Chaps, I got a set of XT 8000 brakes for a bargain price so thought I’d stick them on my 09 Yeti 575. The old XT brakes were 180 up front and 160 on the rear. It being an XL and me weighing in around 15 stone thought I’d upgrade the rear to a 180 so bought a new ice tech 180 rotor and 180 IS adapter. Fitted the front fine however the back doesn’t fit, it almost looks like the adapter is the same size as the 160 although it is not. Should have I got a 180 post adapter instead? Apologies for the probable daft question.

A 180 front would be 160 rear. So if it’s the same adapter you need the 180 rear

Cheers P. The adapter on the rear is a new 180 but appears too small so does the 575 use Post or IS for rear brake mounting? Be flipped if I can work it out!

IS mount holes run across the bike, PM inline with the bike so it’s obvious which you have and not possible to mix them up.

A rear brake is normally 20mm smaller like for like (ie 10mm closer to the axle). Shimano front and back IS to post were not interchangeable though as the holes were slightly offset but that relates to the sideways position of the caliper.

Just looked at photos and the rear is indeed IS. You need either a generic front 203/rear 180 IS to PM or if going shimano be careful due to the off-centre holes I mentioned above. Not sure if it’s the fro t or the rear but it’s one of them.

Cheers Andy and apologies for being stupid. Just for clarity it is a rear brake with a 180 rotor. If I go for the adapter below from CRC which is rear post to IS would I need the 180mm or the 203? Thanks man.
http://www.chainreactioncycles.com/shimano-mount-adaptor-rear-post-to-is/rp-prod13749

Sorry, meant there should be no ambiguity when you know what the difference actually is, if you dont know what the difference is you dont know what to look for though. Should be a bit clearer now? It’s a bit confusing due to the mismatch front and rear.

Yeah middle 180 one should be it as that is a shimano rear specific one. Which adapter did you buy before?

Andy, I guess there is where I’m confused. I bought the Shimano Rear 180mm IS bracket using the link below from Merlin.

https://www.merlincycles.com/shimano-disc-brake-brackets-46083.html

So should I have bought the ‘Front or rear’ 180mm Post bracket?

Cheers.

edit: hang on, re-reading it, no you seem to have bought the right one. Rear 180 IS. That should work fine. Do you have it the right way up?
It should be engraved rear 180 and have an up arrow unless it’s OEM with no markings.

Andy, I’ll double check later once I get home. Thanks.

Andy, here are a few photos I just took:

This is the new adapter fixed:
https://www.dropbox.com/s/cte8m2tt4so9pcf/IMAG0855.jpg?dl=0
https://www.dropbox.com/s/adofshmml3hrsl2/IMAG0861.jpg?dl=0

This shows how far the caliper is off from the adapter:
https://www.dropbox.com/s/74bfydxp9vfds71/IMAG0862.jpg?dl=0

These show the old 160 adapter and the new 180 adapter:
https://www.dropbox.com/s/paalrcihlmmslfn/IMAG0863.jpg?dl=0

This shows they are identical in size..
https://www.dropbox.com/s/kq4quyohsw1ywma/IMAG0864.jpg?dl=0

Ahhh, is the one Merlin have sent me front and not rear specific??

Sussed it. Aye the one Merlin have sent is indeed front specific 180 and not the rear one I ordered. That would explain why it looks the same size as a rear 160mm adapter!

just seen this and yes, it’s a front. F180 is the giveaway. Your old one is just a generic F160, R180 adapter. The proper R180 will be about 10mm deeper.