Bolts broke off in my BW4404

[1998rollover]

Taking apart the AWD case to replace the chain, viscous coupler etc and the three bottom bolts below the drain plug, the heads broke off. There's quire a bit of each bolt sticking out.

The rest came apart with no problem.

Any solutions to get those out without ruining the threaded holes?

 

[Turdle]

I have been here, it's no fun. Thanks to this forum I have some advice to pass on.
Pictures of my results included.
step one-
mix acetone (fingernail polish remover will do) and trans fluid 50-50 and squirt it on the threads from the back side and also down the threads from broken side. Let it soak in over night.

Then weld a nut to the exposed bolt . The nut does not need to fit perfectly, it just needs to hold firmly enough to be welded.

Let this cool down and the broken bolt will almost certainly come out.

I had the best results using flux wire with the gas shield removed on a MIG welder, as suggested by other members on this forum.

 

[ZWilson07]

Is there enough room to get some vice grips or locking pliers on to twist them out?

Outside of that, welding a nut on it like posted above is about all I got without having to drill it out or using a left hand drill bit/EZ out/extractor.

 

[1998rollover]

Tried vise grips on the protruding stubs but no success. Just chews the threads off the bolt. Been soaking them up from both sides with Deep Creep, will try vise grips again tomorrow.

Welding to steel bolts embedded in a magnesium+(what? aluminum?) alloy casting seems like it could end poorly.

In any case I'll need three replacement bolts.

 

[ZWilson07]

Might try putting a little heat into it as well, that also will help pull a lot of the penetrant into it.

 

[1998rollover]

Depends on how much heat the case metal can take. Anyone got a junk TC to experiment on?

Part of the cause of the problem is the bolts used are a triangular profile, thread forming type. The threads weren't cut in the case they were mashed into shape as the bolts were power driven in.

Combine that with the front side of the holes being open and exposed to 188K miles of use, minus any kind of anti-seize and they locked up real nice.

Having the ends of the holes open may be useful. I could block the case up on a milling machine then align each of the holes with the spindle. Drill through with a cobalt bit then try an extractor, or cut enough that a 9x1.25 metric tap will peel out the remains of the bolt threads.

All those holes are getting a tap run all the way through and I'll make sure the open ends of the holes all get a dab of silicone to keep water and crud out.