Tech Q&A

Fix/Workaround: Shimano XT M785 Brake Lever

Meezo's Photo Meezo 02 Dec 2015

First off I must stress that I am by no means a qualified bicycle mechanic, I do have little very little experience with them. Secondly I cannot take full credit for this fix, the idea was given to me by a very very generous hubber who’d had offered to fix for me for free. KUDOS @BikeWhisperer and a close friend @gyro for the time

Ok, then this is not an avid or shimano appreciation thread, nor an avid vs shimano thread.

 

SYMTOMPS:

Pull lever, and it does not return at all or very slow and spongy.

If bike in open sun, levers lock up.

 

POSSIBLE CAUSES:

Dirt and grime build up in the lever cylinder, as well as on the piston. See below

With the dirt and grime build up, when in heat the swelling cause the lockup and no return of lever.

 

TOOLS NEEDED:

2mm Allen Key

Star Screwdriver

Isopropyl Alcohol

Toilet roll/Roller towel

Thin Nose Pliers

1 x 3000 grit Sand Paper

1 x 2000 grit Sand Paper

1 x 1000 grit Sand Paper

 

This is from the shimano site, I will make reference to the number here in my photos as well

xt_brake_lever copy.jpg

For starters is always good to remove the lever completely off the brake line.

Below is an image of a lever I had repaired and one that was going to get repaired, taken as is off the brake system

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Remove 8 in diagram above like below, there a tricky little rubber cover than can be removed with a thin small screwdriver or pin

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Push out 5 using the 2 allen key, this will separate the lever trigger from the rest of the lever

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Use the thin nose pliers to twist and remove the roller connector/part of the lever

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Using the star screwdriver, remove 6

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Turn the lever upside down ie. reservoir facing down and use the screw driver to pop out the plastic roller fitting

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..and finally we get to the problem child, this is just to show you how the piston is actually stuck in the cylinder

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Easiest way to remove the piston and spring is using the 2mm allen key

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This is your best friend keep on using it throughout the process, clean up all you bits you can, all the none plastic and rubber bits I let sit in the isopropyl alcohol for a few mins

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…so time for the fix the red blocks is whats needed to be sanded down using the 1000 then to 2000 then smoothen with the 3000, very very lightly and depending on your piston condition very very little too.

fix.jpg

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PS: it may or may not be easier to remove the rubber seals, just be very careful when sanding around them

 

 

what I do to test I push the spring in with the piston, and see if there’s a “spring” back in the piston by pushing in and out the cylinder

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And the final product!

DSC_0772.JPG

DSC_0773.JPG

DSC_0774.JPG

 

 

DISCLAIMER:

I am not in any way affiliated to Shimano. I will not take any responsibility for any damage done to your lever or other parts when attempting this fix. I am not 100% sure of the repercussion sanding down the old dirt or grime build up, and will not be held responsible if it does fail.

 

Our scholars tell us, that we have to go out to seek knowledge and whatever knowledge is learnt must be shared so it be beneficial for myself but humanity at large…

 


Edited by Meezo, 18 August 2016 - 10:14 .

TNOSE_E's Photo TNOSE_E 02 Dec 2015

BikeWhisperer also gave me the advise on this fix and works a treat.

Meezo's Photo Meezo 02 Dec 2015

so he's hub name is very fitting then... :clap:

Goosebay's Photo Goosebay 02 Dec 2015

Cool thanks!

 

Would probably start with the 1000, 3000 is finer and you should end with that.

 

No return could also be caused by using non-mineral oil in mineral oil systems

taito's Photo taito 02 Dec 2015

sweet

Bobbo_SA's Photo Bobbo_SA 02 Dec 2015

Very cool, mine is currently with Shimano for replacement, have a long wait for the stock to come in so put a different lever on for the interim.

Meezo's Photo Meezo 02 Dec 2015

yes, google it, its definitely a known issue worldwide, i my case the 2 sets i had that failed were about 3 months out of the warranty.

 

they do replace if under warranty no questions ask...

