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Spring caliper

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florence:

Yes.

It's, effectively, the role of retraction acted by the seal on hydraulic design of all brake calipers, that this is substitute for.

The pads MUST be withdrawn from pressure contact (facilitated by that seal retraction) that makes the system work. They are designed differently with various seal retraction geometry for different caliper designs .... 2 pot, 4 pot, sliding one sided operation .... to make them work as designed via precise retraction dimension.

The spring does this,, in combination with the piston seal to give correct operation.

The largest error in nearly all caliper is when the seal groove, geometry, retraction etc are compromised through build up of dirt etc to restrict retraction movement. This ultimately makes the pads drag continually above design target and leads to "casual" glazing, which wouldn't happen if that operation was entirely fulfilled.

Attention to the seal, groove and assembly pays dividend in brake operation.  There's absolutely no weather sealing on these calipers, maintenance is paramount in keeping them as designed.

The most effective assembly lubricant for the seal is silicone grease as it's most resistant to water ingress, change of consistency in use and can virtually eliminate galvanic corrosion which is prime cause of decay in them.
[/quote]

thank you.  Are you saying the spring is necessary and should not be removed?

K2-K6:
Yes, correct.

The seal on this calliper must move in retraction enough for TWO piston to give correct (non braking) clearance. In doing that, the spring "distributes" that clearance equally across the two pads in relation to the disc face .... IF set correctly.

Too tight an adjustment (set point of screw) and it'll not "take" the correct clearance over to that side as it should. Too loose a setting of screw position and it'll take all of the available clearance over to the fixed pad side, leaving the hydraulic side dragging.

Used harder, extensively, and you'd be adjusting the screw daily in effect. This taking the place of a naturally occurring fully hydraulic system design.

Its a hybrid design with compromised operation. Effective, but needing careful attention to function at it's peak.

florence:
That's excellent advice K2-K6, many thanks.  I will leave mine as is in that case, it is working very well, especially since fitting new master cylinder.

Incidentally, taking your point about exposure to the elements, I have fitted a stainless steel piston as previously was subject to annual rebuild of the calliper, mainly due to all year round riding.  This has markedly improved durability and am now on year 3 without calliper rebuild.

On a separate note, the squeaking problem, I have never been able to solve, even after chamfering pads etc.  Strangely, I have found when the brake is well adjusted and working well, it squeaks loudly.  After a time the squeaking diminishes and so does the braking force.  This indicates time for an adjustment, which I carry out, and the squeak returns.  I am used to this routine and put up with it as a quirk of the machine.

deltarider:

--- Quote from: K2-K6 on July 10, 2025, 10:50:19 AM ---[...] The seal on this calliper must move in retraction enough for TWO piston to give correct [...]
--- End quote ---
I'm afraid I don't understand what you mean by 'TWO piston'.
Let me get this clear: is the design thus that ideally that gap between the disk and pad B remains 0.15mm? Or... 0,075mm on either side of the disk?
I don't know about applying silicone grease on the rubber seal. Opinions differ on this.
On the outside after fitting the seal and piston, yes, silicone grease is fine, but in the groove and on the seal itself, prior to assembly... hmm, I have my doubts. I have done it the last time I renewed the seal and I have the feeling it affects its retraction performance in a negative way (less twisting of the rubber). But to be honest... I am not sure. Next time I will only apply some brake fluid just enough to get seal and piston in and then seal the outside with a silicone grease like ATE.
Addition: free length of that spring on mine is 32,5mm.

Johnwebley:
None of these bikes have 2 piston calipers

But for info, twin piston can have a piston either side of the disc ,in this case the caliper is normally fixed, like the early Lockheed caliper in the 70's

But sometimes a caliper has both pistons on the same side, and the caliper moves, slides or swivels





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