Drilling out Rear Disc Bolts?

I have tried to read all the available posts on this topic but can't seem to find what I am looking for. I can now join the club of numerous people who have had one or both of the small bolts on the rear disc strip the socket head out. If BMW could come up with a worse design for that area I'd have to see it. At any rate, I am trying to figure my next move. Everyone says, "Drill them out". I am assuming that means simply drilling off the tapered head. Doesn't that still leave a very short, stubby part of the screw still jammed in the final drive? What then? I also assume that since the muffler is directly behind these screws, that the final drive must be removed to do the actual drilling. Is that right? Even having the final drive on the bench, trying to accurately drill the bolt out of the final drive will just about guarantee that that thread will be ruined. Has anyone tried tapping a hex wrench into the hole, then mig welding it to the bolt head?

What a headache for what should be a simple procedure.....

The tension that caused the screw to be difficult to turn was centered at the contact point between the screw head and whatever it contacted. With the screwhead removed, that tension will be relieved and it could be fairly easy to remove the remaining screw shaft.

This is almost certainly not a "poor design" issue but rather operator error caused by use of inferior quality tools and/or poor technique. A trained, experienced technician most often can recognize the potential for problems before beginning and of course will use quality tools--there is in most cases a significant difference between DIYer skills and professional skills and it's most times worth the cost to have the pros do the work.

lkchris said:

The tension that caused the screw to be difficult to turn was centered at the contact point between the screw head and whatever it contacted. With the screwhead removed, that tension will be relieved and it could be fairly easy to remove the remaining screw shaft.

This is almost certainly not a "poor design" issue but rather operator error caused by use of inferior quality tools and/or poor technique. A trained, experienced technician most often can recognize the potential for problems before beginning and of course will use quality tools--there is in most cases a significant difference between DIYer skills and professional skills and it's most times worth the cost to have the pros do the work.

Click to expand...

I appreciate the answer, but take issue with half, no, most of that. I have followed the recommended procedure, for several hours, that is listed here by many experienced people, as to how to remove those bolts. It didn't work. I was able to loosen one of the screws slightly and carefully back it out. It turned so hard for 3/4 of the way that I thought I might be stripping the threads from the hole. So much for the problem being in the top flange of the screw. No, it's the threads. I have no doubt that when I cut the head off the other one, and remove the disc, that the screw will still be firmly welded to the final drive. I question whether you've ever had to actually take one of these out that was corroded this badly. You'd find the same thing.

Being a DIYer with cheap tools is the problem? In my life I have repaired a considerable amount of items, ranging from three types of BMW motorcycles, to inboard disc brakes on back hoes, steering clutches on bulldozers, and about everything in between. Inferior tools? It's an Allen wrench, of which I own a considerable variety. None of them from Harbor Freight. We are not talking about a $300 torque wrench.

These bolts need to come out to remove the disc, an item that is known even to BMW to wear out. As Paul states in another post, the use of thread locker is unnecessary. The socket is too shallow in the screw to hold the wrench without stripping after it sits in there for quite some time. And shall I mention that these screws are on the rear wheel, often drenched with water, etc, and that the back of the screw is open to the elements as opposed to being a blind hole. Good thinking there.

There is a considerable list of threads on this forum listing many disappointments with how "professionals" at dealerships have done a rather poor job. I personally couldn't, and wouldn't own BMWs if I had to drag them to the dealership for every repair job, and be hit with a staggering bill each time. I do the work myself so it's done to my satisfaction. When I get to the point that I don't want to work on them, or can't, I will be selling the herd and getting a Japanese model.

I used a small dremel cutting wheel to carefully cut a slot in the flat head bolt. I suspect both the heat created by cutting the slot and the clamping force reduction allowed me to remove both of these bolts. If I remember correctly they called for loctite on these bolts which doesn't release until around 250 degrees.

good luck.

I'll try the slot method. I have heated this screw with an oxy-acetylene torch about eight times, once where the outer flange was almost red. I figure I'm way past 250 degrees with the little fellow at this point. It's a '92. Probably never had the brake disc off. You can guess the result.

It's usually not about the quality of the tools or skill of the mechanic on those screws. Some times they come out easy and sometimes they are a bitch. I always use a manual impact driver to remove them. That drives the allen into the hole as it turns it. They still someh times strip.


Those screws come factory coated with thread locker (which I always wire wheel off and then coat with anti-seize).

As you noted, the depth of the allen socket is WAY too shallow for the force required to remove them when old.

To remove stripped out ones, drill a hole in the center and use an EZ-Out or broken bolt extractor. http://www.sears.com/craftsman-10-p...p-00966196000P?prdNo=1&blockNo=1&blockType=G1

Thanks, Lee, for the help. An impact wrench would be a good tool for this job normally. I didn't try that, although as events unfolded, in this situation it might have been a moot point. For some reason I always seem to end up with jobs no one else has faced. In this case the threads were so well locked together that I ended up first drilling off the head. Then trying to use vice grips and penetrating oil to slowly loosen the screw by going back and forth with it until it was so chewed up that there was not enough screw to hold. Still locked in there tight. Then getting out my trusty mig welder to weld a bolt to the remainder of the screw. Then starting to actually twist the bolt (5/16") itself with the socket wrench force. Finally, using the vise-grips again to grab it near the base and slowly turn it out of the hole. Yep, it was pretty well locked in there. And that was after I had used the torch to repeatedly heat the thing. Of course doing that with the disc off you could easily ruin that large seal, necessitating taking the whole final drive apart. Quite a project. I would be curious what my local BMW dealership would have charged me to remove that one screw.

I have ordered two new screws. As you say, step one will be wire brushing the lock-tite off of them, then applying a liberal coating of anti=seize before they go in.

Nice job! Atta way to not let it beat ya.
OM

jconway607 said:

Thanks, Lee, for the help. An impact wrench would be a good tool for this job normally.

Click to expand...

NOT a normal air or electric impact wrench, a MANUAL hammer driven impact driver: http://www.amazon.com/TEKTON-2905-8-Inch-Manual-7-Piece/dp/B000NPPATS

Scroll down to the bottom of the page for further description.


Glad you were able to get it out finally.

With heat to soften the threadlocker, I have generally found that they come out easily. That is how they are supposed to be disassembled. Without heat, they're very likely to strip.

Of course, it all depends on how they were installed last. Too tight, dry threads vs. coated with threadlock, good condition vs half-stripped hex, etc.

My guess on why mine were so tough to get out would be that no one besides myself had bothered to take the rear disc off for 23 years. I imagine that any bike that had had some routine maintenance done on that area in that time would probably not have been locked in so badly. Even so, one of the screws on mine did turn out, although not without considerable force. It reminds me of the exhaust flange nuts on the airheads, that could stand to be removed and replaced every few years at the most, just to keep them from locking up.