The Stovebolt Site Forums The Shop Area Engine Shop 1948 216 with 3 on the tree

Hello All,

I am new to the forum and I have a question regarding the tranny. As I registered, I realized the Stovebolt Forum is for trucks, but I hope you will indulge me since my vehicle is not a truck but a 1948 Chevy Fleetmaster coupe...I just got the car and I want to replace all fluids but I cannot find anything on the transmission. I have the shop manual but there is nothing on transmission maintenance in there. How do you drain it and how do you refill it? Also what fluid do you recommend in the tranny? I am planning on using the same 85W140 in the transmission that I will use in the rear differential.

Thank you

I believe original transmission would be the SM-318 and I have worked on some of the newer mid 60's versions of that transmission. I have 3 of them 1 has a drain plug but 2 do not. The fill plug is on the right side of the main housing and the correct fluid is 90W straight mineral oil. Tractor Supply sales the fluid in 2.5 half gallon jugs as Ford Tractor Fluid. There is at least 2 versions of why you don't want to use a GL-4 or 5 fluid in those transmissions. #1 is that the EP additives are too slick and will not allow the synchronizers to work correctly and # 2 is that the EP additives will damage the brass and/or bronze in the transmission. Am not sure if one or both of those are correct.

I may be mistaken, but wasn't the SM-318 a Muncie "crash box" non syncro floor shift transmission, used before the Muncie-420? I thought the 3-speed column shifts were Borg Warner brand.

The correct lube for the tranny is SAE 90 transmission or mineral oil.
Shown Here on page 47
The transmission was a Chevy design built at the Muncie plant.
The 4 speed would have started with "4" in the model number. Early 4 speeds were SM-420 and later were SM-465

The SM-318 is a truck transmission only application until around 1954 or 55, when it was also used for passenger cars. The SM 319 is thre same basic transmission, with a B-W overdrive fitted to the output shaft. The automobile trans from the late 1940's and early 50's is a much smaller, lighter-duty unit with a different bellhousing bolt pattern. Some of the 1940's transmissions also had vacuum-assisted shift linkage that gives a lot of trouble.

85W-140 is a synthetic gear lube which will cause incorrect operation of the 2-3 shift synchronizer, and will probably cause gear grinding. It would be much better to use straight 90 weight mineral oil in the transmission, and use the 85-140 in the rear end if you want to.
Jerry

Well I stand corrected.

Thank you! That was very helpful