G7117 Axle questions

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ThatXJGuy

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I have a G7117 that I want to keep looking original, but it will be repowered soon with a much more powerful engine and I am wondering about a bunch of things with the axles.

1. How strong are they as far as torque? On one hand these trucks were beasts and could pull anything it seems if you give them enough time, but on the other hand they were pretty low powered especially by today's standards. Im putting in a 6BT Cummins and will have a ton of power in comparison to the original engine. The driveshafts and U joints seem well sized but the slip joints on the driveshafts are like pencils so I'm hoping that there aren't any parts in the axle like that.

2. What axle ratios did the have/offer? I know I can get under there and either pull them all apart and count teeth or spin tires and count revolutions but all of those things are difficult in its current location. I'm about a month or two from bringing it into the shop (hopefully not longer) and I would like to know a bit about them in the planning stages.

3. Parts availability? I crawled under the truck just a couple hours ago and noticed substantial rotational play (backlash) on the rear pinion and I'm not sure whats allowable but it seemed like a lot and got me wondering. Also Hubs, for some reason my truck has 10 lug rear hubs and the original 6 lug hubs on the front. The axle looks original other than the hubs so I'm wondering if somebody just swapped the hubs when something went wrong with the originals or something. Has anybody heard of this before?

4. Brakes. Is there anything weird about these axles that would make it difficult or impossible to do a disk brake conversion? With great horsepower comes great responsibility to make sure it stops. Most axles can be relatively easily converted with weld-on or bolt on caliper brackets and brake disks that will fit. I do know it may be an issue to find disks that will fit the big 6 lug pattern but Im up for that challenge even if it means some machining.

I do have a set of Dually axles from the engine donor truck but I would much rather stay with the originals if that's possible. I don't want this to be a body swap where I really have a dodge truck that looks old. I want my 1942 G7117 to be usable in the modern world. I am planning on keeping MV tires and wheels, original bed and cab and frame, but upgraded mechanicals. I will also be upgrading the suspension and steering, once again with great horsepower...

Before anybody goes bananas on the "keep it original" train: I really wanted to but can't justify finding a transmission to replace the cracked one that's in it, trying to un-seize the engine and hoping its rebuildable, and rebuilding the transfercase which has sloppy shafts on every side, just to have a truck that like most MVs is hard to use on modern roads for modern jobs and at modern speeds. This is my third MV and I love original, but its not in the cards for this one. Its also been very abused and neglected and isn't going to be easy to restore as it is.

I hope this is in the right spot on the forum and I hope you guys have some answers for me. Thanks in advance.
 

ThatXJGuy

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I should have specified that I have the banjo axles. Ill post some pictures when I remember how.

I'm finding it pretty hard to come up with info on these in comparison to my experience in the 5 ton world where info and parts are plentiful. I found a post on Pirate 4X4 about identifying a transfercase that he thought might have been from a G506 and how it was a reverse rotation case... Am I in for a huge surprise when I swap a modern powertrain in and find out I have more reverse gears than I want? That would obviously mean axle swaps for me unless I could rebuild that old transfercase and make it work. I guess unless somebody has an answer for me I had better go out and try to move it a couple feet and see which way the driveshafts turn.
 
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ThatXJGuy

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Here's some fresh pics I just took because I couldn't find the old ones.
 

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NDT

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Yes this truck is not like your 5 ton where all the drive shafts spin the same way.
Does your rear axle have the tic tac toe pattern on the cover? If not it’s wrong.
6bt won’t fit in the engine compartment, maybe a 4 bt will. The stock transfer case might be able to handle 200 hp, I guess you will find out. You are quite right that a stock Chevy is maybe a 40 mph truck and that is screaming. And not real safe on any highway these days.
 

ThatXJGuy

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Yes this truck is not like your 5 ton where all the drive shafts spin the same way.
Does your rear axle have the tic tac toe pattern on the cover? If not it’s wrong.
6bt won’t fit in the engine compartment, maybe a 4 bt will. The stock transfer case might be able to handle 200 hp, I guess you will find out. You are quite right that a stock Chevy is maybe a 40 mph truck and that is screaming. And not real safe on any highway these days.
The rear axle looks just like the front except the hubs. It does have the tic tac toe pattern and both the front and back open up with a ring of bolts. Do you know which direction each shaft needs to spin? Do both front and rear shafts spin the same direction in relation to the truck but backwards of the direction of the transfer case input? Or does the front shaft rotate opposite the rear?

I have measured and the 6BT will fit in there, both width wise and length wise. It will be tightest on the front sides of the engine because the frame narrows so much but it should fit. I will have to be very inventive with the cooling system but even if it takes a remote radiator, I'm up for that. Also I probably can't fit the AC compressor in it's stock location but I may not have AC at all, I probably won't. I may have to build a different floor with a slightly raised center over the NV4500 transmission it will have, but I even measured the distance from the rear of the engine to the shifter and it will be in nearly the same place, just a little farther back if I remember.

I really don't want to swap axles but I will if I have to. It's not that I don't want the work of swapping but I want it to have the original look under there. If I have to, some Rockwells may end up under it but I don't think there's any chance they'll be the same widths or anything else. The steering will end up powered and safer and the suspension will most likely be radically different. I'm hoping that I can keep the obvious differences down to just suspension, so that the untrained eye won't notice from a distance, but it will be safe and even ride nice. I have personal experience building link suspension with coilovers or coils but this may be link and airbag. I'm not 100% decided on that yet. I do want it to have a working truck load capacity.

