UKC

I recently replaced the brake shoes on the rear of a bike because they’d worn out. During this exercise it became apparent that there is a misalignment in the brake calliper (photo attached, it’s not the clearest in the world but I struggled to get a good angle). On one side, the brake shoe lies flush with the wheel rim, but on the other side, there is a considerable misalignment, and the brake pad does not lie flush.

I’m confident that it’s not something I’ve introduced fitting the new brake shoes because on inspection the old ones had worn unevenly in a pattern which matched this misalignment.

I attempted a fix by grinding down one side of a spare washer but this failed as it couldn’t take up the misalignment.

Looking at the whole assembly more closely, I am moving towards the conclusion that something within the brake calliper such as the arm the shoe attaches to may be out of alignment or structurally deformed, but there is nothing obvious to me on inspection.

One possible solution is to replace the calliper, but I’m reluctant to do this without a bit more thought in case the problem isn’t with the calliper. With this in mind, I’d welcome any suggestions from UKC as to possible causes and fixes. I’m currently drawing a bit of a blank and struggling to find any possible solution on the internet (I could well be using the wrong terminology).

The caliper is a Shimano Sora caliper, in case such information is relevant.

Shouldn't you have a dome shaped washer with associated concave washer between the pad and the brake arm?

There should be adjustment in the brake block itself with the above described washers. 

If the arm is not pretty much parallel to the rim, you can carefully bend it using an adjustable spanner or similar. 

Thanks for both of your replies.

I forgot to mention that I'd added in those washers from the brakes of another bike to see whether I could take up the angle (it didn't work).

The thing that perplexes me slightly is that the front brakes have exactly the same setup, but don't suffer this issue.

Bending the arm sounds like it will form the plan of last resort.

As the above said, put back the dome/cup washers that should be between the caliper arm an the brake block. They have more than enough angle adjustment to fix your 'problem'. Your current setup has incorrect fittings (flat washers).

While the brake blocks should ideally have a bit of "toe-in" to stop them squealing, that looks excessive.

If you say the other side is parallel to the rim (and therefore has no toe-in), I wonder if the whole caliper is on squint.

1 - First, take the mudguard off and re-fit the caliper - might be an issue with the mudguard hanger.

2 - You say the front one is ok. I would try swapping the brake calipers over and see what the alignment is like then - that should tell you whether the issue is with the caliper or the frame.

Only tend to see that on V-brakes on mountain bikes (or some older cantilever-style brakes), where there are longer arms and block posts to clear the fatter tyres, which leaves room to add these.

Don't think I've ever seen those on road brakes.

I'd half wondered about the mudguard hanger, but I hadn't considered swapping the calipers over.

Thanks for these suggestions, I'll give them a go.

You won't be able to swap the callipers as the front has a much longer bolt than the rear. Bending the arm is straightforward, when working in a bike shop this was a regular process. 

Can I just say it's nice to see someone with rim brakes? 

A picture of Shimano sora brake pads seems to confirm my thoughts.

https://images.app.goo.gl/U3VMnNcCBSEckR8w9