Caliper "lip seals"?

[69427]

Don't know what problems you had with your zero tolerance pistons, but the incorrect piston groove dia and not enough "squeeze" on the oring probably was a cause of failure. The oring in a caliper application really is static even though over time and with pad wear the oring will travel in the bore. During breaking operations the oring just distorts, not moves, and the memory in the rubber along with the angle of the bottom of the groove acts a return spring to lessen pad drag. That is why they recommend not using the springs on conversions.

A year or so ago I fooled around with master sizes etc and ended up trying front ss calipers with cup seals and without the springs, but using a 1-1/4" mastr to make up for any pedal loss. So far, so good.
I wonder how the cup seals would hold up with an oring tensioner under them?
If GM had to do it all over agian, they would have probably come up with the D8 design back in 65.

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Its nice to banter with someone who is mechanically astute. The Zero tolerance setup will leak eventually. It would be more robust with a bit tigher interference fit on the o-ring. I'm going to disagree with you that the seal is static, otherwise how would you explain piston knock back? The Zero tolerance pistons are still a rather slopy fit in the bore, i would think because of the large expansion coefficent of the aluminum. Stainless or titanium could be fitted a little tighter. The loose fit allows the pistons to move laterally in the bore. My old SS retrofitted cores are actually worn in the bore because of this effect. Most low mileage cars will never see that. I see a lot of failure modes most don't because of the amount of miles i put on my car.

What you explain above is good theory wise but even with bearings set up with no play the spindle is going to move just a bit during hard cornering or a shock loading event such as hitting a pothole which is going to force the pistons back in the bore. The o-ring seals could really use some force to push them back against the pad and rotor. I've found the wilwood 2 pound inline residual pressure valve makes for a firmer pedal. I believe any fixed caliper setup would need these. I use them with my wilwood calipers. Ya got me thinking there with the residual pressure comment.Do you get any decent modulation with the big 1.25 master?

The wilwood setup has made a world of difference. I don't waste track time letting the brakes cool anymore.

Same experience here. I'm incredibly happy with the track performance of my Wilwoods. I also run stainless steel shims between the pads and pistons to increase the thermal impedance between them.

 

[Grampy]

The initial compression of the ring is only used to develop sealing force for low pressures. At higher pressures the seal ("o" ring, quad ring, lip) distorts with the applied load. Elastomers aren't very stiff. The hydraulic forces try to extrude the seal out between the piston and bore. Under pressure the seal ring is pushed into that little annulus and makes the leak tight seal.

I think the seal is basically static. Knock back is run-out induced and even in a sloppy set-up just a few thousanths. The seals can accomodate that much motion the with elastic distortion.

Grampy