SRAM disc brake rubbing - need bleeding?
 

I recently built up a 2020 Supersix evo HM with a new SRAM Red group. (First generation monoblock calipers). I obviously cut the brake hoses for the internal routing and installed new barbs, etc. I was expecting to have to bleed the brakes, but as i was setting up the bike, the brakes felt great - not spongy and braking strong. They do sound 'rough' though, but i assume thats because of new pads. - So i didn't bleed them.

Anyways, no matter how much i adjust the caliper position, i cant get them to stop rubbing ever so slightly. It's only i a little bit, but being anal, and just having built up the bike, it's annoying that it's not perfect. The rotors are not bent.

I wonder if the lack of bleeding could cause the pistons to not retract fully? There's almost no gap between pad and rotor.

Any input appreciated. Thanks!

I had similar problems with my Force build last year. Take piece of paper and put it on the ground under the wheel. It'll help you see the gap on either side of the rotors. Adjust from there.
I dont believe bleeding will have any effect on the return of the piston.

This happens to me occasionally after replacing pads. What I do is clean the pistons (there are many authoritative videos) if I think they’re hanging, or go for a ride and try aligning the calipers again. Failure to purge the system of air shouldn’t cause this.

And what Is01 said.

There are o-rings around the brake piston - which hold the fluid from leaking out.

When the piston is pushed out, it "rolls" the o-ring. When pressure is released, the piston is retracted by the o-ring returning to its original position.

If there is debris on the piston it can prevent it from retracting into the bore as it can wedge the piston in the out position.

Note: Motorcycle and car rotors will kiss the pads as they rotate in their "relaxed" position. You can hear it when spinning the tire unloaded.

There are o-rings around the brake piston - which hold the fluid from leaking out.

When the piston is pushed out, it "rolls" the o-ring. When pressure is released, the piston is retracted by the o-ring returning to its original position.

If there is debris on the piston it can prevent it from retracting into the bore as it can wedge the piston in the out position.

Note: Motorcycle and car rotors will kiss the pads as they rotate in their "relaxed" position. You can hear it when spinning the tire unloaded.

Glitch in the matrix

Thanks for the replies!

I spent some more time adjusting with a tad thicker paper on one side of the rotor than the other - that worked out in the end.
I have another bike with Force AXS, that has the newer two-piece calipers (same as later Red AXS), they seem to have slightly more space between pad and rotor. (might just be a visual trick)

I usually use business cards if the disc is true, and it still rubs,