Caliper Issues, 2009 version of Shimano XT, BR M775 brake caliper
Ive had this set for over 4 years, with no issue until now. In the last weeks, ive noted some brake drag because the inside pad does not extend like the outboard side. It seems this causes the outside pad to have to extend further and when I take my hand off the lever, the outside pad does not retract all the way, thus causing the outside pad to rub.
I tried to recenter the caliper in various ways to fix this, but to no avail.
The brake lever still feel fine and braking performance is still great, except for the pad rub.
The brakes have not been bled for a year or so, but like I said, lever feel and performance is still good, its just that the inside pad does not extend like the outside pad.
Would a bleed help this? Is there a way to rebuild these brakes, meaning can you take them apart and clean the parts?
Any advice is appreciated.
No, a bleed most likely would not help, a tear down and rebuild with new seals is probably what's in order. You could try removing the pads and applying some mineral oil onto the piston and hopefully lubricating the seal, then working it in and out to "un-stick" it.
Thanks for your help. So they can be rebuilt. Do they sell a seal kit. How difficult of a job is that?
Have you tried resetting the pistons back into the caliper and letting them auto-readjust?
Use a tire lever to work them back into the caliper housing which should reset them. If that does not work they may need a rebuild and new seals like the guy above said.
I agree with subsist and also put a bit of SHIMANO mineral oil on the pistons and work them in and out (be careful not to pop them out by going to far). I use a cotton swab.
I had tried to push the pistons back in and reset them several times before I created this thread. I should have mentioned that.
Last night I followed a procedure I found elsewhere on them internets and it seems to work better, but not yet perfect. I held the ouside/working piston in by levering a hex wrench and worked the brake lever to force the inside/stuck piston out. For some reason, when the the outside/working piston is held in, the inside/stuck piston moves much better. Once it was out, I cleaned the piston area with alcohol, pushed it back in with a tire lever, and then repeated several times. I then forced out the stuck piston again and bathed it in shimano mineral oil, forced it back in and repeated several times.
It now works much better, although the inside still does not move as freely as the outside.
I would like to rebuild it, but I cannot find any seals for sale anywhere. Any advice on this?
I had the same issue before. Do you have the yellow bleed block? After lubing the pistons and pushing them in, put the bleed block in and give the lever several hard squeezes to reset the position of the pistons. This step sets the pistons at the correct spacing before you put in the pads. I this works, then the caliper will be fine. If the problem still exists, then there might be issue with the seals, but try this first. Also, as far as I know, Shimano does not sell a seal kit, but i may be wrong.
I would first try the bleed block as above, if really does not work well, replacement may be the best option. Unfortunately, Shimano does not sell rebuild kits. You can contact them to see if they will rebuild it, but it may not be worth it with shipping, parts and such. All Shimano Hydro calipers will work (assuming the proper hose connection, some use straight others banjo). SLX calipers (new with pads are going for $44 @ Universal cycles but may not have the right fitting, I don't recall which the M775 uses) will work or eBay has had a bunch over the years, SLX, LX, XT, ...
I did not have the bleed block, so I used a 10mm hex, which the Park tools website directions indicated was a good substitute
Thanks for your help guys. Its working much better than it was. Eventually I'll probably upgrade to the XT 785s, but Im going to try to get through this season on this set
Last edited by rth009; 08-17-2013 at 08:01 AM.
Reason: question answered
Regarding seals, in the following two threads someone got some custom made seals made to convert a Avid brake caliper to use mineral oil instead of dot fluid for a very cheap price.
If he could get seals made then I see no reason why other people couldn't get seals made to fit a Shimano brake caliper, you'd need to get the exact seal measurements and shape, you'd also need to find someone that could make them and they'd need to be made from the right material. There might even be commercially made seals available of the right measurements, shape and material that would work if you know where to look for them.
Changing caliper seals from DOT to Mineral compatible
Switching between mineral and synthetic oil (rainy day)(no TL;DR)(no chlamydibrah)
Yes, that actually will work fine, just rubber band it in...from experience, it can fall out and the piston can then come out.
I've seen a updated post on another forum thread about his converted brakes, he stripped down the caliper he was having a problem with and rebuilt it.
He said the following:
YEAH BABY, YEAH !!!
Now the brakes are working properly !!
The power is now brilliant and I can get 90% of full braking power (and I mean FULL braking power) from the hoods with one finger, and the modulation is great.
The brakes work even better than I can have imagined at the start.
Last edited by cobba; 08-16-2013 at 05:28 PM.
Just thougt Id post back and say after, cleaning the calipers real well, bathing them in Shimano mineral oil, resetting the calipers with a 10mmhex (with a wrap of electrical tape around it to expand it slightly), and then a bleed, the brakes are working as well as ever again, so IM not going to bother with trying to get seals to rebuild. Thanks again.
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