Shimano XT M785 Rear Brake Creaking

afry

Hi all, in need of some help. Im currently building up a cube hardtail with m785 xt brakes front and rear. Both brakes purchased from the same supplier. Front brakes has no problems. Rear brake when applied there is a horrible creaking noise, its only made when you spin the wheel backwards and brake, it then creaks, and then spin the wheel forward it creaks. It doesn't continually creak if applying the wheel in 1 direction, i.e. just forward.

Its not the wheel as i have swopped with another wheel, with a different rotor and QR. Its not the pads as i have swopped these with the front and is the same.

Proven its the brake because i mounted the old hayes calliper onto the rear and rotated the wheel forwards and back, and applied the brake and no creak, proving the frame and mounts.

Recently I have swopped the hose for a genuine Shimano BH90 replacement to increase the length, the banjo bolt was applied with both o-rings and torqued correctly. Brakes were then bled.

A weird thing noticed was the lever feels hard when applied, however when the pads are removed, i could not get the pistons to move out much even after many pulls on the brake lever, as I applied Shimano mineral oil around the pistons to lubricate them, this seemed to make a slight difference but dissipated after a short while and the creak returned. I would have liked to applied more mineral oil to more of the piston diameter but couldn't.

All bolts and mounts are torqued to manufactures specification and im stumped slightly as to the cause, I have not found anything on the internet, so wondering if anyone has had any experience, problems or suggestions in this area? I suspect possibly the pistons being incorrectly sized and maybe creaking in the bore, but would my brakes be covered by warranty after me fitting a new hose?

Any help would be greatly appreciated.

Alex

cooldad

Ride them for a while and see.

The Rookie

afry wrote:

A weird thing noticed was the lever feels hard when applied, however when the pads are removed, i could not get the pistons to move out much even after many pulls on the brake lever

For the same lever pull they must move the same amount, they may return readily which means you can't pump them out as easily, maybe the rear is low on fluid?

afry

Fare point about the fluid, although the brakes were bled to the book. It doesn't seem right that the pistons will not fully extend, so I will re-bled them in a hope that this might be a cause to the creaking, although still unsure.

And I would rather get the bike working as it should be before I go out hammering the trails, im a believer that a new product should work as required from the off, and no bedding in period or use should improve the condition.

The Rookie

Bedding in is required on any brake, new is irrelevant.....something that is just a fact!
1/ The disc and caliper aren't perfectly suqare, they need to wear to conform to each other
2/ The pads need to advance correctly to the disc, sometimes they do it first lever pull, others they just don't
3/ the pads need to lay down teh working layer on the disc surface unless you are using the same pads as before.

cooldad

afry wrote:

Fare point about the fluid, although the brakes were bled to the book. It doesn't seem right that the pistons will not fully extend, so I will re-bled them in a hope that this might be a cause to the creaking, although still unsure.

And I would rather get the bike working as it should be before I go out hammering the trails, im a believer that a new product should work as required from the off, and no bedding in period or use should improve the condition.

If the lever is firm, they don't need bleeding. Bleeding gets rid of air.
And it will not get rid of 'creaking'.

ricardo_smooth

Shimano servo wave means the pistons don't creep out easily, If you want them to do so, short, repeated lever pulls will work

afry

cool will try the short lever strokes, thanks for the advice, will report back if i find the problem.