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Post by eliminator on Mar 29, 2009 9:50:39 GMT
Cleaned the brakes on the Divvy yesterday.
Toothbrush, tissues, brake cleaner, red rubber grease, copper grease.
Pleased with the condition they were in, still glad I did it though, for peace of mind if nothing else. A joy to behold, push one piston back, watch the other one slide out as effortlessly as a ..................... slippery piston in a clean caliper. ;D
Easy to do, just takes a bit of time, if you have any bike and have not done this. Consider doing it, assuming of course that you have the competence, if the previous owner had kept on top of this, i wouldn't have had to renew bits just after i bought the bike.
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Post by amorti on Mar 29, 2009 10:21:53 GMT
I tried to do that on my 600 a couple of weekends ago... but discovered the reason the brakes had got stiff lately was that the dust seals were bulging out past both pistons! Still, didn't take long, and pads (Kyoto) and seals (OEM) from Wemoto came in about £28, so not breaking the bank either. I put tons of red grease behind and between the seals, my logic being the usual cause of issues (and certainly on my one) is corrosion building up behind the seals, and forcing them out of their seats. Lots of grease there, and it should hopefully be OK! You're not really supposed to leave grease on the piston though, it'll only pick up dirt. It is very pleasing going from having to use rag vs. pliers to get a piston out, on to pressing it home with your finger. Remarkably easy to bleed a single, one-sided caliper, too. Brakes are still crap, mind  |
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Post by eliminator on Mar 29, 2009 11:17:11 GMT
That's how mine went, dust seals blown out due to corossion that had got into the groove where the dust seal fits. I think the red rubber grease protects the piston. It does attract the dirt, but keeps the salt from the pistons, main point being it acts as an additional seal, and stops the dust seals blowing. Grandma eggs, sucks, etc. Something that quite surprised me when I replaced the pitons some while ago, was the clearance between piton and caliper. I thought it would be a close tolerance fit, but it isn't. I seem to recall that the pistons are about 0.1mm smaller than the bore, which explains the ingress of muck to the dust seals. |
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Post by CD on Mar 29, 2009 11:42:47 GMT
It's the seal bending that pulls the piston back when you release the brake lever. If the piston was a close fit on the caliper bore it could snag and cause the brake to bind. As the brake pads wear the pistons push a little bit through the seals. If the seals are over-lubricated the piston can push though too easily so the brake sticks on. Been there done that. :-(
I now grease the seal grooves, but wipe off grease from the inside of the seal before fitting the piston using brake fluid as lubricant. I then put lots of red grease behind the dust seal to (hopefully) keep the weather out.
Dont even think about silicone grease - its too slippery so the psiton slips in the seals and the brake binds.
Grannies & eggs R Us
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Post by eliminator on Mar 29, 2009 13:28:25 GMT
I don't see the idea of the seal pulling the piston back once the lever is released. How are pistons pushed out when cleaning them, and not returned after each release?
It's just like pushing anything, stop pushing and the pressure stops.
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Post by amorti on Mar 29, 2009 16:05:37 GMT
They are a little bit. Watch them carefully next time you do it.
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Post by eliminator on Mar 29, 2009 20:23:49 GMT
I realise they return, but don't think this is any mechanicism to do with the seals?
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Post by CD on Apr 1, 2009 11:58:42 GMT
Its the seals wot do it.  In normal use the brake caliper pistons only move a fraction of a millimetre. The master cylinder has a return spring, but its only very light. Most of the brake pad return action is from the seals deforming slightly. It's why even the slightest build up of carp causes the brakes to bind. |
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Post by HRHpenfold on Apr 1, 2009 13:38:57 GMT
Its the seals wot do it. In normal use the brake caliper pistons only move a fraction of a millimetre. The master cylinder has a return spring, but its only very light. Most of the brake pad return action is from the seals deforming slightly. It's why even the slightest build up of carp causes the brakes to bind. you mean its the seals and any uneveness of the disc, the pads have to be very close to the disc in order to work using a small pull on the lever. You clean and lube with rubber grease regulary and the seals will last a lot longer |
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Post by m40man on Apr 1, 2009 13:45:56 GMT
....you mean its the seals and any uneveness of the disc.... I may have some warped discs for sale soon . |
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