Gentlemen,
I have a unique project and would like opinions. Rebuilding a 1943 military halftrack. I have already bought a 12 valve with p pump. Its almost the exact same size as the original engine. I was convinced that for a transmission I would use an Allison 545. I can find one relatively cheap, and they bolt right up. Now, I'm not so sure. Should I be thinking about an MT643 instead with a lock up torque converter? Also, to make things more complicated, what ever I put in will be divorced to a transfer case, as the vehicle has front wheel drive.
I do not want to sacrifice my front wheel drive. I want to avoid electronics if possible.
I plan on using this vehicle very lightly. Perhaps some easy off roading now and then, nothing too extreme. I will also be able to drive this on city streets! The tracks are made of rubber. So hopefully maybe a parade once in a while. Original top speed on these vehicles was 45 mph at best, and that was probably going downhill.
I'm not the first guy to put a Cummins 5.9 12 valve in a halftrack. It's the engine to use if you don't have the original engine.
I'm an amateur, so your opinions are welcome!

 

I don't have the answers you're looking for, but I definitely want to follow your build...Please keep posting here as you'll find many knowledgeable people willing to help......Ben

 

I'll be happy to post progress. The first picture is what it looked like when I got it home. This picture is my current state.

 

I think some pictures of the powertrain that's in there would be really interesting.

 

This picture is not my halftrack, it is someone else. He kept the original transmission and transfer case. Installed Cummins 5.9. The other 2 pictures are a guy in Las Vegas who used 5.9 and a 727. He eliminated the front wheel drive. I will try and find a photo of the original set up.

 

Cool project.
I can't wait to see this project get some traction [which with tracks like that should be pretty easy].

I will be following along.

 

Really cool project. Do you still have the original transmission and transfer case?

Or at least literature where you can find the gear ratios etc?

@oliver foster let's build that guy a diesel so he's the first one to do a burnout with rubber tracks

 

Original drivetrain specs: (White halftrack)
1. transmission was a Spicer model #3641
2. front axle has gear ratio of 6.80 to 1
3. rear axle has gear ratio of 4.44 to 1

 

This looks like a symmetric arrangement, where you can use a standard transfer case and do not need different ratios front and rear.
(Wheel diameter difference taken care of in the axles)

If you can get the front driveshaft to work you can take a Dodge 12V with a 5speed and a 4x4 transfer case.
If you need the front driveshaft centered you will have to look for a divorced transfer case, like the ones used in the G-Wagon. (Or maybe a bit beefier, but you will run into axle and especially track limits before you destroy a transfer case. )

 

Allison 545 is a 4 speed automatic, do you think that would be ok? The cummins 5.9 and the allison 545 set up was used in buses, dump trucks etc. I checked the rear gear ratio on a "Bluebird Bus" that used this set up and it was also 4.44 to 1. Perhaps you were implying I use a 5 speed manual transmission? I do appreciate your feedback.

 

I thought of a manual trans for ease of installation and setup.
An automatic trans needs to be tailored to the vehicle a good bit or it will drive you mad with bad shifting behavior. (Just IMO)

A manual trans with an hydraulic clutch is easy to drive and also makes the "right moves" and the "right sounds" for a vehicle of that vintage.

About the gear ratio: It is but one factor, the next one is wheel size. This will determine how far you move for one revolution of the shaft. Bigger wheel-shorter axle.
Then you need to take into account the desired top speed or the desired cruising rpm. This will define your highest gear.
Then you will need to estimate the force needed to get the vehicle moving and accelerating at a desired rate. This will lead you to your lowest gear.
Then you will have to split the difference into some more gears.
With the broad power band of the Cummins I think that 5 speeds should be sufficient, and low ratio from the transfer case will help you get things unstuck or broken.
The guy with the 727 will always be in fluid coupling and will make a lot of heat in his torque converter.

If you do your homework with the gear ratios you can use a manual or an auto, where the auto will need a lot of cooling unless it has a TC lockup, and for a lockup you will need a TCM that you can tailor to your vehicle, mount sensors etc to get all this to work.

 

That all makes sense. I agree with this vintage and style of vehicle should probably have a stick. After calculating cost on auto vs. manual, auto would be cheaper. But what the heck, it's only money.
The reason I don't want to go back with original, the manual trans. was not synchronized, which means having to double clutch all the time. Imagine going for a leisurely cruise, double clutching, no power steering, etc.
Now imagine if the bad guys were shooting at you while you had to drive!
Thanks, I hope by June or July to have motor and tranny in the vehicle. I'll keep you posted.

 

The auto will be easier to drive, and if you go non-lockup with mechanical governor you should be able to do this without electronic nightmares.
The only thing is that the auto will need a lot of cooling, but there are nice oil-water heat exchangers, or you may be able to fit a radiator.

If you still have the original powertrain I would try to restore it, and look for options of a synchronized version of that transmission.
I'd at least keep the stock stuff and make only reversible changes.

If you still have the stock transfer case it should be possible to mate your cummins with the chosen auto using a custom driveshaft.

Just be aware that autos usually have a lot of torque at standstill, and you will need to take care not to twist off shafts or break teeth in the powertrain

 

Cool, a local excavator in my home town had one he'd bring out to the local Youth Fair and Parades.....cool as hell and a great childhood memory riding around in it...

 

Its been a huge debate wether or not to go back original. I do have the original drive train. However, parts are starting to get scarce. For example, if my 77 year old exhaust/intake manifold starts cracking, I'm pretty much screwed. The hydraulic valve lift parts are also drying up. New clutch? Very difficult to find. When you do find some of these parts they are outrageous in price. I decided I wanted something somewhat dependable,enjoyable and easy to operate. If I throw a fan belt, I can run down to the local auto parts store, not wait two weeks.
I agree with your statement about any changes to be easily reversible, that's my mindset.
You have also managed to convince me perhaps a standard tranny is the way to go. I'm just not impressed with the NV4500. I am looking at an Eaton Fuller 5 speed. I found one that was bolted to a Cummins 5.9 in a school bus. I think I can adapt it to my original transfer case.