TJ vs LJ: a few thoughts

Dino - KX6D

Radio Guy
Supporting Member
Joined
Jan 29, 2017
Messages
258
Location
La Mirada, CA, United States
I first got into Jeeps back in the 80's. Reading the 4x4 magazines of the times there was a lot to say about the offroad advantages of the CJ-8 because of the longer wheelbase. The disadvantage of the CJ-8 was the rear overhang and most related articles included bobing the tub. I always wanted the CJ-8! I wasn't too familiar with the CJ-6 at that time.

I was excited when Jeep came out with the LJ in 04 and the Rubicon models in 05 and 06 and finally got one in 2010. The LJ shares the same problem, to a degree, as the CJ-8 with the rear overhang. This was apparent in Moab. Oh to have the departure angle of the TJ!

One way to accomplish this is to push back the rear axle on the LJ. Another option is to stretch a TJ to accomplish the wheelbase of the LJ or beyond. On Facebook there is a group that accomplishes the later called "Jeep TJ6 Group" where they actually cut the frame and add 15" of frame inserts. Tub modifications are also necessary.

Here are three pictures posted today and it made me think about a discussion I had with @LarryTJ in Moab. All the advantages of the TJ and the LJ. Very cool!

Here are some pictures of one guy's TJ6 frame. Jeep never made a TJ-6...nevermind...

Here is the text from that post...
"Buddy of mine owns a metal fab company in town. Got him to make my inserts since they are a non-standard size. 25” long, 5 “ per side will extend into the original frame rail."

FB_IMG_1621009715755.jpg


FB_IMG_1621009722126.jpg


FB_IMG_1621009729802.jpg
 
  • Like
Reactions: LarryTJ
Dino - you may recall that I was able to move my rear axle back far enough to eliminate the overhang, without having to modify the frame at all. Part of that was that I run 40’s, coilovers and a highline, but even with the highline I had plenty of room for up travel. I do run a genright stretch tank, but other than moving the tank back all I had to do was install corner armor to move the wheel well. I don’t know if you can move it back far enough and still run coils.

It was still a lot of work, but much less than a TJ-6 stretch.
 
I first got into Jeeps back in the 80's. Reading the 4x4 magazines of the times there was a lot to say about the offroad advantages of the CJ-8 because of the longer wheelbase. The disadvantage of the CJ-8 was the rear overhang and most related articles included bobing the tub. I always wanted the CJ-8! I wasn't too familiar with the CJ-6 at that time.

I was excited when Jeep came out with the LJ in 04 and the Rubicon models in 05 and 06 and finally got one in 2010. The LJ shares the same problem, to a degree, as the CJ-8 with the rear overhang. This was apparent in Moab. Oh to have the departure angle of the TJ!

One way to accomplish this is to push back the rear axle on the LJ. Another option is to stretch a TJ to accomplish the wheelbase of the LJ or beyond. On Facebook there is a group that accomplishes the later called "Jeep TJ6 Group" where they actually cut the frame and add 15" of frame inserts. Tub modifications are also necessary.

Here are three pictures posted today and it made me think about a discussion I had with @LarryTJ in Moab. All the advantages of the TJ and the LJ. Very cool!

Here are some pictures of one guy's TJ6 frame. Jeep never made a TJ-6...nevermind...

Here is the text from that post...
"Buddy of mine owns a metal fab company in town. Got him to make my inserts since they are a non-standard size. 25” long, 5 “ per side will extend into the original frame rail."

View attachment 252377

View attachment 252379

View attachment 252380
There's lots of ways to skin that cat, he should pick one that doesn't affect how the frame flexes.
 
  • Like
Reactions: LarryTJ
There's lots of ways to skin that cat, he should pick one that doesn't affect how the frame flexes.
Are you saying he should use a shorter sleeve? or no sleeve? or are you saying something else? is a properly done butt weld sufficient?
 
