New guy..as of today..with questions about the M37 and engine swaps

[3006guns]

Hello everyone! Yeah, I know.......the subject's been beat to death, but I have a chance at an M37 that has been in a local backyard for at least 20 years that I know of. It looks to be in good shape from about 100' away, but that's all I know at this point. I want the vehicle and will attempt to buy it, assuming the usual things:

1.) It's had no attention in years.
2.) The engine, if not seized, probably needs a complete rebuild.
3.) The same applies to every other mechanical/electrical system.
4.) Rust is usually not much of a problem in our high desert area, but....?

Now, the reason for the post. According to everything I've read over the last few days, the M37 is geared like a tractor with a late 1930's engine design that is limited by its long stroke. It was designed that way! Therefore, any highway driving requires a complete rethink of engine, axle ratios, brakes, etc. I have no intention of making such changes to make a silk purse out of a sow's ear. I'd rather have a modest speed vehicle (say, 50 mph cruise?) with at least "better" fuel economy that will chug around in the Nevada desert, but of course I have to drive on the highway to GET there.

Again, assuming the original Dodge engine is toast, I'd like to put a Ford 300 cu. in. six (much higher rpm tolerance) in the vehicle and a modern manual transmission......either 5 speed or overdrive. The idea is NOT to gain speed, but to keep the rpm's down via a shorter stroke engine/overdrive.

I need two things from the members here......

1.) A link to a good overhead image of the M37 frame/driveline so I can get an idea of the layout.
2.) Opinions as to transmission type.

I should have mentioned that I'm 68, have some shop facilities including a lathe. Welding, fabricating, etc. don't scare me a bit. Wasting energy by making mistakes does though....

 

[snowtrac nome]

I think a 300 6 is too much engine way too tall and too long you would be better served with a 225 slant 6 or something like a 4 liter v6 anything much longer will require firewall modifications and take up valuable realestate in an already cramped cab

 

[3006guns]

Hmmmm....oops. Well, good thing I asked! I was hoping the Ford would work as I really like the torque (I've owned a couple). I read suggestions that a Chevy 235 or 250 might work also, too long/high?

 

[Storm 51]

The Canadians used a 251 in their M37s. It is longer so their radiator moved a little, but everything else works.

You will find that a visit to G741.org is very helpful to your quest for knowledge of M37 variations.

Also, the transfer case is a major problem regarding high road speeds. Because of its design and construction it gets very hot at what most people consider low to moderate speed (40 to 50 MPH). Sustained speeds over 35 MPH make that transfer case very unhappy. Your differentials will also be fighting you (5.83 gears).

That is something to consider prior to ownership.

These trucks were designed and built to follow tanks across broken ground (tanks were slow back then). They were never designed for the autobahn.

Good Luck!

 

[3006guns]

Thank you...........all comments are being filed away in my head, and I'll look at that website you mentioned. I was aware of the transfer case cooling issue, but read about an add on oil sump (tank) to reduce the temperatures somewhat. In any case, the warning about it is good info.

My son.........a trained mechanic of many years......just stopped by and tossed out a Chevy 350 or possibly a V-6 as alternatives. I explained that lower rpms, not speed, was the desired goal without losing 4 x 4 ability. A 225 slant six crossed my mind also, just not sure about clearance issues. Sure would be nice to keep it all "Mopar" though.

Are there any good, clear illustrations of the frame/driveline out there? It sure would make it easier to understand what I'm up against!

At this point I still have to approach the (now deceased) owner's widow and see if the vehicle is even for sale.

 

[Roller]

Check out the m37 TMs that are at the top of the forum.

https://www.steelsoldiers.com/upload/M37/TM9-1840A_engine_clutch.pdf

 

[3006guns]

Roller.......THANK YOU! I didn't notice the TM's before and will check them out, but the link you provided was exactly what I was looking for. I was actually under the impression that the transfer case was on the side of the transmission, not a separate unit. Pretty obvious that I need to learn a lot more. Again, thank you.

On further thought, an overdrive isn't really going to change the TC speed much and that's the weak link in the design. I may have to rethink everything and maybe just be satisfied with some locking hubs (cheap) and taller tires (not so cheap).........then keep the speed down. I still want the vehicle though!

 

[Roller]

The NP200 transfer case is not as weak as you may think, provided the lubricant level is maintained. MyPowerwagon and m37 used the stock transfer case. Power Wagon had a 440 engine, M37 had a 360 Dodge engine.

Frank

 

[3006guns]

Roller, I'm curious........did you change the axle ratios on that 360 installation? You'd have more power obviously, but with the stock ratios your speed couldn't have increase that much...could it? What about MPGs....up, down, sideways?

 

[Roller]

No, I kept the 5.83s, however the NV4500 transmission has 5th speed overdrive and the tires are 38" tall. Cruise easily at 55 to 60, going faster is not comfortable in this vehicle.
MPGs were never a concern, so I have no idea of my mileage.

 

[NAM VET]

Perhaps before you toss the stock motor and fuss with the modifications to make some other powerplant work, it might be worth your while to at least tear down the original motor and see if it is a candidate for a quality rebuild. My own just rebuilt motor, by me, had broken rings on some pistons, bad valves, but was other wise serviceable. So with $1700 worth of machine shop work and a new valvetrain, pistons and so forth, assembled by me with with about a grand's worth of parts, I have a sweet perfectly running motor. And it went right back into the truck with no modifications to anything.

Just a thought.

NAM VET

 

[3006guns]

NAM VET,

You are absolutely, 100% correct.

Since my original posting I've had time to really think this whole thing through. Unless the engine is totally shot (read: rusted in half) it should stay in the vehicle. I haven't even seen this particular M37 up close yet, so immediately planning an engine swap is foolish. There's enough guys out there doing that already and I'm not going to be one of them.

Understand that I work on nothing but antique machinery anyway......old hit and miss engines, tractors, gunsmithing (my own) and respect mechanical things the way they were designed. My enthusiasm was mostly just to get a higher revving power plant, rather than subject the old one to any possible abuse. The more I thought about it, just replace/repair whatever it needs and simply drive it and enjoy it for what it is. If I made any changes at all, they would probably be locking front hubs, a two barrel carb and maybe a modern ignition. That's it.....nothing irreversible.

I've also seen a few for sale here on the forum that look pretty good, but the distance is the killer as always. I'll be reading the forum and asking a few questions along the way before I do anything.

Thanks for helping keep my head on straight!

 

[Roller]

Well thought!

Frank

 

[Tanner]

Sub-2500 rpm at the transfer case is safe limit to reduce overheating -

Tanner

 

[Jesse19rap]

I repowered my 62 m37 with a 4bt Cummins and a ZF5 OD Ford transmission. Used an adapter plate from Destroked to mate the two. I also put 37" Humvee tires on it. I get about 55 mph on the stock gearing and transfer case. In fact, the drive shafts and tranny will slide together without major modifications. A machinist will need to modify the yoke bracket (standard vs metric). It's a great combination! Let me know how i can help.

Btw, I had planned to keep it original until I learned the block was completely shot.

 

[profo]

I got a chevy 350 with 1 ton chevy manual trans in my 67 power wagon with no problem the chevy output shaft and dodge transfer case shaft mate same splines, i had found a two speed pto and it worked with original winch to.

MArty