This is the latest addition to my GMC collection.
It is a combo, semi GMC HALF-TRACK, Heller chassis, Italeri body, Tamiya cabin.
This vehicle is built from a photo taken in BIzerte in 1943.44.
thank you for your messsage.
Pascal76
thank you for your messsage.
Pascal76
14 Likes
Nice build. Can you show the pic that is under it on the base? It looks really interesting.
Did you show this build on the old site a while ago. It seems familiar.
That picture was in a topic on the old site where it was discussed in detail,
for instance a few posts about wheel sizes, gear ratios, transfer cases.
“How would I do it if I ran the repair shop” et.c.
It’s a mean looking truck
Edit: Here is the archived topic on the old site:
https://archive.armorama.com/forums/209849/index.htm
3 Likes
Good evening the answer is on the post before, thanks to uncle heavy, on the other hand I think it is a front half track M2.
1 Like
Yup that was it. Interesting truck.
Super cool truck. Excellent build
The internet remembers this:
“Recently in another blog I was participating in John Berwick posted a very interesting photo from North Africa.”
2 Likes
If the scale models can be believed at all then the frame width of the GMC was narrower than the White or IH Halftracks so was perfect for telescoping one into the other.
This would make for a much stronger welded “lap joint” rather that a more simple but much weaker “butt joint.”
For a well established repair facality this really would not be that difficult a conversion in 1 : 1 scale using battle damaged vehicles. To me it looks like a marriage made in heaven! Possibly only requiring the making of one custom length driveshaft to go between the White transmission and the GMC transfer case.
As said in the earlier thread, because the tire diameter is different between the Half-track and the Deuce, I suspect the front axle to have been totally disconnected from the driveline. (front driveshaft removed.)
Mis-matched tire sizes are death to any 4x4 or 4x6 vehicle.
Either that or the driver was instructed to engage the front axle ONLY when on the softest of sand to allow for wheel slippage.
1 Like
That’s a cool rig!
What was the gear ratios between front and rear axles on the original halftrack?
I would imagine that the rear wheel diameter of the halftrack was considerably smaller
than the halftracks front wheels?
The transfer case (I assume) on the halftrack must already be designed for mismatched rear and front wheel sizes so I wonder if it would be possible to replace some gears to get a new matched “mismatch”?
The other option is too only use all wheel drive when the ground is soft enough to allow some discrepancies between front and rear
This was a subject of much debate when the pics were first posted. I doubt they could use the White transfer box as it would only have one output at the rear - the CCKW rear needs two so each axle had its own drive shaft. I suspect they used the CCKW transfer box, and as you say they accepted the front wheels could only be powered in soft ground. I found the various ratios for transfer boxes and differentials on the axles, and I seem to recall it wasn’t that bad mixing them. (I researched it heavily as I want to build one of my own…)
Of course the manufactures of the Half-track would have made the necessary adjustments to the differential gear ratios at the factory.
The distance traveled in one rotation of the front Halftrack tire must match EXACTLY the distance traveled by the rear tread boggy.
So for the Half-track/Deuce combo the same rules apply. This is not a game of Horseshoes where close gets you some points. Close enough, in this case, is not good enough.
It would be freakishly weird if the two differential gear ratios for vehicles of different manufactures, of different gross weights and with different combat missions JUST HAPPENED to compliment each other while the tires are so obviously of different diameters.
And yes if this were back in the states you MIGHT be able to find another ring and pinion of a ratio that would work but in country, under combat circumstances and working with commonly available parts on hand in a Army motor pool - no.
Also Robin, as to your very last sentence above:
Quote: “The other option is to only use all wheel drive when the ground is soft enough to allow some discrepancies between front and rear.” Eed Quote.
That only serves to support and affirm exactly what I had said in both the original post and here: " Either that or the driver was instructed to engage the front axle ONLY when on the softest of sand to allow for wheel slippage."
Bark; because the Deuce frame slips (telescopes) up inside the Half-track frame I suspect that they (the 1944 GIs) were using both the GMC T-case and the GMC frame mounts for the T-case still bolted to the GMC frame rails. (Just as I have done here on the model.)
