NP200 Condensation

We have a storm system moving into the area today. When I went out to my shop this morning the floor was wet. It was like a lake in there. The cool concrete meeting the warm moist air produced condensation. That got me to thinking about the t-case heating problems. I know that a lot has been written about it and it boils down to some do and some don't. The ones that do seem to be relatively low milage units. They also seem to have almost too tight of tolerances. How many of you with one that gets hot know that they were fire trucks? Here is my theory.

The truck sits for days at a time. A call comes in about a brush fire. The truck is fired up, driven as fast as the driver dares to the fire. It does its job and then is driven at high speed back to the station. The truck then sits for up to days again. While it sits, it mighted get washed, the regular fire trucks get cleaned, equipment gets hosed off and moisture is present in the air. The regular fire trucks go on more calls and get cleaned several more times. The cast iron t-case just sits there at normal air temperature. Moisture in the air condenses around it every night. Some of that moisture is inside of the case. Condensation eventually turns to rust or at least surface rust on the gears. Every time the truck gets used, that rust is cleaned off and becomes part of the oil. That oil circulates the particles all over the case. I don't see how changing the fluid will flush all of the small stuff out. I think everybody will agree that any machined surface that has had rust on it is changed forever in at least a small way. Look at guns. If it is not completely stripped down every time you clean it, rust and corrosion will form on the neglected parts. When you do get to the neglected parts, no matter how much you clean, they are never as good as new again. That is why I think that old fire truck use M715's have a better chance of having a hot t-case. That is part of my theory. I didn't want to get into a science lecture about dew points and relative humidity and such.

Mine was never a fire dept truck and I have the heat problem as bad as I have heard of it in any other truck...
brute4c

I'm in Jon's boat.

Here's my thoughts...
The spare T-case I pulled apart to rebuild looked brand new inside. Of course I never tested it out before hand (nor did I test the clearances) to see if it got hot.

I'd think the condensation theory is an urban legend. The stock system is fully sealed except for an opening in the intake path, assuming any fording valve isn't closed. And with no air flowing through the system, wouldn't it take a long time for any moisture to work it's way back to the T-case?

Another wacky theory for rusty innards - the truck is driven hardand the tcase gets untouchably hot. Almost immediately the driver plunges into a deep body of water, quickly cooling the tcase. The rapidly cooling case has a sudden drop in internal pressure, more than the vent can compensate for, and water is sucked in past the grease seals. Think along the lines of a boat trailer without a "bearing buddy".

I just threw that out but I don't think that scenario could have happened enough times compared with the number of hot tcases.

Chris

OK. It was just a theory. How is your rebuild coming along Chris?

Currently stalled out. It's cleaned and painted, I just need to find a source for the different thickness gaskets and metal shims. The current crop of rebuild kits don't include all that I want.

Plus I gotta decide how I want to set the bearing clearances. If the factory built the cases but a lot were showing tight clearance, maybe I should set them a bit on the loose side, maybe even looser than the low spec? I still haven't heard any definite numbers from someone that's successfully built one. I really want to set the bearings with a dial guage to the point of zero lash, where the book calls for removing shims until the proper turning torque is reached.

On the other hand I don't want to experiment and have to go through it all again.

The heat issue...
It seems that swapping the driveshaft to the center output, along with using lockout hubs would cause a significant drop in temps but some people have said that's not so.

Also Chuck's Trucks claim no overheating problems (large tires, mostly show trucks) unless the oil is low. They mount their cases straight up and down to gain the drop to compensate for huge lifts, maybe they get more oil in than in ours? Maybe adding a 90 degree fitting and a short pipe nipple would allow slight overfilling to improve cooling capacity?

Shoot me now, I've thought about this way too much. I'm determined to have my tcase run cool and quiet as supplied (yea yea, I know a gear drive won't be quiet).

