Commando drivetrain?

So once again i am sitting on the fence about drivetrain choice on the flattie... i wanted to go with a Small block chev and a TH350 tranny buuutttttttt: found a local lead on a guy who is parting out a Commando (i forgot to ask what year). I was picking up my TJ lift kit at the local 4x4 shop and the guy showed me this commando in the back lot (sorry no camera with me at the time). He is using it for parts and said he would give me a good deal on the engine/Tranny and T-case if i want it... steering column too for my saggy swap.
Anyway its a Buick 225 mated to a TH400 to a D20.
I already have right side offset axles from a 78 cherokee sitting in my garage so i'd like to stick with my stock D18 T-case... My question is this: Will the stock Commando TH400 adapter bolt up to a D18 case? I would like to use the Donor buick engine as well as the tranny that is already bolted to it.
I know the TH400 is long and i am willing to lengthen my wheel base (was planning on it actually).. the question is more just on the adaptability of the TH400 to the D18 with stock parts. Is this do-able?

thoughts?

 

No, the jeep th400 in the Commando will not bolt up to the d18. In fact the Jeep th400/d20 adapter will not bolt up to anything but a d20 with stock gear ratio. It uses a bull gear with a different spline count and they only made it for the d20. Plus the jeep adapter is known to be weak. And like you said that would make for a very long drivetrain in a flatty.
Keith

 

The main problem will be the length of the TH400. I've seen it done with a V6, but it may not be possible with a V8.

 

i'd keep the V6 and extend the wheel base... either a stretch in the middle or at the rear end.

Novak's site lists the same adapter to TH400 for both the D18 and the D20. http://www.novak-adapt.com/catalog/kit_124.htm
I know Jeep didnt use the exact same adapter, but wouldnt the priciple be the same in terms of adaptability?

 

yup i did... i'm still not getting it though lol... but thats ok.. it wouldnt be the first time R)

maybe i should keep the full setup; engine/tranny/t-case and just try to track down a rear centered D44.

 

Novak sells a redesigned replacement adapter for the TH400 to Dana 20 as the stock Commando mounts were wierd and weak. Both my '71 and '73 Commandos with the TH400 had bad mounts when I bought them. I bought the Novak parts including the poly type mount for my '71. Both parts will run you over $300, but it looks to be unbreakable--famous words right? Why would you not want the D20 TC? Jeep used D20s all the way up into 1-ton pickups. bg

 

Don't feel like a loner. I sometimes have a hard time picturing what someone is saying. The reason is that the D18 and D20 use different bull gears (input gears). They have different tooth counts. A D18 will mount up to the Jeep th400 adapter BUT you will not be able to find an input, or bull, gear that will fit on the transmission adapter output shaft to drive the transfer case. Does that make it a little clearer?
One more thing to consider is the Commando that the drive train is coming from has a 100" wheelbase. The flatty has an 80" wheelbase. If you run the V6/th400 setup you could move the motor forward to compensate for it a little but you will still have a very short rear driveshaft. Any amount of lift will make things even worse. A D18 will help with it as the rear is lower but it will still be short. My 2a was setup to run a v6/th350/d18. The motor was moved as far forward as possible but the rear driveshaft was still only going to be about 14". If it was a th400/d20 the rear shaft would have only been about 10". It would work but you will be dealing with some fairly severe driveline angles.

Keith

 

There is an out here if you want to use the combination. You could still have the TH-400 and the 18 transfer case. Put the 20 gears in the 18 case, then the gears would mesh correctly with the bull gear you would have to use. That would give you a taller low range, but do-able. Stock 20's came with a 2.03-1 low range and 18's have a 2.46-1 low range. If you want lower I bet Tera has a 3.15-1 set that would work with the stock splined TH400 adapter set up. Might investigate that a bit. Nickmil

 

Novaks adapter kit for the D18 and D20 likely show they same adapter because their adapter 'kit' changes the output shaft on the tranny, so they can use a different bull gear, as long as it has the right tooth count/pitch.

