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Sram Rival HRD calliper alignment and piston retraction issues

pedropetepedropete Posts: 227
edited February 2018 in Workshop
Hello all, would be grateful for advice on the following issues with Sram RIval hydro brakes (or Force or Apex):

Background:
Running Sram Rival 1 HRD with 160mm centreline rotors on a 2016 Boardman CX Team and have experienced consistent eccentric rub at both ends since new. Made several attempts at re-aligning calipers and pushing pistons back without success. Recently changed wheels to Hunt 4Season Gravel Disc and have run for C.two weeks with original centreline rotors on the supplied Hunt 6-bolt/centerlock adapters. Similar issue with eccentric rub that didn’t resolve by re-alignment.

Current situation:
Just fitted new Shimano RT81 160mm rotors and new Evans compatible organic pads (old pads were on the minimum). Still getting slight eccentric rub at the front but, and this is probably the bigger issue, can’t get the rear pistons to push back far enough to accept the new rotor and pads. Did the usual pushback on old pads with flat bladed driver but the rear pistons won’t go back flush with the calliper face. Tried using a plastic tyre lever to push pistons back directly but they just seesaw in and out on opposing sides.

Suggestions?
I’m thinking the rear system may be over filled? Worth trying to bleed off the excess and see if pistons go back flush with body-face?
And what about the eccentric rub? Surely this shouldn’t be happening with brand new rotors? BTW: both rotor packages were intact and show no sign of having being bent/crushed.

Apologies for essay but figure more info better than too little when soliciting tech suggestions.

Cheers.

Posts

  • pedropetepedropete Posts: 227
    For the benefit of anyone else with similar problems:

    Yes, the rear brake was overfilled and full of air (which was an odd combo) but a bleed sorted the issue. And yes, it seems Shimano Ice Tech rotors are just as prone to being p!ssed out of the box as any others, just harder to true than one-piece 6-bolt rotors. Front brake was fine.

    Irritatingly, the rear lever now has a slight dead spot developing just before the point of being fully open. More sleuthing to come.
  • paulbnixpaulbnix Posts: 524
    @pedropete I'm using your thread as I have issues with disc brake rub and I also have SRAM Rival Hrd.

    In my case the rotor that came with the bike was much more air than metal and gave a loud brrrr when braking but it was quiet the rest of the time.

    I got fed up with this so bought one of the cheap Wiggle rotors.

    After fitting it the pad on one side rubs on the disc.

    Initially the rub was severe but now its just a gentle schhhh after I :-

    - reset the caliper by loosening it, pulling the brake on and tightening it
    - bent out the metal spring holding the pads
    - pushed the pistons fully home after pumping them out a bit

    It seems like the rotor is offset to one side - its not bent because the sound is continuous rather than eccentric like yours.

    Any idea what I should try next?
  • pedropetepedropete Posts: 227
    Afraid I’ve never had any luck with callipers self-aligning (pulling lever with the calliper bolts loosened). There’s just too much friction between the calliper mounting points and the frame mount. I do it by eye, with a work light or piece of white paper behind/below the calliper so you can see the gap. Get it as centered as you can and then true the rotor by hand, either with a bit of clean paper towel or a truing tool if you’ve got one. Lots of vids on YouTube showing how to true rotors so well worth giving it a go.
  • paulbnixpaulbnix Posts: 524
    pedropete wrote:
    Afraid I’ve never had any luck with callipers self-aligning (pulling lever with the calliper bolts loosened). There’s just too much friction between the calliper mounting points and the frame mount. I do it by eye, with a work light or piece of white paper behind/below the calliper so you can see the gap.
    I see what you mean now.
    I aligned the caliper by eye but I was still getting a quiet persistent rub.
    That’s when I realised the rear of one of the pads wasn’t moving as much as the other when the brake was released.

    I removed the pads and cleaned the inside of the caliper.

    That sorted it - there must have a bit of dirt stopping the pad releasing.
  • pedropetepedropete Posts: 227
    Yep, seems that it doesn’t take much for the pistons to get gunged up on these, especially if you’re use them offroad and/or in really filthy wet conditions. I did a piston advance and cleaned the sides of the pistons with a dab of DOT fluid. That seems to have cleaned and lubed them up nicely as both now advance and retract pretty consistently. And like you say, it makes alignment much easier too. Just be sure to clean any DOT fluid residue off piston faces and the rest of the calliper before refitting pads - use some isopropyl alcohol or a squirt of brake cleaner on some clean rag or paper towel.

    Just put on new RT81 rotors and Sram sintered pads this afternoon and everything seems to be running well. I’d forgotten how bl%@dy loud sintered pads were while bedding in though! And can’t believe how much work the rotors needed to true up out of the box. Worth it though as shed a sensible amount of weight and ditched the 6-bolt/centerlock adaptors... and they look good too :D
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