The GMC CCKW

THE Lubrication Orders (LO) Suggest that the differentials be serviced (checked) Weekly and Drained at 6000 intervals. This is twofold as it maintains your differentials at safe levels, and gets rid of contamination such as metal particles, brass and steel, that are normal wear and tear. These intervals are based on the type of operation that the Army anticipated the truck to used for-Combat, and operation in extreme conditions. For the collector, this is not going to be a reality, but it is a good idea to drain the gearboxes of your CCKW when you first acquire it. These trucks have sat for years, and many still have the WWII GO in them. This stuff goes sour and in the case of the Split Axle CCKW Differentials, and the other gearbox cases, will react with the Leather Seals and etch the contact area of axle shafts and pinion shafts, causing pitting which will lead to seal failure and leaks. It is a good idea to drain your gearboxes every 5 years .
Do not buy the crap sold at Sam's Club or those Discount Houses that sells for $20.00 in the 5 Gallon Pail. Go to a distributor of Lubrication Products and buy a name brand such as EXXON, Mobil, Texaco, Shell, etc. Your truck will say "Thank You" I buy Kendall at a cost of approx $55.00 for a 5 Gallon pail(35# pail). There are benefits to using quality. The crap at Sams drains out like water after just 200 miles. Good gear Oils perform wonders in the gear boxes, and in the case of Kendall, is the choice of Drag Racers where the Tooth Contact pressures will cause spalling or flaking of metal with the cheap stuff, and the good GO withstands that.. If you ever have to replace a differential in your CCKW you will understand why you should use nothing but the best and hope you never have to change one again. You need shop tools, big time, and lots of money. It is a lot of work to safely block up the truck, remove and reinstall Torque Rods, set up backlashes , preload, etc. Give your CCKW the best shot at longevity. Any good brand of GO-90, or 80W-90 is fine. Do not worry about Hypoid oils, those went out in the 40s-50s, as all GO is now multi purpose. Lubriplate may still supply straight 90 if you want to go to that extra effort.

Good information. I have always used Texaco or Exxon in my truck and that include all lubricants.

Joel hit the nail on the head here. When I acquired my trucks, the diff's probably had the original oil in them. After draining them I pulled the rear covers off and the pumpkins were full of "black goop". I took the extra step and removed the third member, be careful this very heavy, after using 2 cases of brake kleen i got hem clean, I also used a long pry bar wrapped in a rag to clean the axle tubes out, a messy job, bit i got all the old goop out and it is a job i will never have to do again. I use Castrol Go in a 5 gallon bucket $36.00 at Western Auto. If you are changing both axles , transfer and gearbox, you will use almost every drop.

The job was PIA but now that it is done I feel beeter and so does my truck