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Thread: NP200 Condensation

  1. #1
    Join Date
    Dec 2003
    Location
    Giddings, Texas
    Posts
    7,729

    Default

    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.
    Remember if you didn't build it you can't call it yours.

    6.2 powered M715, 5 M1009's, M416, 2 M101's, 2 M105's, 3 M35's, M1007 6.5 turbo Suburban project called Cowdog.

    https://www.youtube.com/channel/UCCz...HGkBCfhXZ5iuaw

  2. #2
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default NP200 Condensation

    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
    Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.

    Pro-choice, that's a LIE, babies don't choose to die!!

  3. #3
    Join Date
    Dec 2003
    Location
    Lone Pine, CA
    Posts
    451

    Default

    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

  4. #4
    Join Date
    Dec 2003
    Location
    Giddings, Texas
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    Default

    OK. It was just a theory. How is your rebuild coming along Chris?
    Remember if you didn't build it you can't call it yours.

    6.2 powered M715, 5 M1009's, M416, 2 M101's, 2 M105's, 3 M35's, M1007 6.5 turbo Suburban project called Cowdog.

    https://www.youtube.com/channel/UCCz...HGkBCfhXZ5iuaw

  5. #5
    Join Date
    Dec 2003
    Location
    Lone Pine, CA
    Posts
    451

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    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

  6. #6

    Default Any one know who's this is?

    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.
    Big Blocks RULE!

  7. #7
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    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
    Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.

    Pro-choice, that's a LIE, babies don't choose to die!!

  8. #8
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

    Default

    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)
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  9. #9

    Default user name change?

    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.
    Liz, covid, murdered 10/19/21

  10. #10
    Join Date
    Dec 2003
    Location
    Lone Pine, CA
    Posts
    451

    Default

    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

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