Afternoon folks, I need some help…

I’ve got a Sram Force Hydro groupset and I can’t get my rear brake to stop rubbing…

There’s a point on the disc where it’s clearly bent slightly causing the rubbing. I straighten it out, align the caliper and after 1 ride it’s bent / warped again.

The problem is I have already replaced the disc itself hoping I just had a dodgy disc or something but after a couple of rides this has warped too.

I’ve never had a problem with MTB discs before but this groupset has been a nightmare.

What could be causing it?

How do you tighten the bolts? I had always been taught to tighten the bolts in a sort of criss-crossing pattern, in case they somehow cause the disc to warp (think this comes from engine mechanics trying to prevent gaskets pinching or folding or something).

I felt I was somewhat prone to brakes developing wobbles, almost something to do with weight and heat build up perhaps, either way I could end up with minor wibbles which had nothing to do with bike being dropped or bashed.

Rotors are center lock so that shouldn’t be the problem.

Just spent an age trying to get the thing to rotate without rubbing. It’s probably me being a bit too OCD but it’s just strange that I’ve never had a problem with MTB brakes.

I’ve just stuck some new pads in too as the old ones were almost out. The clearance between the pads and the disc is practicaclly zero that probably doesn’t help matters

I’ve just stuck some new pads in too as the old ones were almost out. The clearance between the pads and the disc is practicaclly zero that probably doesn’t help matters

That happens when the reservoir is over filled

It can also be a problem with non-OEM pads just being too thick.

Hydro disk brakes will always have only a fraction of clearance, that’s fundamental to how they work (unless the pistons have stuck in the seals, of course). If it’s just light rubbing, it’s not a functional problem. If they’re actually dragging, it is a problem.

One thing to watch is when you come to a complete stop from high speed, especially at the bottom of a long descent. If you hold the brakes on after you stop, you will get a hot spot on the rotor at that point, which can cause warping, and you can also end up with pad material melting onto the rotor so you get a high spot and pulsing as you brake. Good idea to release the brakes after a hard stop to avoid hot spots.

Most people don’t understand that hydraulic brake pistons don’t slide through the seals when you apply pressure; the seals deform and then return to a square cross-section to bring the pads back off the disc. As the pads wear the pistons do creep through the seals but very gradually. So with luck your pads will wear and clear the disc.

Sometimes if you grab a huge handful of brake the pistons do move and the pads end up pressed on the disc. It can take quite a big effort to get them to move back.

NFS (Normal For SRAM)

I very much doubt that your rotor is repeatedly warping. It’s impossible to get a rotor completely true, so it’ll always have a high spot. The clearances on disc brakes are very tight, and if a pad doesn’t retract quite enough, it’ll drag. The high spot in the disc will typically nudge the pad back so that it’s only catching at that one spot.

SRAM brakes seem to be much more prone to this than Shimano. The problem is often attributed to “sticky pistons” although as globalti points out, the pistons don’t slide in normal use, and the problem you have here is that one of the pistons has extended too far (i.e. it’s slid through the seal too far), which might be down to the other piston sticking.

I currently have a problem with my SRAM Force brakes where the front brake is pumping up to the point that the brake is dragging significantly. I’m wondering if the seals become hardened and/or worn over time, causing the pistons to slide through rather than deform them. I have some new seals/pistons on order so we’ll see.

Then I’ll move on to replacing the master piston on the other brake, because the lever on that one sticks and doesn’t return properly.

Good thing about SRAM is you can get spare parts. Bad thing is that you’ll need them.