Post Mount to IS Adapter Misalignment

rtw19
rtw19 Posts: 3
edited February 2009 in MTB workshop & tech
I'm new to this, but there is alot on here about caliper and adpater issues so here goes.

i've got giant mph3 brakes which are IS mount. i recently traded up some forks to a set of reba 2009's which are post mount. i got the bigger disc and the right a2z adapter but the calipers now appear to be slightly misaligned when trying to set up the bite on the disc.

the disc is brand new - perfectly straight. i can get the bite pretty close but i have noticed that the disc is rubbing on both pads of the caliper at once!!

if i run with this and wear the pads down till their right, will it be ok?

Comments

  • supersonic
    supersonic Posts: 82,708
    They can take a coupke of rides to bed in.

    Which MPH3? Do they have the pad adjuster on the lever?
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  • petercarm
    petercarm Posts: 68
    Post mount has many merits, but being non adjustable for alignment issues is a serious retrograde step.

    The first thing to do is to try and make sure there is nothing obvious causing the misalignment. Unfortunately with the Reba, the mounting surface is covered in the powder coat surface and isn't even plain machined metal. This gives lots of potential for misalignment. Also, the Reba post mounts are very narrow giving very little register for the brake mounting. If there are any burrs or chips in the powder coat, these will knock everything out from the start.

    None of the fittings are fitted with dowels or any other proven engineering solution for alignment, so there will be small amounts of play you can achieve at the bolted joints. You may be able to nudge the adaptor over and cure alignment.

    Perfect alignment is when the rotor is centred in the slot of the caliper. It is nothing to do with clearance from the pads. With an aligned caliper if you push back the pads/pistons when they are next used they will self-align (unless a piston is sticking).

    If it all looks solidly put together, but the cumulation of small misalignments is causing the problem, then you need to cure the problem at the point where the caliper bolts to the adaptor. You can do this by having the adaptor "spot faced" in situ, as fitted on the fork. A good bike shop will have the tool for doing this. It will remove metal from the adaptor to leave a perfectly true surface. You will then need to shim the caliper over with IS brake mount shims.

    The only problem with this solution is if you ever unbolt the adaptor from the fork the adaptor may sit differently on the fork when it is bolted back together again.

    This potential problem is common for all post mount forks but of course they are the latest thing and soon we will have no choice but to buy them.
  • rtw19
    rtw19 Posts: 3
    i had a good look at the fixing mounts, and they were all as flush as you could hope for.

    it turned out the the caliper adapter from a2z was just not as well machinied as the rest of the components, and started to push out of line when it was tightened up.

    basically i had to bend the adapter slightly to get the alignment back - now it is perfect.

    i wouldn't normally do this, but the adjustment was so small it wouldn't have much affect on the adapter material.

    thanks for the help.
  • rockylee
    rockylee Posts: 31
    i had some issues with my allignment :(

    i used shim's ( little washers ) 0.2 mm - 0.5 . the bike shop gives em ya free in most cases just to get it spot on .

    hope it helps :)
    Rocky-M-Slayer.

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