brakes on the 72

after i rebuilt all the calipers anf bled the system twice the brakes seemsd to work fine then gradually the brake pedal got softer and softer. the pedal going almost to the floor. the car stops fine except
excseesive pedal travel the brakes grab real quick. there is absolutely no fluid loss. brake pads are all fine. the booster isnt all that old. engine vacuum is correct. not sure if booster would affect engine vacuum or not thx for any help jerome
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JCORVETTE 72&75 wrote:

Sounds like there's still some air in the system; bleed 'em again. Then the only thing I can suggest is that you check run-out between the calipers and the rotors (looking for a warped rotor), as excessive run-out has a tendency to pump air into the system.
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Two things can be wrong here. First is that you still have air in the system. Second, you could be getting a master cylinder failure.
Remember there are 6 bleeders, not 4, that must be bled to get solid pedal. The four rear bleeders are at the TOP of the calipers when mounted, not on each end. Sometimes people put a bleeder screw in the outside lower hole. Do not bleed the lower hole. It should be plugged. The easiest method I have found is gravity bleeding, as it works and is usually foolproof. It is slow, often taking 15 minutes per caliper or more. Have patience and get good results.
Put the car on jackstands.
Remove all four tires.
Fill the master cylinder. If you are using DOT 5 silicone fluid, pour slowly and carefully to prevent air bubbles. Remember to check the MC throughout the bleeding process to be sure the fluid is full. If the MC goes dry, you will have a long time to bleed that air out.
Crack the bleeders on the MC to be sure no air bubbles are trapped there. If you bench bled, there should not be. If the MC has not gone dry, there should not be.
Open a bleeder on the left rear caliper. Wait until fluid comes out. Watch for air bubbles. After you see the last of the bubbles, keep bleeding a short time to be sure there are no more that were just further upstream.
Repeat with the other bleeder on the same caliper.
Bleed the left front caliper. Keep bleeding for a short time after the last bubbles are seen.
Bleed the right front caliper.
Move to the right rear caliper and do this on each bleeder.
Check your pedal. If it still goes soft, repeat the process. However. this time, leave each bleeder open about 15 minutes before checking for air. Remember to keep the MC full during this time. This will flush fluid from the lines out the calipers in case air is trapped in the lines.
If you still have a problem, repeat the long bleed one more time. It is easier to do it once again than replacing the master cylinder. If you still have a failure, then you need to rebuild or replace the master cylinder.
If you are concerned with originality, then you need to rebuild your MC. It is possible that you won't be able to due to rust pitting in the bore, and will need to send it to someone to bore, resleeve, and rebuilt. Some swear by the stainless steel sleeves like the calipers, but others believe that brass sleeves work better in the MC.
Good luck.

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Would this procedure work on a '77? TIA, Frank Bradley......... Veritas Vos Liberabit
after i rebuilt all the calipers anf bled the system twice the brakes<BR>&gt; seemsd to work fine then gradually the brake pedal got softer and<BR>&gt; softer. the pedal going almost to the floor. the car stops fine except<BR>&gt; excseesive pedal travel<BR>&gt; the brakes grab real quick.<BR>&gt; there is absolutely no fluid loss.<BR>&gt; brake pads are all fine.<BR>&gt; the booster isnt all that old.<BR>&gt; engine vacuum is correct. not sure if booster would affect engine vacuum<BR>&gt; or not<BR>&gt; thx for any help<BR>&gt; jerome<BR>&gt;<BR>&gt;<BR>&gt; <A href="http://community.webtv.net/jcorvette/MYMOSAICS ">http://community.webtv.net/jcorvette/MYMOSAICS </A><BR>&gt; <BR><BR></BLOCKQUOTE></BODY></HTML>
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It is the same 1965 to 1982.

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Tnx, Frank Bradley......... Veritas Vos Liberabit
after i rebuilt all the calipers anf bled the system twice the brakes<BR>&gt; seemsd to work fine then gradually the brake pedal got softer and<BR>&gt; softer. the pedal going almost to the floor. the car stops fine except<BR>&gt; excseesive pedal travel<BR>&gt; the brakes grab real quick.<BR>&gt; there is absolutely no fluid loss.<BR>&gt; brake pads are all fine.<BR>&gt; the booster isnt all that old.<BR>&gt; engine vacuum is correct. not sure if booster would affect engine vacuum<BR>&gt; or not<BR>&gt; thx for any help<BR>&gt; jerome<BR>&gt;<BR>&gt;<BR>&gt; <A href="http://community.webtv.net/jcorvette/MYMOSAICS ">http://community.webtv.net/jcorvette/MYMOSAICS </A><BR>&gt; <BR></BLOCKQUOTE></BODY></HTML>
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same thing happened with a 75 vette that I had. it took about 4 times bleeding the system to correct the problem.
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thx guys .i will work on bleeding and checking runout. the MC seems to be fine. we did bench bleed it thx again
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i started on frt wheels of course...right rotor was warped. when i pulled off the right tire the back of tire and wheel were wet from silicone brake fluid i pulled the caliper off and seen where i mess up the piston seals when i repleced them. that can be tricky at times i had the rotors turned and should get it all back to gether today. it still rather hot weather for a non-ac car tho but i will manage. thx for help jerome
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JCORVETTE 72&75 wrote:

Glad to hear you identified the problem.
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