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I will be scraping off 50 years of grease and mud off of my transmission in the AM. This being a 1963 M37, I am expecting it to be a 420 model or an 88950?
On this tranny, is the PN cast into the case on the driver's side? Vehicle shows 66k on the clock, and during the tranny fluid change, there was lots of silver colored metal that poured out of the drain plug.Vehicle needs to be shifted slowly, I always double clutch through the gears. It will hold in any gear that it is shifted into. I have the feeling my tranny jack will be getting used soon.

Look at the top of the shift tower:
One pin on the right side, it's the old one.
Two pins, one on each side, it's the new one (NP420).

outpostm37 wrote:I will be scrapping off 50 years of grease and mud off of my transmission in the AM. This being a 1963 M37, I am expecting it to be a 420 model or an 88950?
On this tranny, is the PN cast into the case on the driver's side? Vehicle shows 66k on the clock and during the tranny fluid change, there was lots of silver colored metal that poured out of the drain plug.Vehicle needs to be shifted slowly, I always double clutch through the gears. It will hold in any gear that it is shifted into. I have the feeling my tranny jack will be getting used soon.

Your truck would have had an NP420 when it left the factory. It's physically possible that an earlier 88950 was swapped in at some point, but unlikely. A lot of the first generation M37 trucks received NP420 transmissions as replacements for the not as robust 88950s.

From your description of how it shifts, I'm guessing that the synchronizer rings have serious wear on them. Did you do a magnet check on the silver-colored shavings in the drain pan? If they're not magnetic, likely the shavings are from the aluminum synchronizer rings. Not good, but not fatal, either.

Could be other internal problems causing the synchronizer wear, so be on the lookout for things like a broken snap ring or a broken snap ring retaining ridge on the mainsheet.

I see one pin on the right side of the shifter

outpostm37 wrote:I see one pin on the right side of the shifter

Sounds like you have an 88950 trans.

These are NP420 mainshafts, but here's the sort of damage to watch for.

Thanks for the help! I am still unraveling the mysteries of this vehicle.
I did change the lube yesterday in the tranny. Bought some GL4 140 gear lube. As the old lube drained, I had it flow over a 3" x 3" magnet before hitting the drain pan. There was metal on the magnet. The previous lube (GL4 80w-90) was in the tranny about 7 months/50 miles or so. The original lube when I purchased the vehicle had lots of silver metal. Aluminum (synchro material) and iron. With the new lube, it does seem to shift better, meaning less grinding.
1) The floor pan over the tranny has a round hole that is about 3-4" closer to the firewall than where the current trans shifter sticks out. The floor pan hole where the shifter sticks out is a home made hole that is rough, like it was made with a hacksaw. Did the 88950 and 420 both use the same floor pan hole? The other hole is covered by metal that has shiny sheetmetal screws.
2) Another mystery is why the throw from neutral to 4th gear is VERY short compared to all the other gears. A symptom of main shaft issues or? When driving, it will stay in the selected gear, no popping out, wether I am on and off the gas, or up and down hills on the road.
Ahh more work to be done.

I don't like thick stuff in the gearbox. Redline MTL works well and typically improves shifting. I believe the new/old M37 transmissions share the same shifter location. Maybe there's some civilian parts in the truck? Is the engine/bellhousing military issue?

I agree with ashyers that a lighter weight oil will work better. My preference is Amsoil SAE 50 synthetic long life transmission lube.

88950 and NP420 transmissions are interchangeable as a unit, so the position of the shift tower relative to the cab floor does not change.

Something's been modified in your truck. Do you have the stock small-block Dodge flathead engine, or something else? Non-stock engine and transmission swaps are a common reason for relocating the shift tower position in the floor.

Here's what a stock shifter should look like relative to the rest of the cab.

Here is the tranny hump in my 230 flat head powered M37. Engine is the military version. Tranny is .... who knows.
Is it possible I have a tranny hump off of some other style of m37 version?

The Canadian trucks used the Chrysler/DeSoto big-block flathead six and a different transmission, but I believe that the engine was moved forward in those trucks, so I don't think that the center floorpan section was different.

The shift tower in your truck does not appear to be from an 88950 or an NP420, or at least not from one of the military versions, which use a stub shaft and a removable shifter cane.

If I were to guess, I'd say that you have a different, non-standard transmission, based on the appearance of the shift tower/shifter cane, and on your comment about the short throw into 4th gear. The shift tower shape sort of looks like one of the two early, non-synchro civilian Power Wagon transmissions.

I bought an m37 a couple years ago that had a non-synchronized transmission from a civilian power wagon. The floor pan was cut just like yours and the shift lever looks similar as well.

Be careful, the bell housing may be different too. If my memory serves the civilian and military bellhousings had different transmission bolt patterns. Hopefully one of the crew can verify if this is true.

Correct, the bolt pattern did change on civilian bell housings and transmissions.

outpostm37, you might want to check out these sections of the jobrated.com website for some good info to identify what could be in your truck.

Transmissions: http://jobrated.com/tranmission-id.html

Bellhousings: http://jobrated.com/-bellhousing-id.html

Elwood wrote:Correct, the bolt pattern did change on civilian bell housings and transmissions.

outpostm37, you might want to check out these sections of the jobrated.com website for some good info to identify what could be in your truck.

Transmissions: http://jobrated.com/tranmission-id.html

Bellhousings: http://jobrated.com/-bellhousing-id.html

thanks for everyones help. Pics/websites will aid in the ID process.

If I remember right power wagons with non synchro transmissions had the same bolt pattern as the m37. Later power wagons with the np420 have a different bolt pattern than the np420 from an m37.