And yes the GMC T-case has two driveshafts exiting to the rear whereas the Half-track would have only one, so they would have had to use the GMC item.
With a 4x4 in all wheel drive, unless you are on VERY SOFT, mud, snow, gravel or sand the fact of even having brand new tires on the front and well worn ones on the rear can cause you difficulties.
The best story of drive-train wind-up was for the Alvis line of three-axle vehicles - Saracen, Saladin, Stalwart. There was no diff between the three wheels on each side which were driven off a common prop shaft from the middle wheel, so every so often on firm ground they had to find a kerb to “bump” up on, allowing momentary wheel spin to unwind the shafts and avoid breakages!
I fully intend to use this as an excuse for my lousy lane-holding…
1 Like
(In case any pedants are reading this, I know I said “three-axle” above, but the Saladin etc don’t have traditional axles spanning the width of the vehicle! Instead they have three independently-sprung wheel stations each side, with drive coming from the middle. The term was merely a short-cut to saying “three wheel stations per side”… Legal defence against nit-picking achieved!)
1 Like
Well I think I opened a big debate on the bridge and driveshaft.
Pascal76
We just LOVE debating around here
usually some useful knowledge gets shared so we all win 
3 Likes
Well guys, as an off roading and scratch building enthusiast, I’ll throw my thoughts into this lively drivetrain discussion!
As I understand halftracks, the front and rear axles have different gearing, tho I don’t think that point is being debated here 
but just making sure!
The gearing ratio is tied to the rotation of the front tires/rolling diameter and the rotation to the rear final drive sprocket pitch, allowing the rear track and front tires to rotate at the same rate (loaded diameter of front tire / sprocket pitch diameter), ok, sorry if everybody already knows this 
Interestingly, if you look at the layout of various halftracks made by White, Diamond T, Autocar and IHC, you’ll see the rear/track had only one drive axle (final drive sprocket in the front, with an idler in the back), so the overall “driveline” could be broadly equated more closely with that of a 4x4 than a 6x6, and by just “eyeballing it” the final drive centerline rear axle) appears to be much closer to the cab than the rear axle of either a traditional 4x4 or 6x6 - which is interesting because it raises questions about transfer case locations and drive shaft lengths.
Though I realize this was not part of the discussion, it’s something I find interesting, and relevant to how the geometry of this type of conversion might actually work - ie - affecting the length of the rear driveshaft, maybe the front driveshaft, any gear splitters/reducers, PTOs, and the (likely) need to relocate or change the transfer case, depending on which donor parts you decided to use.
So if someone were to go about the conversion being discussed, some tedious steps would need to be taken get it all to work. If you used the front half of the halftrack (cab and axle), and were planning to use the rear suspension and cargo bed of a 4x6 or 6x6, it seems you’d likely choose to keep the rear axles (and gearing) from the 4x6 or 6x6 in place. Sorry if this is tediously obvious - I can be slow on the uptake!
Then: 1) change out the front axle under the halftrack (cab/axle) and use one from a 6x6 (to match gearing) or: 2) change the ring and pinion gears on the front axle to match the rear end gears or; 3) leave the front gearing as is and disconnect the front driveshaft.
I’m guessing you’d need to take one of these steps because if you consider the potential difference between the axles/differential ratios might be dramatic, like 1.5 or 2:1 (ie 6 or 7+/-:1 front axle on the halftrack, and 4+/-:1 on the rear standard or halftrack axle), making functional axle rotation/vehicle movement difficult/impossible, even in the slickest of conditions (ie the front or rear axles would be rotating at a significantly different rate than each other) - and steering while engaged - what a mess!
This applies to less complex problems too - say you decide to run different front and rear diameter tires on your 4x4 - you’ll see weird results as your axles are not turning at the same rate - sometimes will feel like truck is hopping, other times, like it is binding - not good in either case
So if I were building this, I’d swap out the (halftrack) front axle with one from a conventional 6x6, and keep the drivetrain (obviously in real life you’d need to confirm distances/fit of transfer case to axles for shaft lengths etc) and axles from the 6x6.
So, if you all take this as the ramblings of an overly zealous suspension enthusiast, well, feel free to disregard it!
Cheers
Nick
1 Like