I bought a high end used bike and it came with Magura brakes (I am at work now and don't know which model but looked them up one time and they were the top ones). Anyways the rear pads scrape against the rotor. If you spin the wheel with the bike on a rack they will only turn about 1/2 as long as they should before friction stops them. They seam to be lined up correctly but no amount of adjusting stops it. Does anyone has a solution for this?
It seams a waste of time to have super expensive brakes that cause drag on they bike while my slightly heavier BB7 drag none.
Upon closer inspection, all of my brake disc are either shimano or avid. As said before the brakes came from an used bike. Are the Magura disk narrower?
Also the disk is only scraping on the pads not any other part of the brake. One side scrapes(bike side) the outer side does not, but it is so close you can only tell by shinning a light past it, less than 1mm clearance.
Peteuga, thanks for trying Magura and be patient for just a moment.
Firstly, this is an easy fix and is most certainly an alignment or sticky piston situation.
I would determine (as you already) have which pad is dragging and determine if there is any room to allow that pad to be pushed back into its bore. If not, then its a caliper alignment issue and you can easily remove mounting hardware and caliper enough to shim the brake caliper away from the dragging pad with thin .2 mm shims provided by us and all other manufacturers. Try not to use normal washers from the hardware store because they are not precise nor consistent in thickness.
It the above situation is not the case and the caliper indeed looks like it is mounted accurately, then I would suspect a sticky caliper piston.
Again this is a straightforward fix and simple to perform.
Remove the wheel and pump the pads together observing that both pistons move toward each other. You may notice one of the two pads/piston slow to move initially so hold the freely moving piston/pad into its bore and then pump the lever blade to force the previously stuck piston.
I hold the free moving piston in its bore with a tire lever wedged in the slot where the rotor spins which make this step easy. Use the same tire lever to then push the newly freed piston back into its bore allowing internal fluid onto the internal part of that described piston and then pump the lever blade again moving the piston outward again. This allow that now wet piston outward and onto the dried seal.
Do this step a couple times and you should have rectified the problem.
Of course there could be more of an issue with the frame tabs needing machining or "facing" which is very common but since you had other brakes mounted on this bike (I assume) with no issues then I won't ramble on.
Below are some videos that may help.
I followed some of the advice posted here but I am still working to get it fixed. The inside caliper was hung and I got it moving again but I think I let it move to far out and the brakes have lost most of their strength. So I am ordering a bleed kit today to try and fix that. I have also ordered some of the .2mm shims. I tried to use some Home Depot washers and you all were correct they were much too thick, 1mm+. I will post again once I try these fixes.
Thanks for the help. My brakes are now fixed. The .2mm shims really did the trick. For people with future problems the previous poster is correct, washers from Home Depot are not going to work so save yourself the effort and get the correct shims. I also had to bleed the brakes since I pushed the piston out too far while trying to make sure one caliper was not hung up. I would say I got the bleed 90% correct, I could not do it by myself and my wife was loosing patents really fast. With more time I could get it right but I have a 3 year old and that just is not going to happen at least not tonight.
The idea is that you get one piston to move out while you hold the other one back. Do this with pads in and much easier to do with two people. I use a Park Tool blue metal ruler, but an old rotor or anything similar would work. Whatever you use, make sure it is clean.
Hold one pad/piston in place while the lever is pulled.
Whether it looks like the other piston/pad that was not held back moved or not (it might be stuck), gently push it back into the caliper body.
Do this a few times on one side and then the other.
For best results, take out pads, swab a very small amount of Magura blood around the piston seals, put back pads, and then do the above. Just be careful not to get oil on the pads..