WA WTB Muncie granny low 4 speed FM-420

[burnem]

WTB one year only 67 4x4 3/4 ton SM420 transmission that is married to Rockwell transfer case, a good used one, or rebuilt. Iam sorry about the confusion in posting this in the 60-66 forum I figured some one might have something.

[ChevyK10Dan]

Originally Posted by burnem

looking for a good core, rebuilt, or a good driver. let me know what you have
It has to be from a 4x4, I don't know about the SM420 or is it FM420 here
is a picture of the case

I could be mistaken, but I don't think there's a difference between the SM420 found in 2wd & 4wd GM trucks from the factory. The 4wd trucks all used divorced transfer cases, which used 2wd transmissions.
I believe there's 2 (or maybe 3) variants of spline count that were used, but from what I remember they all have a 2wd yoke.

There's a few places that make 4wd adapters to mount some of the popular transfer cases to the SM420 and essentially make it like a married transfer case, but that might be hard to find already done for your setup. You might check Jeep and Toyota forum's classifieds as well, the short wheelbase crowd tend to be the ones making that conversation.

The SM465 was offered in a 2wd and 4wd variant if that helps any.

[burnem]

thanks for your response I do appreciate it, that is how a person learns. what I do know is
that in the 67 3/4 ton 4x4 they used that trans and married it to a Rockwell transfer case I have one of those, the feed back Iam getting says the 4x4 trans is different that the 2wd. one of the biggest question I have is witch number is correct some people say its a SM420 and some say its a FM420 maybe I just heard it wrong FM420.

[ChevyK10Dan]

Originally Posted by burnem

thanks for your response I do appreciate it, that is how a person learns. what I do know is
that in the 67 3/4 ton 4x4 they used that trans and married it to a Rockwell transfer case I have one of those, the feed back Iam getting says the 4x4 trans is different that the 2wd. one of the biggest question I have is witch number is correct some people say its a SM420 and some say its a FM420 maybe I just heard it wrong FM420.

Yes SM (1960chevypanel beat me to it) but by 68 I believe GM was using the SM465 not the 420. If it's a married Rockwell, it should be the T221 if I remember correctly.

Do you have a pic of the transfer case and/or adapter to the transmission?

[1960chevypanel]

It's SM (short for SynchroMesh). PM returned.

[burnem]

thanks for all the info mine is a SM420 married to a Rockwell transfer case in a 67 3/4 ton 4x4. as far as I GM did change to the SM465 in 68. I don't have any pictures of the transfer case

[ChevyK10Dan]

Originally Posted by burnem

thanks for all the info mine is a SM420 married to a Rockwell transfer case in a 67 3/4 ton 4x4. as far as I GM did change to the SM465 in 68. I don't have any pictures of the transfer case

I had to look it up, I didn't know GM had a married SM420 to a Rockwell for the year 1967 only.
Up to '66 the Rockwell was divorced with the SM420
'68-69 SM465 with a married Rockwell
'69+ SM465 with married NP205

I'm a '59-66 guy, so the '67-72 is definitely not my specialty.

This thread was revived a few years ago with another member confirming how rare the 67 4wd SM420 is, and what they ended up doing.

http://67-72chevytrucks.com/vboard/s...d.php?t=531769

You might want to contact some of the members from that thread and see what they can tell you.

I haven't been able to find what the difference between the '67 SM420 (i.e. the case, output housing, main shaft, etc.) and the earlier 420's is (besides the addition of a backup light switch) or if the 2wd and 4wd 420's made in 67 are the same case etc.

If you're not able to source the correct 4wd SM420, you might be able to buy a 2wd version and replace the main shaft to the correct one (or maybe have one machined like in the thread above) for your truck, and do a rebuild while it's apart. I believe by his signature his was a 69 though, so it might not be that simple for you. Without knowing what all was changed for the 67 model it's hard to know what options you have (if any) to mix and match parts, and with parts as rare as they seem to be you might be looking for a while.

Best of luck on your search.

Daniel

[burnem]

here is a couple of pictures of my 67 4x4, SM420 married to a Rockwell transfer case this is what I started with I wanted to it halfway original.
things are looking up for me there is guy CA. that has one he will sell and a friend of mine in Eastern WA. has one that he hopes to get it pulled this week end so I hope to be able to pick it up next week

[ChevyK10Dan]

Good deal!
I started to look at the 1967 4wd production numbers and seen how few of that year were made to start with, and can't help but wonder how many are still around after 50+ years.

Thanks for the pictures, it definitely helps clarify, plus I had no idea GM made that setup for 67 specific, my memory kept telling me all SM420 were 2wd; I learned something new!

It is definitely cool to try to keep it as original as possible, and sounds like you've got good leads on getting the transmission checked off the list.

Here's a link to some production numbers if you haven't come across it already, it's kind of fun to look through.

http://67-72chevytrucks.com/vboard/s...d.php?t=104816

[burnem]

ttt