Dex 6 & NP263

[JacobVH]

Changed fluid in my NP263 transfer caseast might. I bought a used unit and rebuilt it after having the pump rub ruin my original, within the last 5000km. figured I give it a check up

I had been using Total MV which specs dex IIIH.
only had dex IV on hand so I ordered more dex 3
didnt notice when it showed up but we actually got dex 6 again, and I put it in the truck.

Drive about 30km since. Truck felt noticeably smoother when in 4hi, usually it feels like it's working harder in 4hi but today it didn't.

Truck is an 05 2500HD 6L that makes probably 600hp at the crank currently, and I drive it hard.

What about these Transfer Cases makes Dex6 unsuitable? I know that later GM transfer cases in 07+ trucks call for dex 6, is that correct?
I was reading that older organic paper clutches like what was used in the synchro for the NP263 didn't like synthetic fluid but I emailed USA Gear before I filled my Transfer Case with synthetic Dex 3 and they said the new clutch I had purchased for the synchro was carbon.

Is there actually any issue running dex 6? In theory dex 6 should have higher viscosity than a dex 3 that's been run for a season and has 15k miles thanks to the improved shear rating of dex 6 Fluids? should also ad that atf like max life has viscosity values similar or below dex 6 but claims to meet dex 3H and autotrack 2, so was this always about clutch material and not about viscosity?

 

[Snagglefoot]

I can confirm the part that 07+ trucks call for Dex 6. At that point GM dropped NP and went with Magna Powertrain.

Also, Dex 6 was released in 2005 and was described as being compatible for any Dexron fluid.

Autotrac 2 was developed for auto transfer cases with clutches.

I can say from personal experience that Autotrac 2 can be used in a Magna Powertrain transfer case because the computer at the dealership listed it for my 2008 Suburban so I ran it for 18 years so far, changing every two years ( when the blue color faded away). I have 287,000 miles on it and it still works great. I did avoid using the auto mode all those years.

 

[SwampSurvivor]

It's a pretty simple chain drive case. It's not going to care what fluid is in it. 263s don't have any sort of viscous coupler or clutch packs in them.

I'd want a thinner oil in those because the pumps on them just can't handle thick oil. It's aluminum so it's a giant heat sink.

 

[Snagglefoot]

Just for fun here is a bottle of Auto Trak II, ( spelled as GM does it. ) It was made for Auto style NP transfer cases but for some reason it showed up as required for my 2008 MP Auto Trak transfer case. I’ll drop by and see if they still recommend it. Otherwise it’s Dex VI.

 

[martinq]

Dex6 is superior to Dex3 in every way, I would not consider or recommend Dex3 for anything other than an old hydraulic jack or a squeaky door hinge ... maybe. The Multi-Vehicle ATFs from Valvoline, Castrol, Amsoil, etc are better yet.

Most transfer cases are very simple transmissions with gears, bearings, chains and maybe clutches / solenoids. I would use a modern, high-quality synthetic that's suited to the task, but if it will work with a GL5 fluid I'd probably use a 75w90 instead of an ATF.

 

[JacobVH]

It's a pretty simple chain drive case. It's not going to care what fluid is in it. 263s don't have any sort of viscous coupler or clutch packs in them.

this is the synchronizer blocking ring that sits in the center of the synchro assembly. The T case I rebuilt had the older style that was probably organic paper fiber, likely incompatible with synthetic fluids and DEX 6 additives. had no clutches left on the inside and maybe 1/16th coverage on the outside. My own T case had some damage to the ring as well, but still had over 1/2 clutch coverage.

I'm assuming that the updated clutch has been designed for compatibility with more newer fluids, however the 2007+ trucks use a different style of clutch. 2007 NNBS trucks call for dex 3 and then 2008 call for dex 6 with the same transfer case design. The chain they use in the 07/08 is the same as the chain used in my 05

That is the only clutch in the assembly, and it's job is to synchronize the front and rear output shaft speeds. I've know this for a while and I try to only engage 4hi under 80kph when going straight at a steady speed, if possible I like to engage it at a slight crawl under 10kph

there are a few other differences, but considering that the 07/08 units are the same but one specs dex 3 and the later spec dex 6. Also the fact that the viscosity difference between dex 3 & 6 is small enough that just moving from a mineral to synthetic (as the switch from dex 3 to dex 6 was) would likely still increase oil film strength (even with the lower viscosity) on the output shaft journal. then you got the fact that valvoline makes a transfer case fluid that is thinner than dex 6 but rated for autrac 2 and transfer cases requiring dex/merc/atf+4 (28.82cst @ 40° C & 5.91cst @ 100°C)

needless to say I'm probably going to be leaving the Dex 6 in and enjoying how 4hi doesn't lug like it did before.

