S Caliper question

[motogman]

I did some searching to no avail so I will ask the question...

On the S alloy calipers / pistons there is the pin in the caliper and an adjustment device that is loosely cliped into the pistons. I believe this device is for control of retraction. The question is... what is it's purpose and how does it function. Is it to provide piston retraction to enhance pad to rotor clearance off brake or is to limit clearance and knock back for shorter pedal travel. I suspect the later based on the vintage but am curious about the experts opinion.

When I get my calipers back I can get some pictures to post.

[Flieger]

They are anti-knock-back mechanisms. They keep the pistons from retracting too far into the bores and causing a long pedal.

[chris_seven]

Budweg describe these as Damper Pistons.

If you look closely at the 'bush' that clips to the piston there is a bronze liner which contact with the oin.

If you slide the bush gently along pin (no filth intended) then it will clear and allow pads to be installed.

If you move it suddenly then the bush will 'swash' and the resulting misalignment makes seal induced knock back more difficult.

Modern Race Cars tend to use a 'knock back' spring behind the piston or a low pressure check valve in the hydraulic line to achieve the same objective.

[66S]

Isnt that a stack of friction washers in the piston and are they necessary? I plan to omit them on my next S caliper rebuild.

[chris_seven]

I don't know what the guys who refurbish the Aluminium calipers do when they re-anodise but I think you would have to pull out the steel pins or they could react quite badly and contaminate the bath.

I don't know if they refit the pins but the friction moving forwards would be all but immeasurable compared to seal friction.

Cardone in the UK always snap the pins out of the early cast iron calipers the refurbish - which I don't like.

In the limit they are not fitted to any modern calipers so they are not going to be issues about removing them.

When we recondition early calipers we always leave them in and working as it just appeals to our sense of originality.

[davep]

Eric Shea at PMB could say more, but I think his anodizer carefully masks the pins. Certainly, the pins are not removed and reinstalled.

[motogman]

When I talked with a very experienced restorer of P brake mentioned above, he suggested to remove the mechanism from the piston to eliminate the function. This feature was on the earlier calipers but was eliminated in later designs.

[Fishcop]

I've deleted the knock-backs in my S calipers - no issues.