XTR Disc Brake headache

[Thermophage]

I'll see if I can put something together if I get some free time. I might have to do it as a video as some of the stuff is hard to explain and comes for years of doing this day in and out.

Yeah that would be awesome.

Every video is the same out there already (that I've found). 

One showing the subtleties of it would be awesome as it's the little things that will really make a difference.

Any idiot can follow the Shimano guide...but tweak them to be amazing...another story.

[Grey Hubs]

You can try calling the Shimano agents - Coolheat. They might point you in the right direction...

[karlito]

That little free stroke screw is useless it does nothing (It make at a 5% difference that’s a lot), but that doesn’t show you how to remove and replace the master cylinder

 

 

 

You are correct, some of the Shimano service manuals state that you should push fluid up from the calliper. This is completely trash and doing this will flod your master cylinder seal and ruin your brake.

 

 

Shimano's should only be gravity bled and there are a few trick to get all the air out and adjust the free stroke that actually works.

 

This is very interesting to me as I have heard this from more than one source recently. I do not understand how the pressure from a syringe can damage the seal, if applying much more force from the lever does not? After all the idea of a lever is to amplify the force. 

 

I have recently stripped my XT brake lever down completely, and I am struggling to understand how this seal can be damaged? But since so many share this opinion I am interested in the reasoning behind this.

 

 

My lever was sticky and I followed the instructions here:https://community.bikehub.co.za/topic/155987-fixworkaround-shimano-xt-m785-brake-lever/

[Lance Stephenson]

1.)It could be that the system has been bled backward (the wrong way) and over pressure the lever whilst still trapping air. 

2.)It could be that the mechanic has used the wrong oil (****** the brake seals up)

3.)The lever is dodgy, and XTR has a warranty, if you are the original owner they will replace the lever for you.

 

I would have the brake bled again, via a more reputable shop!  THe brakes are bled down!  From lever down the throught the calipre.

 

Failing this working......the second problem is proved by the oil that gets pulled out of the system when bled so get the new mechanic to save it.

[JXV]

I have this theory that if your disc brakes work, don't touch them. Other than change pads, I don't let a bikeshhop touch my brakes.

 

My XTR rear brake started feeling as if there's a little bubble in the line the last couple of rides, and especially when on a long dh section, the brake will pull a lot closer to the bar than normal. And so I did the unthinkable and took my bike to my LBS and with a heavy heart I asked them to bleed my super crisp feeling XTR rear brake - only to sort out the 'when hot' problem.

 

I pick up my bike today and worst fear realized, my brake has no more kick back. If you pull any Shimano brake and it has a swift spring back to it's original position. That is no more the case, and mine slowly/sloth-ly moves back to its original position.

 

It is still potent, but there's no modulation, because there's no kickback, so the brake stays where it is, and if you pull too far, wheel just locks up - and very abruptly.

 

LBS is stumped, I'm furious and also stumped. They have no idea why its acting like this or what could go wrong.

 

Anyone know why this would happen and how to fix it?

 

My brake's character is just not what it used to be, and I won't attempt to manual sections like that, and if a Tektro Auriga felt like that, I would still suspect something went wrong.

Did the lbs use Shimano brake fluid in you brakes? Lots of people think any old mineral oil will do but the Shimano type has a low viscosity specifically for performance reasons.

 

If they used DOT fluid by mistake then your brakes are dead. The seals are not compatible, will swell up and the symptoms you describe will occur. SRAM/Avid brakes use DOT fluid and Shimano uses 2.5wt mineral oil. Using the wrong fluid is fatal for either type. When bleeding either type, one has to make sure the bleed kit is not contaminated with the wrong fluid because just a small amount of the wrong stuff will cause damage.

[Spoke101]

This is very interesting to me as I have heard this from more than one source recently. I do not understand how the pressure from a syringe can damage the seal, if applying much more force from the lever does not? After all the idea of a lever is to amplify the force. 

 

I have recently stripped my XT brake lever down completely, and I am struggling to understand how this seal can be damaged? But since so many share this opinion I am interested in the reasoning behind this.

 

brake-lever.jpg

 

My lever was sticky and I followed the instructions here:https://community.bikehub.co.za/topic/155987-fixworkaround-shimano-xt-m785-brake-lever/

 

From my experience:

 

It's not the syringe that does the damage, by bleeding the brake the wrong way the fluid flips the seal the wrong way (this is probably down to excess force on the syringe as there can be some resistance when bleeding from the caliper up. Also don't underestimate the amount of force a syringe can produce in a hydraulic system) then the lever is pulled and this forces the seal into the leaver the wrong way, this damages it and it therefore no longer has an oil tight seal with the lever.

[Meezo]

read through this, if you got time it may be worth a shot

 

https://community.bikehub.co.za/topic/155987-fixworkaround-shimano-xt-m785-brake-lever

[deonkretch]

If under warranty (XTR should be 2 years?) they will replace. Just got a new front brake back from my LBS that was replaced under warranty - excellent service!

[Guest notmyname]

.

Edited January 21, 2016 by Small Fry

[Heel Drop]

what did the bike shop say when they gave you the bike back in this condition - they must have known ?

[nox1111]

Just picked my bike up from a total brake strip and rebuilt - sent off to their (LBS's) specialist.  Not sure how good the person is, but apparently he is meticulous and an XTR specialist.

 

I pushed for time as I'm riding the 24hr tomorrow and need my bike with working brakes.

 

Brake is still slow - it's better, but apparently the specialist said it is what it is now, it is wear and tear and he can not get it any better - which is weird, since it was fine pre the bleed...

 

I'm guessing that sanding trick will sort it out, but that also means that I have to do it myself...  I don't mind doing anything else on my bike, but there's 3 things I like to pay other people to do:

1. build wheels ( I have yet to build a straight one)

2. Rear shock service

3. Brake service

 

Any takers for the brakers?

Edited January 22, 2016 by nox1111

[raptor-22]

Shot GB, How do I check this and how do I fix it? any ideas?

the master cylinder needs new seals and O-rings. the kit is available from Coolheat and I suggest you let them do the work.

 

The other potential problem is that the pistons seals are dry. To remedy this remove the pads and slowly pump the brake till the pistons are 50% the way out. If they look dry here then you will need to grease them with a thin sliver of silicone grease used for O-Rings. Silicone grease won't react with or be diluted by the oil.

Edited January 22, 2016 by raptor-22

[brumby]

Ceramic pistons do break - cause - loose or skew back wheel and spreading the pads without taking the filler screw out of the master cylinder. You then have a broken piece that lodges between the piston and the calliper wall - which pushes your piston further out and prevents it from returning fully. To give a simple example with exaggerated figures a perfectly set-up brake will have both pistons moving 2mm in  when applying the brake and moving 2mm out when releasing the brake . With a ceramic piece lying in the caliper  those figures will now change to 2mm and 0.5mm in and out movement which results in lack of modulation, a brake that locks suddenly and slower return of the lever due to reduced movement of 1piston and flow of fluid which is affected negatively by the piece which has broken off.