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Old front brake: 2007-ish Avid BB7 with 180mm rotor, previously always used IS mount adaptor.
New Rock Shox forks with post mount fitting.
How do I fit the brake? There don't seem to be any 180mm PM front adaptor fittings stocked by the usual online suspects, just 160 and 200. I'd kind of assumed I might be able to screw the brake [i]sans[/i] IS adaptor straight onto the post mounts, but it doesn't seem likely, eyeballing it. Could be wrong there, though. Suggestions?
you need a +20mm Post to post. Assuming your forks are 160mm as standard (some arent).
A 180 post to post adapter should be easy to find, very common.
ebay search brake mount adapter there's loads.
Are a lot of forks not 180mm as standard now...?
surely a post to post +20mm is just a 10mm spacer and a slightly longer bolt?
It's a bit more complicated than that SteveT1 as the caliper is rotating round a different centre than the wheel so the adapter has a different spacing at either end to accomodate this.
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hang on
FFS, I thought that was why IS was brought in - y'know, Industry Standard and all that. Back to mountain biking after a few years out and they've ****ed it all up AGAIN.
montgomery - you know what they say;
"If you don't like the cycle industry standard then wait a minute"
few years out and half your bike's obsolete and no longer supported...
[url= http://www.ebay.co.uk/itm/POST-to-POST-mount-Disc-Brake-Adaptor-180mm-7-inch-Avid-Shimano-5-Colours-/201110814560?_trksid=p2141725.m3641.l6368 ]ill try again[/url]
Thanks, I'll try that Ebay item and, failing that, the bolt set pictured above.
I thought I'd got to grips OK with the concept of tapered headsets, 9/10/11 speed issues, pressfit/external BBs, 26/650b/29" and the like. Now this - what a load of bollocks.
Selection of shimano adapters here: http://www.chainreactioncycles.com/shimano-mount-adaptor-front-post-to-post/rp-prod13747
There are others and I've not use Avid so no idea if you need the cup and cone washers but if you have them on there already then I suspect so along with the correct adapter.
This is what it should be looking like when it's finished (from an MTBR thread):
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I can see the bolts and spacers above fitting, but it's hard to see how that Ebay adaptor linked above (pic below) will fit this setup.
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There are two different kinds of post mount adaptors. The one in the top picture is less common (older?) whereas most modern mounts are like the one in the bottom picture. It doesn't matter which you use - the brake will end up in the same position. The bottom ones are maybe better because you don't have to keep screwing / unscrewing bolts into soft magnesium fork lowers and you can't really get it wrong by using bolts that are too short (I.e. they only engage 2-3 threads in the fork), although they're probably a bit heavier.
How do these adaptors cope with different post mounts, though, e.g. like the one above, or this one below with the posts projecting the same length from the fork:
[img] 
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Or is the latter another old standard (looks like the one I had on a set of 1999 Manitous)?
****in' bike industry.
Can't you just have a look at your bike and realise that it all just bolts together very easily? There can be very few simpler things to fix on a bike.
Basically, most forks will take a 160mm disc and brake without any adaptor. If you want to use a 180mm disc, you buy a 180F mount (also called "+20mm"). Some forks however will use a 180 or 200mm rotor as standard without an adaptor. On these forks (usually the burliest forks with more travel) you can't use a smaller disc.
That picture is indeed post mount. This standard has been around for ages but has only recently become commonplace. I think Manitous have had it for 10 ish years.