Help! Rear disk wearing into brake assembly

Posted: Sat Feb 20, 2016 3:32 am

Hi F'ers

http://imgur.com/a/Wy6G1

Yet another issue... does anyone know what could cause this? The wheels are aligned and nothing is rattling. Theres a slight tight spot when i rotate the rear wheel but nothing serious enough to cause this kind of wear. The heat was so intense it melted of the disk guard Sad

I'm thinking a missing spacer?

- Alec

Posted: Sat Feb 20, 2016 11:31 am

If you haven't had the rear wheel off in the last while for a spacer to be missing then it could be your rear brake piston is not retracting.
I would clean and flush the entire system. Probably need to replace some glazed pads.

Hawk Joined: Aug 17, 2013 Posts: 302 Location: Devon. UK

From your pics it looks like the disc isn't running centred to the caliper bracket and is rubbing/binding on one side.

It looks like you've got an 82/83 wheel and disc assembly but a 79/80 caliper and bracket. The 79/80 discs are a different part to the 81/83 discs and it may be that you need a later caliper bracket to match the wheel/ disc you're using.

Posted: Sat Feb 20, 2016 12:42 pm

Stueecat wrote:

From your pics it looks like the disc isn't running centred to the caliper bracket and is rubbing/binding on one side.

It looks like you've got an 82/83 wheel and disc assembly but a 79/80 caliper and bracket. The 79/80 discs are a different part to the 81/83 discs and it may be that you need a later caliper bracket to match the wheel/ disc you're using.

What he said ... it's a disc / carrier issue, either because you are using different year parts, or you've got the wrong spacer between the wheel and the carrier ... I had that once because I used a later disc on an older wheel, mine ended up glowing bright red and then setting the caliper on fire ... Shocked

Regards,

Max

Posted: Sat Feb 20, 2016 10:49 pm

Arrrrggghhh!

I don't know what bike my wheels, discs or carriers came off.
All my discs are badly worn, especially the front pair. Replacing them is probably Item 1 on my refurb' stage 3 (the expensive bits) programme.
Until now I was blissfully unaware of a difference.

Posted: Sat Feb 20, 2016 11:18 pm

I had the same problem, but did not know why. My rear disc was badly worn, so I ordered a replacement from w wrecker in the US. I had the same fit problem, so I put the old worn one back on and it fit. It looks like you have a boomerang wheel like me and the disc is probably from a comstar.

I was unaware of the issue until I read this thread - now I know why my replacement did not fit.

Posted: Sun Feb 21, 2016 8:11 pm

Thanks for the quick replies everyone! Just to clarify, I need a different disc to match the constant wheels? Or the whole brake assembly?

Posted: Sun Feb 21, 2016 8:56 pm

Either or disc or carrier need to change ... I'd say whichever is easiest for you to find.

Regards,

Max

Hawk Joined: Aug 17, 2013 Posts: 302 Location: Devon. UK

I would go with changing the caliper and caliper bracket for the later twin piston type to match the wheel.

Ideally look for an 82/83 FC/FD caliper and bracket as those were the years your wheels were fitted, but in theory an 81 FB set up should work too as the disc and caliper bracket part numbers are the same as the 82/83 models even though the wheels were different.

Basically as long as it's a CB900 twin piston caliper and carrier it should fit ok.

Posted: Sun Feb 21, 2016 10:43 pm

Thank you all so much! I'll start looking Smile

Alec

Posted: Mon Feb 22, 2016 12:23 am

Could you machine the caliper mount to allow it to come in and allow it to square up with the disc and fit a spacer to the other side to take up the distance. Trying to find parts out here is hard enough, and more so when you are not 100% sure of what you have to start with

Posted: Mon Feb 22, 2016 1:55 am

norm wrote:

Could you machine the caliper mount to allow it to come in and allow it to square up with the disc and fit a spacer to the other side to take up the distance. Trying to find parts out here is hard enough, and more so when you are not 100% sure of what you have to start with

I'll give that a go first, and if it fails I'll start searching for the 82 model

Alec

Posted: Mon Feb 22, 2016 8:57 am

Can I suggest that you remove the disc and carrier and give us some photos, so that the rest of us can see whether we have anything that can help?

Regards,

Max

Posted: Mon Feb 22, 2016 9:07 pm

Alec if you don't know somebody with a mill, go to your local bearing shop and ask them if they know somebody who has one and does these sort of odd jobs, usually somebody retired with a mill in their shed

Posted: Mon Feb 22, 2016 9:58 pm

My neighbour has a mill so I just used that to make a spacer, 0.6mm and placed it between the brake assembly and the wheel. It gives it enough clearance for now until I can find the correct '82 setup to match the wheels