Are you saying he should use a shorter sleeve? or no sleeve? or are you saying something else? is a properly done butt weld sufficient?
If you have a very flexible frame and introduce a very stiff section into the middle of the span, you need to mitigate the stress risers at each end of that or run the risk of introducing cracks. A better way is to use much lighter internal plates, stagger the lengths, so that there isn't a hard line in plane with what would look like a cut vertically through the frame. Or, just use the internal plates with a few plug welds past the joints and then use the plates as a full penetration weld backer for the full frame rail size.
 
If you have a very flexible frame and introduce a very stiff section into the middle of the span, you need to mitigate the stress risers at each end of that or run the risk of introducing cracks. A better way is to use much lighter internal plates, stagger the lengths, so that there isn't a hard line in plane with what would look like a cut vertically through the frame. Or, just use the internal plates with a few plug welds past the joints and then use the plates as a full penetration weld backer for the full frame rail size.
makes sense to me, thanks
 
I didn't even think about the top.
That is the entire premise of the TJ-6. Stretch the tub out to run the TJ Unlimited belt rails so you can run the top that fits with the stock Unlimited rear half of the roll bar. If you don't move it, the frame puts the wheel arch at what is 108" of wheelbase if you maintain the stock relationship.
 
  • Like
Reactions: ColoJeep and Vasq
If you have a very flexible frame and introduce a very stiff section into the middle of the span, you need to mitigate the stress risers at each end of that or run the risk of introducing cracks. A better way is to use much lighter internal plates, stagger the lengths, so that there isn't a hard line in plane with what would look like a cut vertically through the frame. Or, just use the internal plates with a few plug welds past the joints and then use the plates as a full penetration weld backer for the full frame rail size.
When I see a post like this, It tells me just how much someone knows what they are doing. We all need to take note that a person with that kind of experience takes the time to share it.

We live in a world where extremely advanced technicians and tradespeople are getting rarer all the time.

Most of the time they won’t give people the time of day.
 
Blaine has a method for stretching the frame that doesn't require you to use a CUSTOM tube or anything else. And while him and I BUTT heads he knows his stuff and I followed his method of stretching my frame. It works great and seems very solid. I say that since I haven't tested it out yet.

I'd thought about the TJ-6 style of a build but for my trails here in WA it's a little too long. But I'm sure it works great in other places and when you look at NashvilleTJ's rig you can see what that long WB does for you.
 
Blaine has a method for stretching the frame that doesn't require you to use a CUSTOM tube or anything else. And while him and I BUTT heads he knows his stuff and I followed his method of stretching my frame. It works great and seems very solid. I say that since I haven't tested it out yet.

I'd thought about the TJ-6 style of a build but for my trails here in WA it's a little too long. But I'm sure it works great in other places and when you look at NashvilleTJ's rig you can see what that long WB does for you.
@Wildman is another guy on here that has some experience and is totally unselfish....good dude.
 
When I see a post like this, It tells me just how much someone knows what they are doing. We all need to take note that a person with that kind of experience takes the time to share it.

We live in a world where extremely advanced technicians and tradespeople are getting rarer all the time.

Most of the time they won’t give people the time of day.
So true! I would have never that about frame flex. These kinds of threads, and the sharing of valuable knowledge, has accelerated my own learning about this platform.
 
So true! I would have never that about frame flex. These kinds of threads, and the sharing of valuable knowledge, has accelerated my own learning about this platform.
The TJ frame is just slightly stiffer than well done pasta. If you set jack stands under each end of the frame and then unbolt the body mounts, the frame will droop in the middle more than you would expect.
 
...

I'd thought about the TJ-6 style of a build but for my trails here in WA it's a little too long. But I'm sure it works great in other places and when you look at NashvilleTJ's rig you can see what that long WB does for you.
Apparently, what is does is keep me from coming up to the PNW and wheelin’ with you...

🙃
 
  • Like
Reactions: Wildman
Apparently, what is does is keep me from coming up to the PNW and wheelin’ with you...

🙃
There are plenty of trails I can take you on. There are just some that were made for Flatties and have just not been ruined.
But you would LOVE Rimrock and those trails are up higher so the trees are thinner.
 
  • Like
Reactions: NashvilleTJ