Trans crossmember bolts

[JimB]

Decided to replace exhaust downpipe. Tried removing without cutting. Decided dropping the trans crossmember would be the easy way. 1 nut came off, 2 nuts had to cut off, 1 was able to get off with wrench and vise grips. Well now 3 of the studs just spin in the frame. I recently welded in new floor pans, replaced carpet and installed bench seat. So coming in from the top is a no. Looking for suggestions, ideas.

I am thinking of install rivnuts and using bolts. Has anyone done this before? Will they hold? Any better ideas? 1986/7 MJ AW4.

[zomeizter]

Rivnuts work great, I'd go that route if the top of the spinning studs is inaccessible...

[AZJeff]

The rivnuts needed to attach the M10 OEM bolts are gonna be pretty big, and to get a solid clinch of the nut into the frame, you are going to need a LOT of force on the pulling mandrel.

 

I don’t thing the mechanical tool I have would clinch a rivnut that big properly.   Do you have access to a hydraulic clinching tool, because that would do the job MUCH better on a rivnut that big.

[JimB]

This is what I have.

[AZJeff]

That is the tool I have as well.   The biggest size you can pull with those is 5/16-18 thread.  The size of the OEM bolts/studs that retain the crossmember are (IIRC) M10, which the closes equivalent in SAE would be 3/8" diameter.

 

The nutplates Jeep welded into the frame would have had a slight clearance hole around the threaded part, probably about 11mm.

 

I don't see how you are going to clinch a  rivnut of the larger than 11mm using that hand tool.

 

The BEST SOLUTION, of course, would be replace the now-broken nutplates with new nuts/washers in the frame rail.  

 

Option #1:  take up the carpet, cut clearance holes into the floorpan over the frame rail, and use self-locking nuts/washers.  Then cover the clearance holes with sheet metal, seam sealer, and screws or "pop" rivets.

 

Option #2:  Cut a small clearance window in the SIDE of the frame rail, right where it turns to go horizontal, adjacent to where the stripped nut plate is located.  Then create a new nut plate by taking a 3/8" nut, and weld it to a piece of 3/16" thick steel plate.  It is important that the plate you create STICKS OUT slightly on the outside of the frame, so you can hold it with some pliers when threading in the new bolt.   That is why dimension "W" is increased to "W" plus 1/4" in the sketch attached.  Once these are installed, some seam sealer can partially close up the opening created.   The attached sketch will show you what I am suggesting.

[mjeff87]

See if you can buy/rent/borrow the other style of rivnut tool, the one that looks like a pop rivet gun on steroids.  I installed a couple rivnuts in mine to hang a transfercase skid a long time ago, and compressed the handle with a small floor jack.  It worked great.

[AZJeff]

1 hour ago, mjeff87 said:

See if you can buy/rent/borrow the other style of rivnut tool, the one that looks like a pop rivet gun on steroids.  I installed a couple rivnuts in mine to hang a transfercase skid a long time ago, and compressed the handle with a small floor jack.  It worked great.

I think you must have missed the part where I said that the holes in the frame where the original nuts are welded in are probably AT LEAST 11mm in diameter.   That means he will need to install a rivnut bigger than 11mm if he wants to reuse the existing holes.  (He pretty much HAS to reuse the existing holes if he wants the crossmember to be in the correct spot.)

 

Rivnuts larger than 11mm come as M12x1.75, or 1/2-13, and there are no lever-type hand tools that will work with sizes that big.   There are "jackscrew" type tools that will do those larger sizes (as well as hydraulic tools), but they are a bit harder to find from retail outlets.  A picture of one is attached.

[mjeff87]

My buddy, who recently retired as a plant maintenance foreman for a huge chemical plant around here got the tool for me to use from his equipment shop.  It was a bear of a thing to use, I do remember that.  It wasn't something you could pick up at the local Autismzone or similar.  I basically had to use a floor jack to squeeze it.  I do like your idea.

[gogmorgo]

Another option, which I’d do long before cutting holes in the frame for access, would be to drill the hole just big enough to get a nut with the correct thread through it, using a stepper bit to keep the hole on centre, then weld the nut in place. Grind it flush. I’m not saying this is necessarily the most correct way to do it, but I don’t think there’s much better way without access from the top.
 

I’m not super thrilled about rivnuts under a vehicle because corrosion is an issue here, but they do work. If you’re set on using them, a pneumatic tool is the way to go. 

 

https://outilsquebec.com/en/air-tools-and-accessories/7748-air-pneumatic-nut-setting-riveter-astro-tools-prn1.html

 

This one’s only good up to m10 or 3/8”, so you might need the next one up if you have to go bigger, but it’s a lot easier than doing it manually.

[A-man930]

I'm gonna be "that guy"... should have addressed this when you had the floor out!   I encountered this same problem years ago and managed to keep it all together with just those "extra" bolts on those brackets inboard of the frame rails. 

 

Seriously, that was the best time to do a proper, full-strength repair.  Unfortunately, any other method is going to be less than ideal in some fashion.  As mentioned, installing rivnuts large enough will be difficult and you run a very good chance of those developing the same issue as you're dealing with now (spinning).  The slot and plate idea suggested by AZJeff is the most likely to be strong enough and hold-up over time, though, cutting slots in the frame rail isn't exactly without it's own drawbacks.  

 

When I had the floor out it got 12mm nuts welded in the factory locations and all the way to the back of the cab for future skidplate attachment points:  

 

 

[AZJeff]

 

5 minutes ago, A-man930 said:

When I had the floor out it got 12mm nuts welded in the factory locations and all the way to the back of the cab for future skidplate attachment points:  

 

 

that frame channel is impressively clean👍
 

it almost looks like a virgin factory assembly before the floor pan was attached.   How did you clean it, out of curiosity?

[A-man930]

Thanks!  It was pretty rust free before I got in there, just full of dirt.  

Shop vac, needle scaler, air hammer (for rattling loose as much junk as possible), sandpaper, and I might have even stuck a media blaster in there (can't recall).