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Discussion Starter #1
Recently bought a 75 Jeep J20 3/4ton, originally had a 401/TH400 and quadratrac, 37" tires. I want to do either a 4bt swap or 6bt. I have a line on a complete 6bt with 5speed and tcase out of a dodge ram for $4000. The 4bt will be quite a bit more difficult to piece together. I occasionally like to go offroad. Which should it be 4bt or 6bt?
 

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Are you going to do much towing? If no, 4BT all the way.
 

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1989 Jeep Wagoneer, 360v8, 727, stock for now,
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If a 6B will fit I'd do that. Either of these Diesel's will chew up a front D44, be prepared to put a D60 under it.
 

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Discussion Starter #7
Made my decision 4BT because of the weight because I mostly offroad in the mud and snow. Now with the adapter plate can i just bolt it up to my factory TH400 or do i need to mod it or change the torque converter? Which is the most desireable 4BT?
 

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Made my decision 4BT because of the weight because I mostly offroad in the mud and snow. Now with the adapter plate can i just bolt it up to my factory TH400 or do i need to mod it or change the torque converter? Which is the most desireable 4BT?
You're going to have to have a different converter, the stock one will have too high a stall rating (1200-1500 for a gasser) you need 800-1200 (at most) for a diesel. The TH400 you have in there should have the BOP pattern (Buick Olds Pontiac) if i'm not mistaken, I'm not sure if the CJ &'s & J-series pickups had the universal pattern or not (Both Chevy & BOP patterns).
 

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Looks like DarylB beat me to it but I post anyways.

Depends on what adapter plate you got meaning what van it came out of. If it's a GM adapter then yes the TH400 will bolt right up, that's what came with my van (technically the th475). You will want to diesel torque converter so if that's not what you have, start looking. The most desireable 4bt will be the one that does the things you want to do, i.e. towing, cruising, good mileage, wheeling. If you need more power look into turning up the pump, changing the gov. spring, changing turbos, etc. If you have a chance to score a good 4bta (intercooled) choose that one. If not you can always add an intercooler.
 

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Discussion Starter #10
So the cheapest way to go is buy a bread truck with the 4bt/th400 combo swap the 4bt, adapter and torque converter and im golden? No adapter would work with my AMC TH400 would it?
 

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So the cheapest way to go is buy a bread truck with the 4bt/th400 combo swap the 4bt, adapter and torque converter and im golden? No adapter would work with my AMC TH400 would it?
It depends on the bolt pattern, see above. You'll have to change the govenor in the TH400 to a diesel version. You're going to spend more than $4,000 to get a 4BT and swap it in and keep your tranny & T-case. The 6BT deal you mentioned, 5 speed, and (I'm guessing an NP205) would be a better setup than keeping the Auto & Quadrajunk-Tcase you currently have IMHO. That dodge will have a D60 front, you could use that too if the seller was willing to part with it. It would be the ideal setup if you're going to do any offroading.
 

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Discussion Starter #12 (Edited)
You talked me into it but im 2 hours late guy just sold his 6bt/tranny/tcase combo.That may be the way to go anyways . The BW1339 Tcase has an offset rear output, and the rear differential is also offset to compensate for the quadratrac. Not easy to replace the quadratrac because the rear will not match up the new transfercase. Back to the drawing board. I think i read that some of the 4bt adapters bolt up to a my th400. If so buy that adapter and low stall torque converter and im in business. What do you think?

Here is a link with some good info on my current setup http://jubileejeeps.org/quadratrac/index.htm, and my BW1339 Tcase is not junk some consider it the best tcase ever made.
 

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Is this going to be a daily driver or just something to beat around in, in the woods? If it's just a beater I'd stick with the 401 or slap a 258 back in it and run whatcha got already.
 

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Discussion Starter #14 (Edited)
The easiest route of course would be to buy a Dodge ram with 6bt done, but then i would be like every other rig pig up here in the prairies. I want to make my J20 my baby, body and interior to factory spec (baby blue and white), not quite a daily driver, but an all round heavy duty truck that gets high 20's mpg. Im set on diesel but with the classic style of bad ass jeep truck rollin on 37's. I guess i can start with a bread truck with the th400, seems like there are lots of them on dovebid.
 

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The easiest route of course would be to buy a Dodge ram with 6bt done, but then i would be like every other rig pig up here in the prairies. I want to make my J20 my baby, body and interior to factory spec (baby blue and white), not quite a daily driver, but an all round heavy duty truck that gets high 20's mpg. Im set on diesel but with the classic style of bad ass jeep truck rollin on 37's. I guess i can start with a bread truck with the th400, seems like there are lots of them on dovebid.
I "think" it's Mikel or another guy who has a J20 buildup. He went with a D60 front, NV4500 5 speed, and twin T-cases. Sweet looking setup. Check out the buildup threads. For 37's I'd definitely go with a 60 up front. You might even find you a good 2500 dodge 4x4 and just swap your body over on the frame, drop in a 4BT, possibilites are endless. It's all about time, patience, and the Benajamin$ :)
 

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I "think" it's Mikel or another guy who has a J20 buildup. He went with a D60 front, NV4500 5 speed, and twin T-cases. Sweet looking setup. Check out the buildup threads. For 37's I'd definitely go with a 60 up front. You might even find you a good 2500 dodge 4x4 and just swap your body over on the frame, drop in a 4BT, possibilites are endless. It's all about time, patience, and the Benajamin$ :)
Austin's J10 project
Has the twin t-case ,Nv4500 ,Dana 60 .

Scott
 

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I thought of a 6Bt as well but I went with a 4Bt for the weight difference.
Me too....found a jewel of a 6BT for a great price, then found out how much it really weighed!!!!

My '79 has the high pinion Dana 44, so the heavy weight is out.....
 

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AMC th400 problem

The bolt pattenr on the AMC th400 was not a GM bolt pattern. A chevy adapter wouldnt get you there. Amc used a BOP (buick oldsmobile pontiac) pattern. They do make adapter for about 70 bucks to get you to the GM attern needed but never seen it done on a diesel application.

Just something to think about!

What are you doing with your 401?
 

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The adapter on my 4bt that had a t400 attached has two patterns, I had thought one was GM and the other BOP. You can see the two patterns in the pic.

 
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