Aket

I have a real problem with the brakes on my 1981, when I purchased the car three years ago the owner had put new rotors and calibers on the front. I have since replaced the rear rotors and calipers, all rubber lines, new pads, new master cylinder, and new porportion valve. I have had the power brake boost unit apart and cleaned both filters. After all had been done I had a great brake pedal, I drove it for about 20 miles and went home and parked it to come back out an hour later and go for another drive. On the second drive I started loosing brake pedal and by the time I was back home (15 minutes) I had no pedal and the brake light was on. I checked for leaks and found none. I thought I might have gotten a bad master cyclinder so I replaced it again and the same thing happened no brake pedal after the second time of driving and the brake light is on. I marked the level of fluid in the master cylinder before the drive and checked after the light was on and no change. I sure need some help as I have no idea what to do and am unable to drive the car. I have bled and rebled the brakes on each time and find no air in the lines. Hope some one can help!!!!!!!!!!!! Thanks

page62

One or more of your rotors is likely out of round. Because Corvette calipers have springs behind the pistons, this condition causes the calipers to pump air into the lines, causing the condition you describe. It's fairly common...another forum member should be able to suggest the best fix.

Dalannex

Take your wheels off one at a time and then use some lugnut to run back down the studs to hold the rotor tight to the spindle. The mount a magnetic base dial indicator to the trailing arm and position it against the rotor surface that the brake pad runs on. Turn the rotor all the way around a couple of times to see how much runout there is in your rotors. Also, you may want to take your calipers off, then remount the wheels, then without jacking up the car grab the wheel at 3 and 9 and see how much play is in your wheel bearings, rear especially. Removing the caliper before doing this prevents the caliper from helping to hold the wheel straight and giving you a false reading of play. Check those things, then let us know what you find. Also, how did you bleed the brake system???? You should bleed them closest to the M/C, then farthest away. LF, RF, LR, RR is how I do it.


-Justin

bloodvette80

just a thought, maybe the brake fluid your using is causing it?? :confused:

NHvette

Sounds like the calipers pumping air. This makes sense - since an air pocket
will compress more and make the pressure differential switch in the
distribution block (prop valve) to trip the light on. A rusty hub can help to
cause this, or machining of the rotors themselves. By rotating the rotor on
the hub (5 possible positions), the runout can be measured and minimized.
The idea being that hub runout and rotor runout can compensate for each
other to a degree. Definitely check the wheel bearings, too - as suggested above.

:seeya