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Rear frame stiffeners for towing/weight?

SurplusFan98

NAXJA Forum User
Location
LA
I've got a 97 4.0 Manual, and I'm getting ready to do some work on the backend. I already have a tow hitch and a factory gas tank skid attached to the frame. I'm going to remove the hitch, add low profile shackle relocation brackets and an XRC tire carrier which mounts to the frame in the rear. My use case is NOT heavy rock crawling but overlanding and some light offroading. In the future i'm considering modifying the interior of the jeep (adding weight) and also possibly towing an overland trailer at some point (>3000lbs).

I've realized i'm adding a bunch of weight and the backend of the frame will likely bear the brunt of it. This seems like a good time to add frame support since I'm taking the whole thing apart. But, I don't know that I really need it, and I've even seen where some in the rock crawling community say the back ones don't even really provide much support compared to the others. If I don't need these, I can get the rest of the work done in a day. If I do add these, its much more expensive and time consuming, and I'm not even sure the payoff is worth it.

My question is: given my use case, would you go to the extra time and expense to add rear stiffeners before making the other mods?
 
You can achieve most of what you are wanting to do with a good bumper.
https://www.naxja.org/forum/showthread.php?t=1160514

Fair enough. I've purchased the XRC tire carrier. The brackets for the bumper attach both to the rail underneath (with nut strips) and to the bumper mount points at the rear. This would seem to be stronger than the way my hitch is mounted, so I'm not that worried about towing I guess. The hitch and bumper are both rated to 5k pounds. I'm just a little concerned about weight overall on the frame rails. This bumper is like 230lbs before you add anything to it. I'm sure lots of people have done this and haven't had issues. I just don't want to throw all this together only to later decide I should have done the stiffeners, and now I gotta disassemble the whole thing again.

I guess I'm just trying to get someone to tell me to stop my hand wringing and just do it already...
 
I have towed way more than the recommended 5k many times on a stock hitch and see no stress issues yet. You need to worry more about braking. Stock xj brakes are adequate for every day use, you can really feel an extra 1500 pounds behind you, and at 5k? Plan your stops carefully and way in advance!
 
I have towed way more than the recommended 5k many times on a stock hitch and see no stress issues yet. You need to worry more about braking. Stock xj brakes are adequate for every day use, you can really feel an extra 1500 pounds behind you, and at 5k? Plan your stops carefully and way in advance!

Thats a fair point. I probably need to think a little bit more about brakes before I do anything with my axles. I guess making sure that any trailer I might want to tow has electric brakes is a good idea...
 
My assessment is that there is a lot of qualitative information about the benefit of weld-on frame stiffeners. The general consensus is that frame stiffeners help with improving frame stiffness, but considering how they integrate into the unibody frame, I would be surprised if they are highly effective at improving twist stiffness.

If you are trying to improve twist stiffness of the rear portion of the unibody frame, I suggest looking at the JCR gas tank skid. It is unique among gas tank skids in that it not only bolts to the unibody rail but also to the rear cross plate. This will provide a substantial twist stiffening effect. If you are not a welder, I think this is the best cost vs benefit approach to improving the twist stiffness of the rear of the XJ.

A well-built bumper that is firmly attached to the unibody rails will also help a bunch. You might want to consider some heavy duty frame rail nut strips that integrate to the rear cross plate such as:

https://www.ebay.com/itm/163691598618
 
I'm not going to twist your arm one way or another, but rather share my experience.

I recently bought a tire carrier rear bumper, and also already had my gas tank out for other mods. Upon disassembly of my shackle relocation brackets and trailer hitch while prepping the rear unibody area for the bumper mounts, I could not help but feel uncomfortable with how thin the mounting area is for the rear bumper. Maybe I had some rust that made it seem worse than others', but I could easily flex the unibody rail with a screwdriver wedged into a hole.

I decided to plate where the bumper mounts. It was some extra work, but I feel much more confident about mounting a heavy bumper and treating it rough. I also purchased some of the beefy eBay bumper mounts (linked below) to really boost my confidence.

https://www.ebay.com/itm/3740353821...ktjusHjgChr4GP_8GWBLEP4s_33quk7YaAvnjEALw_wcB


9SPaJP0.jpg


FVxDnQm.jpg
 
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Interesting - the brackets XJlimitedx99 linked look to be a clone of the Circle S brackets that Maxbraketorque linked, but at a lower price point.

