The figures i posted  earlier came from two AUTO REPAIR MANUALS , one covering from 1935-49, the other from 1940- 53. after brians reply i have checked two original service manuals i have ,the first one covers fom 1936 -42 , for the trans it says SAE90 fluid gear lubricant shoul be used if the temp is +32f to -10f, below -10 use SAE80, the other covers 1946-53 it just says that SAE90 should be used in the trans. both these manuals are Canadian manuals but the same standard trans was used in both the US and Canadian cars

My 53 Dodge Regent (Canadian Plymouth-bodied Dodge) came from the factory with SAE 10 in the transmission. It was standard, no fluid drive. As far as I can recall, all our Dodge and Plymouth cars with 3 speed standard and no fluid drive came so equipped until  at least late 1954 (I left the dealership at that time and never worked in one again).

Happy New Year to all!

Brian

Brian is right chrysler did start using sae10 in there tran s in 53  but that was only for there fluid drive tranmissions . from 1935-1948 Plymouth used SAE 90 summer and winter from 1949 -1954 they used SAE 80 summer and winter

Don:
In 1953 (if my memory is correct) Chrysler started using SAE 10 engine oil in all their standard transmissions on a year-round basis. I was a bit doubtful so I asked the tech rep the next time he visited our dearlership. He confirmed the use and recommended that all standard transmissions right back to the early '30's would benefit from its use in terms of ease of shifting, especially in cold weather. Since that time I have used SAE 10 oil in all Chryco standard transmissions in all rear wheel drive vehicles with no reported problems whatsoever. Therefore, I'm sure using engine oil in an od is the right thing to do.

Remember, gear oil is designed for use in hypoid gear sets to withstasnd the extreme pressures developed between the teeth. There are no such pressures in a standard spur cut, or helical gear transmission (this includes planetary gear sets). The only possible problem is failure of the seals to retain the oil.

Brian

This is straying from the "rear end" oil question somewhat but my question has to do with transmission oil. After installing an overdrive in transmission in my 40 Ply, I was told to use 15W40 Disiel oil as the lubricant. Does anyone have an opinion on that?
Thanks
Don

I have used several friction reducing additives over the years. SFR (superior friction reduction) was one but I can no longer find it. I use Prolong in my engines and a liquid molybdenum additive in gear boxes and rear ends. I believe in the US it's called 'Mr. Moly' but you can buy generic moly at car product stores. I also use cartridge moly in all grease fittings and load up open frame bearings with it and use it in steering boxes. It has a much higher melting point than standard greases and no break down and separation and? run out of the oil carrier with time. I also use a Prestone additive,beyond Prestone antifreeze, to enhance the lubrication of water pumps. I think that's about it. I've? used this regime for maybe 40 years now.? (I just realized, with my recent application for the old age pension, I should? say I've used some of these products ,and done my own car repairs, for nearly 50 years now.)? ?

We must beware of some of our old seal, gasket or metalalloys (no longer in use on modern cars) may be not compatible to modern lubricants!
Greetings! Go

Plymouths, ""I have used modern SAE 90 hypoid rear end fluid for many years now with no down side. I also add a slip additive"". That's a new one on me. Can you expand on the reason and result of using a "slip additive". Thanks, 32cabrio

Thankyou everyone for the info.

Elmo is correct. I have used modern SAE 90 hypoid rear end fluid for many years now with no down side. I also add a slip additive. Anybody who is new to the hobby and is trying to figure out what lubricants to use in their old car needs to first pitch the original manual that asked you to use such things as 'low pour point oil' or 'high fiber grease'. None of those things exist any more,thank God, and you just need to ask around as to what fluids are used in modern vehicles in the same area of your Plymouth. Any of the modern lubricants are far,far superior to anything these cars used on day one.   

for 37 through 1954  my books says you should be using 90 hypoid oil  winter and summer .

Don't add synthetic. Do you have an Owners manual or shop manual ? What climate do you live in? I will check my manual tomorrow but my car is a '37.

Hello Everyone
? Could anyone tell me what grease to use in the rear differential?.90w or 140w.?? I have a 1939 P8 sedan and would like to change the rear end oil. Can I add synthetic blend to my exsiting oil ?