XT Calipers on Avid Adaptors

gjt

Hi,

I've just got hold of a set of XT M785 disc brakes and I'm looking to get them set-up this weekend but I 've got a couple of questions about mounting them using 20mm Avid adaptors (post to post).

As far as I can tell the Avid adaptor is the same as the shimano adaptor in that it pushes the calipers out 20mm from the post so I assume I'm OK to use it? So my questions are:

1. I assume I don't need to use the Avid mounting bolts and all the washers as these are specific to Avid brakes. Is this correct?

2. Assuming that I don't need to use the Avid mounting bolts that leaves me with the XT bolts that came in the box which look too short to use with an adaptor - does anybody know if this is the case and if so where can I get longer bolts?

For reference this is the adaptor that I am using:

http://www.bicyclehero.com/gb/avid-180m ... wwodog4A-A

Cheers guys

poah

should fit if its for the correct size e.g 203 rather than 200. although I've had issues with them not fitting before other people have been fine

The Rookie

1/ Correct, you need shorter (18-20mm) bolts to suite
2/ No idea, depends, the Shimano 180mm PM-PM adaptor is 'straight through' an uses one set of longer bolts to pinch the lot together so maybe they are sized for that?

There is a small chance the XT calliper will foul the SRAM adaptor and you may need to either relieve it slightly with a file or get a new one.

jimothy78

I've done this, and yes it works. The avid bolts will be too long without all the washers on to use up the extra length, but you don't want to put any of the CPS washers between the adapter and calliper as it would obviously throw the spacing out. However, you can use some or all of the washers on the outside (furthest from the fork, after the calliper) to "use up" the spare length of the bolts whilst you source some shorter ones.

The ones that came with the brakes are probably the right length for a direct fit, so will be too short for use with the adapter. To work out what size bolts you'll need, just fit the calliper with the long CPS bolts until they bottom out (carefully), then back them off a turn or so (you don't want the final fit to have the bolts bottomed out completely) and measure the exposed length. Subtract that from the bolt length and that wil give you the length you need to find.

The Rookie

jimothy78 wrote:

To work out what size bolts you'll need, just fit the calliper with the long CPS bolts until they bottom out (carefully), then back them off a turn or so (you don't want the final fit to have the bolts bottomed out completely) and measure the exposed length. Subtract that from the bolt length and that wil give you the length you need to find.

Or just go to the Shimano techdocs which tell you they use an 18.7mm, hence 18-20 above.

jimothy78

The Rookie wrote:

Or just go to the Shimano techdocs which tell you they use an 18.7mm, hence 18-20 above.

ooops, missed that, sorry. :oops:

gjt

Thanks for the advice guys. I'll use the avid bolts with the washers above the caliper for a quick blast this weekend and will try and get hold of some correct bolts for next weekend. I've noticed on a few posts that Shimano have started using a longer bolt with CPS washers for the through bolt 180mm post to post adaptor - does anybody know where I can get hold of these?

Thanks again guys

jimothy78

The Rookie wrote:

Or just go to the Shimano techdocs which tell you they use an 18.7mm, hence 18-20 above.

Actually, just checked. The 18.7mm bolts are for direct mounting onto the posts (ie with 160mm rotor)or for use with an IS-PM adapter. For a straight-through PM-PM adapter you need one bolt longer than the other, due to the tapering shape. Shimano seem to use 37.9mm and 32.1mm bolts in conjunction with one half-set of CPS-style washers:
http://techdocs.shimano.com/media/techd ... 817097.pdf

Still reckon the best bet is to work it out empirically, as I described earlier, though

cobba

M6 x 37.9mm: http://www.petracycles.co.uk/shimano-spares-br-m595-calliper-fixing-bolt-unit-m6-379mm-p-41383.html

M6 x 32.1mm: http://www.petracycles.co.uk/shimano-spares-br-m595-calliper-fixing-bolt-unit-m6-321mm-p-41384.html

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/BR/EV-BR-M785-F-3161C_v1_m56577569830817097.pdf
&
http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SM/SI_8170A/SI-8170A-001-ENG_v1_m56577569830667774.PDF

gjt

Cobba, Jimothy - thanks for the responses, much appreciated - I'll get those bolts ordered this afternoon

adamfo

I found it a lot simpler just to spend £6 on the correct Shimano front mount adapter, when switching Avid 3 to XT on my Canyon.