Integrating TJ Systems Into a CJ-8 Tub – Looking for TJ-Specific Guidance

[akadeutsch]

Hey TJ folks, Im Keith. Long time Jeep wrench finally ready to build the jeep Ive always wanted. I want to plan for as many issues as I think I might encounter along the way. I have a degree in auto mech, years experiance at a jeep dealer, and a full shop to work in.
I was pointed here because the heart of my project is really TJ/LJ systems integration, not a CJ build, and I’m hoping to lean on the experience in this forum before I start cutting.


What I’m trying to do:
I'd like to drop my CJ-8 Scrambler body on a clean 05 TJ/LJ Rubicon chassis, with the goal of keeping as many factory TJ/LJ systems functional as possible inside the Scrambler tub.


That includes:

• TJ dash or at least all the functions of the TJ, HVAC, and air bags
• Factory wiring architecture (PDC, fuse blocks, grounds)
• Pedals, steering column, and safety-related geometry
• ECU/PCM integration with minimal re-engineering

Rather than adapting all of that to the CJ firewall, I’m exploring grafting the TJ firewall into the CJ-8 tub so the TJ systems can live where they were designed to live.
I have had a great time replacing the fire wall in an old buick and it made the owneer very happy. I feel like I could takle the same in the jeep with good results. But I could be wrong here. Is this a bad idea?


Drivetrain note:
The TJ donor was originally an automatic, but I plan to convert it to the NSG370 6-speed manual first, drive it, and confirm full functionality before moving on to major tub and firewall work. My goal is to avoid stacking unknowns.


What I’m asking for advice on (TJ-specific):

• Firewall reference points that are critical to keep correct
• HVAC vent box integrated from the TJ into the scramber body
• Pedal box, steering column, and HVAC alignment pitfalls
• Wiring harness routing or grounding issues that become problems when tubs change
• Anything in the TJ/LJ platform that absolutely hates being moved or re-positioned?

I’m not under the illusion that this is easy or “bolt-on.” I’m trying to do this once, methodically, and with respect for how the TJ/LJ platform was engineered.


If you’ve integrated TJ systems into a non-TJ tub—or torn one down far enough to know where the bodies are buried—I’d really appreciate any hard-earned insight.


Thanks for letting me tap into the TJ brain trust.


— Keith

 

[OldBuzzard]

I have no experience with a project of this scope. Watching... But here are a couple of observations.

A "good" NSG370 is impossible to find, because they weren't "good" new. So you'll have to settle for a "good enough" NSG370 which you can live with. Staying in reverse is the biggest problem. Apparently, they're pretty well impossible to rebuild.

The PCM for the manual tranny is different from the automatic one. @Wranglerfix can provide the manual one, which costs more than the automatic one.

 

[Abendage]

I had a buddy about 20 years ago that grafted an XJ firewall, dash and drivetrain into a CJ7. Don’t think he retained the air bag functionality but everything else down to the A/C worked. Don’t have any of the specifics you’re looking for but sounds like an awesome project! I think the TJ firewall would be easier to graft into a CJ than the XJ firewall was, so I’m sure it’s doable.

 

[John Cooper]

Hey TJ folks, Im Keith. Long time Jeep wrench finally ready to build the jeep Ive always wanted. I want to plan for as many issues as I think I might encounter along the way. I have a degree in auto mech, years experiance at a jeep dealer, and a full shop to work in.
I was pointed here because the heart of my project is really TJ/LJ systems integration, not a CJ build, and I’m hoping to lean on the experience in this forum before I start cutting.


What I’m trying to do:
I'd like to drop my CJ-8 Scrambler body on a clean 05 TJ/LJ Rubicon chassis, with the goal of keeping as many factory TJ/LJ systems functional as possible inside the Scrambler tub.


That includes:

• TJ dash or at least all the functions of the TJ, HVAC, and air bags
• Factory wiring architecture (PDC, fuse blocks, grounds)
• Pedals, steering column, and safety-related geometry
• ECU/PCM integration with minimal re-engineering

Rather than adapting all of that to the CJ firewall, I’m exploring grafting the TJ firewall into the CJ-8 tub so the TJ systems can live where they were designed to live.
I have had a great time replacing the fire wall in an old buick and it made the owneer very happy. I feel like I could takle the same in the jeep with good results. But I could be wrong here. Is this a bad idea?


Drivetrain note:
The TJ donor was originally an automatic, but I plan to convert it to the NSG370 6-speed manual first, drive it, and confirm full functionality before moving on to major tub and firewall work. My goal is to avoid stacking unknowns.


What I’m asking for advice on (TJ-specific):

• Firewall reference points that are critical to keep correct
• HVAC vent box integrated from the TJ into the scramber body
• Pedal box, steering column, and HVAC alignment pitfalls
• Wiring harness routing or grounding issues that become problems when tubs change
• Anything in the TJ/LJ platform that absolutely hates being moved or re-positioned?

I’m not under the illusion that this is easy or “bolt-on.” I’m trying to do this once, methodically, and with respect for how the TJ/LJ platform was engineered.


If you’ve integrated TJ systems into a non-TJ tub—or torn one down far enough to know where the bodies are buried—I’d really appreciate any hard-earned insight.


Thanks for letting me tap into the TJ brain trust.


— Keith

Man I don't have a good answer for you.

Honestly you would be money ahead just converting the drivetrain to coils or coils overs and go from there.

At least that's my opinion.

 

[akadeutsch]

I have no experience with a project of this scope. Watching... But here are a couple of observations.

