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Repair rear disc/rotor locator screw


ctag

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At 167,000 km I had to replace the rear disk/rotor on my yr-2000 R1100RT. I removed the brake caliper and then the rear wheel. There are 2 locator screws (counter-sunk, Allen-head) originally installed by BMW with lock-tight (no one seems to know why). The repair manual instructs heating to 120 oC and remove. This worked for one screw after heating for approx. 1 minute with a propane torch. This did not work for the 2nd screw and I stripped the head. I tried to collapse the rounded head using a punch and hammer (you-tube suggestion) and after heating again, this did not work. I tried using a torque bit and hammer (also a you-tube suggestion) and after heating, it too failed. The Allen head was by now fairly round. Some suggest drilling the head off to the shank but his would only leave a few mm of the shaft to use vice grips, so I decided to centre-drill the screw and use a screw-extractor bit. I did not have a centre-drill bit so I centre-punched the centre of the Allen screw and used a small high-speed metal drill and machine oil to centre drill the screw completely. There is a cavity beyond the end of the threads in the hub so there is no danger once you are through. I then continued to centre drill using increasingly larger bits. The last bit was ¼ inch, and only slightly smaller than the screw shaft. When using this bit the screw loosened and I used the extractor bit to remove it. The threads in the hub were undamaged, though I came very close to damaging them. If anyone needs to do this, use a final drill size slightly smaller than ¼ inch.

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But in reality, even if you don't put those bolts in there is no issue. They are only used to hold the rotor in place until the wheel is installed. They have no "structural" role.

 

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szurszewski

They use the same arrangement on their cars, but, oddly since the rotors are of course much larger and MUCH heavier, the cars I've dealt with only used one locator screw. I assume they do this as they use lug bolts (instead of stud wheel flange with lug nuts holding the wheel on), and if you didn't have something to hold the rotor in place it would be finicky to line up the wheel, the rotor and the wheel flange (<--- not sure if that's the right term, but I mean the part of the hub assembly to which the rotor and wheel attach).

 

The ones on the cars get stuck too, and they can be pretty easily damaged - I was going to say "but at least they're bigger" - thinking about it though, if you got up to almost a 1/4" bit, they are probably just about the same size.

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