TNOSE_E's Photo TNOSE_E 02 Dec 2015

Personalty,  I think this sticking is due to gunk buildup on the piston that just makes the slide action of the piston and barrel worse over time.  Not Ideal but for the M785 I would do a full mineral oil change as often as possible.

 

To the peeps that had the failure.... Did you use Shimano mineral oil only or another makes / weight? 

Would be interesting to see if it may be a an issue with the breakdown of either oils or not.

I used 10w and 5w oils and only after the failure have I tried using only Shimano....so will see what happens over time.

droo's Photo droo 03 Dec 2015

Personalty,  I think this sticking is due to gunk buildup on the piston that just makes the slide action of the piston and barrel worse over time.  Not Ideal but for the M785 I would do a full mineral oil change as often as possible.

 

To the peeps that had the failure.... Did you use Shimano mineral oil only or another makes / weight? 

Would be interesting to see if it may be a an issue with the breakdown of either oils or not.

I used 10w and 5w oils and only after the failure have I tried using only Shimano....so will see what happens over time.

 

5 or 10wt oil is way too heavy for Shimano brakes - their mineral oil is rated at around 9 cSt with a VI of around 350, while the lightest 5w you get is just under 16. Bel-Ray HVI 3wt is about the closest you'll get at 11 cSt.

 

Oil changes may help, but I'd say the best thing for this would be for Shimano to supply seal kits instead of just binning the whole lever assembly when it jams up.

 

Meezo, good work on the rebuild - let us know how it holds up.

Sidmouth's Photo Sidmouth 05 Dec 2015

this is awesome thank you .

I have been looking for a solution.

 

https://community.bi...ses-rear-brake/

Skylark's Photo Skylark 05 Dec 2015

So perfectly possible to rebuild those levers, just need seals, wonder if there's any common industrial seal that would fit?

Rebuilt my RS fork with orings from bearing man, cost R20 for duplicates of everything! What a pita finding the correct oring sizes though, they use a mixture of imperial and metrics sizes.

Time for some aftermarket company to make seal kits for these shimano brakes, crazy to throw away all that engineering just because 2 rubber seals failed.
Edited by Skylark, 05 December 2015 - 02:49 .

Sidmouth's Photo Sidmouth 06 Dec 2015

Guys, im experimenting with a old set of XTR tail levers,all going good, one issue, the free stroke plastic internal flat it pinned down by the free stroke screw, however it is moving on a pin, I cannot get that pin out?? any ideas

HowardSteele's Photo HowardSteele 06 Dec 2015

"Personalty,  I think this sticking is due to gunk buildup on the piston that just makes the slide action of the piston and barrel worse over time.  Not Ideal but for the M785 I would do a full mineral oil change as often as possible.

 

To the peeps that had the failure.... Did you use Shimano mineral oil only or another makes / weight? "

 

Both my levers  developed piston suck after 2½ years  of use ...about 6 weeks apart. I Only used   shimano mineral fluid ...However in hindsight  from now on will renew oil in brake system about every 14 months on so not just a top up bleed.


Edited by howardsteele, 06 December 2015 - 06:48 .

Sidmouth's Photo Sidmouth 06 Dec 2015

So the XT are different to the XTR, the XT are much easier to maintain with regards to the piston and getting to it, I think the same problem will arise with XT or XTR, same build same piston, I just don't think you can service the XTR because of that pin holding the free stroke flap.

 

From opening these up today it is apparent that the problem is a dirt buildup, i think one should bleed the brakes more often , flushing the dirt out of the system.

Does anyone know if the new XT M8000 re better designed or are they the same.

MarcW's Photo MarcW 06 Dec 2015

Can this be done on the XTR m985's (Race) ? 

Meezo's Photo Meezo 06 Dec 2015

I can't see why not but as Sidmouth has said the internal design might be slightly different.

What has to be said is, is i have a bike with SLX and this gets ridden the most compared my bike with XT, and the SLX has no issues.

Again, as mentioned by Skylark if shimano could take heed they could supply only the piston, I'd buy only SLX pistons and replace the XT's