Shimano XT brakes impossible to bleed..

XL500_boy

Hi. Can anyone offer advice on this one..? I'm trying to bleed the brakes on my MTB - they're Shimano XT, prob about 7 or 8 years old (combined brakes/shifters) & never been bled I reckon. I bought the bike 2nd hand recently & after changing the pads I thought I'd bleed the brakes. I've bled brakes on cars & motorbikes before & understand the process. I've tried it from the top down & with a syringe from the bottom up - neither way will it take any fluid. The mater cylinder just does not want to pump fluid & when trying to send fluid in via the bleed nipple (un-done 1/4 turn or more) it does not fill the master cylinder at all - almost like there's a total blockage). Is this a problem with XT brakes that anyone else has experienced? I have tried injecting the fluid at the nipple with the brake lever in its normal position & also with it in various depressed positions (cap off the reservoir of course). The brake (rear) felt & worked OK before (a bit spongey, but nothing too bad), but now after all the bleeding attempts, has air in it & the lever moves to the bars. It is impossible to get fluid into the system using the standard 2 methods.. Any ideas anyone? Cheers.

CraigXXL

On XT755 and Saint M810 I use the reverse bleed from the caliper up and no problem although you do have to undo the bleed nipple more than a 1/4 to do so. I don't have any experience of the combo brake/shifter levers and if you need to do anything different but have a look on Shimano Tech Docs for the instructions.

stubs

I have struggled with the older XT brakes myself they can be a hair tearing tool throwing custard. No offence but you have taken the rubber bellows off the master cylinder I have seen someone who had a leak then tried filling up the bellows with oil.

Try burping the brake to get rid of an airlock, fill master cylinder reservoir with master cylinder at highest point you may need to remove master cylinder and clamp in a vice or zip tie the hose so it is below cylinder without any kinks in it. Then flick the lever by pulling lever back with one finger as far as you can then release and let the spring flick it back, do this a few times and you will see small bubbles appear in the master cylinder keep doing this I had to do it for nearly an hour once. When you cant see any more little bubbles or you lose the will to live zip tie the lever to the bars and leave overnight this lets any trapped air make its way to top. In the morning cut zip tie burp it a few times and refill. Hopefully this will crack it if not you might have a master cylinder seal gone.

nicklouse

XL500_boy
What part number?

the 765?

http://techdocs.shimano.com/media/techd ... 604906.pdf


sounds like the hose could have collapsed.

XL500_boy

Thanks for the advice guys. Yep I'm not filling the bellows with oil - though I can totally believe that someone could do that I spent a day reading all the experiences of others & also the Shimano technical docs (but thanks for the link anyway) & found nothing similar to my situation.
Considering the "collapsed hose", "air lock" or "blown master cylinder seal" options.. The brakes were working fine before I started too bleed them & in all those cases, I would imagine that I would be able to bottom-up bleed them using a syringe (albeit possibly very slowly) - but I can get almost no fluid into the system (even with the nipple undone a full turn or more) & then what goes in comes back out under the same pressure. The symptoms are similar to as if the hose was clamped shut with a mole-grip just after the master cylinder, except that when I pump the brake lever, there is a small movement of fluid out & then back in again at the slave end (nipple).
The master cylinder does not re-charge with fluid from its reservoir possibly implying a seal has gone - but if this was the case it should be possible to get movement of fluid back to the reservoir using the syringe method. The tube is not blocked as there is out/in fluid movement at the nipple & small bubble have been popping up into the master cylinder during pumping the lever. Basically - I cannot get fluid into the system from either end. Thanks for the "losing the will to live" comment - that's very nearly me!

nicklouse

can you build up any pressure in the system?

XL500_boy

Quick update - I've fixed it!! Woo-hoo!! More to follow in a mo.. Thanks for your last comment about pressure in the system - there is now
Give me 5 mins & I'll type it up here..

XL500_boy

The small grub screw that adjusts the distance of the lever from the bar (embedded in the lever itself, well inside the body of the combo unit) had been adjusted so that the lever was as far from the bar as possible (but not over-adjusted - certainly no exposed threads around the grub & felt about right with my large hands). This was putting a tiny amount of pressure on the piston/plunger within the master cylinder - in effect like pulling on the brake lever a small amount (though not enough to cause a braking effect). So no fluid could be syringed backwards during bleeding & the piston could not retract fully to take in more fluid from it's reservoir (also explains the other symptoms). It all seems to be bleeding fine now - though I've come indoors to relax from all the stress & have a biscuit.
Good title for the thread would have been: "Bleeding grub screws" hehe.
Excellent - thanks all of you out there for your support

MetalMic

Hi XL500_boy, I just want to say thanks for the information though its like from almost 2 years ago! It's really a life saver.

I had exactly the same problem yesterday night when i was installing my new Deore LX butterfly unit and i spent hours trying to figure out what went wrong with the rear brake because the front one works perfectly.

I had to shortened the hose for the rear brake coz its too long and after the installation i just couldn't bleed the damn thing no matter what i tried based on literature and advices from internet search.

That is until i stumble on your post and I immediately checked the brake lever. Guess what, my problem was caused by the same grub screw!

The Rookie

Had the same issue with an old LX of the same vintage........