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Now then. I bought a second hand bike which has shimano deore XT brakes front and back. The back ones are working perfectly but the front ones aren't providing much stopping power and are squealing like a humourous simile.
So far I've...
- Bled the brake line 3 times, which has included taking the lever off and suspending it for a bit to try and get any air out of the line and into the master cylinder. I got quite a bit of air out the first two times but the third time it looked fine.
- Had a look at the pads - they look fine.
- Roughed up the pads and the rotor with a bit of coarse sandpaper.
- Cleaned the rotor with isopropyl alcohol before and after roughing them up.
... but they're still not working. The only other thing I can think off is that there's some contamination in the pads / rotor that I've not been able to get rid off and which (I guess) would require me to buy a new rotor and set of pads.
Is there anything I'm missing? Should I just take it down the LBS? Should I just buy the new pads and rotor?
Ta
Bake the pads in the oven.
sounds like something contaminated
check for leak at hose connection to caliper and around pistons
if pads have been contaminated, you can sometimes clean them back to workable, but replace them, something non-squealy
Why not. They're[url= http://www.chainreactioncycles.com/shimano-xtr-xt-slx-alfine-j-type-disc-brake-pads/rp-prod130823 ] these pads[/url] - i.e. they've got bits of ?ceramic? attached to them. Will they be ok in the oven?
See the link in my post above.
Bake the pads in the oven.
Having read through that - well, most of that - I'll give it a try. Worst comes to the worst I'll just melt the fins somehow and have to buy some new pads and a new oven. Thanks for the advice.
When you bleed the brakes have the free stroke screw as far out as possible and the lever out as far as it will go.. push fluid up into the screw in funnel and then suck it back down and push back up.
I do this until I don't see any bubbles coming out..tap the hoses and hardware during to..
Tighten the nipple..
Then keep squeezing the lever until no more tiny bubbles come out into the funnel.
Remove the funnel and top up the reservoir with more mineral oil.
If you have a halogen hob, just put the pads on that, turn the hob up full blast and cook until they stop smoking..the fins on mine started to glow, which turned the ano gold..
And make sure the disc is perfectly centred between the pads.
Just use a blow torch, its a lot quicker and easier to do.
Plus, don't forget, you'll need to burn the disc too, cos if the pads are contaminated, then the rotor is too.
My mate had the same issue and I blow torched them, then they were as good as new again.
Why the hell would you blow torch a disc? It's made of metal. Clean it. blow torching is likely to do more harm than good.
Are they M785? If so I feel your pain, I have a set that worked flawlessly for a year and then the rear just would not work if the bike had been not used in a month or so (they're on my second bike). I have cleaned and bled (many times), used new pads (multiple times), new discs, changed out the banjo pin with the O-rings, no sign of leaks and still its good for a ride and then back to the same. lever feels fine, just no power.
I had a thread on here discussing the same and was offered explanations. But I'm about to replace it now as it doesn't seem worth the time and effort when you can buy deore for not much and they seem just as good to me.
http://singletrackworld.com/forum/topic/xt785-brake-problem
Sorry, not much help to finding the cause, but I should of replaced mine ages ago and saved the hassle.
Sonnyjim
check the caliper carefully and see if there is fluid leaking from the piston seals when you use the brake? It can be quite subtle.
I've seen a number of bikes through our workshop recently, both MTB and Road with Shimano hydraulic discs, with leaking piston seals. Some of these bikes were brand new, and brakes sent for warranty.
You should never need to apply heat to a rotor to clean it. Isopropyl Alcohol will remove any contamination. Pads I'd always replace if contaminated.
It's not always contamination. I had two sets of XT brakes keep losing power in the way your describe after sitting idle for a week or so in the garage. Every time I rode the bike it'd take several minutes of hard braking to get rid of the squeal and regain some bite. In fact there's a long thread about this problem with certain Shimano pads here:
[url= http://forums.mtbr.com/brake-time/xt-xtr-brakes-get-squeal-power-loss-after-sitting-idle-6-8-weeks-902792.html ]http://forums.mtbr.com/brake-time/xt-xtr-brakes-get-squeal-power-loss-after-sitting-idle-6-8-weeks-902792.html[/url]
One way to solve as mentioned above is to bake them. I remove mine, clean them (and the rotor) with brake cleaner, put the pads in the oven for 20 minutes on a high heat, then hold them over a hob flame for about 30 seconds just to burn off any possible residue. Sand them with coarse sandpaper and reinstall.
Seems to solve it for me.
Baking at 220C for 30ish minutes (followed by cleaning and sanding again) worked a treat.
Thanks hive mind.
I had problem with my XT brakes, the rear was just squealing and no power, I solved by cleaning the discs and replacing the pads with Uberbike finned ones. Been ok since
PS - I also checked (and cleaned) the caliper - I can't see anything on there that looks like it shouldn't be there but I'll keep an eye on it.