XT Deore's - No Power!
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SBenny



Joined: 08 Jan 2014
Posts: 14

PostPosted: Mon Sep 12, 2016 9:20 pm    Post subject: XT Deore's - No Power! Reply with quote

Evening All,
After picking someone's brain - above brake set with new rotors bought. Fitted by LBS, on collecting bike advised they'll won't work brilliantly till bedded in. No problem. This is on 31/08 - now the front is getting better. Rear brake however just has no bite, when bike is in the stand stops no problem but when I'm riding just about slows the bike not bringing it to a stop. Have centred the caliper said on the disc but not much difference.

Is there a simple fix to this or is it back to the LBS that fitted them I go? Rolling Eyes

Thanks Again

Sam

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TeaTwoSugars



Joined: 26 Jul 2010
Posts: 1195
Location: Wigan

PostPosted: Tue Sep 13, 2016 1:17 am    Post subject: Reply with quote

Sounds like they need bleeding to me.

Take the bike back to the shop that fitted them and they should sort them in no time at all.

Or you could get your own bleed kit and do them yourself from now on.

SHIMANO brakes are a doddle to bleed.
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TeaTwoSugars



Joined: 26 Jul 2010
Posts: 1195
Location: Wigan

PostPosted: Tue Sep 13, 2016 1:22 am    Post subject: Reply with quote

Another thing to try is to remove the pads and sand the braking surface in case you've glazed them.
(No need to go mad on the sanding, just enough to remove the shiny surface)

Clean your brake discs, reinsert the pads (careful of getting greasy fingers on them), give the brakes a try.
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Gunner



Joined: 15 Apr 2007
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PostPosted: Tue Sep 13, 2016 7:52 pm    Post subject: Reply with quote

Agree with the above, but does beg the question, "Did you bed the new pads in and if so, how?"
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Magnus



Joined: 18 Jan 2013
Posts: 1512
Location: Leicester

PostPosted: Thu Sep 29, 2016 4:29 pm    Post subject: Reply with quote

Back brakes usually have a smaller diameter disc to the front. This limits there stopping power, which is a good thing.

when you brake the weight of you and the bike shifts from being evenly distributed front and rear to being mainly over the front wheel. therefore you need more stopping power on the front than the rear. to much stopping power on the rear brakes and the rear wheel will be constantly locking up it will be difficult to modulate and hard to control the bike.

maximum braking efficiency is achieved just before the brakes lock. once the brake locks and you start to skid you are then not stopping as quickly but it can look cool leaving a strip of rubber down the road... well if you are 12 it looks cool. Laughing

so what i am saying is, if your brakes are in good order and there is no air in the hydraulic system etc, then what you are experiencing may be normal.

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Nik Gnashers



Joined: 30 Dec 2014
Posts: 265
Location: Lincoln

PostPosted: Thu Sep 29, 2016 4:59 pm    Post subject: Reply with quote

I personally think they need bleeding too.

I have XT 180mm front & rear, and they are very good, I only need one finger on the levers which is what I like, as it leaves the others to always be in control of the bars.

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Kajjal



Joined: 29 May 2013
Posts: 756

PostPosted: Fri Sep 30, 2016 8:52 pm    Post subject: Reply with quote

I am 100kg and use XT brakes, plenty of control and power but if I wanted to I could easily lock up the back wheel.

The first thing to try is get the bike up to speed a few times and pull the back brake on really hard without skidding several times. This will help bed in the brakes and burn off anything on them.

If that fails it might be there is some contamination with oil or similar on the pads & rotors. I had this with my front brake recently and it was next to useless. Removed rotor and cleaned with disc brake cleaner until kitchen rolls stayed clean. Too out old pads and cleaned the caliper with a little disc brake cleaner and then thoroughly with soapy water. Fitted new pads and after a half our ride at speed with plenty of braking back to normal.

If you have the newer XT rather than the older M785 XT brakes they do have reports of manufacturing problems so maybe you have been unlucky.

If the brakes needed bleeding you would find the lever going all the way to the bar and feeling very soft.
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TeaTwoSugars



Joined: 26 Jul 2010
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Location: Wigan

PostPosted: Fri Sep 30, 2016 9:18 pm    Post subject: Reply with quote

Kajjal wrote:
If the brakes needed bleeding you would find the lever going all the way to the bar and feeling very soft.


Not strictly true Kajjal.

The OP's brakes most probably do need bleeding.
The lever doesn't need to be going to the bars to require a bleed to be done.
With them being recently fitted and most likely having their hoses shortened I'd pretty much bet you a pound to a penny that the levers will need burping to restore proper braking feel.
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Kajjal



Joined: 29 May 2013
Posts: 756

PostPosted: Sat Oct 01, 2016 8:58 am    Post subject: Reply with quote

TeaTwoSugars wrote:
Kajjal wrote:
If the brakes needed bleeding you would find the lever going all the way to the bar and feeling very soft.


Not strictly true Kajjal.

The OP's brakes most probably do need bleeding.
The lever doesn't need to be going to the bars to require a bleed to be done.
With them being recently fitted and most likely having their hoses shortened I'd pretty much bet you a pound to a penny that the levers will need burping to restore proper braking feel.


Thanks, that was a bit of a poor explanation of bleeding.
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