I can't ride 45!
Centering/retraction of pistons in XT 4-piston calipers?
I have had a set of XT 4-pot 755's for the past 5+ years and they have been excellent brakes. They have always had a tendancy for the piston on one side of the caliper (the outside on my rear caliper) to expand slightly farther than the two opposing pistons leaving the pads uncentered in the caliper. I can bleed the system, retract the pistons and then center on the rotor but during the ride one side will gradually extend farther than the other and the brake will begin to drag. As the brakes have gotten older the problem is getting more pronounced.
Has anyone seen this before? Clean the calipers perhaps (but how)? Shimano warns agains turning the inner piston does this affect retraction or centering? Is ther anyway to make the pads retract one or two mm more so they are less prone to dragging? Any advice appreciated.
Got 'em on two bikes and had the same problem. First step is to remove wheel, pads, spring etc. Next step is to clean the piston area really well, I use isopropyl alcohol, Q-tips etc. Next, extend the pistons out but not too far or they'll pop right of the caliper. Once you have both sets sticking out, soak the the pistons with Silicon spray lubricant. Let dry for a while and then push the pistons back in until they are flush with caliper. It may take a few tries but eventually any residual dirt will be forced past the piston seals and the action will become smoother. If you perform this simple little maintenance task once every couple of months the problems of dragging, uncentering etc. will lessen and perhaps even disappear.
They are great brakes and oddly enough are getting more of a favorable reputation now that they've been discontinued.
Originally Posted by jasonb
Last edited by lebikerboy; 04-05-2005 at 08:12 PM.
Well its pretty common on any brake system for one side to retract more than the other. One thing you can do is take them off and dismantle them completely. Open up the caliper, remove the pistons and clean everything thoroughly. Takes a while but should leave them like new.
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