the owners manual on my 89' 4x4 says that the m/t takes 30w motor oil. i've never heard of any trans taking motor oil. i did u-joints this weekend, when i pulled the shaft it appeared to have atf drip from the end of the shaft [red] . would it hurt to put gear oil in. i've heard there were early failure problems with some of the 1st gen manual trans . i'm wondering if using a heavier oil would be better?

 

The 1990 service manual I have says the NV2500 5-speed manual transmission takes 10W-30 motor oil. Yup.

 

the heavier the motor oil the thicker it will be when its cold...that means it will not splash like it should and could cause premature wearing on parts...run whats recommended..plus gear lube will making shifting a bitch

 

Use whats in the manual. It all depends on the design of the gears. Some trans gearlube others motor oil and some will ATF.Gearlube can handle the highest pressure and would not foam like the detergent in motor oil. But motor oil lubes better than gearlube at higher gear speed.ATF lubes the best over wide range of speed and temperature.But it can't protect at high gear pressure

 

yea i have a 96 dakota witha nv3500 in it i tried putting 75w 90 in and you could not shift any gears put in some 10w30 and ity worked fine,.

 

For the NV3500, the only recommended lube is Mopar Manual Transmission Lubricant, part number 4761526. (FYI, apparently that P/N was replaced, its now part number 4874464)
The manual specifically states, "This is the only lubricant to be used in NV3500 transmissions. No other lubricants are acceptable, or recommended." (Bold word was shown bold in the service manual)

Please note: the above is the NV3500 transmissions. The NV2500 transmission is recommended 10W-30 motor oil. The AX15 transmission is recommended 75W-90 gear lube.