and the engines starts to idle ruff. Can anyone tell me what's going on hear. I have ordered some new front calipers and brake hoses, the old ones appear to be leaking. I will install them as soon as I get them. I am thinking that my power booster has gone bad. What do all you guys think. Any and all help will be greatly appreciated.

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Old 08-15-2005, 05:23 AM
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Corvettes are well known for caliper problems.....Most people went to the stainless steel calipers to remedy these problems....they are quite expensive. I have heard quotes of $2000 to change them all over.
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Old 08-15-2005, 06:05 AM
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You may have a bad brake booster. If the diaphram is leaking it will cause manifold vacuum loss when the brakes are applied.(Which will cause the rough idle).
I've had good results with gravity bleeding on my 74 vette...but the rear of the car has to be jacked up high enough to tilt the master cyl down in the front to avoid trapping air in the front of the cyl.
Corvettes are also notorious for drawing air into the calipers past the seals if the rotors have excessive runout.
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Old 08-15-2005, 07:55 AM
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I am with BT74 on this one.

Brake booster sounds bad. Was probably on the edge and all that pumping finished it off.

Rich
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Old 08-15-2005, 08:07 PM
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Thanks guys for the responses. How do I check to see if it is the booster? Those things aren't cheap and I hate to buy a new one if that doesn't solve the problem.
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Old 08-16-2005, 10:14 AM
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To check the booster, you should do a couple of things. First....with the engine off, pump the pedal several times to release any vacumn in the system. Then with your foot pushing on the brake pedal, start the engine. When the engine starts, the pedal should fall toward the floor about 3/4 of an inch or so. This shows you that the booster is working. If it does not, either the booster is not working or you have a leak in the hose going from the intake manifold to the booster. The leak could be in the hose, the booster itself or in the check valve located in the hose.
One way to check if the booster or valve is leaking is to run the engine for a minute then turn it off and wait a few minutes. Push down on the pedal and see if you can feel some "boost" from the booster or does it feel hard like it is not working? If it feels hard, try the test again but this time before you turn off the engine, pinch the vacumn hose with pair of vice grips upstream of the check valve (between the valve and the booster). Try the test again, if it works this time, you either have a bad check valve or a leaky vacumn hose. If it still doesn't work, it is the booster.
As for getting air in the calipers....Vettes of this vintage had fixed calipers
( they do not slide on pins). If the rotors are not perfectly straight, the caliper pistons will move in and out following the rotor run-out. They will act just like a bellows, sucking in air with the movement and then blowing it through the square cut seal into the fluid chamber. The only real way to fix it is to take the car to a shop with an "on the car lathe" and have the rotors turned on the car. I hope this helps you.
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Old 09-26-2005, 01:30 AM
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Corvette brake problem

Hi Palmtrees. You actually did not mention what your specific brake problem was...not stopping, noise, pulling??? Were you able to get your brakes working properly. I have an old hot rod that was garaged for 5 years and had a hard brake pedal but really didn't stop the car very well. The hot rod weights around 2000 lbs and the 70ish Corvette brakes are huge compared to other brakes I've seen on hot rods. I did have a problem with the remote booster so I bi-pasted it and it is working without problems but I still have to press hard to get it to stop. "Hard is relative" but I do not know what to expect or what is acceptable. I also found bleeding to be critical and made a difference. Also cleaning the calipers on the outside where the rubber cups protect the pistons proved to be beneficial.
Bottom line. Did you fix your problem? Thanks.
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Old 09-26-2005, 06:19 AM
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I had a brake shop power bleed my Vette brakes. It blew my master cylinder and 2 calipers. I didn't feel they knew what they were doing so I took it to the dealer. The dealer bled the brakes with the engine running and the booster line connected. They blew out the other 2 calipers and one of the new ones. The Corvette manual says to bleed the brakes with the engine off and the booster drained of vacuum.
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Old 09-26-2005, 05:01 PM
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When I built my 74 everything was new and I tried all the normal and factory ways to bleed the brakes. I just couldn't get all the air out, so this is what eventually worked. I used a Mighty Vac; using the pressure side to pump fluid, I disconnected the brake lines at the master cylinder, had my wife pump as I opened each bleeder screw, reattached the m/c lines and pumped at a bleeder screw for each m/c line until there were no more air bubbles at the m/c. (open the bleeder when fluid comes out, pump the pump until it pumps only fluid and stick it on the screw). After I did this I had a perfect brake pedal. Vetts are miserable to bleed so I hope this helps..
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Old 09-27-2005, 01:00 AM
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Hey everyone, finally fixed my brakes. Well actually I had a shop fix them. They changed my power booster, entire front brake lines, front calipers and bled the system. Brakes grab very quickly however the pedal seems to travel a little bit too far. I've never driven a corvette before so I don't know how the pedal should feel. It stops just fine so I am not going to complain.

After getting my brakes fixed I sprung a fuel leak from my rubber gas line which runs from the tank down the side to the hard lines. Fuel was spilling all over my mufflers. For those of you who haven't had this problem yet it is not fun to change. You will have to drop your exhaust system, spare tire carrier, and then remove your tank. Once you drop the tank it's quite easy to replace the lines. Stupid me only changed the one that appeared bad. Little did I know that both were bad. After reconnecting everything and starting it up, the other started leaking, or maybe that was the one all along! Well I had to do it all over again. So you guys be smarter than me and change both lines whether it needs it or not. Once again thanks to all who have given advice.
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Old 09-27-2005, 03:21 AM
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The pedal on my 74 always seemed to down further that I would have liked also, but as with yours, they worked so maybe thats just the way they work. Mine went at least 1"-1 1/2" before anything happened then it was firm and quick to stop. Pics in album.
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