I'm in need of some advice, I trashed my tranny last Sunday and just recieved my rebuilt one that I am installing tomorrow. The problem is that the shop that rebuilt it said to run 20w-50 synthetic motor oil in it which goes against everything I have ever heard about these trannies. They have moved the fill hole in line with the top PTO bolt hole to get the extra quart in it and they have also machined a groove into the bearing carrier on the rear shaft for better oiling (I assume that shaft doesnt get good oiling?). Anyway, should I go with what they say or use the synchromesh like everyone else? Thanks for the input.

 

If they are putting a warranty on it I say to do what they tell you (assuming it's in writing). I can see them refusing to warranty the tranny if you run something else in it. It's scary to think that they wouldn't know what type of lubricant to use in one of their rebuilt trannies.

 

I asked them three times and they were adamant about using the 20w-50 in it. Wouldnt warranty it if I used the synchromesh. Weird

 

Make sure it is all in writing and follow what they say. Better safe than sorry.

 

FYI, motor oils are not formulated with the hi-pressure additives required for geared transmission service, particularly as required by the NV5600 - I run a blend of 8qts Valvoline 5W-15 syn motor oil to 2qts Valvoline 50W-90 syn transmission lube to get the correct viscosity and hi-pressure additive mix - the NV5600 don't even like high-viscosity lubricant, particularly when cold, as in winter

However, follow the rebuilders recommendation, or they will void your warranty - you can call them and ask why they recommend that particular lube, but don't substitute - could be it's just to save money over the way-expensive oem-recommended syn synchromesh lube

 

It sounds to me like the transmisison shop that built your tranny is full of old school gearheads that don't know lubrication and use things like machining grooves where they don't belong to compensate for that lack of knowledge.

You're not going to like the way it shifts with 50wt motor oil in it. Depending on how far away that shop is, I imagine I'd be trailering it over there on a really cold morning so the tech that built it could take it for a test drive. Then see what they say.

 

Man, you must have really beat the s*** outta that tranny!!!!! I used to haul with my truck and we routinely weighed around 25-26K and I only used synchromesh from the day I bought my truck brand new and never ever had a problem with it. The only thing I have found in the tranny other than the normal residue was 1/2 a tooth off the reverse gear (I can feel it when I back up). I can only imagine what running gear oil in that thing would do to it. Don't get me wrong, I come from the day when HEAVY gear oil went into anything with gears but times have changed. My 5600 shifts smooth as butter with synchromesh in it....I'd really find out why they recommend the oil they say to use.

Just my 2 cents worth. Good Luck.

 

Im whith you here. If you have ever had this tranny apart you will know that machining a groove in the carrier will do nothing, because no part of the bearing moves in the carrier. Im thinking this is going to be problem we will hear about again soon

 

The Eaton in my OTR truck used 30w motor oil. I guess Eaton doesn't know anything about lube!

 

We are talking about 50w oil in a different tranny. Maybe you didn't know different types of equipment required different types of fluid.

 

I was referring to the EP additive issue. I used to gross 125k with a turned up cummins ntc and 30w in an rto910 with no problems whatsoever. EP additives aren't everything. There are several viscosity indexes for lubricants depending on the type of lube. Have you ever looked to see how 50w engine oil compares to gear lube? It's up there in the 90w range! I wouldn't worry a bit about using 20w50 as long as the synchros like it. Craig

 

I sure would like to know where some of the builders get their knowledge. It certainlly was not from the people who engineered and built the tranny. I have read, inspected and tried many of their fixes through the years. About 90% of the fixes have absolutelly no merit other than transfered $ to their pockets. A few of the fixes were brilliant and really addressed a problem. Go figure. A good place to look for good fixes are factory TSB's. Most come from the manufactures engineering, however a few are incorporated from field and aftermarket fixes.

 

And the fact is, they won't. That's one reason why synchromesh trannies spec'd lighter motor oils and even ATF back in the day before good synchromesh fuids became widely available. There's other issues like bearings that may not be happy with heavier fluids as well, depending on the design of the gearbox in question.

Dozer makes a good point about the original designers and factory information in this regard, generally speaking.