Best transmission gear oil

Hello all:

What is the best transmission gear oil (weight, etc) for my '49 KB1 that has the original column 3 speed transmission.

Thank you

SAE 50 engine oil work well for most transmissions with the execption of one of the later trans (the make and model escapes me at the moment) that needs 10W-40. When in doubt, SAE 50 engine oil will be a safe bet for just about any trans, and even the one that calls for 10W-40, will not likely suffer if 50 is used.

International Factory Service manual calls for SAE 90 gear oil in Transmission to be changed out every 10,000 miles in KB-1 truck

The manual calls for SAE 140 gear lube (plain) summer SAE 90 winter (plain) which is not the common 90w-140 GL 5 commonly found for rear axles. It is gear lube WITHOUT EP additive package. SAE 50 engine oil has the same viscosity as 90 gear lube, and handles heat better. 90 GL-1 (without the EP additive package) is avaiable at some tractor supply stores 140 GL is harder to find.
These transmissions have bronze thrust washers. Bronze can be damaged by some of the EP additive packages that are used in GL-2 thru GL-5 which is why they are NOT recomended for the trans.
All of which is why I say that SAE 50 engine oil is a oil to use in just about any transmission.BTW it is the "prefered" lube in all modern heavy truck transmission today, and will do well in any older trans.

International Factory Service manual calls for SAE 90 gear oil in Transmission to be changed out every 10,000 miles in KB-1 truck

The above came from the CTS-8 manul and it states: SAE90 winter, SAE 140 summer. Which IS the factory manual for the K line.

The orignal post was what was the "best" lube to use, not what did the factory recomend 70 years ago.
SAE 50 engine oil is the "best", a subjective opinion, but based on the follwing:
Pro's,
SAE 50 oxidizes at a higher temp then any gear lube
It has the exact same viscosity as 90 GL
It is readly avaiable at any heavy truck supply house and most heavy truck shops.
It is non-reactive to "yellow" metals
It doesn't block the function of syncro's
Con's
It isn't listing in a 70 year old manual because it wasn't in production at that time
Gear Lube:
there are 5 (or more) grades of gear lube rated GL-1 thru Gl-5 (these are the most common found in automotive)
GL-1 has no extream pressure additives and is listed in old manuals as "mild" or "plain" gear lube, or R&O (rust and oxidation resistant)
GL-2 thru GL-5 are plain gearlube with extream pressure additive packages
Extream pressure additives are required for Amboid and Hypoid gear sets (rear ends), but are not required for other gears
Pro's of gear lube in the trans:
its listed in the manual
Cons:
GL-1 is not always easy to find
It oxidizes at a lower temp then engine oil
GL-2 thru GL-5 may attack yellow metal in the trans
GL-2 thru GL-5 may effect the action of syncro's
Many aren't aware of the differance between GL-1 and the others and substaute the wrong oil.
Transmission are robust, and will like do ok even if the "wrong" oil is used, better enough lube then no lube. Mfg have worked to reduce the problem of the additive package attacking yellow metal, so this is becomeing less of a problem. GL-2 thru GL-5 is designed for the slideing action of Amboid and Hypoid gearing. This makes it unsuitable for most syncro's and can give a "balky" feeling to the shifts if used in syncro trans's.
Again, I'm not saying a transmission will self destruct with GL-2 thru GL-5 in it, just that it is not the best choice.

the good news is after you put motor oil in your transmission you can always change it back to the right stuff without doing too much damage,

50 weight motor oil will NOT damage these old transmissions!
Bill

I found this an interesting read: http://www.bigmacktrucks.com/index.php? ... r-end-oil/
Also an interesting read: http://www.binderplanet.com/forums/show ... hp?t=46102