Another NP200 heat thread!

[cherylsm515]

the only difference between a m37 and m715 np200 t-case is the speedo meter drive gear & cable hookup drive assy. plus the mechanical parking brake levers on the m37 are totally different so the m715 linkage is too short plus the m37 levers will hit the bottom of the cab when you try to apply the parking brake. you can remove all the incorrect parts from the m37 case and remove & install the m715 parts on the m37 case and all is good. i learned all this the hard way by r/r-ing the t-case 3 times by myself. the cases are identicle other than these 2 points. i found a new old stock m37 t-case and bought it for my m715 is how i learned this stuff. nothing like new........... i run 80w140 castroil full synthetic in mine but i mostly drive to & from the sand dunes and ride in the snow around here.

[fng]

I still ponder the effectiveness of some sort of ducting to increase airflow accross the case in cruise. I have thought of a detachable plastic/fiberglass or maybe thin metal contraption that could be attached easily before any extended driving and removed if going offroad. It works for VW engines!?!
I'm still working on this but I can't see where it wouldn't help.

[white433]

Back before the crash some one listed some seals that did'nt melt at higher temps. My 200 does'nt seem to overheat, but it's a long way to a highway, wonder if anyone tried those seals?

[amphi]

New guy here,

I've also seen some M37 folks using 50wt in the NP200 and running highway speeds, has anyone of you with a temp gauge in the T-case tried to run 50wt motor oil to see a difference? I wasn't able to find it in the search if so.

Welcome and thanks for stopping by.

I don't have an answer for you, but member Randyscycle will probably chime in here as he has a temp gauge installed, has done some testing, and is very knowledgeable.

[brute4c]

The seals for a 205 are the seals that are higher temp...they fit the 200 case.

[Barrman]

Welcome. Another familiar face as a newbie.

Several people have installed temp gauges. Some of us just stop and point an infrared thermometer at the case. Either way, 2500 t-case rpm seems to be the limit for drives of more than 40 miles. I have had 280 degrees on the case surface on mine. Some of those with gauges have pegged over 300 degrees.

Synthetic 80/90, synthetic 80, ATF, synthetic ATF, and any combination of additives you care to dream up have been posted as tried. If the case over heated before, it still does.

Now, here is the weird part. Some people never have a heat issue. They have screamed down the road at 3000 rpm plus on the t-case with no trouble. Center output compared to the offset output only seems to reduce the noise, but not the heat in most cases.

The stock 200 military seal has 2 lips. An oil seal and a dust/crud blocker. They don't like to get hot. The 205 seals will fit right in. They, at least in my experience will seep a little when very hot, but not break down. I can make a 300 mile run at 2500 t-case rpm and notice a few drips on the ground. Yet, until I make another long run, the case will stay dry once it cools off and is wiped off. Yes, I still have oil in the case.

Another weird thing is the rebuild. Spend 200-300 dollars on all new seals/gaskets/shims, make it super clean and right on speck. Then it won't get hot on you. At least that is what many people on here who have done this have reported. However, the same money will get you almost all the way to a 205 conversion. The 205 does not bolt right in. It is easy enough though to make fit. You then have center output, no noise, twin stick ability and a pto port. That is why most of us go the 205 route.

[TxRider]

Yeah it just struck me reading here on this site, the best threads on NP200 heating I've found anywhere btw..

It struck me this could just be an oiling issue, that as RPM's go up the case can't get everything oiled, like the thrust bearings out in the output cones and they heat up..

I'm thinking maybe the 205 runs cooler because it's not using the conical roller bearings outside the case out in the output cones, the ball bearings probably have less friction and make less friction/heat and require less oiling in the first place so just aren't affected as much. That's the only real difference I can see between the two.

In researching my 3053a I'm installing I've been told the manufacturer specifies 50wt motor oil, and recommends to not use 90wt gear oil. And I understand that recommendation goes for several other older trans as well.

And that maybe 50wt engine oil would have different properties under those high RPM conditions, but maybe not. In any case if it's specified as an alternative for the 205 (autozone site) I can't see where it would hurt to try it.

If nobody here does, I certainly will but it'll be probably 3 months before my truck is on the road and I can try it out.

I switched up from 5:83 to to 4.88 gears in my M-37 axles, and it looks like I'll be real close to that 2500 RPM mark on the transfer case RPM at 65.

I've sleeved the yokes and put in new modern double lip seals, the bearings and races looked fine good, a little loose on preload but close enough I left em be. I got my seals from vintage power wagons, but I think I have a Napa # around here as well, and the sleeves are just redisleeves for that size seal.

[Mikel]

I have a friend who has extensive experience in ball bearing design. He's designed quiet bearings for submarines.

He says that tapered roller bearings will put out a lot of heat if the preload is not correct, and that preload will change as the bearing wears.
There are tapered roller bearings in other parts of the vehicle (axles), but those spin at a much lower rate than the transfer case (except for the pinion bearings). An axle also has a great deal fewer moving parts (heat) and has a much larger heat dissipating capacity.

The main difference between a 205 and a 200 appears to be those bearings and that's where I put my money.

[TxRider]

I'll add in what Charles Talbert at Mseries rebuilds has to say about it...

I don't know if he's right on the money or not, but he does rebuild these old trucks and repower them for living and know a thing or two about them.

We have been running 50 weight oil in all our rebuilt transmissions & tranfer cases for several years now. Most manufacturers of the older transmissions & T/C's are actually recommending straight 30, 40, or 50 weight heavy duty engine oil based on the temperatures they will be operating in. The original builder of the transmissions we build & use with our Cummins repowers were built by Spicer (now Arvin-Meritor) doesn't recommend any other oils be used. The original oil spec of years ago was 90 weight, now their technicians warn SPECIFICALLY against its use. Extreme pressure oils are NOT designed for trans & T/C use & can even damage the unit, such oils are to be used in differentials only.

We have found gear boxes run cooler & shift easier using these oils & have never had the first issue to arise from its use. The 50 weight specialty blend we use is simply engine oil with a few additional additives that inhances it for transmission use, manfacturers say it isn't really necessary to use this blend & that the engine oil is fine. We have always tried to go the extra mile to use lubricants we feel to be the best for a given application, we chose this oil as a little added insurance. We get it from Dyson Oil Co, Durant, OK. Their website is www.synergenracing.com The representative we use is Roland Johnson.

Which is one of the reasons I decided to try it in my T-case and Spicer transmission when I get it all bolted in..

[brute4c]

How many trucks over the preceding decades ran 80W90 or higher in their tcase and manual trans and lived for lots and lots of miles...

Not saying 50W is a bad or good idea...just wondering why it has taken well over 50 years for this to come to light.