 

[martinq]

Like I said, Dex6 is superior to Dex3 in every way, I would not consider or recommend Dex3 performance for anything.

There are no applications that spec Dex3 that are incompatible with Dex6. I would recommend Dec6 as a low bar. I would advise you use something that exceeds the requirements of Dex6.

 

[Saturnguy]

There are no applications that spec Dex3 that are incompatible with Dex6. I would recommend Dec6 as a low bar. I would advise you use something that exceeds the requirements of Dex6.

I disagree with that…
Saturn SL2 is one of the few that uses Dex III

I suggest you look at TES-295 or the replacement TES 668.

https://www.allisontransmission.com...nel/parts-and-service/allison-approved-fluids

 

[Saturnguy]

My favorite

Mobil 1 Synthtic ATF, black label bottle

https://www.mobil.com/en/lubricants...s/our-products/products/mobil-1-synthetic-atf

 

[kschachn]

I disagree with that…
Saturn SL2 is one of the few that uses Dex III

I suggest you look at TES-295 or the replacement TES 668.

https://www.allisontransmission.com...nel/parts-and-service/allison-approved-fluids

For a manual transmission, yes there is a specific GM branded fluid. But for an automatic the proper fluid is a Dexron IV license.

 

[D60]

Having owned an '02 NP261 that gave me just a couple drops of black tar, I was intrigued and learned the 261/263 boils off its ATF. No one really ever figured out why. The fix is 5W20 or 5W30 engine oil.

I put 5W20 in said NP261 and never looked back (that's actually not true -- I opened it up upon discovery at 208k freedom units, found no abnormal wear from running on no fluid for who-knows-how-long, installed an MA pump rub kit while I was in there, then put it back together and filled with PCMO). Ran it that way with no issues until ~244k when we sold the truck. Being in CO, 4hi got regular seasonal workouts.

There used to be an ATSG or ATRA article on using PCMO, but I can't readily find it now. Almost surely archived in a deep digital dungeon these days. Post #1 here links an article, but link is dead:
https://www.duramaxforum.com/thread...e-fluid-change-to-5w-30-synthetic-motor.3952/

The eccentric pumps in these don't care, and these cases rely as much on splash lube as they do the pump.

So, you do whatever blows your skirt up but personally in any 261/3 I'll run motor oil. Doesn't mean I'm right, and my ranting is worth exactly what you paid for it.

 

[I<3oil]

600hp at the crank on a 6.0l? Holy cow....I'm guessing turbo or supercharged and other stuff?

 

[JacobVH]

600hp at the crank on a 6.0l? Holy cow....I'm guessing turbo or supercharged and other stuff?

Turbo, was built NA for 480hp and torque. 10.6:1 comp, S475/83, on 4ish psi should be 580-610hp at the crank. honestly not much atm but need more fuel system to reach my 900 crank goal
it's a NP263 HD with the XHD chain so it WI handle a lot of power.

 

[JacobVH]

Having owned an '02 NP261 that gave me just a couple drops of black tar, I was intrigued and learned the 261/263 boils off its ATF. No one really ever figured out why. The fix is 5W20 or 5W30 engine oil.

I put 5W20 in said NP261 and never looked back (that's actually not true -- I opened it up upon discovery at 208k freedom units, found no abnormal wear from running on no fluid for who-knows-how-long, installed an MA pump rub kit while I was in there, then put it back together and filled with PCMO). Ran it that way with no issues until ~244k when we sold the truck. Being in CO, 4hi got regular seasonal workouts.

There used to be an ATSG or ATRA article on using PCMO, but I can't readily find it now. Almost surely archived in a deep digital dungeon these days. Post #1 here links an article, but link is dead:
https://www.duramaxforum.com/thread...e-fluid-change-to-5w-30-synthetic-motor.3952/

The eccentric pumps in these don't care, and these cases rely as much on splash lube as they do the pump.

So, you do whatever blows your skirt up but personally in any 261/3 I'll run motor oil. Doesn't mean I'm right, and my ranting is worth exactly what you paid for it.

