How hot ?

[Charles Talbert]

I appologize for thinking we were talking about the 205 t-case instead of the 200.

Since he had started a thread a while ago mentioning problems when shifting OUT of 4wd (meaning disengaging the front output shaft with a shifter lever) that he was not utilizing a t-case that was full time 4wd like the one you describe, rather a shiftable one like the 205.

Either way, with proper preload any rotating bearing will not produce a large amount of heat, certainly not enough to make the case almost too hot to touch after only 20 miles, unless that 20 miles was done in 20 seconds, but we know an M37 isnt going to do that.

I'm not describing a case that is full time 4WD. The NP200 front axle drive output can be shifted into a neutral position via the control lever. The stock M37 has axle flange hub caps instead of front wheel lock-out hubs as original, and will still drive the front drive section via the wheels rotating even when the t/case front axle section is in neutral.

There is 1 ball bearing on the front axle drive shaft output that will be dormant if front wheel lock-out hubs are installed and the free wheeling position is selected at the hub. Everything else in the case will be in motion 100% of the time the truck is moving. These cases have a natural tendancy to run on the warm side within as little as 4-5 miles. Driving farther than that doesn't get it much hotter, it's just the nature of the beast unless an oil cooling system is put in place.

[MoparFreak69]

I appologize for thinking we were talking about the 205 t-case instead of the 200.

Since he had started a thread a while ago mentioning problems when shifting OUT of 4wd (meaning disengaging the front output shaft with a shifter lever) that he was not utilizing a t-case that was full time 4wd like the one you describe, rather a shiftable one like the 205.

Either way, with proper preload any rotating bearing will not produce a large amount of heat, certainly not enough to make the case almost too hot to touch after only 20 miles, unless that 20 miles was done in 20 seconds, but we know an M37 isnt going to do that.

[Charles Talbert]

I personally would be concerned with that much heat from only running 20 miles in 2wd. When running in 2wd everything in the transfer case is sitting stagnant and not moving, only the input and output shafts are connected and spinning. This means there should just be a couple bearings rotating, which shouldnt produce much heat at all.

The heavy lube you have in there could be contributing to the temps a bit. I would try a lighter lube, something along the lines of what Charles recommended should work perfectly and reduce those temps, providing there isnt other problems within the case itself.

This info is NOT CORRECT for the NP200 transfer case.

The input / ebrake output shaft is turning, the intermmediate gear is turning, the rear output gear is turning, and also the front axle output is turning unless you have front wheel lock-out hubs. The reason for higher than normal heat production is because of the design of the t/case that I just described. Long story short almost nothing is dormant in this case if the truck is in motion; and nothing at all is dormant without lock-out hubs.

[MoparFreak69]

I personally would be concerned with that much heat from only running 20 miles in 2wd. When running in 2wd everything in the transfer case is sitting stagnant and not moving, only the input and output shafts are connected and spinning. This means there should just be a couple bearings rotating, which shouldnt produce much heat at all.

The heavy lube you have in there could be contributing to the temps a bit. I would try a lighter lube, something along the lines of what Charles recommended should work perfectly and reduce those temps, providing there isnt other problems within the case itself.

[Kaiser2boy]

Thanks , Figured I would just check and be sure about it.

[Charles Talbert]

If you could hold your hand on it, you are good to go as far as heat. You could be better though if you would put lighter weight oil in it. The heavier the oil, the hotter it will run.

Straight 40 weight Royal Purple synthetic does extremely well. All our rebuilt cases get an initial fill of that. I know folks running Cummins powered trucks on the interstate at 75 MPH; at times also pulling a fully loaded truck bed and a trailer. No issues. We have done a thermostat controlled cooling system for the t/case that greatly reduces this issue; but I wouldn't say it is a necessary accessory just for knock about driving.

[Kaiser2boy]

Just how hot should the transfer box get? I had Lady M. out for a nice go today , all on nice roads and did not push it. I did not use 4WD at all or LOW .
I got home after about a twenty mile ride and was checking for leaks and put my hand on the transfer box.
It was hot. Not enough to burn me and I could keep my hand on it but boy it was hot. The oil in there is a synthetic 90/120 wt gear oil and it is full.
Will that heat level off or just keep geting hotter as I drive farther?
I drove one of these things back in the 60s while in the Army and we drove 100s of miles only stopping for gas. I never had one blow a box from over heating , blew and engine or two but no gear boxes.