Chris

I've seen several with pipe fitting and an extended oil fill tube. More oil would have to have some type of effect. I seriously doubt that the chucks trucks get any real milage. In Florida, there is a width restriction that the guys at chucks were telling me about and the big meated trucks they build are past that and not street legal. For us, it way too easy for us to drop in a reliably proven engine that will swing more rpm, pull harder and not allow the truck to slow down as if a down shift on an uphill was made, and OD trannies only spin the NP200 faster past it's military suggested '45mph' top speed. I don't think ANYONE, even Jon has had a problem with them at 45mph. In fact, I think I remember Jon saying that when he'd slow to that the case would cool down. The case just isn't a high speed, and high speed/high torque for higher sustained highway speed unit. It is inherently designed to be a slower speed case. Designed for Early Dodge 6x6's and M37's...how fast could it ever have gone? NOBODY designed the thing to do 60mph. Yes, all gear, real tough...but not a speed demon. Deal with it and replace seals, drive slow or try a set of 4.56's...Here's some figures;
5.87 R&P, 35" tire, 45mph, 1:1 Non overdrive = 2536rpm. So there's a stock baseline for 45mph.
4.56 R&P, 35" tire, 58mph, 1:1 Non overdrive = 2539rpm. 3rpm difference and 13mph gain.
With that the case should happily cruise all day long spinning a near identicle rpm as it stated max speed before.
Just for grins;
5.87 R&P, 35" tire, 58mph, .85% Overdrive = 2778rpm. That's quite a bit more rpm and heat.

I'll say it...if you're planning to not get run off the highway, swap out the NP200 for a later unit. If you're happy in parades, farm use, or cruising under 50 with you stock truck you should be fine with the NP200...it's not a bad case, just kind of became application specific over the years.

I know Mozarkid overfills his by parking on a side hill of very steep angle, then shoves in as much of the Redline Shockproof as he can get. With a digital temp gauge, he came to the 2000 FE in Kentucky from roughly St. Louis. He said it would get up to around 300 degrees but would just sit there and go no hotter.
I have always wondered about the cavitation/whipping issues associated with this but he has never reported a problem with this technique...if I remember right, he is putting close to triple the 2 1/4 quart capacity listed for the case.
brute4c

Chris, I saw a NP205 kit on ebay, and sent the dude a note asking about NP200 kits. Here is his reply, you may want to give them a call...

Hi Bob, thanks for the inquiry. We don't see a lot of those NP200's around here anymore. I do have a rebuild kit for the NP200 (K201). Your cost is $141.56 + $10.00 S/H = $151.56. We accept paypal,
Visa/MC/Disc/Amex (call toll free 866-847-5051 or 800-776-1191 ext. 79), money order, check (must clear bank before shipping), and cash (at your own risk).
Thanks,

Spencer Hodes
Transmission Exchange Co.
1803 NE ML King Blvd
Portland, OR 97212
800-776-1191

txchangespencer@earthlink.net (paypal ID)

Hey Bump, that trans place is within 20 minutes of me.... My transfer case overheated doing 60 in the early morning Tucson desert. It was probably 65 degrees outside when it happened. I slowed down to 50 for the remaining three days getting home and did not have a problem again. I did toast my seals and had to pull over every 45 mins to an hour to refill. Now I'll cruise about 55 max on the short 15 mile freeway into Portland. It seems to do fine, but its cold outside right now.... The history on the truck is it was being used to refill big diesel tanks including heavy equipment up a rugged 18 mile road for the Smithsonian Institute. It was atop MT Hopkins at the observatory since 1976. So mostly slow continous use..... Roughly 34,000 miles on it.

Tom,

You just laid out all the facts I'm trying to ignore in an effort to make it run cool. I'm definitely no speed demon but 45 ain't gonna cut it. I go by the tach on the freeway, stick it at 3G and leave it. With that I should be in the 52-55 range and as long as that es off the a-holes in a hurry to get to Vegas, I'm pleased as punch.

And yea, I know Chucks are magazine ho's for the most part.

All the rebuild kits I've seen only include one gasket (manual calls for choosing between several thicknesses) and no preload shims. Plus that price is too much for me. Apparently the 205 used the same shims and the paper gaskets are simple to make once I find the proper thicknesses.

Jon, did Mozarkid do the driveshaft swap too? Lockout hubs? I'll for sure swap the driveshaft to the top - gotta stop by the driveline place to see what they have (looking for something different than what VPW has).

