dismantling shimano XT (m785) brake levers…

So after bleeding the brake as I thought that was the issue, it seems that although I can ‘reverse bleed’ it from the caliper to the lever, and fill the reservoir, there’s NO fluid going from the reservoir BACK into the system. I.e it’s turned itself into a closed system..

I know shimano brake spares are hard to come by, and I’m planning on gutting hte lever tonight to see if the old ‘take it apart and put back together’ idea fixes it, but just wondering if anyone else has had a simila issue.

I’m sure there’s a bit of loose rubber making a blockage somewhere…

DrP

Try altering the reach of the lever one way or the other

Shimano spares are incredibly easy to get, if your LBS has a Madison account (and most do), just get the part number from the Tech Docs[/url] and order it.

For current Shimano brakes, you are using the funnel & a syringe? By using the funnel, you should always have a full reservoir during the bleed process.

Unlike the XTRs, it’s relatively easy to get into the reservoir of the XTs. Undo the bleed screw and torx bolt and the silver cover comes off to expose the rubber diaphragm, similar to what you’d see with the older shimano reservoirs. Mine was full of black sludge after a couple of Alps trips, cleaned it out with some cotton buds and IPA.

If you need any parts DrP I can sort it for you…..

The lever and servo wave mechanism are removable to expose the head of the piston. I’ve never managed to get in any further than that though. If you can’t push fluid in from the caliper end, it sounds like the piston is sticking and won’t return past the reservoir port. In my experience, you’ll need a credit card to fix it from here although I’d love to hear if anyone has managed to get past the piston.

Righto…. So I had the brake completely to bits. Everything out, piston et al…

It all looks fine, but was cleaned up with IPA and then put back.

However, it’s still ‘odd’!
I can reverse bleed as per shimano advice – fluid runs from the ‘system’ into the reservoir.
However, it doesn’t run back.
There’s NO blockage – I can see the master piston returns all the way back, so the oil should run into the system for the reservoir. But it doesn’t.
It’s like a closed system!!!

Arg!

DrP

Have you fully opened the freestroke screw ?

Double post

If the piston is definitely returning, and the port is clear, then that’s obviously not the problem area. Remove the hose from the lever to confirm this, if fluid passes through then you’ve got a problem with the hose or caliper (re-connecting the hose to the lever, and removing it at the caliper will then isolate the problem further).

Coatesy – this is the next step..

really,when I remove the hose, the fluid SHOULD simply just run out the lever, right?
Especially if I were to remove the bleed port screw, then there’s no vacuum and should flow out…

I’ll update tonight!

DrP

DrP, no the fluid should stay where it is when the hose is off. (I’ve shortened 10 Shimano hoses in the last week, trust me…) it should only come through when you actuate the lever. The system isn’t ‘gravity fed’. 🙂

The system isn’t ‘gravity fed’.

I appreciate that, but the bleeding instructions DO actually rely on a degree of gravity feeding…

Essentially, my issue is that the fluid enters the reserviour from below, but doesn’t leave it!!!
Thoughts Pete?

DrP

as per my earlier note, the freestroke screw, if fully in, can block the flow, have you tried process top down with screw fully out ?

screw fully out still causes issues.

Interestingly…..
If I pull the lever all the way back to the bars (when bleeding), then release (slowly OR quickly), it doesn’t ‘refill’ the system’.
But if I only pull the lever halfway back (with bleed screw open, then tightened up), then release the lever..it DOES seem to refill.

Hmmmm

DrP

Is it the master or slave piston you’ve had out? If master, how on earth did you do it?

Master I.e the piston from the lever…..

Remove the tiny grub screw in the pivot..remove the pivot…lever falls away…
Pop out the ‘roller pusher thing’ (two tiny black things will pop off), then the black ‘guides’ that the roller-pusher-thing slides in can be popped out, then that’s it…all apart and you can pull out the piston..

DrP

Last one I worked on, I got as far as the push rod and servowave guide plates but couldn’t see anything keeping the piston in place. Would normally expect to see a circlip or similar in that location.

And getting the lever spring back in was a bugger and a half.

Once you’ve got the servo wave guide plates out, the piston will just pull out..

DrP

Thanks DrP. Followed your instructions and problem solved.