The Stovebolt Site Forums The Shop Area Engine Shop 3 speed vs. 4 speed tranny

I need some advice on whether to install a 4 speed rather than a 3 speed. My main concern is that my clutch & brake pedal assy bolted right up to the 3 speed (stock '40 GMC). When I found a 228 engine it came with a 4 speed but no place to bolt the clutch/brake pedal assy. Has anyone done this swap before? Do I just need to have some kind of bracket fabricated? I'm dong a frame up on the truck right now and want to get working on the tranny, but which one. I believe the 4 speed is an SM-420(?). Someone posted a link with a picture of one that looks identical to mine in another thread. Thanks for the help and advice. Have a great Labor Day weekend and be safe.

It was Fatweed who posted the link to Novak. They show a picture of a Muncie SM420. Looks identical to what I have and the description is the same. By the way, I'm "doing" a frame up, not "dong". Why do typos happen on words like that? Guess that'll teach me to read before I post.

Hit that pencil/paper icon in the post and you can fix your error..I use it all the time.

Neil,

I have a 1940 Chevy, so I don't know if it is the same. But I had a similar problem with my truck. I switched to a 1960 235 and a T-5 transmission. I wanted to keep the original pedals.

If you look at my t-5 rebuild page way at the bottom you will see my solution.
http://home.twcny.rr.com/schickling/1940Chevy/T5.html

The bellhousing comes from Buffalo Enterprises. This may or may not work on your engine. If not maybe Buffalo Enterprises makes a similar one for GMC. I'm pretty sure they have a web page with at least a number to call.

Bill Schickling

The correct 4 speed for your truck will have mounting lugs for the brake/clutch/master cylinder bracket. The SM420 bolt pattern is wider than a stock trans for a 40. You may have a 47 up bellhousing on that 228 which does not have the mounts for clutch and brake pedals.
The 3 speed is half the weight of the 4 speed and the 3 speed has syncros in second and third while the stock 1940 4 speed has none. Unless you want that granny first gear the 3 speed may be a better choice.

If you want to use the SM420, Buffalo Ent can modify your 47-54 bellhousing for your stock pedals or Buffalo makes an adapter plate to bolt to your stock 40 bellhousing that will accept the SM420 or T-5. However, both these trans are longer than the stock trans and require you to change your driveshaft/rear end.

The 4 speed was optional on 1/2 tons and is a real beast (used on heavy trucks). You wouldn't use 1st any way and 2, 3, and 4 are very close in ratio to 1, 2, and 3. For street use the 4 speed is an overkill. 4 speed is also non syncro.

Thanks for all of your replies. It relly helps to make an informed decision. I've decided to go with the 3 speed. I was pretty sure that I'd have to shorten the driveline with the 4 speed and the weight was a factor as well. My whole focus since starting this project was to do a frame-up for as little as possible, meaning not changing much on the truck and keeping things simple and original. Even so, I'm sure I'll be into this thing for at least $12 - $15K by the time it's done. Your advice has made this an easy decision. Thanks.