Seized cab mount bolt removal

[WA1DH]

The rear cab mounts on my 95 K1500 have been bad for a while. I have replacement polyurethane bushings and new bolts, so I decided to try to remove the old mounts today. Everything twisted apart, as the middle of the bolts were pretty much gone. I got into the top side of the mount where the captive nut is welded in the cab and have been working at getting the last inch of bolt out with no luck. I have tried an air chisel to cut a notch and work it out, banging a socket on it and using an air hammer, and welding a nut onto the bolt end. The welded nut kept snapping off and it is still frozen in place. I started drilling it but the bolt must be hardened steel as it was taking a long time for barely any progress. I will be trying a hammer drill tomorrow, but does anyone have any other suggestions on getting this free? I'm hoping I still have threads to grab in the captive nut when I'm done.

Pictures of where I'm at right now, and the replacement bolt. Thanks.

 

[eljefino]

I had this issue on a dodge dakota which admittedly is different.

I wound up bashing upwards, dislodging the original captive nut.

I then used a fly swatter handle with a new nut held in with masking tape, threaded that up into place. Used allthread to catch the nut. Assembled cab mounts, hand threaded another nut on the bottom side, then notched the downward sticking bit of allthread with a grinder so I could grip it with vise grips and finished torquing the lower nut.

You'll have to figure out for yourself if this meets your crashworthiness standards. A washer-nut probably spreads the load better but might be harder to fish in there.

Those are skinny looking metric bolts, are they 11mm? 7/16" is close but IDK if they make allthread in that size. Allthread is also a lesser grade metal.

 

[paulo57509]

If there's a future need, McMaster has Class 10.9 (150k psi) metric threaded rod.

 

[Trav]

Grind the broken bolt flush center punch it and use a cobalt 42 drill bit, start with a smaller diameter and work up or blow it away with a torch and weld a new nut in.

 

[emmett442]

2" metal hole saw, make a hole above the captive nut from the interior side. Cut the captive nut out, assemble cab mounts using regular nut/washer/bolt. Plug 2" hole with rubber plug.

 

[WA1DH]

2" metal hole saw, make a hole above the captive nut from the interior side. Cut the captive nut out, assemble cab mounts using regular nut/washer/bolt. Plug 2" hole with rubber plug.

This is the route I'm taking, but there was an access door under the carpet. I used a hole saw bit just slightly larger than the captive nut and cut it out on both sides. I picked up large fender washers and nuts, just haven't had the time to put it all back together yet. I plan to spray some Woolwax in their to rustproof before I close it up.

 

[Donald]

It's a 30 year old truck in Rhode Island. How good is the rest of the truck? RI uses salt on the roads.