How to stop rubbing on SLX brakes

[GhostSixFour]

So I'm going nuts with my SLX brakes on my GT - the rear brakes just won't stop rubbing. I have done the whole loosen the bolts and squeeze the brakes while tightening the bolts - that didn't work. Then I tried aligning with an old mark one eyeball, that didn't work as I couldn't properly see, even with a torch shining through from the other side.

 

Then I went, loosened the bolts, stuck a business card though on each side and squeezed the brakes while tightening the bolts, no joy.

 

Short of bleeding the brakes I've tried everything, and I'm not sure bleeding will do anything as the pistons seems to retract all the way in. That, and I haven't bled brakes before and I'm a bit scared I stuff it up.

 

This is the rear brakes by the way

[GhostSixFour]

They are mounted with post mounts and I'm thinking of trying to source those spacer things that is like a ball sitting in a bowl... Not sure what they are called.

 

Will that mean a upgrade in disc rotor size though?

[SamL1220]

Have a look at the particular place where the rotor is rubbing, top of caliper? Left? Right?

 

It could be you need to space the caliper further away from the disc, if the rotor is too large.

 

Also look if the rotor is out of true.

 

 

[Cuppa Bru]

The pistons might need to be aligned?

Might want to try following: take wheel off, carefully press brake lever to push out pistons without popping the pistons out completely and wiping off any grime that may be trapped on the grommet.

[Eldron]

Only two things I can think of:

 

1) Bent rotor - I straighten mine with a shifting spanner and light tweaks.

2) Bolt holes don't have enough play to keep the caliper/pads off the rotor. I've had one or two frames where I've had to use a rat tail file to clean up a bit of paint inside the bolt holes to allow the caliper enough play to clear the rotors.

 

Good luck!

[GhostSixFour]

Thanks for suggestions so far. Will try all of this tonight..

[Cylon]

There's a good chance that your rear rotor is slightly warped and needs to be trued as they bend pretty easily.

 

Although you can true a rotor with a shifting spanner or even just your fingers, I would suggest buying a proper rotor truing tool such as this one as it's a good long-term investment. I use mine all the time!

 

Birzman also make a cheap brake gap measurer tool which I find works much better than the business card method to space your brake pads.

[GhostSixFour]

Question. My wife has a 26" bike with centrelock rotors, mine is 29" with 6-bolts. Can I swap the rear wheel to check if hers rubs? Spacing should be the same?

[Eldron]

Spacing will be almost identical - certainly within the tolerance of the caliper adjusment. Great idea. Swap them and see if you can get them rub free!

[Blokman]

Don't mean to hijack , but I was about to post for help when I saw this thread. Also SLX. Also rear .

New bike only done a couple of rides . I have no stopping power at the back, only a screeching noise. When I pull the brake it looks as if the rear disc is being pushed to the outside. Could it be that the piston on the left (that pushes from the outside in )is not coming out properly?

I hope I'm making sense here.

Bike shop will look at it but I cannot get to them now.

[RichieT]

You didn't say if it's intermittent or constant.

If the former, then more than likely it's an out of true rotor, which as the others said you can true up with an adjustable wrench or by hand. It's just fiddely trial and error work.

A tip I used once with an Avid rotor which was bent all ways... take out the pads >> then re-position the caliper so it's off to one side >> just, or nearly touching one side of the rotor and tighten >> spin the wheel and now you can see where it touches >> mark the spot >> note which way it's out of true >> remove to bend it a bit >> then repeat until it's straight.

This way the caliper body gives you a fixed point from which to work.

 

If it touches constantly, then my guess is that the pads aren't releasing properly. Not sure what to suggest, but check that your pads are straight and the spacer spring is free and able to push the pads outwards. That no dirt or corrosion is preventing the pads from free movement

[RichieT]

One other thing that I've experienced is the the outer circumference of the rotor touches the inside of the caliper, so you just have to put some marker ink on the rotor or the inside of the caliper to check if it is.

Then just file off a bit of the caliper until it stops touching.

[usxorf]

Don't mean to hijack , but I was about to post for help when I saw this thread. Also SLX. Also rear .

New bike only done a couple of rides . I have no stopping power at the back, only a screeching noise. When I pull the brake it looks as if the rear disc is being pushed to the outside. Could it be that the piston on the left (that pushes from the outside in )is not coming out properly?

I hope I'm making sense here.

Bike shop will look at it but I cannot get to them now.

 

Most slx brakes will have a lazy piston, I know mine do, and unevenly spaced pistons can feel like you have no braking power.

 

It helps to center the pistons when doing the initial setup and periodically. Give your back brakes an eyeball and check that the pistons are evenly spaced. I physically restrain the stronger piston while pumping them out until they end up somewhat even.

[gminator]

I had a similar issue! Tried everything even pushing the pistons all the way back with a space. But the one piston just doesn't push out properly and then after while its the same problem.

 

Took the bike to CWC this morning hopefully they can sort it out, really I hope i don't need to chuck the caliper...

[Super Sywurm]

So I'm going nuts with my SLX brakes on my GT - the rear brakes just won't stop rubbing. I have done the whole loosen the bolts and squeeze the brakes while tightening the bolts - that didn't work. Then I tried aligning with an old mark one eyeball, that didn't work as I couldn't properly see, even with a torch shining through from the other side.

 

Then I went, loosened the bolts, stuck a business card though on each side and squeezed the brakes while tightening the bolts, no joy.

 

Short of bleeding the brakes I've tried everything, and I'm not sure bleeding will do anything as the pistons seems to retract all the way in. That, and I haven't bled brakes before and I'm a bit scared I stuff it up.

 

This is the rear brakes by the way

 

I had the same problem with my GT, I just sold the bike!!!

[GhostSixFour]

Update - switched wheels and the disc spun like a hero.

Took my wheel to Northcliff cycles and got a new disc put on - problem solved.