Has anyone had drain back issues with 2nd gen Corvette calipers? There on the rear of a 32 3 window Ford. 1-1/8 bore master cylinder, under the floor. I have installed 2 sets of 2psi check valves from Wildwood. If the car sits a few minutes the Pistons in the calipers retract. Yesterday, I made some .060 shims, 4 total, installed behind each brake pad. Situation improved, but still puzzled as to why the residual pressure check valve isn't doing its job..
Sounds like you may have wrong or mis- installed caliper piston seals ....will Pistons retract with no fluid in caliper ?
I didn't think calipers would retract like a spring loaded shoe. More like minimal runout kept the pads and calipers separate.
The square cut seal on the piston does retract the piston slightly so there is no drag but it should not keep retracting, I would say there would have to be excessive runout of the rotors to retract that much. Is there a pulsation or anything?
you have a newer style pull back seal/boot in the caliper , they do this specailly if the low drag boots were used many of the G racer crowd have them redone this way .
Thanks fellas, the rotors are true. Caliper Pistons will retract when the car is at rest. I wasn't aware of the newer style piston oring designed to do this. I'm thinking that if there was a check valve available with a pressure rating between 2 and 10 psi, the problem could be fixed.
Duh! Brain fart there, these would be calipers used with gms quick take up master cylinder, the calipers retract to ensure no drag for increased fuel mileage etc.
So, I'm told that Wildwood used to offer an adjustable risidual pressure check valve, that's what I need...
the design has been around since the mid 1980's also a hi temp boot will do the same as its stiffer , sometimes they offer a thicker pad to compensate as it allows a higher pedal ( less fluid usage ) . as for the valve its ussually in the master cylinder ( rapid take up ) or ABS units on Oems , that one reason why race guys pump there brakes several times before they go out and play . I would look for a stock style as if its a " race or performance unit " it ussually has these boots
If the callipers are higher than the M/C you will need a 2lb residual valve to prevent fluid flowing back. It needs to be low enough pressure to allow the square profile seals to retract but high enough to hold the weight of the fluid. It almost sounds like you have pad knock off ,caused by the calliper not being perpendicular to the disc [even though the disc is true] Pull the wheels and get somebody to really jump on the brake ,and see if there is calliper or bracket flex.
All good suggestions... I went back and checked the caliper brackets for twist or miss alignment and found everything to be true. The plan will be to make another set of shims, slightly thicker to reduce overal flow requirements unless I run across an adjustable residual pressure valve. Perhaps there's something that will work from a different industry..
Shimming the callipers is not a fix , or you'll need to carry shims for a road trip to compensate for pad wear Check to see if the residual pressure valves are not installed backwards. I would recommend swapping front and rear residual pressure valves around to see if that is the problem [ one could be faulty ] If you have any anti-squeal plates [or any shims] pull them all out ,to eliminate any possibility of springback. Check to see if the pads are straight, I've seen them curved like a leaf spring before [XA Falcon] and also check to see if the pads can slide freely . One last thing, check for side play in the rear wheel bearings [when cold] , your car could settle when parked and cause pad knock-off [ this is why road-racers use rear floaters ]
I'm assuming when you say second gen you mean C2 or the original 4 piston Delco design.... I have don a lot of work with this caliper in race cars and have never seen one " self- retract...". First thing I would do is a caliper rebuild.... If you mean the 84 and later caliper, I believe they have a seal design that can pull back the caliper piston-don't really know them. If so, I think you would need more residual pressure to keep the piston out?
Let me check the year of these calipers and get back with the info. They may be the later design. Thank you all for your suggestion... Oz
It's been awhile and I got back into the coupe brakes. They look like early 80s but I have no way to know for sure. Whoever installed them originally, used front calipers in the rear. After Bakersfield, I'll change them for rears and hook up an e brake. I pulled them one at a time installed a wooden spacer, stood them on end, bleeders straight up instead of 45* There was a tiny bit of air as the pedal responded by not hitting the floor on the first pump. Shame on me for not doing this to begin with...
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