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Freeing seized SM420
#1356681 Thu Apr 23 2020 01:08 AM
Joined: Sep 2007
Posts: 407
R
Shop Shark
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.
Re: Freeing seized SM420
Rusty Shackleford #1356687 Thu Apr 23 2020 01:39 AM
Joined: Jul 2019
Posts: 277
B
Shop Shark
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.

Re: Freeing seized SM420
Rusty Shackleford #1356689 Thu Apr 23 2020 01:57 AM
Joined: Apr 2008
Posts: 785
F
Shop Shark
I understand that Novak Transmissions do a lot of SM420 work. Google them, they may have a customer service line that can help you.


Ed
Re: Freeing seized SM420
Rusty Shackleford #1356691 Thu Apr 23 2020 02:11 AM
Joined: Apr 2005
Posts: 8,662
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
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.๐Ÿ› 


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
โ€˜65 Chevy Biscayne 4dr 230 I-6 one owner (Iโ€™m #2)
โ€˜39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"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!

Re: Freeing seized SM420
Rusty Shackleford #1356702 Thu Apr 23 2020 04:29 AM
Joined: Mar 2013
Posts: 176
Q
Shop Shark
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.

Re: Freeing seized SM420
Rusty Shackleford #1356703 Thu Apr 23 2020 04:40 AM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Freeing seized SM420
Rusty Shackleford #1356707 Thu Apr 23 2020 06:28 AM
Joined: Apr 2005
Posts: 2,529
C
Shop Shark
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.

[img]https://i.postimg.cc/qg0ngJcq/1940-Pontiac-Cpe-003.jpg[/img] [postimg.cc]

[img]https://i.postimg.cc/9R47H0yF/40-Pontiac-engineand-trans-003.jpg[/img] [postimg.cc]


Evan
Re: Freeing seized SM420
Rusty Shackleford #1356716 Thu Apr 23 2020 11:38 AM
Joined: Nov 2011
Posts: 2,566
P
Shop Shark
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.

Re: Freeing seized SM420
Rusty Shackleford #1356747 Thu Apr 23 2020 02:49 PM
Joined: Jan 2013
Posts: 1,642
S
Shop Shark
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
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: Freeing seized SM420
Rusty Shackleford #1356803 Thu Apr 23 2020 10:09 PM
Joined: Mar 2004
Posts: 4,506
M
Shop Shark
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.

Mike B smile

Re: Freeing seized SM420
Rusty Shackleford #1356804 Thu Apr 23 2020 10:24 PM
Joined: Sep 2007
Posts: 407
R
Shop Shark
Here's what the top looks like inside the transmission. Hard to see what lurks underneath. I already have a rebuild kit.

Attached Files
Transmission Inside.jpg (169.19 KB, 148 downloads)
Inside

It's a small world, but I wouldn't want to paint it.
Re: Freeing seized SM420
Rusty Shackleford #1356807 Thu Apr 23 2020 10:33 PM
Joined: Sep 2010
Posts: 474
K
Shop Shark
the top of the internals look good


kevinski 1954 GMC 9300 Welcome to the virtual Garage
Re: Freeing seized SM420
Rusty Shackleford #1356810 Thu Apr 23 2020 10:40 PM
Joined: Mar 2004
Posts: 4,506
M
Shop Shark
Your gears look to be in rough shape to me...the wear pattern surfaces are all pitted.

I'd look for a trans with better gears and put your new kit in that one...

Mike B smile

Re: Freeing seized SM420
Rusty Shackleford #1356818 Thu Apr 23 2020 11:21 PM
Joined: Aug 2001
Posts: 4,196
Shop Shark
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


Of all the things I've lost in my life, I miss my mind the most!

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
More pix on Photobucket
'46 2-Ton grain truck
'48 3/4-ton grain truck
'50 2-ton flatbed
'54 Pontiac Straight Eight
'70 American LaFrance pumper fire truck.
Re: Freeing seized SM420
Rusty Shackleford #1356838 Fri Apr 24 2020 01:27 AM
Joined: May 2015
Posts: 2,373
K
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
Yep, Make some yard art out of that one. wink


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Freeing seized SM420
Rusty Shackleford #1356849 Fri Apr 24 2020 02:08 AM
Joined: Apr 2005
Posts: 8,662
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
Maybe heโ€™s just looking for a challenge to keep occupied during this mess. chug


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
โ€˜65 Chevy Biscayne 4dr 230 I-6 one owner (Iโ€™m #2)
โ€˜39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"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!

Re: Freeing seized SM420
Justhorsenround #1356850 Fri Apr 24 2020 02:23 AM
Joined: May 2015
Posts: 2,373
K
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
Originally Posted by Justhorsenround
Maybe heโ€™s just looking for a challenge to keep occupied during this mess. chug
That could be. We all need something to do. grin


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Freeing seized SM420
Rusty Shackleford #1356862 Fri Apr 24 2020 04:21 AM
Joined: Sep 2007
Posts: 407
R
Shop Shark
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.
Re: Freeing seized SM420
Rusty Shackleford #1356879 Fri Apr 24 2020 12:59 PM
Joined: Mar 2019
Posts: 736
G
Shop Shark
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.

Re: Freeing seized SM420
Rusty Shackleford #1356882 Fri Apr 24 2020 01:23 PM
Joined: Nov 2011
Posts: 2,566
P
Shop Shark
Originally Posted by Rusty Shackleford
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.

Attached Files
IMG_1406.JPG (478.16 KB, 76 downloads)
Re: Freeing seized SM420
Paul_WNC #1356952 Fri Apr 24 2020 09:34 PM
Joined: May 2015
Posts: 2,373
K
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
Originally Posted by Paul_WNC
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. thumbs_up


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Freeing seized SM420
Rusty Shackleford #1356961 Fri Apr 24 2020 10:54 PM
Joined: Sep 2007
Posts: 407
R
Shop Shark
Paul_WNC, that looks awesome. Very Creative!!


It's a small world, but I wouldn't want to paint it.
Re: Freeing seized SM420
Rusty Shackleford #1356964 Fri Apr 24 2020 10:59 PM
Joined: Sep 2011
Posts: 703
B
Shop Shark
Paul, does it have a name?


BC
1960 Chevy C10 driver 235 T5 3.73 dana 44
1949 GMC 250 project in waiting
1960 C60 pasture art
G.M dealer tech since 1980 & counting
Re: Freeing seized SM420
Rusty Shackleford #1357036 Sat Apr 25 2020 11:40 AM
Joined: Nov 2011
Posts: 2,566
P
Shop Shark
Rusty,

Don't want to hijack your topic. Can make you a fantastic 2-fer deal on the SM420 if you can source a reasonable shipping arrangement.

The best name we have gotten for my "junkyard dog" is Gnarly, but other suggestions are welcome.

Paul

Re: Freeing seized SM420
Rusty Shackleford #1357220 Sun Apr 26 2020 05:57 AM
Joined: Sep 2007
Posts: 407
R
Shop Shark
Thanks, Paul. I've got a line on a transmission locally. I can imagine shipping 135lb (that doesn't fit in a USPS flat rate box) could get expensive!


It's a small world, but I wouldn't want to paint it.
Re: Freeing seized SM420
Rusty Shackleford #1357228 Sun Apr 26 2020 12:26 PM
Joined: Nov 2011
Posts: 2,566
P
Shop Shark
Good deal! Hope it works out.

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