The Stovebolt Site Forums The Shop Area Driveline 1963 frame. is sm420 trans the same as 59

A guy near me has a 1963 rolling frame with a gmc v6 in it and a sm420 4 speed. can i use that trans in my 59 and will the rear end bolt into a59 frame? Thanks


So the trans and rear made it safely home. Using the spin the drive wheel and watch the pinion it looks like a 3:40 rear axle. the trans looks all there but the front spline (see pic) looks like the shaft cover is missing. the part the throwout bearing rides on. found a parts pic and it list a cover seperate from the bearing cover. any ideas?

Is the frame a leaf spring rear or a coil spring rear?

You didn't say what series trucks you're talking about, but the SM-420 will be the same. The only difference will be if the trans has a parking brake (band or dual shoe) or not. With that said the rear bearing retainer plate can be swapped from one to the other to make it work.

I can't help with the rears, you might need to break out the tape measure and compare them yourself.

Mike B

There were internal changes to the SM420 throughout the years. I replaced my 1954 SM420 with a 1967 one. The newer one has a better oil seal on the front, new syncros are available and it has a backup light switch. The Novak site has the details of the changes.

https://www.novak-adapt.com/knowledge/transmissions/manual/sm420/

Thanks for the info. update looks like its a 3/4 ton frame the rear looks different than my 59 . can i put better gears in a 63 ? like 3.70 ? trans had the e brake on the back like mine. looks like a road trip coming up

GMC in that era use Dana rear ends, you can gets lots of ratios for them.
Show us some pictures of what you got!

not here yet but owner says its a dana 60. will send some shots when its mine.

Went to see the frame today. has a dana 60 rearend that looks like it will swap into my 59. thinking whole rear. springs and all. dont know what the rear gear is but google says anywhere from 340 to717. trans looks different than mine top cover is the same but lower case is different. google says the gmc were able to attach a pto. any gmc guys want to help? frame has a 305? v6 in it looks complete but what to do with it. ? still thinking on this.

So, where are the pictures? It's hard for us to play along without them...

Mike B

ok here are the picts frame trans and rear. the trans case looks different on the bottom than the one in my 59. different lower case.