The Stovebolt Site Forums The Shop Area Driveline ID trans and advice on disassembly

Hello!

I've never had a manual transmission apart, but I want to learn how to tear down and rebuild one. I was at an antique farm engine show today (my other hobby), and, for $10, picked up what I believe to be a 50 - 60 Saginaw 3 spd. I figured for $10, it would be a perfect candidate to practice on. The casting #s are: Main case 3845122 (with K94 under that), side cover 3845044, tail shaft 3707195.

Question - IS this a '50 - '60 Sagninaw 3 speed with a non-synchro 1st gear?

If so, could this tranny have been used in a '59 truck? - I ask because I own a '59 Apache, and want to use the shop manual to help guide me through the teardown procedure.

Although I wouldn't use it in my truck (mine is a 3600 with an SM420 4 spd), I figure that it's probably a fairly simple transmission to get my feet wet, and, if I already have the instructions, so much the better.

I might try to rebuild it, depending on the cost of the parts. If not, I'll just reassemble it to get the practice.

Any watch-outs with this particular transmission?

Any other sage words of advice for first time transmission disassembly?

Thanks...

Chris

4.103 Transmission case casting 3845122

http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0372.htm

Here are some pictures of an SM420 rebuild that I just finished up for my
‘50, 3600. Best advice I could give you is to get a GM manual for the
trans and study it before and during your rebuild.
http://www.pbase.com/dennygraham/sm420_rebuild&page=all
There used to be a complete manual on TCOMP but I’ve been looking for an
hour and can’t find a trace of it.

Denny Graham
Sandwich, IL

Is this it, Denny?

http://chevy.oldcarmanualproject.com/booklets/49fsstoindex.htm

Here's a sneaky trick I've used for years when assembilng standard transmissions. The cluster gear needle bearings have to be held into place on most of them with grease, as they're loose-packed without a cage to hold them in place. The thrust washers on each end of the cluster gear are also a PITA to keep in place while the pivot shaft is inserted. Getting the cluster gear into position without dropping needle bearings or losing a thrust washer will increase your vocabulary of cusswords, guaranteed! If you use a piece of wooden dowel rod cut off to the right length to hold the needle bearings and thrust washers in place while you manipulate the cluster gear into the trans case, it will slide out as the steel pivot shaft is inserted. Just make the dowel exactly the right length to fit between the front and rear holes in the case. Sand the dowel to the right size to be an easy slip fit through the holes in the case. In a pinch, I've also used a cut-off piece of garden hose for the same purpose. My tool box used to contain an assembly dowel for Ford and Chevy transmissions, so I didn't have to cut up a broom handle or a garden hose every time I built up a transmission!
Jerry

Yeah Tim, that's the one. God, I looked for that everywhere, don't know why Keith doesn't double list it and add it to the Transmission index. Thanks

That's a very thurough guide to the SM420 rebuild. Has a lot more info than the booklet that Novak sends you with their SM420 kit.

Good tip Jerry, I've used the same thing before on the Chevy 3speed transmissions. The SM420 has a steel sprin retainer that holds the needles in the clutch gear. It gets pushed back into a recess when you slide the gear onto the main shaft.

Denny Graham
Sandwich, IL

Spools from thread used to work pretty well. I would a but through the hole and use my drill press for a lathe. I think spools are plastic these days.

Yep, your dating your self Ken, only place you can find wood spools is in an antique store.
DG