SRAM Red AXS Disc Rubbing

david.hills

Hi All,

I recently fitted a brand new SRAM Red AXS HRD groupset to my Trek Domane. It's fantastic except for one thing - the clearance between the disc brake pads and the rotor is tiny. Something in the region of 0.25mm either side of the rotor. As a result, it's almost impossible to avoid disc rub.

Things I've tried so far (in no particular order):

1. Centering the caliper, multiple times. Both by eye with a white background and by using a folded piece of card.
2. Cleaning and greasing the pistons (with DOT specific grease).
3. Changing the pads.
4. Bending the pad spring to provide more push-back as the pistons retract.
5. Bleeding the system, twice, following the SRAM instructions to the letter. I'm confident there's definitely no air in the hose at this point.
6. Truing the rotor.

It seems to me that the problem is that the pistons hardly retract at all when pressure is removed from the brake lever. As mentioned above, they move back perhaps 0.25mm on each side of the rotor. My Shimano Ultegra system on the other hand retracts something more like 1mm on either side of the rotor.

Does anybody have any thoughts before I take it to the bike shop? Has anybody else had issues with SRAM AXS HRD brakes?
I hate to admit defeat but I'm out of ideas at this point.

Thanks in advance.

Alejandrosdog

Sram: lovely stuff until it’s been used

redvee

Try a different wheel with CL opposed to 6 bolt or vice versa. I've got wheels with both fixings and there is a slight difference in the rotor placement in the frame, nt much but it needs the calliper aligning when I swap wheels. If you don't get any joy I'll take the complete groupset off your hands for £250

fenix

Alejandrosdog wrote:

Sram: lovely stuff until it’s been used

I was scathing of SRAM when it appeared. Who will use that rather than Shimano/Campag ?

Oh millions of us. I love mine - but I'm still on rim brakes. I've heard too many people not getting on with discs of all types but maybe they are luddites like me too.

david.hills

redvee wrote:

Try a different wheel with CL opposed to 6 bolt or vice versa. I've got wheels with both fixings and there is a slight difference in the rotor placement in the frame, nt much but it needs the calliper aligning when I swap wheels. If you don't get any joy I'll take the complete groupset off your hands for £250

Thanks for the suggestion redvee. Unfortunately all of my road bike wheels are centre lock so it's not something I can easily try.

I did however just find this official SRAM document that I hadn't previously seen. It has a couple of suggestions that I'll try tonight - https://www.servicearchive.sram.com/sit ... nglish.pdf

gezebo

Have you considered if it’s worth facing the Calliper mounts?

Alejandrosdog

gezebo wrote:

Have you considered if it’s worth facing the Calliper mounts?

Good call!

Skaramanga007

How did you get on?
I’m having the exact same issue , and done everything stated above to no avail

izza

I had a similar issue with my Madone. Used Shimano rotors and it has worked seamlessly ever since.

Skaramanga007

izza wrote:

I had a similar issue with my Madone. Used Shimano rotors and it has worked seamlessly ever since.

You used Shimano rotors on the Sram calipers and that solved the problem?

david.hills

Hi All,

Sorry for the lack of updates - I followed the procedure in the SRAM service document that I posted above - https://www.servicearchive.sram.com/sit ... nglish.pdf

See the sections in the document named "Disc Brake Pad Gap Reset - Monoblock caliper only" and "Disc Brake Pad Retraction Reset - Monoblock caliper only ". I ended up carrying out both of those procedures twice and it seemed to resolve the rubbing (on the workstand). I then carried out the bedding in procedure - https://sram.zendesk.com/hc/en-us/artic ... eparation-

I've ridden for a few weeks without any further problem.

As for Shimano rotors - I tried that too (had a pair lying around) but no success there for me - the braking made an awful sound.

-David.

bradgillespie

david.hills wrote:

I've ridden for a few weeks without any further problem.

Thanks for updating this. Really, glad yours worked out. It gives me hope. I've tried the same procedures twice as well but the spacing on mine is still terribly tight -- 0.25mm either side of the rotor. As a result, avoiding light rubbing is almost impossible. Now that your's is working well is the gap much larger than before?

I'm wondering if mine are overfilled and a full bleed is required as well. Do you think doing a bleed played a role in the fix? Or should I give the gap and retraction reset another go?

david.hills

Ah yes I forgot, I also bled the system for a 3rd time and managed to get a few more air bubbles out. It wasn't a full bleed - I just filled the syringes and pumped back and forth a few times while tapping the hose.

I still don't have loads of clearance, but definitely more than before - something like 0.5mm either side of the rotor. It's just enough to avoid rubbing after some careful centering of the caliper against a white background and a few final tweaks to the rotor trueness.

The only other thing I would add is that I really did pull the levers pretty hard when following the reset procedure.

Good luck with yours, I hope you manage to make progress.

-David.

bradgillespie

Perfect. Thanks for taking the time to provide the additional clarification. Fingers crossed!

bradgillespie

If anyone is curious here are a couple of photos of the the gap between he pads and the rotors after I worked on it. (the gap is a “bit” bigger than appears in the photo due to perspective). I wish there was another 0.5mm of clearance on either side, but it is at least workable now.
https://ibb.co/rF6F5WJ
https://ibb.co/5xnXHcg

akaspin

Maybe somebody here knows more. I found that SRAM silently replacing Gen1 SRAM Red AXS HRD "monoblock" calipers with Gen2 "2-piece". Gen2 calipers looks like polished Force AXS ones. I very curious about the reasons of replacement.

In https://www.servicearchive.sram.com/sites/default/files/techdocs/gen.0000000005964_rev_d_etap_axs_hrd_service_manual_english.pdf both "Pad Gap Reset" and "Pad Retraction Reset" are referred only to "monoblock" calipers.

bradgillespie

akaspin said:

Maybe somebody here knows more. I found that SRAM silently replacing Gen1 SRAM Red AXS HRD "monoblock" calipers with Gen2 "2-piece". Gen2 calipers looks like polished Force AXS ones. I very curious about the reasons of replacement.

You might find this article interesting. Specifically:

"According to SRAM brake product manager ... pad clearance remains the same, but the more reliable seal rollback (which determines effective pad clearance) should make it easier to adjust the calipers so they don’t rub on the rotor."