I have an SM420 that is seized. It had some water in it. The gears and synchros look to be in good shape but the transmission won't spin. The reverse lever mechanism moves well There is a lot of info on here and on the web about freeing up seized engines and stuck bolts but not transmissions. I did find a YouTube video about a guy who bought an SM 420 and he sprayed kerosene on the gears to make sure they were moving ok. I don't think his transmission was stuck - he just wanted to ensure movement. Any one have any suggestions as to what I can do to free up my transmission? Would filling it up with kerosene and letting it soak work? I want to get it moving them rebuild it. Thanks in adavance.
It's a small world, but I wouldn't want to paint it.
Diesel and pb blaster works. Try putting a pipe wrench on the smooth part of the input shaft not the splines and give it some hits with a hammer. Probably have to work it back and forth.
Fill it with Evaporust and let it set overnight. Pour out the Evaporust and spray with PB Blaster or Kroil and let set overnight again. Then fill with Kerosene and start working it. A little gentle persuasion with a wooden mallet might help. Good luck.ðŸ›
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)
There is a countershaft in the bottom below the main shaft,if the trans had water in it ,there is a strong possiblity that the bearings could be rusted up and siezed. If you were to get it freed up and turning,i wouldnt use it. Id take it apart and replace bearings and whet ever else it neede. If you cant get it to turn at all, tear it apart and see what whats going on in there.
Fill the case to the top with Diesel fuel and let it sit for about a week. Bolt a piece of 1/4" X 2" steel flat bar about 3 feet long onto the 4-bolt output flange with an equal amount of the bar sticking out on both sides. Use a big dead blow mallet to thump the bar back and forth in both directions until the output shaft frees up, then put the transmission in 4th. gear so the countershaft will turn and free up the bearings that support it. Once the transmission turns freely, dismantle it completely and replace all the bearings.
I'll be surprised if the gears don't whine so loudly when they run that you'll need earplugs to drive the truck. 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!
1940 Pontiac 3sp trans from car that was always garaged BUT clothes dryer was vented into the garage it sat in for 20 years. Second pic is after it sat overnight with muriatc acid solution. Was treated not to run but to be able to disassemble. Turned and shifted fine after acid treatment but bearings sounded like it was full of gravel.
If the part isn't that rare, I would junk it and find a better one. As stated previously, rust pitting on the gears will make the transmission louder than normal. To bad you are on the other side of North America, I have a couple nice SM420's sitting around waiting for someone in need. If you want to free it up just for fun, filling it up with old drain oil and letting it sit for a few weeks or months will usually do the job...no heating or beating necessary.
Just go find another trans, they are plentiful, why mess with something like this. Most transmissions out of 1/2 tons show pretty minimal wear IMHO, a great place to start.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
I agree with Paul...lots of us have SM-420's laying around...you can buy a good used transmission for half the cost of the Master Rebuild Kit, which doesn't include any gears.
I agree with some of the others advice. Find one in better shape and go with it. That one will just give you problems on down the road.
Don
1967 GMC 9500 Fire Ladder Truck "The Flag Pole" In the Stovebolt Gallery '46 2-Ton grain truck | '50 2-ton flatbed | '54 Pontiac Straight Eight | '54 Plymouth Belvidere | '70 American LaFrance pumper fire truck | '76 Triumph TR-6 Of all the things I've lost in my life, I miss my mind the most!
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.
Maybe he’s just looking for a challenge to keep occupied during this mess.
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)
Maybe he’s just looking for a challenge to keep occupied during this mess.
That could be. We all need something to do.
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 got lots to do. LOL If I'm going to put time into this, I want to be able to use it when I'm done. I'll have to start thinking how an SM420 would look in the yard!
It's a small world, but I wouldn't want to paint it.
Looking at the pic. The big gear at the bottom is supposed to slide forward. A closer look, looks like the teeth it rides on are all chewed up and wont let it move.
I've got lots to do. LOL If I'm going to put time into this, I want to be able to use it when I'm done. I'll have to start thinking how an SM420 would look in the yard!
This is how I recycle some of my old useable Chevy parts... We Stovebolt folks are quite creative, I am certain you can come up with something
In all seriousness, I would hunt for a better gearbox. They are out there.
This is how I recycle some of my old useable Chevy parts... We Stovebolt folks are quite creative, I am certain you can come up with something
Nice! The Junkyard Dog, protecting that pile of valuable parts.
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.
