OK, before I pull this thing apart I have a question. I've been reading as many posts as I could find on the SM 420 and looking at as many photos and other info. I have not seen a photo of a 420 that has a rod coming up the side of the shift lever with a tab at the top to pull so that the shift lever can move all the way to the left to go into reverse. Mine has that rod. Everything else about it looks like a SM 420. I just want to make sure I've got the right transmission info before I pull it apart. This is what it looks like. The shift lever will not go all the way to the left without lifting up on the lever that pulls the rod up. But it still will not go into reverse, with the engine running or stopped.
No, that's the earlier type "crash box" non-synchronized transmission. In that box, the gears are actually moved in and out of mesh with each other instead of staying meshed all the time and synchronizers doing the actual engage/disengage functions. The only non-synchronized gear in a SM-420 is the 1st.-reverse sliding gear. (granny gear) Chances are that the sliding rail in the shift tower that engages reverse is stuck or rusted into the neutral position. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thank you for the info. So if I take the top off I should find the rails that move the gears? I’ll drain whatever oil is in it and clean it out with kerosene and check the rails.
Looking at your third photo, there are three small projections at the rear of the top casting, the one with the shift handle in it. There is a shift rail and a lever arm that engages a gear ahead of each of them. Carefully remove the top of the transmission with the shifter in the "neutral" position, and you should be able to use penetrating oil and/or a little heat to get those rails freed up. Make sure all the gears slide freely while you're in there. On reassembly, make sure those lever arms engage the proper slots in the gears. The crash box is an extremely simple transmission to work on. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Got her in the garage this morning and pulled the cover off the transmission. Here's what I have. There was very little fluid in the box when I drained it and I'm not sure what kind of fluid was in there. The gears spin freely. The dogs on the cover move from side to side but they won't move back and forth on the rods. I've sprayed everything with some degreaser to clean them up while I go pick up some kerosene to really clean every thing. If the logistical part of my little gray cells are working right the long dog on the far right side of the last photo should be the one that moves the reverse gear.
So my questions are:
1/ should I be able to slide the dogs along the rods in the cover easily? 2/ If I should and I can't should I give them a little tap after soaking them in penetrating oil? 3/ Any else in the gear box look in need of help? 4/ An other guidance is always appreciated 5/ What kind of oil is best to use in this type of transmission?
There are springs and balls the engage the notches you can see on the shift fork rods, so without the leverage that the shifter gives you, may be hard to move. My guess is you're just not using enough force. They're supposed to be hard to move so that they stay in the gear selected.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
I've pulled pretty hard on the lever when the cover was on the transmission and it didn't budge. The notch you're referring to is the one on the right hand rod below the fork, correct? I took the cover off with the shift lever in neutral. Would there be a notch under each of the levers so keep them in the neutral position too?
I'm going to continue to clean it all up and let the oil soak in and give it a try again later.
Yes, the forks should slide on the rods. The notches in the rods are engaged by spring-loaded balls. You might have to apply a little persuasion to get them to move. There will be a "neutral" notch that is engaged right now. Try clamping a piece of heavy angle iron into a big vise and bolting or c-clamping the cover to it so you can apply some leverage to the shift handle while you're tapping on the shift fork. Yes, the long fork is the reverse lever. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thanks everyone!! Lots of lubrication and just a little "persuasion" and the reverse fork moves along the rod. Now I can back her out of the garage!! And go for a ride!! Well first I'm going to finish cleaning everything and adding oil. Oh yeah, any particular type?
Use the Stovebolt search and enter “Transmission oil” you will get lots of fine reading.
Martin '62 Chevy C-10 Stepside Shortbed (Restomod in progress) '47 Chevy 3100 5 Window (long term project) ‘65 Chevy Biscayne (Emily) ‘39 Dodge Business Coupe (Clarence) “I fought the law and the law won" now I are a retired one! Support those brave men/women who stand the "Thin Blue Line"! Hug a cop! USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
Have fun learning to shift that transmission without creating a few pounds of gear tooth debris! It's definitely an acquired skill! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I hear you Jerry. I'm '73 so I've driven a few, but it's sure been a while. I've looked at all the gears in there and they all look perfect, so any debris will be all my fault, lol. I've got some Valvoline 80w-90 that specifically says it's for "non-synchronized transmissions". Question do I just put it in before I put the cover back on or do I have to put it in through what appears the fill plug at the back of the trans?
I just put it in from the top and buttoned her up and she shifts just fine, at least enough to go around the block. Thank you to every one who helped get me through this. I'm sure I'm going to need a lot more advice as the build progresses. This is the place to get it!
Definitely fill the tranny before you put the cover on. Lots less mess that way. Pull the fill plug on the side and watch for the oil to dribble out, then stop filling.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
