Shimano M785 Bleed Issue... Pulling Out Hair

Psychotext

Starting to get really wound up by trying to bleed my Shimano M785 brakes. Front one is perfect, exactly as I want it, but I just can't get the rear one to work without letting me pull the lever to the bar when I brake.

Have bled it three times now, and on the last two there's clearly no air bubbles in the system anywhere. When I have the bleed block in the calliper at the end of bleeding the brake it works exactly how I'd want it to. Very firm to press, basically perfect. When I take the bleed block out and put the pads / wheel back in it's straight back to pulling to the bar again. Getting so frustrating.

Anyone got any ideas? I tried bleeding it with the free screw half out, but that didn't seem to make any difference.

Psychotext

I'm actually tempted to buy another bleed block and shave the sides a bit. If nothing else it'll be much closer to the standard width of the disc / pads on the rear.

holiver

It must be frustrating! Which procedure are you using? This one might be worth a look:

http://www.epicbleedsolutions.com/blog/ ... no-brakes/

If you are having issues after completing that, it may be worth returning the brake?

Psychotext

Yeah, that's the process I'm using. Seems it's not unusual though: http://singletrackworld.com/forum/topic ... 5-bleeding

Advice there is

once you have completed the bleed process, you can "trick" the caliper into thinking there is a bit of pad wear, and so get a more positive bite point feel.

To do this, take out the bleed block and put pads in, then put about 1cm of fluid into the funnel, slowly pull the lever once (with lever at horizontal position and nipple on caliper CLOSED) and release.

I don't have any pad wear that I'm aware of, but that's the next thing I'm going to try.

stubs

I had a bit of trouble bleeding my rear XT785 brake after ripping the hose off the caliper. I fitted a new caliper banjo bolt and refilled and bled the caliper but I couldnt stop the lever travelling too far.

In the end I gave up on the Shimano procedure and just left the bleedhose on the caliper with gravity pushing the fluid down from the bleed funnel for about 30 to 40 mins with the caliper dangling vertical from the master cylinder. Took nearly 100ml of oil slowly going through the system (I reused the oil). Eventually a stream of tiny bubbles came through and lever worked just fine with the block out and the pads in.

Never been keen on pushing oil/fluid up from the bottom paranoid I could be pushing dirt up to the master cylinder.

Psychotext

I tried the "hack" from the other site and whilst it's not where I'd want it to be, it'll be useable for the time being.

Might try something along the lines of stubs's solution at some point. That, or hand the whole thing over to a pro and see what they can do with it.

Psychotext

Had a pro look at it... no improvement. Have a fairly long period without riding now so I think I might go for some more extreme options. Past that all I can really do is buy a different brake. Stupid things, the front one is perfect.

benpinnick

Ghetto bleeds normally sort the pull out. If you have a funnel put it in the lever with the lever horizontal. Keep the wheel in, pads in no bleed block. Add some oil to the funnel. Pull the lever repeatedly, flick it, bash it ect. It should stiffen up nicely. Take the funnel off and add a drop more fluid before replacing the cap

jimothy78

Strikes me if the lever is firm when the bleed block is in place, then it's not really a bleed issue, but rather too much freestroke when the block is replaced with the pads and rotor.

This could be because you haven't allowed the caliper pistons to advance and "settle" in the correct place for the amount of pad wear you have. Even then, if you find they're still settling too far out for your liking, don't the 785s have bite-point adjustment? Have you tried winding that in a little?

Psychotext

I've tried new pads, made no difference. I've also tried bleeding it with the pistons slightly out, which made a tiny difference, but not enough. Bite point is in as much as it can be (I've also tried bleeding it fully in, and fully out, also no difference).

I'm assuming either a manufacturing defect, or the most awkward pocket of air ever. Strangely they don't get any worse, so it's not like there's air getting in somehow. What's more annoying is that my first set was perfect... until the piston exploded.

stubs

Tie the brake lever back to the bar with a zip tie or a strap of some sort. leave it for about 24 hours and hopefully it will sort it.

Psychotext

That's an interesting one. Any particular theory behind it?

stubs

Not entirely sure why it works but it has worked for me in the past. Could be a combination of several things, the air bubbles are compressed so can get out of nooks and crannies, pushes the pistons out and lets the piston seals settle so the piston has less clearance, allows bubbles to settle in the highest point the bleed port.

As I say not sure why but it has done the job.

poah

are the pads quite far from the disc? if so take wheel out and compress lever to move pads in and then remount wheel. pads should be closer to wheel now