Chris

I am pretty sure he did both of those as well...if I got it right, he uses the 140W-250 shockproof redline lube...heavy duty!
brute4c

Why not pipe the fill and drain together, except install a resevoir or trans cooler in the middle of the tubing. Heat would cause gravity flow( circulation).

The condensation theory makes a great deal of sense, but why doesn't the same phenomenom happen to the tranny???

Now thats thinking outside the box....the tcase box that is...good point...
I wish I could work on the truck right now cause I would like to put the cooler idea on there with one of those fan on the cooler types...and see what would happen trying to drive it to the FE...would be interesting to me at least...would take the towbar along anyway just to be safe...
I'm also thinking of riding some in the truck on the way down...if I can bring it... NECK!!...and watching the temp gauge on the tcase just to see if it gets any kinda heat going just rolling along...
brute4c

I was reading a book the other day about Carrol Shelby and his Cobra's. It mentioned that the Cobra's sometimes ran in two different races in two different classes the same day. The only difference between the stock and unlimited sports car class being the rear end oil cooler. They just unhooked it, plugged the lines and ran the car in the stock class. They would then hook it back up to run the unlimited class. It didn't go into details or show pictures. How would a rear gear cooler be different from a t-case cooler? Also, how did it circulate the fluid?

Heat rises, that is the principle of my idea. Not sure on thiers. Don't know if mine would work, but any other option would require a pump. The expense of the pump would negate the whole idea as you might as well get the 205 and be done with it.

Gravity heat systems were used to heat buildings for decades. A boiler in the basement would heat the water, it would naturally rise to the upper floors and the water that cooled down would fall down the return lines back to the boiler. Supply leaves the top of the boiler, return enters the bottom.

So for a cooler to be sucessful....hopefully...does it need to have its intake port plumbed to the upper, fill port, on the tcase AND be higher than that port also? So the bottom port of the tcase would need to be plumbed to the lower port of the cooler and does it matter where the coolers lower port is in regard to the tcases bottom port?
What about air in the system...if the cooler is higher than the tcase fluid level, would something air lock like the stupid heater core on the van likes to?
brute4c

Inlet of the cooler would have to be level with the fill of the t-case. I would install a tee facing up in this location so that you could slightly over fill the case insuring that that system wouldn't air lock. The horizontal line at that location would be the highest point of the system. I would install the cooler in a manner that would allow downhill flow to the bottom of the case.

Another option would be to install a fliud to fluid heat exchanger at this location and cool the t-case with engine coolant.

Surely I could find some cutoff switches for inline...thinking one on the tcase filler hole and one on the drain hole, then a straight pipe on the fill hole to the cooler with a tee fitting and another cut off in that line...and a tee fitting and cutoff in the lower line...that way, on the upper line, the cutoff switch on the fill port could be closed for when the cooler is being removed, serves as the fill plug, then with a tee in the upper line and a 2nd cutoff, the top of the tee pointing upward would be the fill location...highest point...and the cutoff after the tee and before the cooler would allow only the fluid from the fist cutoff through the new filling tee to be 'loseable' when removing...on the bottom, cutoff in drain hole then a tee then another cutoff and then hose to cooler...the tee here would allow use of a tcase temp gauge on one end and the cutoof and hose mount on the other and give the lowest profile under the truck...a tee with the cutoff in it would be ideal...dont know if such a thing exists yet...without the gauge, an elbow could be used instead of a tee down there. With the 2nd cutoff on the bottom, the only fluid loss there would be from the cutoff in the drain port through the tee fitting to the next cutoff...wouldnt have to worry about the cooler draining out on removal...seems it would be neater and quicker to remove...like drive somewhere by road with the cooler on and stop for 15 minutes and remove it so you can wheel without the stuff sticking down to get snagged on...then would go back on pretty easy afterward too...
Does this make sense?
brute4c

Yep, I followed it, had the same thoughts myself. Tee fitting with cutoffs in them are available, but pricey. What about hydraulic quick connects? That would rock.

Now thats even better....me like...thanks Doug!!
brute4c