I bought the 65-82 Brake Kit from Zip Products back on 4/22/2003 to replace the calipers on my 75. I have successfully done this on various Vettes in the past. I replaced the calipers and the brake lines that came with the kit. Bled the brakes using the buddy method several times. After bleeding and testing. The pedal when all the way to the floor. Very little difference in peddle height or feel after multiple bleedings. So I pulled the master cylinder and found that it was leaking at the rear into the power booster. So I replaced the power booster(what a pain) and the master cylinder. Bleed the brakes using the buddy system. Very little or no change to the pedal feel. So I gravity bled the brakes. Again no difference. I gave up and took it to a mechanic that is in our Corvette Club and works on Vettes all the time. He basically checked everything and repeatedly bled the system. No change. He tried a different master cylinder and checked the length on the rod in the power booster. Power bled the brakes. Still no pedal. There are no external leaks. Do you guys have any suggestions? Could one of the calipers be causing the problem?
:banghead: :banghead:

 

All I know is tapping on the calipers to free the air bubbles helps a great deal. Sounds like you have covered all the other bases.

 

How quickly after bleeding do you lose pressure? I know I had one caliper 'sucking air' and it would take a 5 to 10 times breaking before I lost pressure on my manual brakes. It was one of the rears and I had both replaced. Been 4 years with no lose of pressure. You might have some rotor run out causing one of the pistons to pulsate in and out causing it to suck air in. I also had no signs of leaking.

 

Thanks for the responses. I have done the tapping on the calipers. No change. The brakes loose pressure immediately. Turn on the motor, push the pedal. It goes to the floor. If I drive it, the brakes will stop the car but the pedal is mushy and goes to the floor.

 

:confused:
find out which wheels work by slamming the brakes on grass or gravel.


[Modified by Matt Gruber, 11:36 AM 6/10/2003]

 

my guess is that the proportioning valve is stuck to one side.
see brake tips in my sig.

 

For bleeding brakes, check out the product review section, i purchased the motion industries pressure bleeder, $69. by far the BEST tool purchase i have ever made, should have bought this thing 15 years ago. have tried for years to bleed the brakes on the '69 and using this tool was the first "text book" brake bleeed i have accomplished, 15 minutes total time and the brake pedal is the best it has ever been and only used 1 quart of fluid, unlike the gallons i used to push through the system before! the next step(this will only work with rubber lines i think, braided ones i'm not sure of), One thing to try in order to isolate if the problem is with the front, rear, side to side or master cylinder is, using a shop rag so as not to damage your brake lines pinch each rubber brake line closed with a pair of needle nose vise grips, just enough pressure to close the line off. if you pinch all three and you have good pedal then the master cylinder is good and has no air, then remove one vise grip at a time, and when the pedal goes away you know if it is front, rear, or side to side. if with all the lines pinched you do not get a good firm pedal, then there is either air in the M/C or the internal seals are bad(and yes, they can be bad out of the box, happended to me twice). i suggest the motion industries product for bleeding, its basically a converted bug sprayer with all the M/C attachments, but youi couldnt build it for what they are charging, and i had it 3 days after placing the order! hope that at least helps isolate the problem as to what part of the brake system is at fault.

 

Thanks again for the responses. The mechanic was going to check the porportioning valve today. If that doesn't do it then I will try pinching off each calipher at the rubber line to try an isolate the problem.

 

pinching the brake lines is a bad idea. Have you ruled out leaks?

 

Also there was a post about a month or two ago about the same thing turned out to be the wrong booster from AutoZone I believe.
Gary