It was with conflicting information that I decided to change the fluid on my NV5600. The odometer showed 110,000 miles. The 'oil' I drained out was still of a golden color, not burned or dark, and was definitely a synthetic.
The 'oil' change of choice was Red Line MTL, a fully synthetic manual transmission fluid. It didn't hurt that it was available locally for $9.99 a quart. I put 5 quarts in (slight overfill) by parking the truck on an extreme sidehill with the filler hole up.
It has been in there for a couple months now, enough time to run the truck and Lance camper in 100 degree weather, and also freezing temperatures.
The shifting is very smooth, smoother than with the original fluid, through all gears, and does stay the same whether hot or cold.
So, thumbs up on this stuff.
regards, as always, jefe

 

Im needing to do the same thing where is the hole that you drained and filled it up with.

 

Hey, Cowboy, (I've always wanted to say that as a salutation)
There is no drain plug. Only a filler plug on the driver's side of the box. You'll need to remove one or the other (might as well do the driver's side) PTO cover to drain. Clean it up and use "The Right Stuff" gasket sealer to button it up. Most folks on here overfill the box with fluid.
Do a search with 'Red Line MTL' on here and you'll find a good article or two on how to do it and what to watch for.
regards, as always, jefe

 

Thank you I really appreciate it. How do you like that redline MTL

 

I know a couple of years ago when I replaced mine, Redline recommended a 50/50 mix of MTL and MT90 for the NV5600. If I still had the e-mail from them I'd post it, but it seems like they thought the MTL might be a little too light by itself. Running that mix, mine shifts much, much better than it did, especially in cold weather.

They might have changed that recommendation by now, though.

 

 

Valv,
Did that tag come from a NV5600?

 

Yes, it came from MY NV5600 from www.zbag.com

 

If Gm synchro mesh is the same as pennzoil syncromesh that stuff is terrible. I did that in mine ( 6 quart overfill and everything) and it shifted like crap. But I am not sure if they are the same. I will be putting redline in.
-Alex

 

it's not the lube, it's the transmission!!!!!
why do you think it's not made any more?
but using different lube helps some!

 

It's not made anymore because the company was a joint venture between GM and Chrysler, and it doesn't exist anymore.
Very good transmission, abused by many and cussed by few (one of them above)
This is my 3rd truck with same transmission and I can guarantee there's no others out there. Ford has the ZF 6 speed which was worse, and the new G56 isn't even better. Browse the 3rd gen section, you'll find many positive praises about this tranny.
They use Amsoil Syncromesh, not Pennzoil, and they warranty it 1 year unlimited miles, that will give you a hint.

 

My NV 5600 is a fantastic unit, no issues. I use Redline MTL and it works far better than when it had the factory oil in there...

 

Is it a notchy trans? Absolutely! However mine went from pretty good to crap when I switched to the pennzoil syncromesh. My trans handles my power and doesn't break, I can't complain.
-Alex

 

i had mine rebuilt at less than 80,000 because of bad synchro's... i fought the bad shifting for at least 30,000 miles... i changed the lube three times before the rebuild,i used factory, valvoline, and redline and it always came out with a lot of brass in the oil........ so the rebuild followed, end of problems ( junk synchro's were put in the first NV 5600's) build date on mine is 6/2000,