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ThingOne
Thrashed
Joined: Mar 05, 2007
Posts: 2,025
Location: 172.20.0.151
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 Posted: Sun 6th Jul 4:51pm Post subject: Xt Brake Caliper Question |
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One of the pistons in my rear XT disc brake keeps sticking, in that one of the pistons comes way out and the other hardly at all.
The short term solution is to hold back the one coming out all the way with a screwdriver and pump the brakes which forces out the other piston, but this solution is only temporary.
How do you free up a sticky piston?.. is it ok to remove the pads and drench in CRC ?.. or is there a recommended method.
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musket
Mangled
Joined: Sep 28, 2002
Posts: 8,572
Location: Transient
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| Posted: Sun 6th Jul 4:53pm Post subject: |
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CRC has no place near bikes.
I've seen mineral fluid used to lubricate XT pistons, but you really need to clear out whatever is causing the friction.
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Wobbler
Mangled
Joined: Nov 21, 2005
Posts: 13,058
Location: doing a skid
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| Posted: Sun 6th Jul 4:53pm Post subject: |
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Remove the pads, clean everything up with a cotton bud and slap some mineral oil on them, pump them in and out a few times slapping some more oil on them.
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Mr_Bob
Mangled
Joined: Apr 14, 2005
Posts: 10,821
Location: Tga
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| Posted: Sun 6th Jul 4:57pm Post subject: |
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Dis assemble brake caliper, pop the pistons out, re-grease seals on the pistons with rubber grease, rebuild, bleed the brake, and it will sort it.
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ThingOne
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Joined: Mar 05, 2007
Posts: 2,025
Location: 172.20.0.151
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| Posted: Sun 6th Jul 5:00pm Post subject: |
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| Mr_Bob wrote: | Dis assemble brake caliper, pop the pistons out, re-grease seals on the pistons with rubber grease, rebuild, bleed the brake, and it will sort it.
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OK, hopefully not too tricky.. What is rubber grease, is regular grease no good?.
Might try the mineral oil trick first, I assume by mineral oil people mean the same stuff used as brake fliuid, You only seem to be able to buy about a litre of that at a time!
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Wobbler
Mangled
Joined: Nov 21, 2005
Posts: 13,058
Location: doing a skid
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| Posted: Sun 6th Jul 5:03pm Post subject: |
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Yeah the brake fluidy stuff, if stuff is coming out as you pump the pistons in and out wipe the parc off and repeat, keep doing it till there is no more tihse coming out, I wouldn't got dissembling xts if you can avoid it due to the mono block carry on.
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Mr_Bob
Mangled
Joined: Apr 14, 2005
Posts: 10,821
Location: Tga
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| Posted: Sun 6th Jul 5:07pm Post subject: |
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rubber grease = sometimes called O-ring grease
it's red and keeps the seals working a lot smoother.
try taking the brake pads out, and try to free up the sticky piston by stopping the one that moves more freely, and squeezing the lever.
then try spraying silicone spray onto the piston, once it's free and moving, then clean the caliper before putting the pads back in, and give it a try.
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Nick_K
Joined: Oct 05, 2004
Posts: 9,712
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| Posted: Sun 6th Jul 5:18pm Post subject: |
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I've also had good luck doing a simple clean and lube.
Remove pads
Pump pistong so they are nearly all the way out
Good clean with hot soapy water toothbrush an earbuds
Lube pistons with the mineral oil you use in the brakes.
Push pistons all the way in and leave them like this overnight.
Problem sorted.
Last edited by Nick_K on Sun 6th Jul 5:51pm; edited 1 time in total |
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ThingOne
Thrashed
Joined: Mar 05, 2007
Posts: 2,025
Location: 172.20.0.151
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| Posted: Sun 6th Jul 5:49pm Post subject: |
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| Nick_K wrote: | I've also had good luck doing a simple clean and lube.
Remove pads
Pump pistong so they are nearly all the way out
Good clean with hot soapy water toothbrush an earbuds
Lube pistons with the mineral oil you use in the brakes.
Push pads all the way in and leave them like this overnight.
Problem sorted. |
Ta, sounds like a job for next weekend.. im knackered, I think riding around with my brake half on didnt help today. 
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Oli
Mangled
Joined: Aug 03, 2005
Posts: 31,885
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| Posted: Sun 6th Jul 6:14pm Post subject: |
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| Nick_K wrote: | I've also had good luck doing a simple clean and lube.
Remove pads
Pump pistons so they are nearly all the way out
Good clean with hot soapy water, toothbrush and/or earbuds
Lube pistons with the mineral oil you use in the brakes.
Push pistons all the way in and leave them like this overnight.
Clean excess oil off.
Problem sorted. |
This works 9 times out of 10.
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konaking
Flogged
Joined: May 28, 2006
Posts: 2,368
Location: Northshore Auckland
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| Posted: Sun 6th Jul 6:16pm Post subject: |
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take pads and pistons out try brake clean
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danose
Mangled
Joined: May 27, 2004
Posts: 10,593
Location: Nose City
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| Posted: Sun 6th Jul 6:22pm Post subject: |
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| Oli wrote: | | Nick_K wrote: | I've also had good luck doing a simple clean and lube.
Remove pads
Pump pistons so they are nearly all the way out
Good clean with hot soapy water, toothbrush and/or earbuds
Lube pistons with the mineral oil you use in the brakes.
Push pistons all the way in and leave them like this overnight.
Clean excess oil off.
Problem sorted. |
This works 9 times out of 10. |
yep - generally it's just trapped crud in the gap between piston and cliper - even quicker solution is pads out, syringe full of ipa into piston gap, cycle piston and watch black crud pour out - repeat a couple of times and all fixed
really common prob down here mid-summer - ultra fine clay dust gums up things beautifully
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Colin
Scheming Dreaming about Singletrack
Joined: Jun 08, 2003
Posts: 5,005
Location: Wellitrack
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| Posted: Sun 6th Jul 6:31pm Post subject: |
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| konaking wrote: | | take pads and pistons out try brake clean |
mean words no could of use punctation anything and random
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jamieinauckland
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Joined: Oct 05, 2005
Posts: 1,455
Location: deep in the bush
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| Posted: Sun 6th Jul 7:04pm Post subject: |
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mineral oils is not brake fluid. Don't put any kind of brake fluid near your brakes. It will rot your seals.
The mineral oil people are on about is just a light form of normal oil. You can buy it from anywhere that sells shimano or Magura stuff.
To lube them, take the wheel off and remove the pads. Slowly pump the lever so about 4mm of piston is showing. Careful that the pistons don't pop out. clean in there with a cotton bud then lube the pistons with some oil. Repeat a few times and they should be sweet. If not they'll need to be stripped and rebuilt.
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Stun
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Joined: Jan 03, 2003
Posts: 35,324
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| Posted: Sun 6th Jul 7:23pm Post subject: |
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| Mr_Bob wrote: | Dis assemble brake caliper, pop the pistons out, re-grease seals on the pistons with rubber grease, rebuild, bleed the brake, and it will sort it.
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This is the last option to go down in my opinion - especially if it's the twin piston XT, vs the old 4 piston jobbie.
First up, try bleeding the brake. The piston may not be retracting properly due to air being trapped in the caliper.
If that doesn't work, try the piston cleaning trick as other have suggested.
The twin piston XTR's have had a few issues with sticky pistons, most of which can be fixed with a VERY thorough bleed.
I've pulled apart a lot of 4 pot XT / Grimeca / XSIV calipers back in the day, and really, it doesn't need to be done until it's completely knackered. Most often, when the pistons are leaking... 
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