M37 transfer case

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BruceAFrank

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This subject has been dormant for a while, but I think I might have some helpful info on the NP200 and NP201 divorced Transfer cases. I bought my first 1956 S120 4X4 IHC Travelall in the mid 1970s. The International comes with the NP201. Else where in this thread their is a statement that a bearing and seal kit for one did not contain all the pieces needed for the other. First, I have diagrams and parts lists for both the 200 and 201 and I can find no parts that are not interchangeable and parts count for both TCs are the same. The kit for the Dodge military vehicle NP200 and the kit for my International NP201 are duplicates of each other. But, there is a difference I'll get to.

There are also statements that the NP200 and the NP201, seem to have lubrication problems when driven highway speeds for long distances. My first S120 was driven daily and on many long trips on interstate highways at the speed limits. I had not heard of the problem with these transfer cases and lubrication. But, I used 90W gear oil and with STP added.

I bought my first S120 off of the University of Utah surplus dept, originally owned by the Geo Physics dept. Students had abused it and though it had only 80,000 miles on it the front axle was bent and differential casting BADLY cracked and the engine had a leaking head gasket that had frozen the engine, a BD240. A minor rebuild gave me a functioning 4X4. Burned some oil, but not bad.

Later, after a botched full overhaul by a student needing a project at the local tech school, I replaced it with a Chevy 292 CID straight six. Good bit more power; better fuel mileage and most important a higher turning RPM. I drove the vehicle on dozens of trips putting 4 to 5 hour 75 mph interstate travel on it with only one problem. Bearings worked perfectly, but the output gear was a problem.

The gear was somebodies' bright idea that did not work. It was a two piece gear with the inner part of the gear attached to the outer gear via castellated style teeth what were cushioned with die springs in holes in the teeth. I gather that ideally the teeth didn't make contact with each other but the power transmission from the shaft to the outer drive teeth was cushioned by those springs.

The space limitations did not allow for heavy enough springs and they got beaten up by the back and forth movement which literally chewed them up and filled the bottom of the case with little half moon shaped pieces of spring coils. Once the springs were gone the castellated teeth slapped back and forth moving about 1/8". The noise was sort of a clop-cloppity sound that was detectable even at highway speed. I later heard IHC mechanics call it the "knock-gear".

I did try rebuilding it and the springs lasted about 8 weeks. I did it again but this time I welded the slots between the inner and outer teeth in the web of the gear. Preheated the gear to 500 degrees F on a wood stove in the shop and welded it with 11018 stick electrode. Then placed it back on the stove to cool down slowly as the fire in the stove died. Some people say these gears will break if welded. Not if done correctly. Mine was and I put 200,000 more miles on that gear with not even a slight problem.

Getting late. I'll pick it up tomorrow with an update and pictures.
 
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Dodge man

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There are also statements that the NP200 and the NP201, seem to have lubrication problems when driven highway speeds for long distances. My first S120 was driven daily and on many long trips on interstate highways at the speed limits. I had not heard of the problem with these transfer cases and lubrication. But, I used 90W gear oil and with STP added.
Bruce,

I would think that the 5.83 rear end gears used in the M37 would be a major factor in the NP200/201 failures at highway speeds. That's going to require some high RPMS of everything in the drive train.

Thanks for the information and looking forward to hearing more.
 

BruceAFrank

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A quick note. The 5.83 gear may be the problem. My Travelall ran 3.73, which was a good bit better for highway. The limiting factor was max rpm of the BD240 was about 3800 rpm with a recommendation not to constantly run higher than 3400 rpm. But with the replacement Chevy engine, its power and rpm capacity allowed me to run 75mph and higher. I like to think I lucked into durability with the STP. My most recent acquisition, of a "new" S120, is going to be my test bed for synthetic gear lube. Later.
 

