UKH

I've just fitted new SRAM discs and Shimano Deore brakes (Calipers) to my bike.

Discs are 160mm (checked by measurement, and stamped).

The brackets on my bike for mounting the callipers are stamped with 160 / 180mm subject to direction of how they are bolted on. I can't be certain, but believe the brackets came with the bike.

Same components front and back.

Old system (Cable Tetrek I think they were?) lined up perfectly. 160mm discs, same brackets.

Now, witht he new discs and calipers, the front lines up perfect, but the back is such that the pad is overhanging the disc by about 3mm. You can see the wear line where the inside of the disc isn't being used. Wish I spotted it before trashing my pads.

I could just buy another 160mm mount, but see no reason why it would fix the issue.

Wheel is seated in the drop outs correctly.

Any idea what's going on?

I could upgrade to 180mm, keep the bracket in the 160mm position and have a 17mm spacer made, but this seems like a bit of a faff. Or machine the bracket down by 3mm, but this sounds harder to do.

Well, first thing to do would be to compare the old disks with the new ones and see if they've got a deeper braking surface.

Second, compare the old pads with the new ones and see if they are deeper.

I think it means front - 180 rear - 160. I also think you've got it the wrong way round.

You've been overthinking the 'air in the hydraulics' thing and now the whole job has gone all plane-on-a-treadmill.

OD on the old dics are identical to the new ones.

I'll compare the pads when I get home.

Discs and callipers came as a kit and the front lined up perfectly so I don't believe there's a compatibility issue.

I've not touched the bracket and the old system lined up perfectly.

If it was the wrong way round it would be out by 20mm.

Or maybe 10mm?

Is it that the bike was originally 180mm discs on the front and 160mm on the back and you've replaced that with 180mm both ends? So your disc on the back is 20mm too big in diameter.

Have you tried flipping the bracket/caliper?

160mm front and back, replaced with 160mm front and back. Not change to the OD of the discs at all.

It's definitely only out by 3mm. But you raise a valid point, I was thinking diameter, not radius, so it would be 10mm out if it was the wrong disc, but it's much closer than this which is why I'm scratching my head.

Not yet, will try tonight.

Are these photos of after the change?

Looks like a hell of a lot of wear for new SRAM rotors.

After the change.

It's only got about 10k on it. I know it looks like a step, but it's just an illusion so the disc is still like new. 

Not checked the pad, but even if I can fix the alignment issue, it may need changing.

It just looks like it might work with the bracket the other way round to me, if that's not it could it be that you're using a post mount brake caliper with a IS mount bracket?

In which case you'll need an IS to post mount adapter

https://www.tredz.co.uk/.Shimano-Post-Type-Calliper-Adapter-For-Rear-Disc-B...

I got my photo, and traced over the bracket, flipped it, and it does push the calliper towards the axle, but it looks like the movement will be way too much. I'll find out tonight.

As for the IS to Post mount, this is what I think I already have, although I may just have to try another to see if I get the same result. Maybe Carerra had a slightly out IS mount position, and had special brackets made, which somebody swapped. Who knows?

Failing that, apparently Hope make 163mm discs which may be my only solution. But if this is my solution, it's going to bug me forever not knowing why I needed 3mm oversized discs.

I think I'm getting calipers and mounts mixed up... Would love to know if you figure out whats up with it. Good luck!

If flipping the mount doesn't work try flipping the caliper.

Yes, you already have IS to PM bracket.

Giant also made 163mm rotors for their MPH brakes. Which was a pain when I swapped to Shimano brakes! But you shouldn't need them anyway.

I took a photo of my own trying to figure this out, I'm using a 163mm rotor, the bracket does look a little different to John's.

Is the new disk exactly the same size as the old one?

Any word on whether the pads are different (I mean, I think they should be, the correct pads for the Deores will be different to the Tektros/TRPs I believe)?

I've checked my bike with 160mm rotors and post-mounted brakes and the orientation of your mount looks correct to me.

I'd forget thoughts of out-of-position rear IS frame mounts, if front and back were fine before with the cable-pulls and the front is fine now with the Deore, there's something else which is preventing the pads not being in the right position on the rear rotor.

I've tried flipping the bracket. It pushes the calliper in too far so I can't get the wheel on. Flipping the calliper would mean very awkward hose routing so not going down that route.

They are different. See image. This still shouldn't cause the issue however.

The outside diameter (the bit that matters here) is identical to the mm.

That looks to me like the distance from the hole to the top of the pad is slightly smaller on the Deore compared to the Tektro.  Are you able to measure this distance?  Alternatively, put them both on a pin together (pads facing) and take a photo end-on.

Maybe the mount is out by 1-2mm and it didn't matter with the old brake pads... Would grinding 1-2mm off the back of the bracket work?

Did your old calipers have conical washers that might have created a different offset to the rotors? 

The Tektro pad to hole centerline is 1mm longer, but I'm not sure this tells me anything. The pad and calliper are designed to work together so should result in the top edge of the pad being a fixed distance from the mounting point.

I think this is probably the case.

I've thought about this. I'll probably get a new bracket first, to to see what difference that makes. And then I can have a go at modifying it. I don't have a mill, and the machining needs to be done pretty straight otherwise the calliper could rock.

Nope

It's almost certainly the adaptors. It won't be the pads, the caliper only ever goes one way up and the disc will, almost without question, be the size it says it is.

You've checked it's the right way up and if any washers are missing they'd be making things worse so that's not the issue. I'd guess you just need to try a different adaptor. In theory any should work with any brake but occasionally you get a combo that doesn't. A shimano one should sort it out.

It's 'discs' sorry couldn't resist after you brake post

Which model number deore calliper and which model number pads have you fitted?

You say the brakes came as a set but they are SRAM centreline disc rotors and Shimano calipers. I don't know who would sell you that as a set! 

I've seen this issue before on SRAM brakes, but never Shimano. As others have said, it doesn't matter what the brake surface of the rotor looks like (as long as you aren't braking on the 'arms' of the rotor) but what the brake pads look like. If they are overhanging the outside of the rotor then they will eventually get little lips on them which near the end of life will mean they the lips touch and your brake is pistons are pushing each other rather than clamping the rotor. 

At this point, you are better to keep using the current setup as long as you have decent braking otherwise if you move the caliper, then your pads will be braking across this wear line.