Brake caliper piston seal design

[Philrock]

Some time ago, there was a discussion of Brake Caliper sealing in thread108-98668 . This thread is now closed, but I would like to re-visit the topic. There was mention of o-rings that are trapezoidal in cross section. When pressure is applied, the o-ring distorts, and when pressure is released, the o-ring returns to its original shape, helping to retract the piston. This is in a design where the seal is in a groove in the cylinder wall.

I would be interested in seeing more detail on such designs. I spent some time searching on the web, but got nowhere.

 

[MikeHalloran]

I think the current typical design uses a square cut ring in a trapezoidal groove, which is easier to machine than a square groove. Essentially the same deal.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

My impression is the same as Mikes.

It really is a very simple device. The only complexity is the relationship between the flexibility of the rubber ring and the friction on the piston and the force required to retract the piston. Oh and keeping it the same on both wheels is another important point.

Regards
Pat
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[MikeHalloran]

The current design has simple geometry, but it's the result of decades of evolution, or devolution.

Early disc brake seals and retraction mechanisms were very complex. Most of them worked when new, but didn't age well.

Simplicity won out, but _everything_ to do with that seal is now critical; surface finishes, dimensions, hardness, changes in hardness with age, fluid compatibility, all that stuff.



Mike Halloran
Pembroke Pines, FL, USA