Disc brake woes..

[davidj]

Added my first ever Orange to my constantly changing collection this week. I removed the Avid Juicy3s and fitted some XT brakes. No matter what I do I cannot stop the rear caliper rubbing.

The outside piston is doing 90% of the work and never returns enough to clear the rotor. I have the caliper set out as far as it can go. I have swapped pads and return spring with the front brake, front still works fine. It isn't a comparability issue as it is a Shimano wheelset with Shimano centre lock rotor on a Shimano IS to post bracket and the Shimano caliper and Shimano pads. I have had everything apart to ensure it is all sitting flush and tried another wheel and that is the same.

The XT caliper came second hand and I know it hasn't had much use over the last few years. So would you just keep riding the bike and "exercising" the caliper, bleed the caliper (can it be air at one piston and not the other) or can the calipers be stripped and serviced on the patio in mid November?

Bike is rideable, but it annoys me I cannot get it working as it should.

 

[scottproonly]

Re:

I wouldn't strip a brake that doesn't need bleeding to start with -sometimes it's hard to replicate the factory bleed.
Have you tried lubing the offending piston with a small amount of mineral oil? While you're at it lube both

Kes

 

[davidj]

Re: Re:

I wouldn't strip a brake that doesn't need bleeding to start with -sometimes it's hard to replicate the factory bleed.
Have you tried lubing the offending piston with a small amount of mineral oil? While you're at it lube both

Kes

That sounds doable, thanks.

 

[mattr]

clean first (cotton bud with mineral oil on it) then lube and refit.
Might need to force the sticky piston to come out a bit.

Carefully. If the piston comes all the way out it's easy to damage the seal when you refit it.

 

[davidj]

Re:

I managed to get the sticking piston to come out further by wedging the good piston in place. Not sure how far it can come out though without going too far. I was able to wipe around the edge with mineral oil.

It may be my imagination but I think it is slightly improved, I will ride the bike around a bit and if it is still sticking give it another go next week.

Thanks for your suggestions, at least I am on the right track now.

 

[mattr]

pistons really don't come out as far as you think!
Safer to have it not out far enough, and douse with mineral oil and clean thoroughly. Rather than having it in pieces, easy to clean and impossible to reassemble without damage!

 

[davidj]

Re:

Thanks Matt, seems to be massively improved over the start point following my ride. I will have another go next week when I have finished my shifts and I am sure that will get me to an acceptable place.

 

[davidj]

Re:

After two attempts of following the above suggestions I do believe I now have the lazy piston performing again. I had to strap the working piston in place with a washer and zip tie, after a few strokes of the lever the lazy piston moved enough to let me clean around the edge. I probably have to do a little piston balancing later but right now I am happy to let it work hard.

Looking at the front brake and I may need to do the same, nowhere near as bad as the back but some attention can't hurt.

Thanks again for all your suggestions.