Rear brake capiper leaks

[Frederic Brooks]

Hi:
I rebuilt the rear brake calipers with new seals and dust covers from the dealer. It has only been a week and now it is leaking fluid again

Is there a better set of seals and dust covers; or any better ideas on what to do?

[Nessism]

How did the piston look? If it is pitted you need to replace it. As far as "better seals" go, factory parts is the only way to go when it comes to something like this.

[Zooks]

I disagree about the factory seals. After market can be just as good. They are all made in a factory somewhere. A lot of vehicle manufacturers outsource this sort of stuff anyway. You just need to go with a reputable brand.
I do agree about the pitting or scoring of the piston / cylinder though. Sometimes you can get away with honing the cylinder with a honing tool. Only if it isn't too badly damaged though. Other than that - replace it.

[Frederic Brooks]

Hi Nessism:

The cone does have small pits in it, so looks like a new one is in order. Thanks for the quick reply. Have fun

[Frederic Brooks]

Hi Zooks:

Thanks for the tip on factory seals. The cup does have small pits in it, so I will replace it. Hey have fun.

[Nessism]

I disagree about the factory seals. After market can be just as good. They are all made in a factory somewhere. A lot of vehicle manufacturers outsource this sort of stuff anyway. You just need to go with a reputable brand.
I do agree about the pitting or scoring of the piston / cylinder though. Sometimes you can get away with honing the cylinder with a honing tool. Only if it isn't too badly damaged though. Other than that - replace it.

I don’t mean to start an argument but the brake caliper has a stationary seal held in a groove machined into the bore of the caliper. The critical surface is the piston not the bore, thus honing the bore would do no good and might even damage the groove. A better solution in terms of cleaning the caliper bore is to use a scotchbrite pad, paying particular attention to getting the seal groove clean. Lube the seal with clean brake fluid during assembly.

The factory rebuild parts are relatively cheap considering the critical function they perform. My opinion is to use stock parts when possible for things like this since there is no question as to their suitability, which is something that can’t always be said for aftermarket parts.

[TooManyToys]

As others have mentioned, the two critical surfaces are the piston's OD, and the tangential groove that the O-Ring sits in. The groove is the hardest to clean, but can be wirebrushed with a small brass wirebrush.

O-Rings are not always the same from different manufacturers. The aftermarket sources usually have a standard spec rubber that they use. However, the OE manufacturer may adjust the durometer spec of the O-Ring depending upon the amount of seal rollback they are designing the system to. Caliper rollback equals the total clearance between the pads and rotor.

The amount of rollback is critical in the amount of displacement used when applying the master cylinder, and how much running clearance is needed to prevent the rotors from wearing unevenly, typically, but incorrectly described as rotor warping.