A "good" NSG370 is impossible to find, because they weren't "good" new. So you'll have to settle for a "good enough" NSG370 which you can live with. Staying in reverse is the biggest problem. Apparently, they're pretty well impossible to rebuild.

The PCM for the manual tranny is different from the automatic one. @Wranglerfix can provide the manual one, which costs more than the automatic one.

I thought th NSG370 was the one everyone wanted. Ive never come accross a manual transmission I couldnt rebuild. Whats the problem? Ill have to look into that more. Thanks for the heads up.

 

[akadeutsch]

Man I don't have a good answer for you.

Honestly you would be money ahead just converting the drivetrain to coils or coils overs and go from there.

At least that's my opinion.

if saving money were the only aim i guess I'd just put the CJ-7 front end kit on the 05 Rubi LJ and get the scrambler decals for the hood. But I have a clean Scrambler. but the carburated 258 sucks and the no het vets suck. Im close to procuring this 05 LJ Rubi So I figure... WHy not cut them both up swap the bodies and build two unique rigs. an 05 Rubicon Scrambler (my dream Jeep) and a bear bones 81 TJ with twin sticks and locking hubs that I might want to throw a plow on. Saving money is not the goal here, although my budget wont be upsurd. I see an oppertunity to combine all the skills Ive honed over the years to put together a unique Jeep. Thats hard in the jeep world because generally speaking if it's Jeep it's been done.

 

[John Cooper]

if saving money were the only aim i guess I'd just put the CJ-7 front end kit on the 05 Rubi LJ and get the scrambler decals for the hood. But I have a clean Scrambler. but the carburated 258 sucks and the no het vets suck. Im close to procuring this 05 LJ Rubi So I figure... WHy not cut them both up swap the bodies and build two unique rigs. an 05 Rubicon Scrambler (my dream Jeep) and a bear bones 81 TJ with twin sticks and locking hubs that I might want to throw a plow on. Saving money is not the goal here, although my budget wont be upsurd. I see an oppertunity to combine all the skills Ive honed over the years to put together a unique Jeep. Thats hard in the jeep world because generally speaking if it's Jeep it's been done.

You money your choice man!

If I still had my 84 Scrambler ain't no way it would get cut up. But I grew up on CJ's and they hold a special place in my heart.

 

[inkedrose]

Super curious about this build please post pics as you go. Be a good spot or you to come back and look on things

 

[John Cooper]

Super curious about this build please post pics as you go. Be a good spot or you to come back and look on things

Isn't the CJ dash narrower than the TJ??

 

[OldBuzzard]

I thought th NSG370 was the one everyone wanted. Ive never come accross a manual transmission I couldnt rebuild. Whats the problem? Ill have to look into that more. Thanks for the heads up.

The tranny is great on paper. It would be great in reality if they hadn't made it of glass. As I understand it, parts for it are pure unobtainium.

I actually like mine. But I know its bad habits (reverse), and I have to account for them.

 

[GoldenGorilla]

Sounds like a very cool project.

The CJ8 firewall and dash are more rounded than the TJ dash, and probably a bit lower and perhaps narrower. You might have to fabricate some sort of hybrid. In today's world it seems like 3d scanning would be the ultimate cheat code to map these onto each other. I would think the position of the shifter and 4wd linkages are also items you'd want to bring in from the LJ chassis to the CJ body, so really the whole center console stack. As I recall the CJ-5/7/8 all had the shifter position much more forward in the cab than the TJ. And I think you would want to start from an LJ donor if possible and even then the CJ-8 frame is still a bit longer so some stretching will be necessary somewhere.

KeyParts has alot of the CJ8 parts available for restorations and perhaps might have some useful dimensional info.

I thought th NSG370 was the one everyone wanted. Ive never come accross a manual transmission I couldnt rebuild. Whats the problem? Ill have to look into that more. Thanks for the heads up.

Despite the NSG370 being used for the last 2 years of TJ production and all the manuals in the JK, access to parts for rebuilding them does seem to be an issue.

I've driven my dad's LJ Rubicon with this transmission and mine with the NV3550 5 speed and the ratios of the NSG370 are much better suited to the somewhat narrow 4.0L powerband than the prior 5-speeds at higher speeds (40mph+). The feel of the NSG370 even when operating well is a bit odd in the 1-2 shift. I asked my dad if he had any issues and he said occasional issues shifting into reverse. After changing my clutch, the 1-2 shift in my NV3550 isn't always perfect either.

The Aisin AX-15 has much better availability both of replacement units and parts than either the NV3550 or NSG370.

 

[akadeutsch]

Its tough to build with no parts and I know that AX15 is bullet proof. But this got me researching the 42RLE that came in it. I had one of these in my 00 WJ, A pretty reliable unit if you could keep it cool. Easy enough to do with a big cooler, and the right gears. I remember some searching on the hills but I always thought a small 2200 stall converter would help add line presure to stiffen up the shifts and maybe hold her in gear on those hills too. Any experiance with this? A quick word with the ECM to manage the shift point just a touch deeper into the RPMs, might could help whip this old dog into shape. Leaving it stock would save some time. "Keep it simple stupid" says the guy with the plan to cut up two unicorns. I see the irony. Truth is I had not dug into the automatics too much till now. Without that special table to keep the clutch pack in order, the lock rings in place, shims straight, and springs in order its just too easy to miss something. If I could leave it stock and make it driveable that might be the win too. And this is why Im here. For your wisdom. Thanks jeepers!