I've recently noticed that my rear brake was binding so I removed, cleaned and rebuilt the caliper with new seals i also replaced the pads with new ones. Put it all back , bleed the brakes but pads still rubbing on one part of the disk, so replaced disk with a new item from Moto Bins because I thought maybe that could be warped ( It was very worn ) But after all that , the brake still rubs on the disk in one spot.  Any ideas anyone on what the problem is.

thanks Phil

Just a thought. Is the disc sitting tight on the diff housing? Make sure both surfaces are good and clean.  Try marking the disc and housing, take disc off and rotate 90 degree and see if it's sticking in the same place.

Could be that the original problem is with the master-cylinder (piston not returning properly).

But would that cause binding in just one spot? Wouldn't it bind on the full rotation of the wheel?

Thanks postman will take disk off and clean everything and do what you've suggested then see what happens. May be its something to do with the hub?
I think if it was the master cylinder then it would probably bind all around the disk.

I'd be tempted to take the caliper off, remount the wheel and give it a good hard wriggle to see if there's any movement in the bearings.  Not saying it is, but it's one more thing to check/eliminate. 

The diagnostic process never changes:
1) List what could be the cause of the problem no matter how outrageous, in order of likelihood 
2) Work out a method to test each possibility. 
3) Test and eliminate each possibility till you find the cause

I have had the small bearing seize and spin in the housing before, granted that was a heavily loaded sidecar/trailer combo on a 9,000km trip so it had good reason to fail
In the end we had to replace everything bar the crownwheel and pinion. Thankfully I had a previously buggered spline donor for the bits required.

Al

Thanks AL-58
This will be on my check list. I will also take the wheel off and grab the disk and see if there's any movement in the bearings when I try and wriggle it round. Its going to be a busy weekend good job I'm off this week end.

The disc can be cupped rather than warped, the cupping creates a bulge in one spot even though the bottom and the top of the disc rotors surface is measurably good, and it will cause a fine contact to take place. So once the usual issues are dealt with and the mounting contact patches are clean and not causing any issue consider the disc for a small bulge in the centre of the rotors contact patch with the pads, it is ground off with something as simple as a stone to hone that little patch.

K75cster wrote:The disc can be cupped rather than warped.

Is that condition probable given that it is a brand new disk from Motobins?

I'm tending to agree about the line of investigation around bearings.

Could the caliper be sitting skewed on the final drive?  Maybe you should measure the runout on the disk relative to the final drive housing to see if it is within spec.

Robmac No not likely at all untill someone gets one, on the odd occasion one slips through, same story with the auto industry lemon, but they are more common. The symptoms fit a failing bearing or an odd high spot on the disc sometimes caused by a disc getting hot when skinned