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