What is the difference between Zero Tolerance O-ring pistons and other O-ring pistons? I found out about these pistons from a post in the archives tha says after these were installed into their calipers they no longer had problems with leaky, air sucking calipers.

 

I believe Zero Tolerance was the original maker of the o-ring style pistons. I've had mine in service since the early 90s.
If that helps.......

 

I've not heard of "zero tolerance" o ring pistons. the standard O ring calipers are sleeved with stainless steel and are slightly smaller in diameter than stock. The lip seals used in stock and O ring calipers are the same ones, the lip seals adjust to fit. O rings fit a smaller diameter bore, and the sleeves come out correct.

The O ring calipers seem to be more resistant to sucking air, provided that the runout of the rotor is within limits. Too much runout, and nothing will work.

And just for info, I rebuilt my calipers last winter- they were already sleeved, so I cleaned and painted them, installed O ring pistons and slapped them back on after repacking all the wheel bearings. All the rotor runouts were middle to high in what I'd consider acceptable and so far no problems.
I think the recommended limit is .005, but it may be less. I've got one that is .0075. I'm watching all of them, but after 500 miles it's good.

 

My information is a few years old, so I can't stand by it at this time 100%. A few years ago I replaced my lip seal pistons with o-ringed pistons purchased from a major Corvette vendor. The groove in the piston must be machined to receive the O-Ring. Because the o-rings apply more pressure to the caliper bore than the lip seals, the pistons cocked in their bores because there wasn't enough piston skirt to keep it straight with the added pressure from the o-rings. These were the same lip seal pistons machined to accept an o-ring with no other modifications. I then purchased the Zero Tolerance pistons (they were very expensive) but they had a little more skirt area to keep them straight, however, they did not fit the bores properly and I paid a machinist to open up the bores to accept the Zero Tolerance pistons.

There is another issue though, I think Redvetracer used these ZT pistons and because they are solid billet aluminum, on a roadcourse they transmitted a ton of heat to the brake fluid and he experienced significantly reduced braking performance.

If I had it to do all over again, unless the o-ring piston design has been improved (using the same material as stock pistons) I would buy the lip seal pistons/calipers and rebuild them every few years. I have spent a ton of money on my brakes and they aren't that great.
I believe there is another source for these aluminum pistons but I am not sure who it is. At the time ZT was the only game in town and charged accordingly.

Good luck.