Ok I know it isn't the most exciting subject in the world, but while the bike was on the center stand (to fit a new tyre) I could feel the brake disc was probably warped as I tried to spin the back wheel. It was binding in areas and free spinning in others. It has been like that since I've had the bike but it felt a bit worse than before.
I put my DTI on the disc and it confirmed it wasn't true. Well it was true that the disc was not running true...If you see what I mean.
I had painted the wheel while it was off, but the disc felt warped before. Should I remove all the paint from the disc mounting areas anyway? Could that effect the run out?
I couldn't find in the manual what the rear brake disc run out tolerance was, but I guess that it becoming very hard to rotate the wheel in a certain area was not good.
I bought a new EBC brake disc and fitted it to the wheel/bike. I thought I'd check to see what the DTI says and it was worse than my old disc!
My DTI is imperial and I'm more used to the metric system anyway. But I was getting 1.6 revolutions on the DTI for the old disc and 2.2 on the new one.
Any ideas ? At least from someone who can read a DTI
First, get all the paint off of the mating surfaces between the wheel hub and the brake disc. .002"- .003" difference in paint thickness at the disc mounting area will translate to .010" at the perimeter of the disc. A disc that's warped more than .010" or mounted incorrectly will be felt in the brake petal or hand lever depending on front or rear. Same thing for variances in disc thickness of more than .005" will feel like pulsing .
What Kawboy said. Years ago I purchased a near-new bike that had significant pulsing of the front brakes. I assumed it was a warped rotor but the bike only had a few hundred KM's on it - but the rotor was definitely 'out of true'. When I took the rotors off to be 'trued' I discovered there was a thin gasket - referred to as a 'damper' that was torn and missing pieces in several places which caused the rotor to be bolted to the wheel unevenly. Once I installed new gaskets and reinstalled the rotors - no more pulsing. Bit of a head scratcher - the torn damper must have been installed that way at the factory as the rotors had never been off before.