Had to change pads in rear caliper due to a massive bind on in very narrow and hilly road situation. Put new oem piston seals and O rings in and bolted everything up. Now comes the problem--- I can only fit the outer pad after taking it down 3mm so that it will slide in. The bike has only done 14k miles from new[1985],I bought it 3yrs ago with only 4k miles,this is the first time I have had to touch the brakes. It is as if the caliper is of center and yet  I cant see how this can be so. Any body any ideas?

Have you checked if the rear wheel still has the shim fitted against the final drive surface, that might put it out of line a bit?
RT

Did you check that the piston slides freely in the bore without the seals. Often a build up of crud on the piston or in the bore will prevent the piston returning all the way and becomes a problem after new pads are installed.
The other thing could be that the piston in the mastercylinder is suffering from the same problem and holding the caliper pistons from returning.

Many thanks RT and Rick G, I cleaned and re sealed both pistons pushed them both fully back then fitted the calliper. This was when I found the Outside pad would not fit.  I have a spacer shim between the back wheel and the disc, should there be one between wheel and Hub? Only got a stone age manual from "H" and this is not very clear on this.I can still use the bike but I would like it to be right. Regards Gordon

The 1.5mm spacer goes between the wheel and the disc not the disc and hub. Release the bleed nipple and let any pressure out, it may only be air but if there is pressure there then a constant binding on the disc will be the outcome.
If that is the case then investigate the master cylinder for binding and not returning and so not releasing the pressure in the system.
The hydraulic braking system is one thing that does suffer from low miles. The MC gets a build up of crud which jams the piston partway down the bore and keeps the brakes partialy on.

Thanks Rick G The problem showed itself before I had tightened the bleeder or even refitted the brake pipe, I had also checked the full movement of the Master cylinder piston. When you look at the gap between calliper and disc the gap on the inner side is far greater than on the outside. It is as if the calliper is not centralized and yet it can fit no other way.---Might have to kick next doors cat round the garden for inspiration.

You haven't reversed the disc have you. You will know as the countersunk socket head screws dont fit.

Not touched disc Rik G but set screws are in place. Going to find that cat. Many thanks:

 
 Had discussion with cat-- problem appears to be disc has gone cone shaped by approx. 1.5mm from outer rim to rivet ring. there is no distortion in the trueness of the disc it has just dished.Will have to get new/replacement disc. This is the only thing I have found not to be ok so will try it. Thank you all for your time and help. There is a free web site where you can see blow up drawings, BMW Motoradd International, use the classics section it is a free service from Bmw but you can get part nos off it for suppliers ie. James Sherlock Devon UK Motobins etc:cheers:

Ah Ha I have one of them here, came in a box of bits AL-58 gave me one of these days I will make a new disc on the centre.
I use an EBC fully floating disc and it is much better than the original.

That disk was one result of riding a sidecar around OZ with a camper trailer attached.  Total weight at the weighbridge when I got home including me and the dog was 880kg.  The poor bike.  The brakes really copped a hiding on that trip.



Al