Brake will not align

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Brake will not align
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flag yeagermeister28
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Posted: Dec 15, 2020 at 12:39 Quote
Having an issue with my rear brake. Shimano MT-520 4 pistons. Cheaper models but have been fine up until recently.

Noticed recently that my rear caliper will not align properly. The caliper is maxed out on its mounts pushed fully inward to the wheel and the interior pad is still contacting the rotor. Caliper will align when loose but torqueing the bolts causes it to lean into the rotor.

So far I have tried:
1. Cleaning pistons (exterior were a bit sticky but now pushing evenly and issue still persists)
2. Checked the rotor is in fact true, and even tested with a new rotor and issue persists
3. Adjusted caliper by hand and eye which seemed to eliminate the constant rub and let the wheel spin free, but interior pad is still closer and touches rotor first pushing it into the outer pad. Had to really force the caliper to its absolute limit and verrrry slowly inch the bolts in to keep it from moving. Seemed excessive to go to these lengths just to align it.

Called the LBS to ask about facing the post mounts. They're booked out until after the new year. Will still get it in to get checked but not sure if this is causing the issue or not.

Any other ideas or things to check?
flag eshew
Posted: Dec 15, 2020 at 15:25 Quote
Are you using the conical washers?

IF you aren't using those try them between the bolt head & brake to see if that helps keep things straight. https://www.universalcycles.com/images/products/medium4/40430.jpg
flag m1dg3t
Posted: Dec 15, 2020 at 16:49 Quote
Are you loosening the caliper bolts, applying the brake, and tightening caliper bolts while brake is applied?
flag johnovey
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Posted: Dec 15, 2020 at 17:06 Quote
I have sometimes had to put a stainless steel washer with a tiny bit of grease on it between the bolt head & caliper.
This usually keeps the bolt from dragging the caliper over. Easy on the grease, as you don't want any on the pads or disc.
flag yeagermeister28
O+
Posted: Dec 15, 2020 at 19:42 Quote
eshew wrote:
Are you using the conical washers?

IF you aren't using those try them between the bolt head & brake to see if that helps keep things straight. https://www.universalcycles.com/images/products/medium4/40430.jpg

Yes sorry probably should've clarified. Currently using conical washers between the caliper and bolt heads.

m1dg3t wrote:
Are you loosening the caliper bolts, applying the brake, and tightening caliper bolts while brake is applied?

Yes this is what I normally do, but when the bolts are snugged in it forces the caliper to lean and makes it impossible to keep the inner pads from rubbing. Even tried using a Hayes alignment tool between the pads and rotors with no luck, the inner pads just push into the rotor and flex it.

Was able to align by hand and checking the gap from the top view. Still uneven and rotor sits closer to the inner pad, but doesn't permanently rub as bad. Makes the bike rideable but not the full fix I'm looking for. Had to REALLY push the caliper in while slowly tightening the bolts to try and fight the forced lean as they torque down.
flag dwee
O+
Posted: Dec 15, 2020 at 20:33 Quote
Do a routine brake bleed.
flag Reaperactual
Posted: Dec 15, 2020 at 23:31 Quote
Sounds very similar to issue I was having on my 2 year old SLX two pot rear caliper. After aligning perfectly by eye the pads won't centre in the same place with one or the other pistons pushing more, flexing the rotor and the inevitable rubbing.

After countless bleeds, a full caliper strip down and thourough clean, flush/bleed the problem came back after a week or so.

Mine wasn't a mounting problem it was down to sticky, lazy pistons which mades it impossible to get alignment dialled in.

Then the front started doing the same. Learned my lesson with the rear so didn't mess around with that one just swapped it for new too. All good now.
flag yeagermeister28
O+
Posted: Dec 16, 2020 at 7:39 Quote
cobba wrote:
Is the caliper attached directly to post mounts or is there an adapter between the caliper and the post mounts?

Is the rotor 6 bolt or center lock?

Adapter between caliper and post mounts

Rotors are centerlock
flag bobo2
Posted: Dec 16, 2020 at 11:33 Quote
check the surface that the caliper sits on. When manufactured some bikes dont offer 100% straight contact on all plains because they are not faced properly. mostly seen on bikes of a certain price point but sometimes mistakes happen. we always face the brake tabs to ensure 100% accuracy.

another thing to check is the wheel. on wheels with threaded axles the adjustment of the hub greatly matters to the alligment of the disc in relation to the caliper. with thru axle wheels this is highly unlikly.

thrid problem it could be is an issue with the pistons not retracting back into the caliper properly. certain brake models dothis more then other (eveyone remebers any older avid brake older then 4 years typically gets this problem)

the pulling the brake lever and tightening the bolts will only allign it 80-100%. alot of the time you need to make a adjustment without squeezing the brake lever.

also if the rotor isnt 100% straight then youll be cursing too. make sure its really really straight!

hope that helped and im betting its needing to be faced properly.
flag Reaperactual
Posted: Dec 16, 2020 at 11:49 Quote
Wait until the New Year and let your LBS fix it.
flag yeagermeister28
O+
Posted: Dec 17, 2020 at 7:56 Quote
bobo2 wrote:
check the surface that the caliper sits on. When manufactured some bikes dont offer 100% straight contact on all plains because they are not faced properly. mostly seen on bikes of a certain price point but sometimes mistakes happen. we always face the brake tabs to ensure 100% accuracy.

another thing to check is the wheel. on wheels with threaded axles the adjustment of the hub greatly matters to the alligment of the disc in relation to the caliper. with thru axle wheels this is highly unlikly.

thrid problem it could be is an issue with the pistons not retracting back into the caliper properly. certain brake models dothis more then other (eveyone remebers any older avid brake older then 4 years typically gets this problem)

the pulling the brake lever and tightening the bolts will only allign it 80-100%. alot of the time you need to make a adjustment without squeezing the brake lever.

also if the rotor isnt 100% straight then youll be cursing too. make sure its really really straight!

hope that helped and im betting its needing to be faced properly.

Thanks for this info. I'm leaning toward post mount facing being the culprit also but will have to wait to get it into the LBS for them to check.
flag yeagermeister28
O+
Posted: Dec 20, 2020 at 16:53 Quote
Finally had time today to work on the bike and take a deeper look at the brake and solved the issue.

Unexpected, but the issue was actually the hub. The end cap to the cheap stock Shimano hub had turned loose a few rotations so the hub was slightly wider than it should be. Maybe 1-2mm so barely noticeable. This kept the rotor in the same spot but pushed out the seat stay and caliper caliper causing it to contact the rotor no matter how inward it was set.

Tightened down the end cap and reinstalled the wheel and now when aligned the caliper sits dead center on the mounts.

Also took the time to upgrade to metallic pads and ice-tech rotors that I've had for a while. Took it for a ride after bedding them in and its perfect.
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