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08-06-2020, 01:24 PM #1
New pads in XT brakes: separating the rotors
(Oops, said rotors in the headline, what I mean is the pistons)
Have had this problem twice now: when removing old, very worn pads, I cannot separate the pistons wide enough to insert the new pads. I have tried using a tire lever to push them back, and have also removed the brake oil cap to allow the line to bleed as I push on the pistons. In one case I got barely enough room to put the pads in as well as the tire/rotor, but in the most recent case I was not able to get any additional room.
Is this a common problem, or what I am doing wrong?
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08-06-2020, 01:29 PM #2
sometimes non-shimano pads are a bit thicker and have to be sanded down?
if you have not done a bleed in a while, the air in the line will not allow pistons to retract all the way?
if its not dragging much, just shuttle a lap and go 15 km/hour to a stop 10-20 times
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08-06-2020, 01:33 PM #3
Do you mean that there's not enough room to insert the tire lever or you can't push them back with said lever?
I've had to use the angle part of my levers (the hook side) to push on the center of the piston and use the edge of the caliper to create leverage to retract the pistons on XT 4-pots. They do not want to move back...
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08-06-2020, 01:44 PM #4
If the bleed port is open and you still can't push them back, that would indicate a problem with sticky pistons or bungled seals.
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08-06-2020, 01:47 PM #5
OK, you did open the lever all the way back as well? I use a box end wrench to widen the pads.
Well maybe I'm the faggot America
I'm not a part of a redneck agenda
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08-06-2020, 01:47 PM #6mental projection
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Use the old pads as a "cushion" to press the pistons back out. Use a proper tool to push the pistons back. Tire levers will probably be too wide for that. Use a large flat bladed screwdriver or the ParkTool "chisel" If they still don't retract take the cap off the mineral oil reservoir on the lever and attempt to press the pistons back again.
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08-06-2020, 07:38 PM #7
Had some stuck SRAM pistons and followed the Park Tools video to floss the pistons w an old shoelace soaked in isopropyl. Worked like a charm to unstick them.
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08-06-2020, 08:36 PM #8
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08-06-2020, 09:56 PM #9
This is what I do. The old pads are more worn down so its easier to get in between them with a tool to push them back. I use the widest flat head screw driver or sometimes a box end wrench. Anytime I've had trouble I drip some shimano brake fluid around the pistons for lubrication. Usually works.
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08-07-2020, 12:20 AM #10
If you’ve done a lever bleed/fluid top-up partway through the life of your pads, make sure a bleed port is open when you push the pistons back to allow excess fluid to leave. Otherwise you can blow a seal (don’t ask me how I know this).
This sounds like sticky pistons. Pull the lever a few times with no pads in to get the pistons to protrude more (but don’t go too far) and clean them with rubbing alcohol or brake cleaner using a q-tip or flossing with string. Lube the pistons with mineral oil then push the pistons back in. Clean the calipers well to remove any extra mineral oil before putting the new pads in.
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08-07-2020, 09:59 AM #11
Question; have you ever bled the brakes with the pads in instead of using the bleed block?
If so, you might have too much fluid in the system.
Rebleed using the block.
I find it's safer to press in the pistons with the old pads in place. Just use a screwdriver. This helps them to compress evenly and avoids contact to the, somewhat delicate, ceramic pistons.
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08-07-2020, 10:03 AM #12
This worked pretty well -- I had been using tire levers which did not have a lot of leverage. I tried this exactly, but with a thin wrenchy thing, and got them opened up much further -- but still not quite far enough, just a hair short of getting the rotor in. Which would imply sticky pistons. But I hesitate to fully pin it on that since this exact thing happened with XT brakes on another bike, which led me back to operator error. Will try the piston lube method next. Thanks.
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08-07-2020, 10:44 AM #13mental projection
- Join Date
- Feb 2004
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- 208 State
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- 2,577
Like others have said, make sure to remove the new pads before you attempt to lube the pistons with mineral oil. Before even considering putting the new pads back in place be sure to clean the caliper thoroughly with a good contact non-residue cleaner or just some isopropyl alcohol on a rag. Wipe down well or else you'll be replacing the contaminated pads and out $26.
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