Mission: transMISSION

[ZAEDOCK]

I started thinking about the SM420 transmission in the Scrambler dude's tire sales thread and how I should pick up a spare or two. Well, I decided to give Craigslist a quick check this morning. I found a guy selling one, who happened to be on the way home from work.








So, $100.00 and a hour of car resto, rat rod, & Jeep talk later, I dragged home a SM420. Apparently, he had it listed for $150.00 for a while with not one bite. He changed the price to $100.00 about 1/2 hour before I checked it out this morning. Cool score! She glides into all gears and also came with the parking brake assembly (which I might use with TJ rear parking brake cables). The gears look nice and clean inside and I already have a couple of gasket kits in the basement. According to the date code, it was built on June 16th, 1950.

[Carl McFly]

[nostaw]

Nice.... I was wondering what that extra handle was... Must be the parking brake you mentioned.

Is the thing coming out the back below the yoke the spedo?

Since it has a yoke on the back I presume this is a 2WD version.... Do you have a divorced TC, or can you convert it?

I know zip about the SM420 other than it is a cast iron case, are well known for strength, and some have a really deep granny low 1st...

JW

[DOUG]

Nice score Joe!!! Looks so small compared to an NV4500...

[ZAEDOCK]

Nice.... I was wondering what that extra handle was... Must be the parking brake you mentioned.

Is the thing coming out the back below the yoke the spedo?

Since it has a yoke on the back I presume this is a 2WD version.... Do you have a divorced TC, or can you convert it?

I know zip about the SM420 other than it is a cast iron case, are well known for strength, and some have a really deep granny low 1st...

JW

Yep, that's the speedo cable. The adapter I have replaces the entire rear retainer/yolk assembly and then a spud shaft slides over the existing output shaft. If I had to, she could be swapped in a matter of hours.

SM420's came with either 2WD, a divorced t-case or a married Rockwell T221 (Daddy of the NP205).

1st gear is 7.05:1. The tranny that's currently in my YJ was out of a 1953 2.5 ton Chevy dump truck. To my knowledge, only the Clark 280V has a lower 1st gear (7.48:1), but that's a big, heavy tranny with 5 foward gears with 5th being 1:1 (i.e. no overdrive)

Nice score Joe!!! Looks so small compared to an NV4500...

It's shorter (obviously, no OD), but a bit lower (mine is level with my belly skid). IIRC, the case is only 10.7" long, so it fits well in a SWB Jeep. There's a big hump on the other side though, that houses the reverse idler shaft. I believe throwing a Dana300 behind it has issues with clearing. Only the lucky bastids with LWB Scramblers can run HD overdrives. I spin about 3 grand doing 65-70, but that's perfect for a 4 popper.

Here's a pic I found of the famous SM420 hump:

[scrambldcj8]

Man, I didn't know you were looking for an SM420? As I said the one I found was about a mile from my house.....don't have a use for it but when I saw it I knew what it was and how "kewl" they are for those swb guys...and just had to have it.....LOL

[ZAEDOCK]

Let me know if you ever get rid of it. I found another '67 married to a T221. The guy wants a couple of hundred, so not too bad.

Like I need more stuff though.......

I have an extra 60* GM bellhousing and had the crazy idea of using a late model 3.4L mated to the SM420 in my buggy instead of the 4.0L on deck. *sigh* - too many options, not enough time.

[scrambldcj8]

Will do...just have it cause it was a neat find while hiking....not what you expect to stumble upon!

[ZAEDOCK]

Will do...just have it cause it was a neat find while hiking....not what you expect to stumble upon!

I found an NP435 at a local farm while apple picking a few years ago, but they didn't want to part with it.