Thank you so much for the reply. I guess I need to bring it in the shop and get going on it really. It's a dream project I have been wanting to do for the last 5 years or so, and I'm not going to give up easy.
 

mudflap

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On the G-506, like the GMC G-508 with Banjo axles, the front driveshaft turns in the opposite direction as the rear.

The reason for this is that the same differential carrier assembly is used on both the front and rear axles. However, the front carrier is turned upside down in order to keep the ring and pinion running on the drive side of the teeth (as opposed to coast). This necessitates that the front driveshaft rotate in the opposite direction.

As for axle ratios, all of the GMCs and every Chevy I have seen have an axle ration of 6.67.

Seems like I have seen that ten lug hub conversion someplace else , like on a non-military truck forum such as stovebolt. I'm guessing that there must be some interchangeability between civy and military axles.

Domestically, Sam Winer in Ohio has parts and entire axles. He advertises frequently on e-pay.

Hope this helps...
 

gentrysgarage

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What's the saying Been there Doing That...or Still living the Nightmare? Just kidding somewhat....LOL

You should subscribe to my thread M135 S & M build and my YouTube channel for someone wading in deep for highway speed and safety hot rodding. This was orignally meant to replace the chassis on my G-7123 COE, but the kids liked it toooo much so it got the green light for build up and the COE is left sulking in the garage till I have another frame for it (40+ years of hauling grapes and blow torch mechanics) will seriously pretzel a frame and the space in the driveway for said frame.

Here is a quick lesson on WWII mentality on these vehicles. In a nutshell they were disposable. They were never meant to come back nor last 70 years. They put the emphasis of metallurgy on the airplanes not these trucks. Heck I bet Foote still lists the replacement axle shafts for these to this day.

Thus since I needed another frame I sourced the younger brother the M135/211 for the frame and axles. They didn't have the wartime rationing of materials or the tempering ovens. Just stronger all round.

There are measurements in one of my videos comparing the GMC 302 (the upgraded 270 that was in the CCKW) to the Cummins 6BTA, but the stock radiator is thicker by far than the war-rationed G506...but it will give you a bassis.

Transfer case I feel there are two options;

1, Change out for the M135/211 again metalurgy and materials...heck even stock 235s can split those cases how much more a torquey 5.9?

2. Flop the front hogshead and shorten one of the axleshafts (I think the shorter one was stipulated in my research...haven't gotten that far to verify which one) and run a divorced NP 205. I have upgraded the 205 to a T-136-27 as I plan to work this old man of mine...but a fun occasionally used truck the 205 should be plenty strong.

Axle:

I have come to the conclusion that the next one I do I will go with a Brownie overdrive box as it took 2 years and over 1,000.00 with shipping for the discontinued and virtually unobtanium 5:43 ratios. Also the M135/211 has 27 spline axles and again better metalurgy READ STRONGER.

For safety and stopping power, I am doing a disc brake conversion on the front.

For the wife I am doing the power steering conversion.

Worth all this ...only time will tell. But once you start "upgrading" it is a snowball rolling downhill...getting bigger and bigger! But hey who doen't like a little challenge in life?
 

WW2Chevy

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Just a word of warning... these trucks are notorious for snapping rear axle shafts. I've seen them wherre the longest rear shaft is twisted along its length, just like a candy cane I've also seen the spline end of the shaft snap clean off. Nothing for speed, but man they have the torque!
 

Vintagefarmer

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Youve got a real long road ahead of you to swap in a 6BT. Ill admit I thought the same when I drug home my CCKW last sunday but after thinking on it for a few days I decided against it and opted for the 150 horse 302 instead of anything else. It will look original with the added benefit of way more power. Your 6bt swap is going to be hindered to a spectacular degree due to the RPMs the engine will have to spin to move the thing as a reasonable speed. My federal spins 3k at 60 with stock size tired a 7:1 gears in the rear. While the 6.67s are indeed better then that, they arnt by much. I think youll either end up shoving in a brownie as suggested above or swapping axles. Really, an axle swap on a 506 wouldnt be terrible due to the normalcy of the layout. A CCKW on the otherhand is a completely different animal. haha
 

ThatXJGuy

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Thanks for the replies! I have made a couple decisions since I last posted most notably being a new frame for the truck. I'm going to build one from scratch out of 2x8 tubing which will increase greatly the strength obviously, and the more I looked at mine the more I realized how bad of shape it is in. Too many goobered on welds and torch cut holes and added chunks here and there for me to feel comfortable. Also, I did some more measuring and found that the frame width of the G7117 is the same as that of the Dodge in the engine bay area so to my pleasant surprise, keeping the original frame width will perfectly fit the body and bed of the truck, as well as it's new powertrain, even AC and whatever else. The current frame is already about 2x8 channel but way smaller up front with just a slight hump over the front axle. A straight 2x8 should keep a pretty original look except in the front wheelwells and I may do some modifying of it up there if I need to.

I'm disappointed to hear that the rear axle shafts are pathetic. Are the diffs super tough to where if you had a new axle made it would be good? I know that's a wild shot in the dark but considering everything, custom made axles may not be out of the question but if the diffs aren't much better then it would be for nothing. Maybe I just need to be looking for different axles, there's an awful lot of issues with these between the goofy rotations and the steep ratios and the biggest issue: weak shafts. Maybe it's going to be on 5 ton Rockwells. I'm actually not too afraid of the axle ratio because that just means I can run bigger tires, but only if the axles can handle the torque. I have a set of 1400-20s that look tempting but I may need to go with a modern tire for highway friendliness.

Again, thanks for the replies, I'm going to look into some of the things you have mentioned.
 
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