The Stovebolt Site Forums The Shop Area Driveline Napco Drivetrain Questions

I have a 1955 or 1956 chevy with the napco conversion. It has 3100 emblems on the sides of the cab, but I was told it is a 3600 because the front axle and transfer case have plates on them that say 3600, as well as the wheels having 8 lugs. I am currently looking for a steering knuckle for the driver's side as I broke the one I have when loading it onto a trailer, due to the wheel being locked up. Just trying to figure out exactly what I have so I can get the correct steering knuckle. Any information about the napco drivetrain would help as I'm still pretty new at this. I got the truck just over a year ago.

1st picture: Transfer case which I rebuilt and restored about a year ago
2nd picture: Front differential plate on the napco
3rd picture:Front of truck showing the whole front axle
4th picture: Side of truck show 3100 emblems
5th picture: 8 lug wheel on front axle
6th and 7th pictures: The broken driver's side steering knuckle I currently have that needs replaced
8th picture: Truck vin #, maybe be able to figure out exact year and model of truck?
9th picture: Number on passenger side steering knuckle (not broke)
10 picture: Number on drivers side steering knuckle (the broken one)

Joshua,

As we have already covered the ground in your Truck Parts Wanted Swap Meet ad on some of the info related to your broken steering knuckle, I can offer a bit more on the Cab "ID" plate from your 8th picture.

Using info from this 1956 Chevy Truck source document, your "Cab" ID plate number decodes as:

3A = 3100 (1/2 Ton) Truck

56 = Model Year 1956

O = Oakland Assembly Plant

019541 = 18,540th truck assembled at the Oakland Assembly Plant

While this confirms that the cab is a 1956 3100 model, and the fenders in front may be as well, the "3600" stamped on the transfer case and front axle NAPCO data plates indicate that your chassis and body don't seem to be an actual match. The 8 - lug wheels front and rear, along with the rear axle style match a "3600" 3/4 Ton truck, not what would have been originally under the 3100 cab and front clip.

I am no expert when it comes to identifying NAPCO equipped trucks, but there should be some other ways to help identify what chassis (frame) and engine you have to see if they too support the "3600" 3/4 Ton NAPCO gear. There should also be some tell-tale NAPCO items inside the cab, transfer case shifter and at least one or more NAPCO instruction/warning decals that help further figure out what you have.

Perhaps there are some fellow Bolters that have more NAPCO info and experience/knowledge that will chime in here and help figure out what you have, and a way to move forward with repairing the front axle???

If nothing else, you have a few more bits of info to help you know what you have in hand.

Have a great weekend!

Dan

55.2 and newer frames had the serial number stamped on the top of the drivers' side front frame rail. That should give the information to find what the original truck was.

I had figured it was a 1956, I'll have to look around the truck some more for other numbers. Thanks for the helpful info!

Whereabouts exactly was the serial number on the rail? The frame has been cut at the very front and had a 1/2 plate welded on it where the engine mounts. I couldn't find any numbers on it. No numbers on rear diff either. I have a picture of a number on the back face of the 4spd Trans, not sure if it is a serial number or just a part number. Engine block is currently at shop right now.

The numbers will be about 3 inches behind the front cross member, on top of the frame rail.

Sooo..
I'm not exactly sure where the front cross member is, or was, but there's a 1/2 plate welded to the frame that the front of the engine mounts on right about where you said the number was, so it may not be there any more. Also I found this info plate inside the cab on drivers side. Just out of curiosity, what was the original color of the truck based on paint code? The truck was a county/national forest service truck originally I believe and I had always thought forest green was the original color, but I suppose the paint code will either confirm or deny that. I also have never seen any other napco plates inside of cab, maybe ripped out as there are many things like glovebox door, turns signals, and all but one of the gauges vandalized once upon a time. Paint code says 723.

Paint code 723 was called Forest Green in 1956.

Here's a clip from paintref.com showing that code and color (although the color chips are not necessarily true after being clipped and sent thru a couple computer displays.

Ok, I thought forest green was the original color.
Thank you!

Having its cab changed at some point in its history is a very common occurrence. Cab gets rusty, beat up, wrecked and go find a better one. Weekend worth of work for a couple of buddies and they had a “new” truck.

Isn't there a Napco website out there on Wild Wild World of Web? A friend of mine has mentioned it to me before.
He solve a lot of his Napco headaches there.

Didn't NAPCO do 4X4 conversions on trucks other than GM? You might want to expand your search for that steering knuckle to trucks other than Chevy. Chances are that some Ford, Dodge, and possibly International 4X4 conversions might have used the same front axle assembly.
Jerry

I have seen a few rare ford's with napco. However, I have seen a couple knuckles for sale so far, and they seemed like the right ones, just didn't see until it was sold. I've looked for other Napco websites, and there's just not much out there. I mainly just need a steering knuckle right now. Extra info is mostly just a plus, but not necessarily a must. I do appreciate any info though as it helps me know exactly what I have.
Thank you for all your help!
Joshua

As others have said, you have 1/2 ton sheet metal...the 5000 pound GVW also confirms this.

The chassis stamped serial number will be on the drivers side, on top of the frame rail straight down from the firewall, aft of the steering and parking brake. It should match the door post number less the 3A series number. It will take a wire brush and scraping to see the stamping.

Maybe the Gov't ordered short wheelbase pickups with 3/4 ton suspension/axles...3/4 and 1-ton pickups sold to the public were all long bed trucks.

