I put some new (second hand) forks on my hardtail, and cannot get the front brake to stop rubbing; always on the same quarter of the wheel turn. The disc doesn’t look warped to me, although I haven’t measured run out with a dial gauge or anything technical so it is possible, but it was fine before the fork swap. What is odd is that if I align the calliper by eye, looking down the pads, i can get it to not rub, but as I tighten the calliper bolts all is well until I tighten the bottom one it’s last quarter turn, then the rub comes back. Slack it off a bit, it goes away. Just the bottom one mind, the top can be torqued correctly. Any ideas what it could be?

Yeah – the caliper is moving as the head of the bolt rotates against it. You will have to hold it in place or set it slightly off so that it moves into the correct position.

Or your brake mounts are squint and need faced (could just be some overpaint)

It’s moving when you torque the bolt up tight.

As you righty-tighty the washer / bolt head binds slightly more on one side (top/bottom of the slot) and pulls the caliper just a smidge off line. Usually outwards on bottom bolt iirc.

Look at it for which way and either compensate with a bit of offset or hold caliper with some grips.

I find alternating top bolt, bottom bolt not more than 1/8 turn at a time helps it not slip too.

I spent a while today installing a new front disc, caliper, etc and it was rubbing straight out the box.

If you’re careful when doing up the caliper you can get it to stay in place if you already have it lined up by eye.

I often use an elastic band on the lever in order to put the brake on when the bolts are loose, then tighten up the bolts carefully and 80% if the time it’s good with no rubbing.

The other 20% I’ll tweak the caliper a little bit, and true the disc a little also if needed. Good luck. 🙂

I’ve got this issue with a front disc I’ve installed. Mine is an old us mount fork with an us to post mount adapter but the calliper is ever so slightly off centre. I’m thinking of getting some really thin washers to slightly space the calliper onboard.

Which brakes are you using and what calliper mounts have you got?

hold the lever on tight when doing the last bit of the bolts up, then if the caliper tries to move it has to also ‘bend’ the disc at the same time.

If that still doesn’t work then use a spark plug feeler gauge* between pad and disc on the side that rubs so that even if it moves a bit then the gaps still there when the gauge is removed

* or a business card, or a few fold of paper or….. I just had a feeler gauge handy when I needed to do the same and now it lives in my bike toolbox.

Do this….

alternating top bolt, bottom bolt not more than 1/8 turn at a time

I’ve had the same problem ad used the suggestions above to get it fixed. Quarter turns of each bolt at a time. And put a business card (or something slimmer) between the pad and the disk on the side that is rubbing. Then undo the bolts, pull the brake lever and re-tighten. It should keep the pads slightly off the rotor.

If its only rubbing for the same quarter of a wheel turn, then you have a slightly bent disc. You can very easily straighten it by pushing (or pulling) that part of the disc with your fingers, without taking it off. It will only need to move a fraction of a millimeter. Work out the middle point where the disk is rubbing, and press in (or pull out) on the rotor at the edge. It should be enough to move it ever so slightly, and straighten.

Thanks for the replies; I’ll try and see if the disc is warped as mentioned, as I’m pretty sure I’ve tried all the other suggestions – apart from facing the post mounts. Actually, thinking about it, the fork, although used, only appeared to have been used with cantis or mini v’s, as the bungs were till in the post mount holes for the caliper, so I’ll check for any errant paint.

Hayes do an alignment gauge for about £10 on Chainreaction, effectively two feeler guages that go either side of the pads.

Doesn’t always get it perfect but it’s certainly better than nothing at all.

Just as an update, I removed the calliper, scraped the ends of the post mounts free of any overspray, then got a chair so I could sit while my bike was in the bike stand and really slowly tighten each bolt a tiny bit at a time. This got it so that just a tiny part of the disc was rubbing, and your could see it was ever so slightly out of true. So using an adjustable spanner as a make do truing fork, I managed to straighten it and get rub free running. Yay!

Then I went on a 7 mile quick thrash off road, and the rub has some back ever so slightly for a tiny part of the wheels rotation, so I will try truing them again as I wonder if I was too gentle with it and it’s pinged back to being warped.

Ive found that when I’ve straightened discs in the past they tend to go back after a while.

I’betting the caliper bolts have been over tightened at some point leaving indents in the caliper into which the bolts relocate themselves and cause the caliper to move as you tighten it up.

Sounds like disk was warped as well.

As above.

Check the soft alloy dome washers have not been crushed or snapped from over tightening.

I had one once where the domed washer (the one that lets all the the others in the stack swim around) had split. When tightening it down it opened up and skewed the calliper.

It’s quite hard to spot whether a rotor is warped when it’s only slight!