Bicycle Mechanics - help needed with sticking XTR caliper piston
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i've just brought a set of 2007 XTR disk brakes [second-hand], all is good except one of the front pistons doesn't return fully. i've tried prizing them apart fully which is ok, but, when i pull the lever one of the pistons stays a little further in than it should, so if i set the capiler up perfectly with the rota in the middle it mildly rubs on one side.
i could live with this but you can feel it when braking; the sticking side pad is mildly pushing the rota over and the feel is not perfect, like most other brakes you have a lovely feeling of both pads slaping on the rota at the same time. this brake one side makes contact then the other.
i've thought about put a small amount of lube on the sticking piston but i don't what to damage the seals in any way.
any idears on how to get both pistons working prefectly in time together?
08-04-08, 02:45 PM
theres a spring between the pads that pushes them appart(when installed) maybe its damaged...take the pads out and check to see everything is ok. after that
if the pads look ok bleeding the brake is always the easiest thing that you can try
if NEITHER helps...hopefully you know the person you bought them from or can at least get in touch with them. xtr comes with a 3 year warranty for the ORIGINAL owner. hopefully he/she ill be nice enough to go through the process with you.
i would advice against doing anything that would void a warranty even if your mechanically able....using the warranty is always the best choice in imo
08-04-08, 09:38 PM
Yep, check that the spring is in place and the caliper appears to be properly assembled. Assuming that the assembly is good and assuming that the brake lever has good pull and feedback, pull the caliper off the bike and remove the pads to prevent them from being contaminated. Carefully squeeze the lever until the pistons are extended; it's not necessary to extend them all the way. Once the pistons are extended dribble a drop or two of mineral oil on the exposed piston. Squeeze the pistons back into the caliper, squeeze the lever to extend them a bit, and dribble another drop or two. After that, reassemble the caliper and reinstall it ont he bike. Align the caliper position so that the pads don't rub the rotor and tighten the mounting bolts. The brake fluid will help to lubricate a sticking piston.
If the problem is fixed I'd go ride it to give the caliper a workout; don't allow it to sit or you may be doing this all over again. After a few rides and some normal use your caliper should be in good shape. If not, try bleeding the brakes and failing that you may need to rebuild the caliper but I don't know what options you have for that with XTR.
thanks for the help, i'll try those tips out when i get chance
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