The Stovebolt Site Forums The Shop Area Engine Shop SM 420 to open driveline?

I have a '49 3600 that I am convering to 1/2 tom running gear to be able to put disc brakes on the truck. I have a friend who is giving me a 10 bolt with 3.42's in it. I really like the old granny low 4 speeds. Is it possible/hard to convert the SM 420 to an open driveshaft to match up with the 10 bolt?

One easy way is to just pick up a SM420 already set up for an open driveline out of a newer truck. They were used for a long time and should be easy to find. Here is a bit of info on them:
http://www.novak-adapt.com/knowledge/sm420.htm
Bob

All you need is the rear bearing retainer and yoke from an open driveline equipped SM420. It will bolt right on to your trans. Rather than having the bell end for the torque tube, it will be more flat with a seal in it.
PM me if you can't find one.

Have you considered an overdrive transmission like a T-5?
What are your plans for the truck?
Will a 3.42 rear give you the speed and rpm you want?
What will you do for a parking brake? Many SM420's have them on the back, that may be the way to go.

Grigg

Steve, are the tail shafts the same on both open and closed SM420's???
Denny Graham
Sandwich, IL

Yes, the tail shafts are the same.

Also, keep or sell the old enclosed-bell assembly from the 420. It is useful to people who want to use an open driveshaft 420 on an enclosed driveshaft truck

The output shafts are all the same, 10 spline except for a rare 2 ton version that has a fine spline output shaft. I've never seen one. I think I read that info on the Novak Conversion site.

Looks like we found some trans-a-mission experts here. The later cases are different in that they are ribbed. Are the gears and shafts interchangable between the early and late cases or were there different models? Like the cluster, sliders, main shaft etc.?
Denny Graham
Sandwich, IL

Kirk:
If you want disc brakes on the rear, the 2002 Firebird disc brakes will bolt on to your Camaro axles.

I just did this last month, real simple. Like they said, swap the yoke and cover and your set.

Denny I think there was a difference in the synchros only, but the gears, countershaft, blah blah blah, should all be the same. They did make a few goofy splined sets in military and big trucks that may require a different seal or yoke. I wouldnt know exactly as I havent seen any of them.

Theres a few rarities out there and they even used some of these trannys in odd applications far past 1968, up into the early 80s I believe.

You can identify the date of your tranny by looking at the code stamped on the right hand side above the inspection cover. Usually has a serial # (5-7ish #s) and an ID #, usually a 4-5 letter/# sequence. First should be a letter indicating month (A-jan, B-Feb, etc...),Next number is the day of manufacture and the last 2 are the year of manufacture. Mine was something like D163, April 1st 1963.

Hope some of that helps. Jeff

This link has been posted many times in this forum, but it has some good info.
Novak Conversions

Hi, I have the SM420 and plan to match it with a 235 (as soon as I find one) in my 53. Where can I find the stuff (rear bearing retainer and yoke) to convert the truck to an open drive train? Is it as easy as placing an add in the Parts Wanted section? I have never seen one on EBay or other advertisements.

Is a rearend from a 55-59 a good and easy swap for the 53?

TIA

They used sm420s typically from 47-68 so probably the best bet is to pull one of a junk yard truck. Placing an add in the swap meet area cant hurt either!