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JustEmptyEveryPocket

Transmission Cross Member Bolts

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87 MJ 4.0L with brand new to me AX-15.

 

Truck is running and driving (thanks for all the help and advice in a previous thread) but I now have a new issue, hence a new post.

 

While driving to work I heard several thunks and what sounded like gravel hitting the undercarriage. Not unusual since I live on a gravel road. However, when I got to work and peeked under the truck I saw that the passenger side of the transmission cross member had lost a bolt, and the other two (I only have three, as the PO torn away part of the inner bracket somehow, losing the fourth bolt spot) were backed about halfway out. Obviously when I installed everything they were put in fully and torqued down properly.

 

I pulled out tools and tried to retighten the bolts in the parking lot, but they kept popping back off. It felt like some threads were catching, but after a few turns the bolts would drop back down. My only assumption is that the nuts in the frame rails are rusted out and have lost their threading, or have broken loose completely. Opinions on what I should do from here?

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Maybe the PO retapped the bolt holes.  Try getting bolts that are a size larger - probably metric sizes.

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It's very common for them to rust as exactly you described here  the rust belt. You can cut the heads off and pull what's left out with a magnet if it doesn't fall out and install these

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They come in many sizes and grades. It is your easiest route probably if you don't wish to cut and weld.

1498736165_Capture_2018-12-04-08-29-46.png.e7541c7a9c536a34f0bd97aec45a5084.png

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I'm going to try drilling them out to a 25/64 size (next closest size that I could find) and tapping for 7/16x20 bolts. This is assuming the threads inside the captive nuts are just rusted out, but there is meat left to form new threads. 

 

If that fails, I found some rivnuts (nutserts?) that are threaded for M10x1.5. I will drill out the hole to 17/32 to accommodate them. If I go with this route, do I need to somehow knock the captive nuts off? I have never used rivnuts before, but it seems like they would only work in the sheet metal thickness of the frame, not with the extra nut inside.

8 hours ago, 87MJTIM said:

Maybe the PO retapped the bolt holes.  Try getting bolts that are a size larger - probably metric sizes.

Tim, pretty sure the PO never touched these holes. The truck had a BA 10-5 when I got it, and there wouldn't be a reason to use the holes further back that I know of. Plus I ran a tap through them to start with, and it definitely felt like it was grabbing threads and cleaning them out. I am hoping (like I said above) that the threads were too rusted to hold the weight and stripped out.

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