I've thought about it, wasn't sure about the friction reducing stuff and it's effect on the synchro clutch

it's definitely more viscous so that would be good from a protection standpoint

mine had pump rub and 100ml of fluid was drained, a lot of stuff look and sounded okay but the collar and output shaft were scored, chain was toast, and synchro cluth was starting to fail

 

[D60]

I've thought about it, wasn't sure about the friction reducing stuff and it's effect on the synchro clutch

it's definitely more viscous so that would be good from a protection standpoint

mine had pump rub and 100ml of fluid was drained, a lot of stuff look and sounded okay but the collar and output shaft were scored, chain was toast, and synchro cluth was starting to fail

Well all I can tell ya is we regularly pulled the lever (**1 = floor lever as God intended) at highway speeds and never a problem. Many winter ascents & descents on Wolf Creek Pass, La Veta and Poncha.

 

[JacobVH]

UPDATE: I've decided just to get a synthetic ATF With a high viscosity index rated for Allison C4 or Dex 3H
was hoping for TotalEnergies FLUIDMATIC XLD FE as it has slightly lower viscosity but ended up ordering Mobile Synthetic ATF™ as it's certified by Allison for TES-295
the fluid I had previously used was Total Energies FLUIDMATIC MV. Yes it's splitting hairs, but I'd rather a fluid slightly thinner when cold, and slightly thicker when hot. I was basically getting the worst of both worlds with the fluid I had previously used, it was thicker when cold, and thinner when hot.
also USA gear said that I would be best off running dex 3, sure it might not matter a ton but I'll definitely get better life. 0w20 motor oil is tempting but it's also thicker than ATF

 

[JacobVH]

My favorite

Mobil 1 Synthtic ATF, black label bottle

https://www.mobil.com/en/lubricants...s/our-products/products/mobil-1-synthetic-atf

That's what I decided to go with.

 

[kschachn]

UPDATE: I've decided just to get an synthetic ATF With a high viscosity index rated for Allison C4 or Dex 3H
was hoping for TotalEnergies FLUIDMATIC XLD FE as it has slightly lower viscosity but ended up ordering Mobile Synthetic ATF™ as it's certified by Allison for TES-295
the fluid I had previously used was Total Energies FLUIDMATIC MV. Yes it's splitting hairs, but I'd rather a fluid slightly thinner when cold, and slightly thicker when hot. I was basically getting the worst of both worlds with the fluid I had previously used, it was thicker when cold, and thinner when hot.
also USA gear said that I would be best off running dex 3, sure it might not matter a ton but I'll definitely get better life. 0w20 motor oil is tempting but it's also thicker than ATF

Can you explain how the high viscosity index helps?

 

[JacobVH]

Can you explain how the high viscosity index helps?

A higher viscosity index means that tempature affects the fluids viscosity less.
for example oil A might be
36.04Cst @ 40° C & 6.8Cst @ 100° C 154 vi index
-42°C pour 208°C flash
Oil B
36.3Cst @ 40° C & 7.4Cst @ 100° C 176 vi index
-51°C pour 220°C flash
these numbers are used to calculate the viscosity index

now while the differences are not huge, oil B is basically equivalent at 40° C and thicker @ 100° C. This means it is able to maintain its viscosity with tempature change, aka higher viscosity index

the index while calculated with those tempature values, shows how well the oil will maintain its viscosity outside that temperature range. an oil with a higher viscosity index should have a lower pour point and usually has a higher flash point. essentially since it's viscosity is more consistent / changes less with tempature it will protect better when hot and flow better when cold.

Typically PAO based oil will have a higher viscosity index.

I might be splitting hairs here but in -25° C to 40°C weather where I live and varying short and long trips oil B Mobil 1 Synthetic ATF™ will likely be better for the task.

 

[D60]

A higher viscosity index means that tempature affects the fluids viscosity less.
for example oil A might be
36.04Cst @ 40° C & 6.8Cst @ 100° C 154 vi index
-42°C pour 208°C flash
Oil B
36.3Cst @ 40° C & 7.4Cst @ 100° C 176 vi index
-51°C pour 220°C flash
these numbers are used to calculate the viscosity index

now while the differences are not huge, oil B is basically equivalent at 40° C and thicker @ 100° C. This means it is able to maintain its viscosity with tempature change, aka higher viscosity index

the index while calculated with those tempature values, shows how well the oil will maintain its viscosity outside that temperature range. an oil with a higher viscosity index should have a lower pour point and usually has a higher flash point. essentially since it's viscosity is more consistent / changes less with tempature it will protect better when hot and flow better when cold.

Typically PAO based oil will have a higher viscosity index.

I might be splitting hairs here but in -25° C to 40°C weather where I live and varying short and long trips oil B Mobil 1 Synthetic ATF™ will likely be better for the task.

I'd like be in the spaghetti sauce aisle when you're shopping.....