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#1397225 - 03/09/09 01:24 AM NP 203 transfer case
JoeG Offline


Registered: 03/07/09
Posts: 2
Loc: Oregon
I'm looking for a suggestion for the oil to use in a NP203 transfer case.

The owner's manual recommendation is to use SAE 30 non-detergent motor oil. Is there something that would be better from the perspective of protecting gears than a motor oil?

For those not familiar with the NP 203: It is an all wheel drive transfer case for full size pickup trucks. The transfer case has a two speed gearbox at the front much like a non-synchro manual transmission rather than the planetary set found in most transfer cases. It has a differential behind the range box and a chain to the front output.

The lubrication for the range box is just like a manual transmission. The lay-shaft sits about 1/2 submerged and carried oil lubricates the main shaft bearings and gears.

The differential is lubricated by oil carried by the chain using an oil catch. The rear output bearings are then lubricated by splash captured off the differential.

I've read warnings on the internet to not use gear oil because the rear output bearings don't get oil from the multiple relay of oil up from the sump. So it would seem that a lighter oil would be necessary. But I question the long term life when lubricated with a motor oil vs. an oil package designed for gears, roller bearings and ball bearings.

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#1397293 - 03/09/09 05:52 AM Re: NP 203 transfer case [Re: JoeG]
ac_tc Online   content


Registered: 05/06/08
Posts: 508
Loc: sweden
75w-90 GL4 gear oil or
Any of the GL4 approved ATF´s or
and this is a longshot- THF/ STOU oils for farm equipment.
They are usually a 10w-30 motoroil with GL4 approval.
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#1397322 - 03/09/09 07:34 AM Re: NP 203 transfer case [Re: ac_tc]
Jim Allen Offline


Registered: 08/12/05
Posts: 4477
Loc: NW Ohio
I used 75W90 Amsoil in an Off-Road Design Doubler, which used the range box from a NP-203, for many years with no trouble. That doesn't answer your question as far as the canter diff and t-case goes.

The SAE 90 gear oil grade runs through the lower end of the 40 grade engine oil viscosity and into 50 grade. That's not far off the specified 30 grade, which falls into the 80W and 85W gear oil grades. In fact,I have seen a 85 grade oil specified in old equipment, which would be roughly equivalanet in viscosity to SA 30 motor oil. Bottom line, is an SAE 90 close enough? A good synthetic may have the flow characteristics to do the job, as opposed to a typical 85W90 dino that may not. The NP203 has no pump to worry about.

I concur with AC-TC, tractor Trans Hydraulic Fluid (THF) is a possible answer. It's usually a thickish 20 weight for use in tractors that use the the diff and trans as a sump for the hydraulic system. It's pretty robust stuff with the kind of additives needed for a trans and diff in a tractor. I've used it in chain drive transfer cases with no problems. Most of the oil companies make a version of it. Some of the stuff from the tractor companies, such as Case-IH's Hy-Trans and John Deere's Hy-Gard, are highly regarded, but there are some generics to be found at places like Tractor Supply.

The other possibility is an MTF (Manual Trans Fluid), many of which are designed to replace ATF or engine oil in manual transmissions. They typically work well in chain drive transfer cases and are considerably more robust than ATF. Viscosity-wise, they usually run about a 20 grade. I have such a fluid in two of my own chain drive t-cases right now.
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Keepin' the Good Old Days of Four Wheeling Alive

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#1398219 - 03/10/09 12:07 AM Re: NP 203 transfer case [Re: Jim Allen]
JoeG Offline


Registered: 03/07/09
Posts: 2
Loc: Oregon
Thanks for the idea of THF. Brilliant, I never even considered that.

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#1419680 - 03/30/09 11:25 AM Re: NP 203 transfer case [Re: JoeG]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
DO NOT USE 75w90 in a 203 or you WILL burn it up. While that might work fine in the range box portion of the tcase, the chain drive does not like heavy oils.

Use any 30wt motor oil and change it every so often...I have ran 10w30 in them for hundreds of thousands of miles. The thinner oil is needed for proper lubrication, and the thicker oil doesn't allow that.

At most I would consider one of the synchromesh fluids, but if motor oil works, why?
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#1419808 - 03/30/09 01:31 PM Re: NP 203 transfer case [Re: deeter16317]
PT1 Offline


Registered: 02/06/07
Posts: 5746
Loc: near the mistake
How about Rotella 30w? or Redline MTL or MT90?


Edited by PT1 (03/30/09 01:32 PM)
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#1420096 - 03/30/09 06:25 PM Re: NP 203 transfer case [Re: PT1]
unDummy Offline


Registered: 02/01/03
Posts: 8756
Loc: RI
And a straight weight SAE30 usually doesn't flow too well when cold. With that theory, one would think they would simple burn up during the 1st cold weather spell. The lubrication issue is usually caused by improper part-time conversions. And, a full time chain just won't last as long as a true part time xfer case's chain. So, the chain will stretch regardless, and becomes a maintenance item.

