NP200-NP205: how similar are they?

[MasterYota]

I've read some conflicting information lately so I felt I would ask those who know best if they could shed some light on the situation. First a little background.

I'm in the planning and prep stage of building my 52 M37: D60 front, GM C14 rear (4.10:1 gears), 428CJ, NP435. My question(s) concern with the tcase. I know they are noisy, and prone to overheating, and that the best way to cure that is to convert the NP200 over to a centered shaft. Another option would be to hang a divorced NP205 in its place. Here is where my confusion lies.

I have read that the 200 and the 205 are basically the same unit, even so far as some of the internals are interchangeable. I have yet to read which parts are interchangeable though. Do any of you gentlement know?

Is there any advantage to combining the two cases (200 and 205) into one useable one? Are the weak links of the 200 solved in this manner? (excessive heat being my primary concern).

I know that the simple answer is to hang a newer dodge, (or IH) divorced 205 in place of the 200, but I don't have access to one, and I've searched high and low with no results. My next question would be: can a married 205 be converted into a divorced 205 by using parts from the 200, or the more common Ford divorced 205? I have a couple of married GM 205's kicking around, but alas nothing that bolts up to the Ford version NP435. I belive that a married 205 would produce a front driveshaft that is too short for comfort.

Any thoughts or experiences on the matter would be greatly appreciated!

Ray

[712edf]

something you probably already know anyways

The np200 came as a twin stick in Dodges and disappeared after 1968. That's when the single stick np205 (divorced) appeared. Everything went fulltime np203 (married) in 75 and Dodge never used a divorced case again. The married np205 appeared in the 80's in the larger trucks.

I have no idea what interchanges between the two (200 & 205) or between married & divorced (205) version. Also 435's in Fords weren't identical to 435's in Dodges which may be a factor if you go the married route.

To my knowledge all 205's in GM's were married and all t-cases in Fords were driver's side drops.

Your easiest option is to find a 69-74 divorced 205 from a Dodge. IH will work with some mounting mods.

Divorced 205's are out there, keep looking.

[Gordon Maney]

I believe there is some confusion here; mixing posts.

I can't find my Hollander manual just now and I am working to assemble an issue, so can't do a lot of digging.

The NP200 was the Power Wagon and M37 transfer case. Essentially also the WWII 1-1/2 6x6, although reduction was a different ratio.

The NP 201 and 205 were later, and went to centered differentials. The 201 was used in the W-series trucks, also called Sweptlines. I am uncertain about the Power Giants. Maybe Ron from Indiana will come along and comment on that.

The 201 was used up until 1968, I believe, and the 205 after that. The 201 has two shift levers and the 205 had one. They are similar inside, but not exactly the same. I believe bearings and seals, for example, are the same. It has been so long since I did a 201 I can't remember all the differences.

They are all pretty strong; even the 200 has been used quite a bit in pull trucks over the years. The 205 is just about indestructible even in pull trucks and I am thinking the 201 should be, too.

The 201 and 205 were both used in Dodge and IH, though I believe the cases in the IH trucks were different with respect to mounting holes and bosses.

[712edf]

You are correct Gordon, I was referring to the 201, not the 200 that was mentioned. My bad...

Military jeep m715's also had one of the divorced t-cases mentioned (200 or 201) as well.

I am not very knowledgeable outside the w-series trucks.

[Gordon Maney]

I am guessing the M715 has the 201.

[MasterYota]

If the main source of discontent with the NP200 is excessive heat, would a gear ratio change solve that? My thoughts are as follows: Excessive rpm with the 5.83 gears forces the tcase to operate at a high rate of speed when travelling at highway speed. Correct?
My plans at the moment call for gearing in the 4.10:1 area, which should (in theory) cause the tcase to turn at a slower rate of speed for the same given highway speed. Less rpm would mean less heat buildup. Correct?

If this is a viable alternative to swapping in an NP205, then the NP200 should hold up just fine.

Has anyone tried to relocate the fill plug on the 200 to allow for additional fluid? Is this a good idea, or a dead end? I would imagine that extra fluid capacity would be a good thing in a unit known for excessive heat buildup.

[pieter]

For what it is worth -

After the Iowa Rally, I had the opportunity to stop at Bob Jones house and drive his 6x6. In looking at the details of his truck and having him show me some of the design details; He pointed out that he installed a gear lube cooler for the transfercase. It will open a valve to the radiator once a certain temperature is met.

That might be an option for you if you are worried about heat.

Pieter

[Gordon Maney]

If the main source of discontent with the NP200 is excessive heat, would a gear ratio change solve that? My thoughts are as follows: Excessive rpm with the 5.83 gears forces the tcase to operate at a high rate of speed when travelling at highway speed. Correct?
My plans at the moment call for gearing in the 4.10:1 area, which should (in theory) cause the tcase to turn at a slower rate of speed for the same given highway speed. Less rpm would mean less heat buildup. Correct?

If this is a viable alternative to swapping in an NP205, then the NP200 should hold up just fine.

Has anyone tried to relocate the fill plug on the 200 to allow for additional fluid? Is this a good idea, or a dead end? I would imagine that extra fluid capacity would be a good thing in a unit known for excessive heat buildup.

It does not take much overfilling to introduce a number of new problems you don't want. Too much fill and you will add heat and you will certainly add foaming. I would avoid that approach, I believe.

[Gordon Maney]

For what it is worth -

After the Iowa Rally, I had the opportunity to stop at Bob Jones house and drive his 6x6. In looking at the details of his truck and having him show me some of the design details; He pointed out that he installed a gear lube cooler for the transfercase. It will open a valve to the radiator once a certain temperature is met.

That might be an option for you if you are worried about heat.

Pieter

That is a really well engineered truck, isn't it?

The cooler idea is a good approach.

[MasterYota]

I only bring up the overheating problem as it seems to be the most common complaint. The lube cooler idea seems like a good plan, but did Bob indicate how the lube is pumped through to the cooler and then back to the tcase?

Has anyone had good results using an oil stabilizer (like Lucas products) in the tcase along with the gear oil to prevent foaming? I've used it myself alot, but in more modern tcases with better oiling setups.

Also, does anyone know if the speedo can be adapted to read correctly with a different gear set?

Thanks alot for the answers guys, I really appreciate the knowledge base around here.

[pieter]

The lube cooler idea seems like a good plan, but did Bob indicate how the lube is pumped through to the cooler and then back to the tcase?

To be honest, I don't remember if there was a pump in the system or if it just circulated by pressure/heat??? Guess I was a little stoked at the time from being allowed to take the rig for a spin.

I'm sure if you email him, he'd be more then happy to explain what he did to make it work and probably an idea on how well it works and what kind of temperatures he see's.

I know he did make a comment that if he was going to keep the truck, that he would probably move the cooler to the front of the truck. Currently it's about an 8"x8" radiator that is mounted horizontally just inside the left frame rail in front of the 5th wheel plate. Basically, it doesn't get any airflow like a normal radiator in the front of a vehicle.

Pieter

[pieter]

That is a really well engineered truck, isn't it?

yes - Bob's 6x6 is a very well engineered and thought out vehicle. There are a lot of details i saw that I never noticed until he pointed them out to us.
And to drive it is pretty awesome as well :o)

Pieter