SRAM HRD pistons won't retract

So - after taking the bike off the smart trainer, the pads on the rear wheel were partially on. I can only assume I pulled the lever when on the turbo, though I don't recall doing so.

All the usual tricks have had no effect, and removing the pads shows the pistons aren't fully retracting. Trying to push them in with a tyre lever is getting me nowhere... any ideas, short of taking it to the LBS?

one shouldnt try to push pistons with the system closed as it can force the seals and can even damage them. Take the bleed port screw out of the lever under the rubber hood and then lever them out slowly and hopefully you can return some of the fluid in the pistons back to the lever reservoir without spilling it/overflow.

Right, thank you. When you say 'lever them out' do you mean pull the brake lever or push the pistons back in.? The pistons are stuck out.

Google ‘SRAM advancement procedure’ for sticky pistons. Basically you just push them back in with a tyre lever a few times.

Yeah, tried that and they don’t move…

Open the reservoir, push pistons out. If that doesn't work LBS is your friend.

Also try lubing them with a bit of DOT fluid to help get them moving again

Yep, LBS job chaps. Opened the screw and minimal movement.

Spoke to them just now and they have advised full bleed and see if that sorts it, then go from there if not. Thanks anyway.

In the unlikely event the caliper is knackered, do Apex HRD calipers play ball with AXS shifters? Just thinking that I could borrow one off the Cx bike in the short term...

SRAM says risk of fiery death. Never tried personally

1 Attachment

• mtb-and-road-hydraulic-disc-brake-lever-and-caliper-compatibility (1).pdf

So, update on this.

LBS bled brakes. Worked fine for 5km. Now back to square 1.

What now?!?

Sounds like they are seized. Sram uses dot fluid which is hygroscopic and will absorb water which can then rot your brakes.
Or more likely the seals swell up and grab onto the pistons. So they will pump out toward disc correctly but either retract super slow or just stay out.
Advise new pistons and seals for caliper. When changing ensure seal recesses are spotless with zero corrosion in there.