From what I can tell, the two products look identical. I have the Circle S ones myself, and while I did have to oval a couple of the frame rail probably more due to my Jeep than their design, the install was pretty painless/easy (I did post my experiences over on the Mod Tech board, should turn up easily by searching).

Also, I agree with maxbraketorque's point that things like stout bumpers, belly pans, gas tank skids, etc. that tie the two "frame rails" together will do more for increasing twist stiffness than plating the rails individually will because now you've braced the two frame rails against each other and reduced the lever arms that the twisting forces can act upon.
 
Interesting - the brackets XJlimitedx99 linked look to be a clone of the Circle S brackets that Maxbraketorque linked, but at a lower price point.

From what I can tell, the two products look identical. I have the Circle S ones myself, and while I did have to oval a couple of the frame rail probably more due to my Jeep than their design, the install was pretty painless/easy (I did post my experiences over on the Mod Tech board, should turn up easily by searching).

I actually bought the Circle S brackets, not the ones linked. I just googled "Jeep cherokee rear bumper brackets" and grabbed the first eBay link I found to post that reply. They look identical.
 
It may sound strange, but I suspect that a well-integrated set of rock rails will also help with controlling twist stiffness. If the rails strongly tie the unibody sheet metal pinch weld to the unibody rail, then that should help control twist. I came to this conclusion after some discussion with RCPhx where he said he sees no flex in his XJ that does not have plated unibody rails. The notion with the rock rails is that any frame twist will be counteracted by the rails that span between the unibody rail and the sheet metal pinch weld.

To get the greatest benefit, I think the rock rails need to be welded to the unibody rail and very securely bolted to the sheet metal pinch weld. RCPhx's rock rails look the best to me, but he's not selling those. I settled for the AJ Armor rails. These have a strong tie to the sheet metal pinch weld. They have two attachment points on the unibody rail with the rear attachment reinforcing the front mounting point of the rear leaf spring. I would have been happier if they had three attachment points. I will probably add a third myself.
 
I got center stiffeners, but the pan later cracked on the hump under back seat my guess it was from twist. then again maybe the pan cracked as I made the center too stiff? With frame stiffeners, the pan still is acting as the cross pieces of the frame " ladder" i am a bit disappointed in this.

For bumper, I inserted some thick wall rectangular tubing, with flanges welded on the back end of the tubing to attach my tire carrier bumper and hitch to.

It is a uniframe, and without some wild changes, it is what it is.
 
I got center stiffeners, but the pan later cracked on the hump under back seat my guess it was from twist. then again maybe the pan cracked as I made the center too stiff? With frame stiffeners, the pan still is acting as the cross pieces of the frame " ladder" i am a bit disappointed in this.

For bumper, I inserted some thick wall rectangular tubing, with flanges welded on the back end of the tubing to attach my tire carrier bumper and hitch to.

It is a uniframe, and without some wild changes, it is what it is.

Interesting to hear. This is the first I've heard of frame stiffeners not being a cure-all for frame flex issues. Something that prevents twist across the unibody rail loading points is needed.
 
I suppose tying in a stiff cage will hep. the stiffeners I think help bending up and down, but since they dont add anything across the jeep, rather only lengthwise, they dont make a ladder frame.

i am thinking a ladder frame will resist twist, as the rungs of a ladder frame help I think resist twist. the floor pan is the rungs of the ladder, and it is not beefed up by the stiffeners.

Just my hunch
 
I suppose tying in a stiff cage will hep. the stiffeners I think help bending up and down, but since they dont add anything across the jeep, rather only lengthwise, they dont make a ladder frame.

i am thinking a ladder frame will resist twist, as the rungs of a ladder frame help I think resist twist. the floor pan is the rungs of the ladder, and it is not beefed up by the stiffeners.

Just my hunch

You are correct in your thoughts, that's why I don't see any flex because of a total package of crossmembers!
 
I wonder if adding a cross member like the tranny mount , but further back will help with twist? Can go too far back as the drive shaft needs to have space. My rig has a lot of articulation so clearing the driveshaft is an issue if adding "ladder rungs" unless I do some wildly bent upside down U shaped cross piece

Thoughts?
 
I started with my long arm cross-member, it spans 16" out of 2x2" angle!
17520005_zps1ejc8y51.jpg
 
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