Not a very exciting thread, this!
Brake disc securing screws often break off, but it's not normally a problem because the wheel bolts hold the disc tight against the hub. Except that it really can be a problem. Every time the wheel is removed an unsecured disc can move slightly away from the hub. Never mind, the caliper and pads will stop it dropping off. Yes, but the slightest speck of muck dropping between the hub and disc may upset the runout and create brake judder. Maximum allowed runout is 0.1mm. I find that correctly fitted Brembo discs usually have a runout between 0.03 and 0.05mm. You only need a tiny speck of muck to upset this.
I've had this problem on my R for several years when the wheel has been taken off, usually when having tyres fitted. I tried to drill out the remains of the broken screw but HSS drill bits just break off. I asked my specialist garage to drill it out when they were doing some suspension work. They declined, saying that the screws get hard and brittle because of heat from the brakes and are near impossible to get out if they break off.
Anyway, 6 years later I was fitting new discs, so decided to have another go at the remains of the screw. I got some 3mm cobalt steel drill bits - at least one was sure to snap. I planned to carefully drill through the centre of the screw and remove the remains with a small screw extractor. The drilling worked but the screw extractor just jammed in the hub. Change of plan needed.
I managed to enlarge the hole gradually using a series of slightly larger HSS bits - 3.5mm, 4.2mm, 4.5mm and finally 5mm. After checking this was the correct size hole for the securing screw, I tapped out the hole with the correct metric tap. Success! I now have the new discs correctly secured to the hub and no trace of judder.
Brake disc securing screws often break off, but it's not normally a problem because the wheel bolts hold the disc tight against the hub. Except that it really can be a problem. Every time the wheel is removed an unsecured disc can move slightly away from the hub. Never mind, the caliper and pads will stop it dropping off. Yes, but the slightest speck of muck dropping between the hub and disc may upset the runout and create brake judder. Maximum allowed runout is 0.1mm. I find that correctly fitted Brembo discs usually have a runout between 0.03 and 0.05mm. You only need a tiny speck of muck to upset this.
I've had this problem on my R for several years when the wheel has been taken off, usually when having tyres fitted. I tried to drill out the remains of the broken screw but HSS drill bits just break off. I asked my specialist garage to drill it out when they were doing some suspension work. They declined, saying that the screws get hard and brittle because of heat from the brakes and are near impossible to get out if they break off.
Anyway, 6 years later I was fitting new discs, so decided to have another go at the remains of the screw. I got some 3mm cobalt steel drill bits - at least one was sure to snap. I planned to carefully drill through the centre of the screw and remove the remains with a small screw extractor. The drilling worked but the screw extractor just jammed in the hub. Change of plan needed.
I managed to enlarge the hole gradually using a series of slightly larger HSS bits - 3.5mm, 4.2mm, 4.5mm and finally 5mm. After checking this was the correct size hole for the securing screw, I tapped out the hole with the correct metric tap. Success! I now have the new discs correctly secured to the hub and no trace of judder.
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