2011 SHIMANO XT disc brakes. At the start of every ride there is no power, just lots of squeal. After dragging them a bit and a few hard stops on the first desent they quiet down and stopping power returns (both back and front). A few days later on the next ride however (no maintenance in between) I get the same noise and lack of power until I repeat the above process. Cleaning the discs (with disc brake cleaner/IPA) and putting in new pads has not solved the issue. Is it possible there could be a minute leak at the calipers that is continuously (but very slowly) contaminating the pads between rides? During a ride, once the noise has stopped they appear to be working optimally so they can’t have lost a significant amount of fluid. Any ideas?

How do you store the bike? If in such a position that any air can get to the calipers or hoses that may be the problem.

Bike stored upright in ‘normal’ position, with both wheels on the ground, so shouldn’t be an issue.

Sounds to me like you need a brake bleed for the loss of power. Have you made sure that the calliper is aligned with the disc properly? I do find Shimano brakes to be quite noisy anyway, have you tried sanding down the disc a little? sometimes you can contaminate the rotor and lightly sanding down the rotor does help.

Had a similar proem recently.

Bled the brakes, sanded the discs and changed the pads, then bedded them in again.

I don’t know which part cured the problem, but they have been spot on since.

I have bleed them, sanded the rotors and used new pads. Fine for a while, then the problem occurs again. The fact that stopping power is fine mid ride suggests a bleed is not the issue (bleed recently anyway, didn’t make a difference).
This is what makes me think the system itself could be contaminating the pads. Anyone had this happen?

We had a set of Zee’s that leaked because the pistons had come out a bit to far. Had to push them back in, replace pads and rebleed the whole system.

Are you using sintered pads? Could both surfaces be oxidising?

At that age i’d guess leaky caliper seals and a new set of brakes needed. Common on shimanos and parts to repair aren’t available.

angeldust – Member

The fact that stopping power is fine mid ride suggests a bleed is not the issue

Not really- it’s perfectly possible for air to migrate in use and pretty common for riding to solve issues temporarily. What might be intesesting is to tie back the levers overnight, just give them a very quick 2 or 3 pulls then ride, see if that creates a difference (this helps migrate air into the reservoir- not a fix but a change)

In some ways your symptoms do sound like mild contamination but not entirely, new pads should at least change that if not fix it.

Not really- it’s perfectly possible for air to migrate in use and pretty common for riding to solve issues temporarily. What might be intesesting is to tie back the levers overnight, just give them a very quick 2 or 3 pulls then ride, see if that creates a difference (this helps migrate air into the reservoir- not a fix but a change)

True, but I’ve bleed them several times, so I’m confident there’s no air in the system. Thanks for the suggestion though.

My similar vintage Deore front brake did exactly this. Tried all the things you’ve done, but eventually gave up and bought a new set (Deores are only 70 pounds though, so not too painful).

Those that got new brakes – did you get new rotors as well?

Same here, on XTs and SLX. Tried everything, ended up replacing them both. Seems to be common with Shimano when they have been sat unused for a while, sleals go.

This is on a second bike that isn’t used as often as my primary bike, so that could be the problem.

I get similar on the wife’s bike. Intermittent use.

I’ve tried everything except new brakes, which will be next.

It makes the occasional ride with the mrs a bit of a grind coz she hates it and I get nagged!

Sort of glad it’s not just me.

Does the feel of the lever change during riding? Ie spongy then firms up? Or is it pretty much constant?

Lever feel is consistent, which is one reason I don’t think it’s a bleed issue

Those that got new brakes – did you get new rotors as well?

I had some spare new rotors, so put them on just in case