My truck example: Part time 4wd-- 200k miles and about 40k miles in 4wd. Neighbors full time 4wd truck- 80k miles on it = 80k miles of wear on transfer case. I have more then twice the mileage on my truck but 1/2 the wear on the xfer case chain.

Example: SAE30 Pennzoil is 11.5cst at 100c and 98cst at 40c.
Redline MT90 is 15.6cst at 100c and 90cst at 40c.
Amsoil MTG is 14.7cst @100 and 85cst at 40c.

Which one would you want? Better flow when cold and more protection when hot?

If you fear the thicker gear oil, the MTL, MTG, MTF, Synchromesh GL4 gear oils provide GL4 protection, and aren't any thicker than a 30wt motor oil.
Any 75w85 gear oil is another option, home brew or straight from the bottle.

With advancements in lubrication over the years, I wouldn't waste my money on ol' school fluid recommendations or hearsay fears.
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#1420174 - 03/30/09 08:13 PM Re: NP 203 transfer case [Re: unDummy]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
Any 30-ish weight oil will work fine...as noted, I typically ran 10w30 PZ because that's also what I ran in the engine...for simplistic sakes if nothing else.

I also know from experience, that running anything in a typical 90 weight will tend to cause major problems. Its a splash-type lubrication and, unlike the later NP/NVGs that ran ATF, doesn't have a pump.

I have personally placed over 250k on two separate NP203s (including a lot of offroad)...and I have witnessed a friend burn two up (one with under 50k, and a new replacement in under 60k) by using 80w90. He claimed to know more than those that designed it, changing from the 30-weight to 80w90 upon receipt.

Just an observation...


Edited by deeter16317 (03/30/09 08:14 PM)
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#1420219 - 03/30/09 08:47 PM Re: NP 203 transfer case [Re: deeter16317]
unDummy Offline


Registered: 02/01/03
Posts: 8756
Loc: RI
80w90 is usually a mineral weight. I'm recommending a full synthetic for better flow, hence 75w.

And, the 203 has a pump. The chain also can carry a thicker oil further for better lubrication.

Concerning your friend, failure analysis would've been interesting.

This transfer also recommend 10w40 motor oil besided the 30wt recommendation(year/make differences). 40wt motor oil is the same visc as a typical 90wt gear oil. No excessive failures with 10w40 reported? Adds more to the [censored] hearsay.

Ruling out poor maintenance intervals, low fluid levels, hack part time 2wd conversions,.... lube type usually isn't the cause here.
_________________________
Those who say it cannot be done, should not interrupt the person doing it.
Your automaker lied!
Is this a spelling/grammar forum or BITOG?

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#1420626 - 03/31/09 09:54 AM Re: NP 203 transfer case [Re: unDummy]
deeter16317 Offline


Registered: 12/07/07
Posts: 1339
Loc: SE, PA
 Originally Posted By: unDummy


And, the 203 has a pump. The chain also can carry a thicker oil further for better lubrication.




The early versions did not have a pump...they were splash lubed. I had one I split the range box from for a guy to use as a doubler.

And even following that logic...the pump intake, in later tcases spec'd for a lighter fluid, will typically rotate out of the sump because the pump twists on the shaft because of a higher viscosity oil. This causes the tcase to burn up from lack of lubrication, even though it is filled to the proper fill level.

I'm done here. I have experienced NP203 failures, and the single commonality was the fluid type used...regardless of theory.
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2004.5 Dodge 2500 Cummins

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#1420760 - 03/31/09 12:17 PM Re: NP 203 transfer case [Re: deeter16317]
Jim Allen Offline


Registered: 08/12/05
Posts: 4477
Loc: NW Ohio
unDummy: I just looked through three factory manuals from '77 to '79, one Ford, one Mopar and one GM, and the only thing I see called an "oil pump" is a slinger (that looks like a speedo drive gear) designed to feed the rear output shaft bearing. Doesn't look like if would be affected by oil viscosity much, if at all.

Deeter: my opinion is that you are overstating the gear oil issue. I'd agree with you if we were talking an old-school 80W90, but as Johnny recently pointed out to me in another section, a modern 75W90 synthetic flows better than many mineral 10W30s (for which the unit was originally spec'ed).

I guess JoeG has left us now after getting his answer.
_________________________
Jim Allen
Keepin' the Good Old Days of Four Wheeling Alive

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#1610032 - 09/24/09 04:43 PM Re: NP 203 transfer case [Re: Jim Allen]
CrAlt Offline


Registered: 04/03/05
Posts: 132
Loc: CT
So JoeG what did you end up using?

I have a 77 NP203 and i think im just going to use ST 10w30...because thats what i have tons of.
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