np-200 and heat?

I have seen this posted so many times, and maybe I just don't get it. So correct me if Im wrong, but isn't the heat in the t-case caused from running the truck so fast with the stock axle ratios, and wouldnt a np205 have the same thing happen? Or, if the rear output shaft was switched to a straight through type set up, would this problem would go away, and there for, the problem doesn't happen to the np-205 because of the rear output? I have not yet driven my truck this fast, or I would have figured this all out. Much of this is just thinking out loud, but Im guessing its both the high rpms and the off set rear of the np-200 that is causing the high heat or cooking of the lube. So, off the top of my head, wouldnt the 205 and the 200 then be almost identical if I was to change the out put to a straight through?
I guess I could look up both, in my books, if I could get to them, but they are in my garage and Im in the house. Oh, and my back wont allow me to make that trip.:lol: When I step wrong, I get PAIN:eek:

This has been discussed since the beginning of time...LOL

The gears in the 200 and 205 are cut differently, seems to be the general concencious of why the 200 builds more heat than the 205. Many theories on coolers/fluids and changes have been debated, but it seems the cheapest and most logical conclusion is that if you want to drive over 45 for extended periods of time, you need to swap to a 205. Center output may help a smidge, but it's not the cure.

Yep to all that....

The NP202 and NP205 are 60's updates to the 40's design that brought forth the NP200...the changes that were made in that update allow the NP202/205 to live comfortably in an environment the NP200 cannot....and wasnt desgned for anyway...remember, it was designed for vehicles, flatheads, with governors at 2800-2900 RPM's max. THE M715 does 3400+ RPM's at 60 MPH stock...

OK, so running 456's, overdrive and turning around 1800 at 55 will the 200 live? I'd like to just leave mine where it is(If I don't just use the j-truck drivetrain that is).

Mine never seemed to overheat. I took mine on a 40 mile round trip at 55 with no problems.

I have run mine with a temp gauge, synthetic lube, driveshaft swapped to center output....

On a warm to hot day:
about 1 hour at 60 and the temp goes through the roof
about 1¼ hours at 55 and the temp goes through the roof
I found that at 50 MPH max and letting the truck slow down on hills...keeping the RPMs roughly constant...the temp stays just barely in the safe zone.

In my truck, once 240 is exceeded on the gauge plumbed directly into the drain hole of the NP200, the temp goes up at an alarming rate....like from 240 to 280 in a quarter mile or less...and still climbing...

Keeping my speed to 50 and letting it slow on hills left me looking at just under 240 most of the time durng daylight hours. Once the sun went down AND we climbed a big hill that brought a definite drop in ambient temperatures, the gauge dropped some. We could run 55-60 for several miles, then have to slow back to the 50 method until it cooled again.

These are my experiences, your mileage may vary...

Jon, I remember back some time ago on the old site you did that to your t-case. If its not too much trouble can you tell how much of that test truck as I will call it, was stock? Axle ratio, tire size, tornado 6. Thanks.

The driveshaft was swapped to the center position, lockout hubs on the front axle, civvy 2 barrel carb and civvy ignition on an otherwise stock 230. Eaton full synthetic lube in all gear boxes.

Gears, tire sizes, trans and tcase otherwise stock.

Speed was checked by Wi715 in chase truck on that trip with GPS...he was a little surprised I could keep the speed so steady on such a long trip...50 was actually 49.7 MPH almost all the time...close enough...

Thanks Jon!

the np200 is straight cut gears and the np202,205,s are helical gears like the diffs.do yourself a favor and swap em out.

The transfer case heat issue is treated like Voodoo by a lot of people. They know it is there, don't understand it and either ignore it or become scared of it. Each of us can only speak of our own experiences for the most part too.

Mine is like Jon's. Center output and sustained speeds above 50 mph cause really high temeratures. I don't have a gauge plumbed into it. Using my infrared thermometer the case on mine has gotten as high as 278 after driving with stock tires at 60 mph for 45 miles. This was while driving to the 2005 Texas FE. I had 180 miles to go and slowed down to 45. The case was between 230-244 the rest of the trip. Coming home I never got above 50 and the case stayed at 218-222 when I checked it in every town I passed through.

I don't think the center output helped me much in temperature, but it sure did get rid of the noise.

One year later, I towed a M715 behind my M715 to the 2006 Texas FE. I only checked the case once because I didn't even smell it getting hot. It was at 219. I learned my lesson and never exceed 50 mph indicated on the speedometer if I have to drive more than 10 miles.

It all comes down to what has already been posted. If you plan to turn the transfer case at more than 2500 rpm then it will probably over heat. If you let it get hot and stay hot, your seals will fail. Then all your lube will come out and you will have a really hot chunk of solid metal under your truck. Consider a driveshaft speed of 2500 as the t-case redline. 2200-2300 should be your normal cruise t-case rpm and right at the top of the "green" range.

Anything above that and you need a different t-case in 95% of our trucks.

Barrman, have you put the I.R. on the axle diff for comparison? Just curious.

NP200 does NOT have straight cut gears. Not sure how many times Cowan will say that but it's incorrect. I believe some of the gears may be interchangeable with the NP205 in fact - don't quote me on that.

One major factor is that the NP200 in stock configuration transfers torque through three gears/shafts/bearing sets. This is three times the loaded, rotating mass of a NP205. The straight thru design in 2wd only loads the bearings on the upper main shaft and the other two gearsets just spin happily along with no torque load on them.

I'm still puzzled why many of the NP200 straight thru conversions don't help much with the heat, though.

Chris

There are also fine gears...np200...and coarse gears....np205....

The fine gears make more noise and have more friction....like a fine thread bolt versus coarse....

I have front lockout hubs so I have never checked the front pumpkin, ever. My hubs are usually about ambient temp or maybe 1-4 degrees higher and I check them along with my brakes on long trips every time I stop. The brake drums are usually the same as the hubs.

I have never had a temp higher than 112 on the rear pumpkin. I checked it a bunch when I installed the locker 2 years ago. It was never higher than about 20 over ambient. I got the 112 on a summer day when the tires where showing 130, so I stopped worrying about the rear. I will check it Sunday after driving at warp speed for 40 miles if we get to go get my Duece.

There was an article in Jan 07 Jp magazine that briefly describes both cases. It says the gears are helical-cut just not at the pitch of the 205. It speculates at the cause of the heat being from "lack of use and pitting and galling of internal components", although I like Chris' explanation better. It lists a top speed of 55 and suggests lower axle gears to decrease the speed of the case.

I was also curious about normal axle temp. I thought I read in the manuals that full floating hypoid axles operate at very high temp.

I didn't get a single temp reading yesterday. I did run about 65 for 2 miles trying to keep up with Sermis in his Duece on a long flat stretch. I could smell the NP200 after the first mile. We got back into hills and he slowed down to 45-50. The smell went away and I didn't think about it again until I read this this morning.

Sorry. I did drive the M715 to work today pulling a M37 on my trailer. Hopefully I will remember to get temps when I get home this afternoon.