Never buy a truck used for mobile repairs.

85 D250 with Utility bed, 120,000 miles on the odometer.
The NP435 trans is occasionally very hard to shift from 2nd to 3rd (employee power shifts to beat Chubbies???).
So hard that at times I have had to go back to 2nd to regain enough road speed for 3rd!!!
Novack recommends 50W lube for their rebuilt transmissions along with the family fortune for the last 2000 years (O'Reilly's ain't much cheaper) while Haynes says to use 90W.
I've got 80W/90 in it.
Any suggestions?
Budd
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On 10/30/2015 05:43 AM, Budd Cochran wrote:

The 435 is an excellent, heavy-duty truck transmission designed and used in 1/2, 3/4 and 1+ ton trucks. It is a well-built transmission and remains easy to locate and generally inexpensive to buy and maintain. The strength, relatively short size and the gearing of the transmission make it a good choice for a variety of situations. This transmission is 10.8" long and features an aluminum top cover that is retained by eight bolts. The NP435 case is of cast iron. The NP435 is a top loaded, top shifting truck style transmission. The NP435 enjoys a very low compound gear at 6.68:1 and as such it is a popular choice for those wanting a very low crawling gear. There are two-wheel-drive and four-wheel-drive models; the critical difference being in the bolt pattern of the rear adapter housing or tail housing.
When filling your 435 with gear oil, we recommend that you select a conventional mineral oil or a para-synthetic in lieu of a full synthetic oil. Properly assembled manual gearboxes do not have the thermal strains seen by combustion engines or hypoid gears. Synthetic fluid in these gearboxes, while not harmful, is probably an economic waste.
Hypoid gear oil is sulphurized higher than transmission oil and can be mildly corrosive to the non-ferrous alloys used for synchros, bushings and thrust washers in these transmissions.
An 80W-90, API-GL5 or MT-1 rated fluid is very good. Some claim faster shifts from using a 50W engine oil in their transmission and we do not consider this to be contraindicated unless you operate your vehicle in a very warm environment.
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On 11/1/2015 4:06 PM, magmet wrote:

What's this? A direct quote from Novack that didn't help a bit when I read it on their site.
FYI, I use only petroleum based lubricants because they're cheaper and have worked for over a century.
Budd (10 years as a heavy equip mechanic but it was 39 years ago and I don't remember like I usta could.)
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