The GMC CCKW

Unlike commercial 10 wheelers that have power dividers and the ability to lock out the power to the Intermediate axle, CCKWs and other 6X6 Army trucks of WWII have full time power to both rear Axles. The rear tire wear is accelerated somewhat because of this.
Joel

But the upside is that this is what endows them with their tremendous traction off road.

2 words:

MATCHED TIRES

Remember that if you have different sizes, one rear end will 'fight' the other rear end thru the transfercase and 3 drive shafts

I got about 30,000 miles out of my rears. Fronts 4-5k

Thanks for the good information. I have matched tires all around on my truck, but I don't drive her more thant 300 miles per year.

The Split axle CCKW seems to be more sensitive to mismatched or underinflated tires. It will give you a whump, whump, whump noise in back at speeds over 20-25 MPH.

Once you get used to your truck, it will "talk" to you, as the clunks rattles and vibrations all have a meaning. I used to fly as Crew Chief in fixed and rotary wing military aircraft, and the helicopters would talk to you, especially if the rotor Blades were not tracking precisely, there would be a "one to one" vibration (one vibration for each revolution) and your helmet would sort of move up and down, gently slapping you in the head. Same thing with the CCKW,a bent drive shaft gives a one to one vibration, and the troop racks may do a dance to it. Each truck has its unique habits or personality, some are real smooth, others will never be. I tried to smooth out mine by balancing the drive shafts, and have done all but the intermediate drive shaft, not necessary on a CCKW but it helped.

You can learn a lot about your truck if someone knowledgeable about mechanics follows your CCKW at just 25 MPH and observes if the wheels ate in track, wobbling, or out of round. (do not ask your wife, as they usually cannot translate what they see in words you will understand) I have compared notes with friends and my father in law who is a master mechanic, wives are all the same. Two of the most common frustrating acts, are to ask your wife to help bleed the brakes, or just touch the starter switch to get the ignition points on high cam- it does not make good teamwork. Mine does do a good job operating my Multifuel Pipeline Truck (with high heels on) to winch out my stuck M-37 from snowbanks.

A simple observation you can make yourself is to lookdown at the transmission shift tower while you are driving and if it is oscillating within the hole in the floorboard, you have a balance or out of round situation, likely, a bent drive shaft.

We get slightly less mileage out of tyres altho' we have always been very careful to use matched sets,I attribute this to the extra drag from the shorter wheelbase. We used to notice a difference on the fleet of modern trucks we used to operate and we would also see a difference between
drivers, some drivers are much harder on their vehicles than others and this shows in a number of different ways.

Following up on what Joel said about the cckw talking to you.

I may have mentioned this in here before, but years ago I was up in northern NH with my deuce and I was leading a convoy in the morning.
We started out on back roads and then got onto a smooth highway. At about 40 mph I heard a noise that she never makes. I stated to my wife that there was either something drastically wrong with the truck, or I had a flat on an outside dual in the back and was running on the inner tire. At that time I was running older, slightly smaller tires on the inside and had a new matched set on the outside.

We stopped and sure enough, the outside dual was flat!

I find this to be true in any vehicle one travels for an extended length of time. I have an old 87 Ford Bronco that I love to drive. I noticed a different noise coming from the transmission area one day while driving her home from work. The same noise was there going to work the next day. I took it to the Ford dealership and I had a transfer case problem developing and had to have it rebuilt.