Broken Rear Subframe Bolt

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Innocent Fool

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Took the LS in for a 4 wheel alignment and found out the rear drivers subframe bolt is broken off inside the bushing. I'm hoping I can get to it and work on it from the top inside the car but expect to cut a hole in the floor to access it. Anyone have any pics where the end of the bolt would be to give me an idea where to cut the access hole from inside the car?

I'm hoping I can pound it out from underneath the car and pull it out from the top. Anyone have any ideas?
 
If it is the rear most bolt, I can't help you. If it is on the rear subframe but the front bolt, I can help.
 
Innocent Fool said:
It's the rear most bolt that attaches the subframe to the body on the driver's side
Click to expand...

Ok sorry, I can't help with that one. It almost seems like you will need to drop the subframe to fix this, I had one bolt seize and take out the threads, and I don't see any way to pound that through. The threaded holes in the car unibody frame are an inch thick. Your best hope for a workaround would be to drill the bolt out from the top. I would try to do some reference point measurements, and transpose them to the inside of the trunk to get a general area to work in. If you could drill a small hole into the broken off bolt. and go in like an inch with a 13/64ths drill, you could then thread it to 1/4-20 with a tap, then thread in a 4-6 inch bolt to that hole. Then, stay with me now, you could find a way to magnetize the bolt with an A/C power source, which then could be used to locate the magnetic field inside the trunk with a traditional compass or metal filings to line up in a pattern inside the trunk in the void space that is where the bolt is. From there, if you get a definite match of location, hit it with a 1.5" hole saw to expose the top end of the bolt. I'd cut the bolt off flush with the threaded hole, then center punch the bolt and start drilling. A 1/5" drill will clean that old bolt out and leave you with a clean hole to use a 6" bolt to hold it together. An axle nut fit perfectly over my broken threaded hole, and I then used a pair of 5/8" thick washers to provide a good surface for the new nut to go on, along with a lock washer. Put the new bolt in from the bottom and use the nut and lock/flatwashers up inside to secure it. Hopefully, your inner bushing tube is not broken apart inside that bushing.

Another method of locating the nut area inside the trunk could be the careful application of heat to the added on 1/4" bolt to get the large bolt hot enough to heat up the sheet metal over the bolt inside the trunk.
 
If it were me, I'd do the whole job from the bottom up. If fact, one of the jobs on my list is to replace all the attaching bolts and bushings. The last time I did such a job I made use of hockey pucks as pads and used a length of stainless steel all-thread and two nylock nuts at each attachment point.

KS
 
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