The Stovebolt Site Forums The Shop Area Driveline 4 Speed Transmission

My 1955 2nd Suburban is going through a complete rebuild and now it is time to look at the transmission. When purchased the truck was extremely noisy from exhaust leaks, bad wheel bearings, loose driveshaft, sloppy rear end, etc..., but Hey it ran well. The only thing I can say about the transmission is that it has some beaing noise while sitting in neutral (Stops by Pressing Clutch Pedal) but ran well for several thousand miles with no problems shifting and no falling out of gear.

My question is should I go ahead and have the transmission opened up and at least have the bearing replaced or should I just put it back in and drive it until there is a problem. I tend to believe that "If it ain't broke, don't fix it" but everything else was broke and has now been rebuilt or replaced.

If I am to rebuild it, how do I identify it what is it called other than Heavy Duty 4-Speed? Where do I find a bearing/gasket kit? Are there other parts that probably need to be replaced as well.

Thanks in advance for your help!

Hy Burb'r, your transmission should be an SM 420, they are a very popular transmission, used up to the early 60s. There are lots of parts sources for those trannies, just type SM420 into your search engine and see what comes up, you could also use the search feature here as well, good luck, and if it was my truck, I would rebuild the transmission, hope that helps.

You may find its not a transmission problem, but instead your throwout bearing is bad. Check it first before disassembling the trans.

regards,
Leon

X2 on the throwout bearing.

The clutch & throw out were replaced not long before my purchase but the disk is shot due to engine oil leaking out the rear main, not very smart of the PO.

Maybe the oil washed out the throw out bearing lube but it seems smooth when turned by hand. How would I check it other than for smooth turning? Also, wouldn't the throw out make noice when the clutch was pressed and not the other way around or am I confused?

You are correct Burb. The t.o. brg will make noise when the clutch is depressed. A noise in neutral & the lower gears is usually the front drive brg. If the trans. is out you can check it by removeing the brg. retainer. Wash the brg with a little brake clean & shine a light in it while turning the shaft. Check for rough places, & scores on the races & balls. If it has any the brg. needs replaced. It can be replaced without tearing down the trans.

The truck is down now with the engine out and the tranny sitting on the floor? Then fix it now if there is anything questionable about it now. If not you'll be kicking yourself in the butt later.

I ordered everything to rebuild a SM-420 from "S.K. Performance Transmissins, 9900 Glenoaks Blvd.,#1,Sun Valley, CA 91352. Phone Number: 818-768-7606. I delt with a man named "Steven Kolar." Very nice people and they worked real good with me. Note I'm in Mississippi. Hope this will help. I'd say it can be rebuilt, money wise, for a couple hundred bucks. Mine was.

Thanks for your tips guys. I was leaning toward a rebuild but you guys tipped the scale for me. A few hundered bucks is cheap insurance to not have to pull it out again.

Several weeks back I disassembled my SM420 to have a look see, mechanic by trade I like to look at everything to be sure, if gaskets are only required putting it back that is easy. I did find the needle bearings to be heavily pitted. I was able to find a rebuild kit minus the synchro rings. Those I eventually found and now feel better with new parts. I started to assemble yesterday and my wife commented that I was looking really happy about something, wonder why. Today it gets finished with primer and paint to be attached once again to the rebuilt 235 waiting anxiously for its partner. Have fun with yours, it feels better to see everything knowing that you've made the proper replacements. Bearings are cheap, and there won't be nights thinking if I shoulda, woulda, coulda.