Does anyone els have issues with aligning rear disc brakes?

[Offroader]

The fronts align very easily, but the rears are always an issue to get aligned. I usually spend a lot of time to get them aligned.

One of the issues I see is that when I tighten the caliper down they move considerably in the rear.

There must be a reason why the rears are so much harder than the disc brakes on the front.

It is also not the rotor being out of true because I always true the rear rotor with a dial indicator to within .125 mm.

I'm just wondering if other people have issues with mainly the rear or am I just doing something wrong.

 

[hypertoric_amplituhedron]

Yes, this is common. And, it usually is the rear caliper that wants to walk when torquing the bolts. The best practice depends on whether you have pad adjustment knobs on the caliper or gimble washers (all avid brakes have this, not so much the others). If you don't have gimble washers, try to lightly tighten the bolts in sequence, while applying pressure to the caliper to keep it aligned with the rotor.

I like to use brightly colored paper in the background to see the gaps between the pads and rotor. While cranking the two bolts down, bit by bit, the caliper will want to twist. You may have to loosen one bolt, to move it back into place. You may have to do this a few times as well, to get the metal surfaces to compress and seat properly.

 

[Offroader]

I actually shine a small led flashlight through the caliper to see more easily.

Any idea why the rear brakes move so much compared to the fronts? They have the same mechanism to bolt them down.

Here is a pic of the rear brake caliper.

 

[ferret]

Offroader,
to prevent the caliper from moving during the tightening try the following method:

First partially tighten the bolts so that the heads touch the caliper but don't apply pressure to it.
Make sure that the caliper is aligned correctly and tighten one bolts about 1/8 of a turn then the other bolt about 1/8 of a turn.
Check that the alignment hasn't changed.
Continue tightening the bolts 1/8 of a turn at a time alternating between them until both are fully tightened.
Make a final check that the alignment hasn't changed.

Avner.

 

[MadRhino]

The brake mount on your frame had been faced to align perfecly with the rear hub that it had originally. Installing a hub motor, it is most likely that it did result in the original mount facing not being perfect anymore. That is why the rear is harder to align than the front, and probably never as good. Re-facing the brake mount is the solution.

 

[E-geezer]

Stick some avid washers on there and be done with it

 

[ScooterMan101]

Besides wearing a LED Backpacking headlight , I angle the bike to have a contrast between a white or very light object under the bike so I can see better the space between the Disc and the Pads/Caliper ,
Also
For the Avid BB7's I use one business card or two on one side and gently push the caliper up against it , being careful not to bend the Disc, then tighten.

On The Shimano Hydraulics's , I use a business card between both sides of the Disc and Pads , and gently tighten the Bolts.

At my age / eyesight it is not a quick job, just like what you and others are experiencing. Often many attempts before getting it near perfect or perfect.

 

[MadRhino]

Well, when the same caliper does align easily on the front, but pita on the rear, there must be some alignment problem with the rr mount facing. This is not uncommon, for hub motors are fitted with custom dropouts or torque plates. I have had this problem with my bikes, until I succeeded building a perfectly straight fit.

Of course, the problem can be solved every time you adjust the caliper with f***ing patience, but nothing is better than doing it good once and for all. After it is good, it does stay fit much longer too. When your caliper does wear the pads straight and equal, and doesn't need adjustment at middle pad life, you have a winner.

 

[brumbrum]

My solution for my cromotor vs Hope caliper is two credit cards between the face of the motor and the face of the caliper piston. Tighten up and then pull out the wedged in cards. Alignment is good and also makes sure theres enough space for the caliper not to rub on the motor face.

 

[WoodlandHills]

BB7 calipers let you adjust the position of both pads, so once you position/shim the caliper over to the center of the rotor you can bring each pad in individually until it just clears the rotor. Then you can loosen the caliper mount bolts with the self-aligning washers, hold the brake tight and then tighten the mount bolts. This will set the pads parallel to the rotor. Then go back and reset each pad to just clear the rotor. Repeat until satisfied: this gives the best grip on the rotor w/o pushing it to either side.

Is this fiddly and time consuming? Absolutely, just like everything else on a bicycle! It's just the nature of the beast, you can minimize the hassle with money by buying hydraulic brakes and internal geared hubs, but it will never go away. Just my 2cents.... :?

 

[E-geezer]

You guys do realize the SOP for disc brakes is to simply clamp the lever with a strap with the bolts loose, let the caliper align itself on the disc and then tighten the bolts? With mechanicals, set the pads the correct ratio first. If you use the SRAM cup/cone washers it's painless. Hydros should retract the correct amount and mechanicals, you simply back out to get the clearance you need.

I've never heard of anyone having to use shims on the disc. I'm not sure what you all are doing.

 

[WoodlandHills]

You guys do realize the SOP for disc brakes is to simply clamp the lever with a strap with the bolts loose, let the caliper align itself on the disc and then tighten the bolts? With mechanicals, set the pads the correct ratio first. If you use the SRAM cup/cone washers it's painless. Hydros should retract the correct amount and mechanicals, you simply back out to get the clearance you need.

I've never heard of anyone having to use shims on the disc. I'm not sure what you all are doing.

My pair of $399 fatbikes sometimes require shims between the caliper adapter and the mounts on the bike. I find that a thin AN washer will do the trick to center the caliper to the rotor. This allows the self aligning washers to do their job without being pushed laterally. Interestingly, moving my three 135mm IGHs among the two bikes requires different shim combinations and it is most noticeable with fat new pads which have minimal clearance between pad and rotor, even with both adjusters backed out. Once you get the caliper centered it is basically as you describe.

I guess it depends on how close you like the pads to be to the rotor and how little play you have at the lever before the brakes bite. It also depends upon how much little noises from the drivetrain and brakes bug you.... They drive me crazy! With the bike clamped into a work stand, just clamping and tightening as you suggest without centering the caliper results in tiny pinging and scraping noises as I spin the wheel. To stop them I have to back the pads out too far for my liking, thus my method..... :wink:

 

[MadRhino]

My solution for my cromotor vs Hope caliper is two credit cards between the face of the motor and the face of the caliper piston. Tighten up and then pull out the wedged in cards. Alignment is good and also makes sure theres enough space for the caliper not to rub on the motor face.

Yep, spacer on one side of the mount face can save (or postpone) a re-facing job. Yet, the cards do remind the old days when we used playing cards to make a motor noise on the spokes.

 

[Offroader]

My solution for my cromotor vs Hope caliper is two credit cards between the face of the motor and the face of the caliper piston. Tighten up and then pull out the wedged in cards. Alignment is good and also makes sure theres enough space for the caliper not to rub on the motor face.

Interesting idea because the space between my caliper and MXUS motor is about the space of a couple of cards. Will have to try this next time. It should allow you to easily space it out by placing the card or shim up against the motor. Probably better using thin cut pieces of paper to get it perfect.

It would have also saved rubbing the paint off the edges of my MXUS motor when trying to align it and the caliper rubbed up on the motor.

 

[brumbrum]

My solution for my cromotor vs Hope caliper is two credit cards between the face of the motor and the face of the caliper piston. Tighten up and then pull out the wedged in cards. Alignment is good and also makes sure theres enough space for the caliper not to rub on the motor face.

Yep, spacer on one side of the mount face can save (or postpone) a re-facing job. Yet, the cards do remind the old days when we used playing cards to make a motor noise on the spokes.

Yep, a playing card and a washing line peg to clamp the card onto the frame. things were a lot simpler then for sure.