76 brake problem

[k9judge]

Just put two new calipers on the front. The back two calipers were not touched as they appeared to be ok. Drove two weeks, then low pedal and brake light came on. Air seems to have gotten into the back brakes somehow. Any ideas how this could have happend? Back brakes were bled and pedal came back up and brake light went off.
Denny

 

[wolf_walker]

Did you bleed everything right when you put the calipers on the front?


If so, you may well have out of true disk's on the rear, that will cause pumping in the rear that can pull air in. It's a very "vette" thing...

 

[69MyWay]

K9judge,

Sounds like air in there. It seems like the brakes will start to fail after one or two other things go bad.

I would also take a close look at the master cylinder, and of course inspect those rear calipers. Something is letting air in.

Normally I would say that you are out of true round in the rear, but if they worked fine before the front failed, and you did not remove the rear rotors, then is must just be a typical failure.


Good luck.


BTW, my wife and mother in law use to raise beagles. Now, they do some part time judging at local/regional shows. Would K9Judge have anything to do with that too?

 

[Nut]

K9judge,

This sounds more like cavitating caliper pistons. One or more of your rotors are just ever-so out of round and this causes the pistons in your calipers to cavitate. And like Wolf said, it is a "Vette thing". The cavitating will cause air to be sucked into the calipers and yet not a leak anywhere. Having the rotors turned and trued to each bearing assembly should clear up the problem. This assuming of course the other items Chris mentioned are OK.

Good luck. It's not a hard problem to correct.

.............. Nut

 

[wolf_walker]

One thing I never quiteunderstood is exactly where it gets the air in at? You would think it would leak visably. Guess that's one or the reasons so many people overlook the rear rotors though...

 

[Nut]

Wolf,

The air gets sucked in at the rubber rings around the pistons. The newer O-Ring designs from Vette Brakes cures this problem. They are worth the small $$ to get. Haven't had a lick of a problem since.

........... Nut

 

[wolf_walker]

Well I figured it got in there.. Just how does it enter a solid piece of rubber that's fluid tight? I wouldnt think it could move the piston off canter enough, but..?

 

[JohnZ]

Chevrolet issued a Technical Service Bulletin in 1982 (which isn't in any of the pre-1982 Shop Manuals, naturally) instructing dealers to use a silastic sealer in the piston grooves where the boot seal goes and on the outside of the boot seal where it presses into the caliper bore, to eliminate moisture intrusion past the seal that could cause corrosion and air intrusion past it that could cause a low pedal, any time they rebuilt Corvette calipers. The TSB was very specific about the importance of having the groove in the piston and the seal bore of the caliper absolutely clean and dry before applying the silastic sealer so it would adhere to those surfaces.

There was only one more production year left on that caliper design once they finally owned up to the corrosion and "air-pumping" problems with it, so they weren't about to do a redesign; the sealer application was the "field fix".