The Stovebolt Site Forums The Shop Area Engine Shop Transmission Question.

I am trying to find out which model transmission I have in my 195? Chev pickup. It's a 3100 and the title says it's a 1951. The vin # on the door post matches that on the title,but I guess anyone can buy these plates and stamp any # on them and mount them. Anyway, I looked in my Chevrolet restoration packet and it says the trans. # for a 1951 , 4 speed will begin with the letters, UK,UL,UM for a 4 speed of this year. In parentheces, it says (RPO 318) which I don't know what that means either. Then for the larger trucks the first two letters in the trans. # will all start with a U. The # on my Trans. is VP 91663 Does the V indicate the truck may be a 1952 or perhaps that the trans. is out of a '52 ? If so what model truck is it from, 3100 or 3600 or 3800 or larger?? Also what does the RPO 318 in the restoration manual stand for? Thanks.

i don't really have an answer for pretty much all your questions cause i don't have a clue with all them letters and numbers but my guess if you trans is a 4 speed that its a SM420 was told that 1967 and earlier 4 speeds were the SM420 and 1968 and after 4 spees were SM465

Nate

if the title and tag say it's a 51, why question that? if it has a 4spd in it, it's the SM420 no matter what the numbers on the case - you sure it's a V and not a poorly cast U?

the numbers don't mean much anyway cuz the facts don't always match the books - the SM420 was the only 4spd in every model for 51, and really the same in any model, except maybe a different rear shaft - RPO=Regular Production Option, meaning there were other trans options that year, ie: a 3spd

you might look for a date code on the trans case to see if it's Dec 51 or earlier to get an idea if it's been changed in the past 54 years

Bill

Elmer

RPO stands for Regular Production Option. In my '54 truck data book, RPO 318 is a Heavy-Duty 4-Speed Synchro-Mesh Transmission. To be more specific, for a 3100, it is R.P.O. 318B.

I hope this helps.

The first letter of the transmission serial number is the model year designation. For the 4-speeds, U=1951, V=1952. The second letter tells both the series of truck in which it was installed and at which plant it was built. For the second letter, K,L,M are for the RPO 4-speed used in the 3100 and 3600 trucks, D,E,F are for the standard 4-speed used in the 3800 trucks, and N,O,P are for the standard 4-speed used in the 4000 and 6000 series trucks. The build sequence number starts at 1001 for each prefix.

Thanks ; Very helpful info. The first letter is definately a V. The second a P, so it looks like a trans. out of 1952 ,4000 or6000 series. Before I took the engine out for rebuild I drove the truck and it shifted fairly good and smooth. Made kind of a growling noise when I let off on the gas. Everything else seemed good. I am wondering if I should take it out now and have it rebuilt. I am taking apart the body peice by peice right down to the frame so it would be easy to take it out. Does anyone know aproximately how much it would cost for the rebuild, parts and labor. Thanks again for all the good advice.