BruceAFrank

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That first '56 S120 Travelall was primary transportation for my business (Baffle Stove Company) painted desert camo with the company name on the side and a full luggage/pipe rack on the roof. Set up with both front and rear swing-away spare tire carriers and class IV hitch system with seating for 9 (quick removal), all of which I built myself. Used to get asked if I was part of the Safari Tours that took tourists out of Moab through Canyonlands. No, but I did cover hundreds of miles of Canyonlands in that vehicle.

First gear is so low I have never felt the need for an under-drive, as seems to be the standard today. The BD240 in first gear NEVER failed to climb anything on which it could get traction.

Back on point. While I was trying to fix that "knock-gear" I kept hearing rumors that New Process manufactured a solid replacement gear for that NP201. But, I never saw one and never met a mechanic who'd had one in his hands. When I moved from PA to CA some 17 years ago, I had a '68 Suburban 4X4 with a 327 v-8; my '56 Travelall with a newly repaired fender; a Datsun B-210 and a 1991 Ford Explorer. We gave the B-210, which was in good shape and ran well, but had a funky 3rd gear, to one of the movers loading our life's possessions into the moving van (Punk teenager who broke the trans before he even got it home 'cause he was bound and determined to cram it into 3rd gear). Thought seriously about what to do with the Travelall and where I would put it at the house in CA. Foolishly gave it to a co-worker, let me say again FOOLISHLY gave it away. Gave the Suburban to a guy who wanted it for fishing and hunting...a good home. And, we drove the Explorer pulling a trailer (with an airplane on it that I was restoring).

Four years ago my wife got tired of my whining about that old Travelall and she blurted out, "Well, just go find one!" Took me a year to find one that wasn't junk. I found a "restored" one within driving distance, but the price was out of reach at that time. I kept in touch with the owner and 18 months later I came up with the money. Called and he still had it! Looked at it one week end and bought it the next weekend and drove it home from Reno, about a year ago. I was so enamored at finding it I really did not see all the minor work still required. On the drive out of Reno, to CA, I realized that the "knock gear" had not been fixed.

Other things needed to be done as I searched for that elusive solid gear to replace the knock-gear. After several dozen phone calls, and the purchase of another knock-gear that I would weld up and swap, one of my calls connected with a guy who said that he believes the solid gear was the same as the OEM part in the NP200. I ran across an article about the use of the NP200s in military Dodge vehicles.

I also found the name of a parts supplier on the Binder Bench forums, Vintage Power Wagons <dodge@vintagepowerwagons.com>. I called and spoke to a gentleman about whether the solid output gear from the NP 200 would replace the two part gear in the NP201. "Sure, we do it all the time!" Couldn't believe my ears! I asked if they had any in stock and what was the price. Yes, and the price was $125. Here is my credit card, please ship it NOW. I received it a week later. A brand new gear still in the unbroken military packaging with a manufacture date of 1954.

I compared every measurement and the knock-gear and the solid NP200 gear were identical in all dimensions.

GearsSideBySide2.jpg GearsSideBySide.jpg

I am currently, finally, in the process of removing the transfer case and hope to have the gear installed in the next week. Any questions? Just ask.

One last thing, In the process I found a builder who told me that the complete guts of the NP205 could be installed in the NP201 case offering an alternative for my inability to find a replacement for the knock-gear. He said that the gears were not interchangeable with the gears individually, but all gears and shafts, complete, would fit the NP201. I do not know if that is actually true.
 
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BruceAFrank

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Some more experience (research) over the last couple of years, I thought worth sharing. One of the major differences, between the NP200 and the NP201, is the primary cause for highway failure of the NP200, where the NP201 lasts. In 4wd both transfer cases turn a main drive shaft and an idler shaft. Two gear shafts turning generates MUCH higher temps than a single straight through gear shaft generates.

On the highway in 2wd the NP201 runs only one shaft, so highway speeds creates much lower operating temps than is generated if the idler shaft is turning. The NP200 runs the idler shaft whether in 4 or 2 wheel drive. That heat thins the gear lube frying the bearings and galling the gear contact surfaces.

So even running high ratio differentials, the NP201 easily survives that high speed operation...and 70mph with an NP200 may kill it in just a few miles.
 
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