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Joined: Dec 2005
Posts: 35
I know there are kits out there to rebuild the SM420. Does anyone know of a book or website that can walk me through it? The more detail the better, I've never messed with a transmission.

Joined: Feb 2006
Posts: 1,868
Shop Shark
Depending on who you order the kit from they should come with fairly good instructions. And most of the shop manual for the years that used the sm420 have pretty good info to.

On the 2nd link just dont do the toyota stuff!

Good luck, Jeff

Hey guys, hows the weather? grin

Lifes to short to worry about how short life is.

1951 Oldsmobile Super 88 w/303 and hydramatic
My 1953 Chevrolet
1947.1 GMC Art Deco COE / 1947.1 Gallery
1972 C-10 1/2 Ton & 1972 C-30 1 Ton
Joined: Aug 2007
Posts: 304
Shop Shark

Joined: Feb 2007
Posts: 191
Shop Shark
Novaks, has all you need to. There are a couple different out fits. Several guys on here have rebuilt theirs, many their first try, myself included. Its not to big a deal, easy as transmissions go, I have been told. I and several others have had good results, go for it and good luck. Novaks has a good web site with lots of info.

Joined: Oct 2006
Posts: 11,770
Come on Tom, finish your story! If I was sitting across the table at the coffee shop I'd have a few questions for ya, like; Where did you get your parts from? Was it a kit or did you just order individual parts? How long did it take to get all the parts together? What kind of problems did you encounter during the rebuild? Did you need any special tools? Did you have, or use instructions, such as a book, a manual a single loose leaf sheet, an exploded view, a photo description, just info from threads here on the forum? Have you re-installed the transmission and how does it feel? Did you find any wear on the shifting forks, the gears? Does it feel any tighter or smoother when shifting with the new synchros and bearings? Does it run any quieter than before? Did you do it with the engine and cab all in tact or do you have the truck all tore down to a bare frame? Did you replace the clutch and TO brg while you were in there?
Did ya do that huh, Did ya????

Excellent film booklet ya linked us to at tocmp Jim, Iíve never seen that one before, but that's the one I'm gonna have next to the camera on the bench when I tear into mine. I spose I'm gonna have to spend the rest of the morning downloading and printing it out. My thanks also to Shawn McLain & George Phillips. Do any of the vendors sell that booklet; I haven't run across it before.
Looks like I'm gonna need to spend a little time in the machine shop making up some new "Special Tools". That's half the fun of these projects. The staking tool for the reverse idler bushings looks like itís gonna be the toughest one to make. And it looks like one will need to buy a reamer or better yet, take the idler to a auto-machine shop to get it honed after staking the bushings in place. (Keep line boring in mind here). Thatís probably the best choice; I learned that after spending a couple hundred bucks on reamers for the front spindles.
A couple of things I find interesting, are the needle brg retainer, never saw one of those on the three-speed trans, I always just loaded the brgs with heavy fiber grease. Also they call for staking the front brg retainer nut but with todayís thread locker chems that are available, I think Iíd clean the threads real good and use a dab of Locktite.

Are shifting forks available from anyone, they always show wear on the side shifters and can account for that slop ya feel in the shift lever.

God, I hope the replacement transmission parts are better made than most of the other reproduction parts Iíve gotten. I have to rework at least 80% of the repro parts that I buy.

Denny Graham
Sandwich, IL

Last edited by Denny Graham; Sat Dec 22 2007 01:40 PM.
Joined: Dec 2005
Posts: 35
Thanks to all, good links. I should be able to follow along.

Joined: Feb 2007
Posts: 191
Shop Shark
Denny, I used a rebuild kit and everybody knows you always replace the clutch and t/o brg any time you have it apart, or atleast thats what my brother in law told me after I had it all back together. Of corse I did not and now I am just waiting for the clutch to act up. Dumb mistake on my part, not the first and probably not the last no doubt. Good thing I can see some humor in it or I would be in trouble, cause I seem to do that kind of thing more than I should. My truck had a brownie behind the sm420 and the brownie had busted parts and lots of damaged parts. As bad as it was in side I thought I had better have a look in the forward transmission to while I was at it. The 420 was in much better shape, no busted teeth or any pieces of parts down in the bottom or nothing. Everything looked pretty good in there, just replaced the bearings and one or two bushings and all new seals, Novaks had any parts I needed. Seems to shift fine and is alot less noices going on, I can actually hear my radio now :-)I use my truck weekly around town and its the newest vehicle I own, besides my 05 Harley - thats my daily transportation. I am always wondering if something is going to go boom, but so far its working fine.

Joined: Oct 2006
Posts: 11,770
Thanks Tom, I drove stuff like this i.e., late 40's and early 50's cars and trucks for years, and always made it to work. Of course I should mention, that was in the late 50's and early 60's. But there is a lot less to go wrong with them than todays vehicles. As long as ya can keep the earl in them they will run forever.
Novacs seems to be the place. I've been looking at their site for a few months now. I'd like to go through the trans this winter.
Have a good holiday
Denny Graham
Sandwich, IL

Joined: Sep 2011
Posts: 69
Hey all,
Here are my videos I took during my SM420 rebuild.
Long video, full overview:
Clutch hub and clutch keys:
Main shaft overview:
Pressing on the clutch hub:
Input shaft needle bearings:

I hope these help. This site has provided lots of helpful info for me, I wanted to contribute back.

1949 GMC FC253 - 1 Ton Dually
1966 Buick Wildcat Convertible
Joined: Sep 2007
Posts: 432
Greg, thanks for posting these videos. I've been collecting info on a rebuild and have the filmstrip pdf and pics form Sstock. These should help me amass enough confidence to start my rebuild soon.

It's a small world, but I wouldn't want to paint it.

Moderated by  Phak1, Woogeroo 

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