After reading numerous threads on failures and overfill cures, I called my dealer in Madisonville, TX. They have an excelent reputation for sales & service. They sell a lot of 1 ton diesel trucks, with small town friendly service, all but missing today. I talked to the tech manager about failures. He indicated that all he saw were NV5600's where people ran them out or low on lube, from a leaking seal.
I suspect this may explain many failures, but not all. He also indicated that the lube repacement period was 30k miles.
He saw no real benefit to the extra lube, especially if you had a leaky seal.
Comments?

 

I would have to agree a leaky seal could lead to a low capacity and cause problems.
Mine is filled to the top bolt on the pto cover with oem lube which is syncromech I think. Also added was some lucas stuff (can't remember what tha was). It's been that way since '99 or near 180k. I have never had a seal leak nor changed the fluid, I do check fluid level and it's has always been full to the top bolt. It shift's great, actually much better than my dad's (could be driving styles).

 

I have to agree, low on fluid or the wrong type of fluid can kill the tranny.
I'm running an extra quart in mine and also using synthetic fluid (Amsoil MTF).

MikeyB

 

I reviewed my owners manual last nite and it calls for NO Changes. When you think about it, how many times have you ever changed fluid on a car/light truck manual tranny? Considering the loads these are under, I think 50k miles may be reasonable.
Also, the original lube is Synthetic, so I am not sure why so may second guess the factory. who has spent much money and time to arrive at the existing solution.
Does anyone have the specs on the original OEM lube? I beleive I read that was made by Texaco?

 

supr, I read that it was a "psuedosynthetic" a dino oil that has been refined until reached true synthetic specs. I'm not sure, maybe someone will correct me if I am wrong. I agree, we go overboard with these trucks. I'm guilty as well. My 87 6.9 was hard to shift when I bought it at 40k miles. I replaced with a fully synthetic and it shifted WWWAAAYYY better. So I did same with my new truck, it already shifted great, probably a waste of time and money,(it did make it shift even better) but I may change it again in 75k or so. OOPS just noticed I was in sec gen, sorry. Otherwise I have never changed diff. fluids etc,since I don't haul heavy every day and there is no combustion taking place. I guess since this truck was so expens. I will follow manuf. instr.

 

I beleive the stock fluid is a Texaco product. Referred to as lifetime. I didn't like the sound of that so I serviced the tranny. Mine was changed at around 55K and was dirty and pretty cloudy. I got the usual fine silt and tiny bits of yellow metal from the synchro's in the drain pan. I replaced it with a full synthetic(Redline MTL) and overfilled it by one quart. It shifts better after its warmed up but cranky into 3 and 4 when cold outside. I don't do any heavy pulling. I switched out my diffs with Royal Purple synthetics and am glad I did. The rear was very dirty and the front resembled a milky honey colored snot. I thought it may have had moisture get into it but the dealer tech said that its color and consistencty was normal for the OEM product it was originally filled with. I think I made good decisions here regarding preserving/extending the useful service of this truck. I hope it pays off!