When Bruce had the tyres on his 75s changed the tyre fitter encountered a problem fitting his RH front caliper. As the brakes had to come off to allow the rims to be powder coated I decided to have a closer look. The LH caliper has normal bolts the RH calipers upper bolt is normal however the lower bolt is shouldered and the mounting point on the fork leg is partially tapped out. Has anyone encountered this before?
Regards Martin.

MartinW wrote:When Bruce had the tyres on his 75s changed the tyre fitter encountered a problem fitting his RH front caliper. As the brakes had to come off to allow the rims to be powder coated I decided to have a closer look. The LH caliper has normal bolts the RH calipers upper bolt is normal however the lower bolt is shouldered and the mounting point on the fork leg is partially tapped out. Has anyone encountered this before?
Regards Martin.

The one with the flange on it is for the front bolt of the rear caliper that also holds the bracket for the speedo sensor wire. Somebody probably got them mixed up when servicing all of the calipers.

Thanks Duck but why was the hole tapped and a standard bolt was too large to go through the hole.
Regards Martin.

MartinW wrote:Thanks Duck but why was the hole tapped and a standard bolt was too large to go through the hole.
Regards Martin

The unthreaded part of the "fit bolt" (parts catalog name for the flanged bolt) probably didn't go in all of the way in so whoever got the bolts mixed up probably had to drill the caliper mounting hole a little to make it fit.

The diameter of the hole on the fork leg that the shoulder went through was the same diameter as the other caliper mounting bolt holes. The threaded part of the hole was too small for the standard caliper mounting bolt to go through.
Regards Martin.

Got me. Both the fit bolt and the other caliper bolts have the same M10 threads. (I know because I replace all of the caliper bolts with SS bolts on my Ks.)

Does the bike have ABS brakes?  I know that on my K75RT one of the front caliper bolts has that flange and that when I take the calipers off I have to keep track of where it goes. 

The MaxBMW parts list shows that flange bolt installed in the upper mounting hole of the caliper, but it doesn't say which side.  Since the only difference between the sides is the wheel sensor for the ABS, I think it has something to do with controlling the position of the ABS sensor on that fork leg.  That is where it is located on my RT.

Bruce's bike did have ABS which was removed. However the caliper wasn't touched. Another mate has a 91 LT with ABS removed so I might have a look at that and see if it also has a modified bolt.
Regards Martin.

Yeah, the parts diagram does show a flanged bolt on the front ABS:

https://www.realoem.com/bmw/enUS/showparts?id=0572-USA---K569-BMW-K%2075%20S%20(0563,0572)&diagId=34_0637

I just went and looked at a 93 K75RT-ABS parts bike that I have and it has a flanged bolt installed in the upper bolt for the caliper on the side with the ABS sensor.  (Right)

If the caliper wasn't touched, then the flange bolt would still be there.  If the sensor was removed, the bolt would go on the side with the notched ring.

Thanks I'll do a bit more checking.
Regards Martin.

Those bolts belong to calipers on ABS machines.
The reason is, that it's very tight fit, as you adjust the sensor (with fillingplates) the sensor will always have the same gap to the ring,
after removing and installing the caliper on the bike.
With this also it prevents damage to the sensor by installing the caliper wrong to the bike as it should have a normal bolt.

An ABS caliper has an other ordernumber than non-abs calipers

Thanks to all who helped solve the issue. I'd already come to the conclusion that that was what it was for. Bruce and the tyre fitter apparently had a hard time fitting the caliper on his last tyre change due to that bolt. So as the bike will not be having it's ABS reinstated I've modified the caliper to take a standard bolt.  I got in contact with a mate who also has a 91 K100 LT with the ABS removed and got him to take a piccie of his caliper and it doesn't appear to have that bolt. I might be seeing this bike today so I'll have a closer look.
Regards Martin.