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I'm currently building up my dream bike around a salsa timberjack frame with alternator 2.0 dropouts. Everything was going smoothly until I went to fit my magura MT5 rear caliper, I have attached a 180mm IS to PM adapter (the max rotor size salsa say will work) but when I try to attach thr caliper to the adapter it makes contact with the frame first due to being a bulky 4 pot caliper. Am I doing something wrong or is there a workaround?
How close can it get? Other brake mounts may provide clearance otherwise you might be able to use a few washers to space it out if it's currently a close fit.
Try a bigger rotor just in case it fits, maybe not a floating one but a one piece cos they are a bit thinner.
Is that adapter definitely the right way around? It looks wrong to me, it could be the angle of the photo mind
That was my thought as well but looking at pictures of built bikes I think the dropout makes it look weird. One of the full bike models does appear to feature a 4 pot SRAM caliper though
Assume you mean the upper outer piston zone of the caliper fouls?
A different is>pm180 adapter might give a slightly different angle to rotate the caliper clockwise and allow clearance.
Try a Shimano/SRAM/n.e.other adapter.
Feel you pain, a FSA kforce caliper doesn't fit inside a last gen spark rear triangle.
Turn adapter round so long bit is at the top - does it fit then? If so, does wheel with rotor fitted on fit and allow brake to work?
Have a look at the Hope N mount. That looks like it might rotate the caliper clockwise very slightly. Depending on how much clash there is, perhaps a 183mm rotor and the Hope B mount although that looks like it might be a worse fit.
I appreciate you already have the brakes, but it might have to be a 2 pot caliper on the rear if you want to stay with Magura.
If you want one to try for fit etc I have a Magura 2pot surplus to requirements, happy to post to you
A little update, I managed to get it to fit but had to use a 3mm spacer on each post so now I think the caliper sits at 186mm rotor size, which doesn't exist. Do you think if I went for a 183mm rotor that it would work without too much loss of performance? I'll also be looking into different mounts as mentioned above and will report back with my findings.
Thanks to the guy offering up the 2 pot, so kind of you but it's a bit of a dream build for me and 4 pots are a part of that dream
If the outer 3mm of pad doesnt wear then the brake pads may foul each other at some point and stop the pads biting on the rotor. I'd also have thought as it doesn't make full contact there could be heat issues on steeper/longer descents as the bit of pad in contact is working harder for the same braking effort?
As its the rear its probably not such an issue, but up to you. Think I'd look for other adaptors that may have a different angle or look for what I think is old stock/standard 185mm rotors. Think hope do them for example
which doesn’t exist
Avid and Hope definitely make/made 185mm rotors which will be close enough.
Otherwise, for £3 this one looks like it rotates the mount more than the magura one?
https://www.chainreactioncycles.com/lifeline-is-to-post-disc-brake-mount-adaptor/rp-prod155579
So I solved this issue after a lot of internal screaming. The answer is using a 160mm lifeline is to pm adapter and then a magura qm40 20mm post mount adapter on top. I tried a lot of combos and this one worked perfectly. Thanks for everyone's help with this, got there in the end
Show us the full build!
That certainly looks like a good fix. Something at the bank of my head though says that isn't right and you can't just space out a rear is to post adapter like that - otherwise an is to 180mm post would be exactly what you've done (iirc, it *is* what you've done for a front IS to post)
Yep I can honestly say I'm not clever enough to know why this setup puts the caliper in a different place as opposed to just using a 180 is mount but it does.
If you look on Google images 160 and 180 IS adapters are very different
Should have the bike built up this weekend and will post some photos.
Yep I can honestly say I’m not clever enough to know why this setup puts the caliper in a different place as opposed to just using a 180 is mount but it does.
It's to do with a rear is mount not being concentric to the axle, so to shift the caliper into the correct position you need to both space and angle it, simply kicking out the spacer by another 10mm your pistons might not be in the right place.
Eg the front one might now be positioned for a 175mm rotor, the rear for a 185mm.
Of course you may also be lucky...
Just take out and check your pads regularly to begin with...
Isn't it because an ‘IS to post 180’ spacer could place the calliper anywhere around the circumference of the rotor, as long as the rotation matches. Your two part option has in total more spacer at the front and less at the back, which shifts it round. If you were so inclined you could make a single spacer that did that, it’s just the normal on isn’t that.
So forgive the rubbish drawing...
Black is a 160 rotor and the axle.
Red a 160 is to post adapter
Blue a 180 rotor
Green is an *identical* line. It's the correct length for the lower mount (because that's the one I drew and copied) but it's short for the higher mount
Obviously the drawing isn't especially representative/accurate.
I had an equivalent issue with a 29 Scandal, a 180mm rotor and a Guide RE calliper.
In the end a load of Googling got me to a 'standard' 180mm brake adaptor with two sets of cup/cone washers. One set between the calliper and the adaptor and another set between the adaptor and the frame.
A 2-pot calliper is easier as your only trying to centre one piston, whereas with a 4-pot...
Thanks for that, I've got a much better understanding now and now understand why this technically shouldn't have worked.
As I say I tried a few different combos, the first was a lifeline IS to PM 160 with a lifeline 180 PM to PM and that left the caliper in almost the same place as your diagram. I then switched the lifeline 180 PM to PM with a magura 20mm adapter and that placed the caliper perfectly in line with the rotor, the pads clamp so that the top of the pads is flush with the top of the rotor.
I will report back to this thread with some updated pics of the pads in a few months to show everyone how this fix has lasted
why this technically shouldn’t have worked
Lucky is often better than right
Should Salsa be looking into this and producing an adaptor? Is it just Magura 4 pots or will it be the same for shimano as well? If its all 4 pots then its a frame issue surely...
If its all 4 pots then its a frame issue surely…
Yeah but nah but.
Sure there's a compatibility issue there but that's not too say it's a frame issue. You just have to use 2 pots, not 4.
Maybe Shimano, magura et al need to look at their 4 pots and see why they're not compatible with certain frames...
It's only really a frame issue if you can't use any (or if the next frame is fine and the OP's isn't)
FWIW mind I'd say IS mounts have very limited place on a frame in 2022, on a replaceable dropout is absolutely not one of those.