Stripped head - rear brake rotor/disc

Lentarn

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Just started work to replace the rear brake disc, 4 of 5 of the bolts free and the 5th has melted like cheese (think its t40). I have new bolts and a new disc - what's the best way of getting this thing out? Hammer in the next size up of tox or drill it out or does anyone have some better method - access is limited as you have to go underneath the final drive. Small job becomes a big job which is nice for a saturday morning. Thanks in advance for any advice
 
The bolts all have loctite on them, so heating will help. then try a bigger bit, even try an allen bit. Support the back of the boss when hammering. I would try hammering the bolt head first to reform the socket...

There is a problem with cracking of the bosses which the bolts screw into on the earlier bike, warranty replacement if found. Newer bike ('10 on?) have a new spider ,
 
Use some heat. You can heat bolt from the wheel side of the final drive to loosen the threadlock. A soldering mat allows you to protect the surrounding parts from heat damage if necessary.

You should be able to fit an allen bit or torx bit to get purchase. Try different sizes to see. Getting it out again is a problem to deal with afterwards. Personally, and this may be unnecessary, I would refit the other bolts (clean off old threadlock first) to hold the disc while doing this.

If you have a low torque impact driver (as opposed to proper impcat wrench) this might be worth a short burst. Easier than hammering your breaker bar or ratchet.
 
I wouldn't hammer this particular part. Look at what you're hitting .... You've every chance of distorting the wheel/brake disc flange.

It's very easy to drill it out as you have full access to the other end of the bolt.
 
When I changed my disc I heated up the torx bit with a blow lamp, then placed it on the screw head to transfer the heat for a couple of moments - this loosens the threadlock.
As Steppers nearly says "don`t do it!" A larger torx or allen bit can be sacrificed first before resorting to Bf&I.
 
thanks all for the advice. Put heat on and got the bolt hot but i just can't get any purchase on the head as it is really rounded off. Contemplating whether to drill it out, which I haven't ever done and I'm a bit nervous about or whether there is anything else I can try short of getting in to a mechanic - I'm guessing that even a no bike mechanic would be able to do this kind of job. Did wonder whether putting some liquid metal onto a smaller sized tori that fits in the hole and letting it set but guessing that might just compound the problem
 
I think you could safely drill the head off the screw by selecting a bit same size as the shank od, then drilling through the torx socket hole. Maybe start one size smaller, then drill again, head should fall off.
 
Sorry if this is obvious, but in case worth mentionning - do you have the back brake mounted and the pedal depressed to secure the disc? If not, this might help in getting purchase. 2 of the other bolts in to hold the disc also worthwhile. In terms of getting purchase on the bolt, in my experience - less than many others - you can normally wedge something in there. An impact driver might work well. I have an old 14.4V Dewalt that works well in low torque situations. A T40 is around 6-7mm I think, and it is worth trying with 5, 6 and 7mm allen bits as well as the torx. Might even be worth trying with a flat head bit in an impact driver if you can wedge it into the bolt head. An alternative is to give it a light tap to get the bit seated with a wooden block supporting the rear of the flange - like Steptoe said, don't swing on it as you don't want to damage the flange. Others can say if they think even a couple of taps is a bad idea. Personally, I would try this before drilling out. And remember a small amount of heat before you turn it.

If you do get to drilling out, you have the option of going from the nearside or offside. I was going to write front or back but thought better of it. If you haven't done this before it is probably worth watching some videos on it to work out how and to see what you will need to get the head off and to remove the threaded length and clean the threads. If possible it would be good to get the threaded length out whole with a ezout or similar so there is no damage to the flange threads. With the head drilled off and the threadlock heated to release, you should be able to remove it either side. You might get lucky and find a drill bit in a pilot hole will rotate the thread out (or even the whole bolt from the rear - clockwise from back is anticlockwise from bolt head end). Worst case you can drill it out from the rear with successive drill bit sizes and clean the threads up. But do be careful doing this as replacing the flange is not something you will want to tackle.
 
Try liquid Ez-grip - it really does work with rounded off allen and torn heads. It’s saved me many times over they ears.
 

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Thanks all, i'll try some of that ez grip and if not i'll move on to drilling it out. Just hope I haven't buggered the flange. Thanks again - really do appreciate the advice and time you spend
 
Try liquid Ez-grip - it really does work with rounded off allen and torn heads. It’s saved me many times over they ears.

That stuff looks great. Thanks for posting.

Only other comment, as I realised after I posted above, is that the shank of the disc bolt is larger than the thread portion so will only come out on the offside / final drive side
 
As allready mentioned the bolts are fitted with Locktight, or "Thread locking Compound" in BMW language.

I recently changed my rotor, and I used an electric heat gun to warm up the flange. It did not take much of warming up to make a huge difference.

If this was my problem I would start by drilling out the head of the bolt, there by releasing the disk as well as reloading the bolt from any tension. Then I would access the flange from the Wheel side. I would start by drilling a tiny hole from the rear of the bolt. Then I would warm up the flange and use a larger drill (but small enough to not damage the threads in the flange)

Hopefully this drilling would make the bolt unscrew it self.
 
I think when the head is off, the disc will come free and leave the butt of the screw there to be gripped with good quality vise-grip. Deffo heat it up before trying to unscrew.
 
Bolt is out thank god. Local guy helped me out - no way I would have had the confidence to do what he did. Blowtorch, GT85 lubricant and a bit of smoke and a lot of patient tapping with a small chisel and a hammer to rotate it. Took over an hour for him to do it - not the worst he had seen but not the most straightforward either. Thanks to everyone who commented - learnt a lot and more confident for next time this happens. To dd something back, he did the tapping with the bolt when it was positioned just above the final drive - there is just enough angle to do this.
 
Thanks, that sounds like more faff than drilling it out, but great that it is sorted.

If you have one, post a photo of the offending bolt
 
If you have the aluminium disc carrier you should get the bike to BMW to have a steel one fitted on their recall system.
 
I would have welded a m8 nut to it,the weld heat would melt the threadlock it would be straight out.:thumby:

That's what I did with two of the Yamaha disc bolts. Another time I think an old allen/torx key in the socket (to protect it and just striking up a few arcs would give enough "sharp" heat to loosen it. The same method worked on the silly socket nuts they used on the exhaust manifolds.
 


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