SM420 4 Speed 7:1 Chevy Transmission

[pvienneau]

Pulled a 4 speed from our 49 build that could be rebuilt, however, I found one local from a newer truck that was running fine when pulled. Is 300 a good price for a 4 speed 7:1 or is this a bad idea. I want to keep the truck with its 4 speed and with a straight newer 6 (full compression) and need advice if I should grab this tranny now or wait maybe get the engine and tranny together? Any infor about this tranny would be greatly appreciated.

[mark '87 930]

Pat, You're a little far away, otherwise i'd offer you mine. The sm420 is a good truck transmission. It is a very noisy one, but i found that they (or maybe it was just mine) shifted very well, like a truck transmission should.

First gear is pretty much useless unless you are pulling tree stumps out of the grounds, literally. Final gear (fourth) is a 1:1 ratio, which is why i went to a different route for overdrive.

honestly, I think $300 is rather high for one of these. I've seen them sell up here for between 75-150. That said, they say they are working transmissions, but no one really knows until you expect it.

[dwcsr]

Originally Posted by pvienneau

Pulled a 4 speed from our 49 build that could be rebuilt, however, I found one local from a newer truck that was running fine when pulled. Is 300 a good price for a 4 speed 7:1 or is this a bad idea. I want to keep the truck with its 4 speed and with a straight newer 6 (full compression) and need advice if I should grab this tranny now or wait maybe get the engine and tranny together? Any infor about this tranny would be greatly appreciated.

At 300 I'd rebuild mine as long at the gears aren't broken or badly chipped. Its a simple trans to rebuild and part are available still that way you know what you have. I just finished a 1 ton that has a 292, sm420 and a 411 rear and you don't use 1st unless its got a heavy load on it or you need to pull a tree down

[tinyjaime]

On That tranny I see for around 100 advertised. Some people just give them away to get rid of them too. If your going to spend 300 bucks just rebuild yours. If you got the original 3:90.1 rear gear you might consider putting a t5 in it so you got over drive mine is .72 final gear in my t5. Give you a little more speed and lower rpm especially with 28 or 29 inch tires. Just a thought.

[mark '87 930]

What's wrong with the transmission? I have mine for sale, but more than will go to give it away to a fellow trucker. It's not perfect (leaks and has a broken mounting ear) but it shifted perfect.

[pvienneau]

This is exactly the information I was asking about. I saved myself $300.00 cuz of you guys. I will take your advice and maybe rebuild. All gears look great. The trans was frozen when I bought the truck. Opened it and just rusted from being exposed for 10 years. WHen I do find engines they typically come with trans. I found a guy with a c10 engine trans from 62 in my home town, However it has the 3 on the tree.