On one of our children's frames has been a pain to setup the rear brake on since new and I've finally worked out why. One of the post mount bolts is badly out of alignment and is pulling the top of the caliper to the left. This is compounded by the long bolt of the 140-160mm adapter but even with a 140mm rotor the caliper is pulled so far to the left it drags. In the past I had rotor shims fitted which meant you could just about get it to work but those have been used elsewhere while this bike was between children. I'd like to fix it properly by an not sure if the correct way. It did not look like a cross threading issue as the bolt turns easily and the thread looks clean. I think the hole is misaligned. I assume fixing will mean drilling out and fitting an insert which is beyond my skill set. Any other ideas to get it straight? I'm wondering about and hope +20 mount where the mount bolts to the frame and the caliper separately to the mount modified so the top can be pushed to the right (using convex washers so can be tightened).
compounded by the long bolt of the 140-160mm adapter
I don't know how well it would work but if the mounting is faced ok and it's just the bolt hole that is out I'd try replacing the adaptor with a Hope K type adaptor. The Hope adaptor bolts to the frame then the brake mounts independently to the adaptor.
Blimey, that's well out of whack!
An insert, by which I assume you man a helicoil would be for repairing a thread, not correcting ovality, which is what you would end up with if you drilled it out.
I can't really think of an obvious/easy way to fix that.
I think the mount is faced ok. Hope K was what I was thinking but would need the hole turned into more of a slot. I've tried with a L to prove this.
Blimey, that's well out of whack!
Yeap, way out. I was thinking a larger hole then tapping and fitting a thread reducer but there may not be enough meat in the mount to do that.
You could still it out, fill with steel putty resin and then, once it has cured, drill and retap, possibly consider a helicoil
What does the mount look like from the side and what is it made of? Couldn't the front "peg" be bent inwards a little?
It's aluminium and there is a brace to the rear peg. If you bent it then it would need facing.
You can get post mounts faced flat. May be that combined with the hope mount could compensate for the offset thread
For a first, non-destructive, cheap, fix I’d look at using a set of spherical washers above and below the caliper eg like early Avid/Sram brakes. This will allow the caliper to sit flat (hopefully) regardless of the mount position. You’ll then need to faff around with spacing, but it’s easy to try
That's exactly what I'd do - a cheap set of V-brake blocks would have the right amount of concave/convex washers of the right size and you could probably pick them up from Halfrauds on your way home from work.
That's exactly what I'd do - a cheap set of V-brake blocks would have the right amount of concave/convex washers of the right size and you could probably pick them up from Halfrauds on your way home from work.
When i worked the shop as a mechanic I had a big 5L tub of bits n’ bobs and nuts/washers etc for this issue, I imagine most shop mechanics are of the same mentality (I’ll keep this as it may come in handy at some point) so ask at your local shop
The caliper sits flat with conical/spherical washers on the bolt and always has. The issue is the the bolt drags it so far to left that the disc barely turns between the pads. I've ordered a hope mount to modify as that leaves the frame alone.
If you can get the caliper flat with conical washers but it's too far left, could you add some washers under the rotor bolts to push the rotor out towards the space the caliper is in? That's if the difference between the two bolts is not so great that it doesn't work.
That was how I had it in the past but it needed constant fiddling and was never quite right. The rotor shims are now in use elsewhere though it had so many if I went that way again if get some of the 1mm ones
Ideally I think it would be a warranty job, perhaps you're past that time though? A photo of the wider set-up might help with other suggestions but it looks like a tricky one to sort.
It a vitus kids bike from pre chiggle explosion so no joy there. I'll take some extra pictures.
It's a bit beyond me, but I was wondering whether there's enough adjustment to the left in the bolt that's true, to get the calliper parallel to the rotor. If it's a 6 bolt hub would it be possible then to space out the rotor?
-- Edit --
bikesanboats got there first!
Ok, you may not like this as a solution, and I'm sure a bike shop would not entertain it from a safety/liability perspective. I'd probably risk it myself on a rear brake of a bike that wasn't subject to Gnarcore riding, like my commuter bike.
Extend the slot on the calliper a bit. Just enough to get the adjustment and not close to the edge of the metal. A round needle file would be the weapon of choice for this job because you won't take off too much, too quickly.