 

I'm thinking it would be easier to find a center chunk D44 or even 9

 

The main problem with a centered output would be the driveshaft angle, I'd think. Even if you scoot the engine forward, the rear driveshaft will be very short. The D18 output sits lower than the centered D20 output, so using the D18 with an offset axle will give you an advantage in driveshaft angle. Note that the flat fender Jeep with a TH400 I've seen was at stock height, and was intended for casual driving by the shop owner's wife. I don't think there's any way to use the TH400 in an 80" WB and provide much rear axle movement... you can probably make it work, but this setup might be a significant handicap on the trail.

Not trying to be negative, but instead to point out the issues in advance. If you have to have an automatic in an 80" WB, I'd think you'd save yourself a lot of headaches by going with the V6 and TH350.

<edit> Reread the original post - if you lengthen the WB, the centered 44 and TH400 would be fine. If you're going to build your axles, another alternative is a Wagoneer M20 ... the M20 from a Wagoneer/Cherokee (1980 or later) is stronger/better than a D44.

 

why wont the adaptor for the TH 400 to the model 20 work for the model 18, dont they share the same case if you use a large hole model 20

 

The factory TH400 output shaft needs a 15-spline bull gear, and the poster above says that there's none that's compatible with the D18. Looking at Novak's chart of gear interchange, it appears that's not strictly correct.

The two 15-spline gears that are available are PN 946785 (26 tooth, 17.5 degree bevel) and 940472 (26t, 20 degree). It looks to me like the 940472 is compatible with the 937339, a 6-spline T-90 D-18 gear. Note this is the early (small hole?) D18, with a 26t input gear. The later D18 uses a 29t input gear, which isn't compatible.

 

I have run several flatties with the 231/400/20 setup and have no problems. The front driveline is actually a much better fit with the 400 pan than the 350. A 14" driveline in the rear is very doable when you start with the grille and then hang a radiator as far forward as possible. Next hang the motor as close to the rad as possible, everything fits just fine as long as you don't want 8" of lift and 36" tires.

 

well i am running 35's now, my next rubber purchase for the flattie will probably be 36" boggers. But i dont mind stretching the wheelbase a bit if thats what it takes. i guess i should be looking for a centered rear axle then

 

I have a couple of questions that might help you pick a new winter project.

Are you a GM guy? If so and you want the 225/th400/Dana18 then buy an adapter. This I think would be the cheapest if you can get the jeepster parts for a fair price and there in good shape. You might have to alter the wheelbase but you say thats ok.

If you want a SBC V8 I would use a TH350 or a 7004(only about 2" longer but shorter than a TH400) and mate it to your 18.

If you open to other combos and your not dead set on using the offset Cherokee axles look into a AMC V8/TF999/Dana300, it's not that long and the 999 has a 2.74 1st gear and the 300 has a 2.62 low range.

Or a SBF/C4/Early Bronco Dana 20. If you find a straight shift vs J shift 20 it most likely will have a 2.42 low range. This is what I run in my flatty and I have a 84" wheelbase.

I hope this doesn't stir up the pot to much but I thought I would toss in my .02, happy thinking.

 

i've decided to stick with my original plan:
SBC, TH350 adapted to the D18, Dana 44's (the ones i salvaged from that old cherokee with the passenger side offset). Same spring under lift i have now, but outboarded spring mounts.
Still working on collecting parts... i'll probably buy the adapter last unless i can find a good deal on a used one. I've already found a local classic jeep restorer who will buy the original drivetrain from me.
I'm not in a huge rush so i'm not going to start tearing her down until i have every last part that i need. i don't want her up on jackstands while i can still enjoy driving her

 

I know you can put the guts from an 18 into a 20 case, big hole/small hole,(and maybe I'm missing something here) if you do that couldn't you also change gears to the 15 spline 29 tooth gear (auto) from the 6 spline 29 tooth (man.)???

Dale

 

O.K. I looked at the Novak site (good info).....guess I'm to used to the 18!!!???

Dale