Mike B

I'll have to look again for that number, thanks for the extra info! I think the truck might be a long bed, it's about 87 inches or 7ft 3in from the back of cab to back of frame, but the rear bumpers been welded and jimmy rigged over the years so hard to say if it was even longer at one point. I think it may have been a factory stakebed, but I don't know how to prove that.

So I took a wire wheel and polished around the steering gearbox on the top of the framerail and I still didn't see any number. Either I'm in the wrong place still, or the number was just very faint. I was also wondering what the original color of the engine was for a 235 in the 1956 truck. One in it looked to have been orange once upon a time

Just went out and looked at my 55.2. My numbers are 9 to 10 inches in front of the steering box. On top of the frame rail.

I'll have to look closer right there. Thanks!

So I went about 10 inches in front of the steering gearbox and took a wire wheel to the frame and finally found the number. It was invisible before wire wheeling. A couple of the numbers are faded but I think it says 255000o27o. I was told it should match up with vin number which it doesn't.

Glad you found the numbers.

Joshua,

Just an added note here that you may want to use this Tech Tip to help highlight and better see your discovered original chassis VIN.

Once you do that, you can use that info to search the GM Heritage site and learn more about what chassis you actually have.

Maybe repost a new picture after trying the Tech Tip so we can see what it shows???

Dan

Joshua,

After a bit more research, your VIN should include a "letter" character just to the left of the "255..." that we can see in your picture (see screen grab of your picture with added red arrow).

Give that "Tech Tip" I mentioned above a try and show us what may be revealed and we can try and better lock down your info.

FWIW, the "255O" at the beginning of your pictured VIN indicates the frame is a 1955 2nd Series built at the Oakland assembly plant. The rest of the numbers after that would indicate what "unit number" it was coming off that assembly line. A letter "J" at the beginning of the stamping would confirm you have a "3600" 3/4 Ton truck chassis.

My info came from the 1955 2nd Series resource file at the GM Heritage Centers Vehicle Info Kit site.

Dan

I don't think the frame numbers show the letter character at the beginning, only the serial number tag on the A pillar does.

Brian is correct, the Series code '3A' was not stamped on the frame rail (at least not during the TF years).

Measure the wheel base, if its 114" it's a 1/2 ton 3100 short bed. If it's 123" it's a 1/2 ton 3200 Long bed or 3/4 ton 3600 (they never made a 3/4 short bed)...the 3200 and 3600 share the same frame. Looking at your pictures in the first post the rear spring hanger looks pretty close to the cab making it a short bed. A picture of the side of the truck would confirm this.

Mike B

The wheelbase is about 123 inches from wheel to wheel, so not short bed or 3100 frame. My guess is the national forest service or county when they ordered the truck, had a 3600 frame and running gear paired with the 3100 cab. Not sure why that would be, but I'm inclined to believe it's all original since the cab is originally forest green and the really old front tires have LINCOLN COUNTY stamped on the inside of them, so I think the frame and cab have been together paired since they were new. Not unless for some reason they took the cab off of one of their other trucks that was a 1/2 ton and put it on there themselves. That or they used a 3100 cab, a 3200 frame, and 3600 running gear which doesn't make any sense. So I think the frame is 3/4 ton. What do you guys think?

I have a 1956 3200 and it is 123" inches. the 3600 is also the same frame and same length. I call the 1956 3200 a "Mid Bed" its not a true long bed with 8ft bed which they went to after 1956.

That's a cool truck. What type of bed are you going to install on it?

Cab didn't come with the frame from the factory. Because the frame and cab serial numbers aren't the same.

Ya I'm thinking the cab and frame have been paired almost since new still, just not from factory. I plan on making a flatbed for it that you can put stakes on the side to make a stakebed, which I think is what it was originally being a government truck.

Other than tires marked "Lincoln County", is there anything else that make you think this is a Gov't truck? The 723 Forest Green paint color was a very common color for 1956. It will be almost impossible to know when the Cab got put on the frame AND when the NAPCO parts were added...could have been one year ago or 50 years ago...

Mike B

Well I know nothings been touched for decades as the guy I got it from dugvit out of blackberries where it was completely submerged for decades, nobody even knew it was there. Question is if the cab swap was in the fifties or in the eighties or somewhere in between, just not after that. Seeing the lincoln county on the tires is the only reason on the whole truck that I suspected it was a government truck, knew nothing about the truck when I got it except that it was a napco. Napco parts look like they've been on the frame since new. Cab, front clip, and possibly engine look like they were replaced once upon a time, as the whole front bumper was ripped off and the front engine support is just a massive 1/2 inch plate that runs from one framerail to the other. Maybe a tree fell on it parallel to the truck, but they decided to reuse the truck because it had the Napco drivetrain. My question now is how to determine if the engine is numbers matching, so I can know whether or not engine is original to frame. I think napvo components and transmission are original to frame, but who knows.

It would also make sense to be a government truck in Lincoln county as much of lincoln county are coastal range mountains, hence the special order for a napco to drive all the mountain roads, just a thought.

Joshua,

On your question concerning the engine ID, post a new thread in The Engine Shop to begin that conversation.

Best if you can provide pictures of the engine block/head casting codes/dates and serial number as those are essential in trying to help you figure out what you have. More on this topic in your new thread in the Engine Shop.

Dan

There used to be a great one, but it has gone the way of the dinosaurs.

That's too bad, a napco website would have been pretty helpful.

ALL NAPCO conversions in 1955/56 were done by the dealer or owner with parts bought from a local NAPCO dealer, there were no "factory" installed units...your truck was born as a 2-wheel drive truck.

Mike B