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JeepDipper 02-03-2012 11:06 AM

4bt swap questions
I plan on doing a 4bt swap . But I don't know what axles I should run maybe 1 tons . The question I wanted to know about is can I run my d30 and d35 for awhile then when I get my one tons I can install them . Just wondering if it will work.

MikeMTJ 02-03-2012 11:10 AM

You'd probably be fine on the street. Otherwise, you're running on borrowed time. That even holds true with the anemic 2.5L.

TheTJRod 02-03-2012 12:00 PM

You don't necessarily need 1-ton axles. Though really this requires us to know what tire size your going to be running. If your running stock 29's then the d35 will be just fine for on road use. You plan on using the 33's, just drive like a granny and it will last the time it takes to find and prep bigger axles.

If your keeping the 33's a d60/d44 or F9/d44 will do good and keep your weight down, these would probably be good up to 37's(the d44 front shafts being the weak link). If your going over 37's then 1-ton it up with 14bolt or other and a d60 or similar front.

TheTJRod 02-03-2012 12:05 PM

Might want to add, that if your going through the trouble of doing an engine swap and axle swap. Try to get the strongest you can. That 4bt is much heavier than the I6 and all stronger axles are heavier than the d35/30 so you will have to beef up the suspension a lot to handle the weight and torque. I can understand why you want to space everything out. Hope your in a state that doesn't require emissions or inspections. I can't do this swap till I move out of my county at least as emissions are a pain. Also most 4bts will be older than my Jeep(I think this is a law in most states too).

SirGeorgeKillian 02-03-2012 12:27 PM

My thing is, if you are swapping axles, and plan on a 4bt, do it right the first time. Yes 1 ton axles are overkill, but that then makes your drive shaft the weak point. A drive shaft can be replaced with a few basic hand tools, and you can usually get home in front wheel drive. Can't say the same thing about a broken axle shaft.

I am running a Ford 10.25 in the rear with a D60 up front with my 4.0. If I ever decide to swap to a bigger engine, that is one of the many things on a to do list that I don't have to worry about.

JeepDipper 02-03-2012 03:20 PM

My plan is to run 40 or 37 in the end and stretch out the wheel base . And I don't want to be worried about breaking a axle when I'm on the trail or driving home from work . And emissions is nothing to worry about in my county .

SirGeorgeKillian 02-03-2012 04:28 PM

If your end goal is to run 40's with a 4bt, you are wasting your time and money investing in anything but 1 tons.

JeepDipper 02-03-2012 05:32 PM

yea that was what i was thinking. and do any of you know who makes good drive shafts . and i was think a 14 bolt floater was my rear axle cuz i can get one pretty easy around here. But the con is they hang down so ill be hitting every rock on the trail.

JeepDipper 02-04-2012 06:01 PM

what transmission should i run . I have a auto in it now which is good for trails . But i want a manuel trans.

TheTJRod 02-04-2012 09:46 PM

Depends on the 4bt you get. If it's a Chevy then the TH400 will bolt up. You want to use your A/C then get a ford 4bt and use a AX15 or NV4500. Check out this site. They specialize in Jeep 4bt conversions and sell transmission adapter plates. They also have parts lists and other info that could help. You can use your stock a/c, gas tank, and radiator using the parts they have.


We use 4BT Cummins engines for our swaps., and recommend the AX-15 transmission or an NV4500 also works well. 3.07 gears with 33” tires will get you the best fuel economy. You can also use a TH400, TH700R4, or Ford AOD if you prefer an automatic. (may require modification)
I bet the ax15 would be the easiest to use as you can keep your t-case without any mods or adapters. The ax15 has a 3.83 1st gear and the nv4500 has either a 6.34 or 5.61 depending on year. Also the nv4500 is stronger though it is longer. I would suggest the ax15 still for a manual for our short wheelbase.

Also about the 14bolt. You can shave the housing down. There are all sorts of kits you can buy and how to's. You can gain up to 1" from just cutting the bottom lip off.

How to shave a 14-bolt

14 Bolt Shave Kit (Gains 2")

boMMerG 03-21-2012 10:06 PM

Would I need to install a intercooler?

Nailhead432 03-22-2012 03:32 AM

Install an EGT (exhaust gas temperature) sensor (before the turbo) and gauge and drive it. If your EGT's are getting upward around 1100 - 1200 degrees, you will need an intercooler and possibly water injection. With a stock 4bt, I'm sure your not going to see temps that high. If you are going to upgrade injectors, turn your pump up, stronger valve springs, and bigger turbo, then an intercooler may be needed. You won't see any substantial, real world power added or increased fuel economy installing an intercooler. Besides, mounting an intercooler, especially if you want to keep your A/C, is going to be very tricky. Send me some pics if you go that route.

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