Recommended Oil for Manual Transmission

I always use standard gear oil in my trannys, but i would use whatever your users manual states.

I'm afraid the answers will not be easy unless you figure out WHICH transmission it actually is. There were several possible - this is the MOST likely - but not the only. To be sure get under your truck using this guide

http://www.motivegear.com/tech_info/tranny_guide/tranny_guide.html

Since from the web I'll give you another link to read

http://en.wikipedia.org/wiki/New_Venture_Gear_3500_transmission

from the same site:

• 5W30 engine oil does not contain additives for use in manual transmissions.
• Additives in standard gear and axle lubes will etch the bronze synchronizers and 80W oil will not properly flow into the NV3500 bearings.

WARNING:DO NOT USE REGULAR REGULAR GEAR & AXLE LUBRICANTS IN THIS TRANSMISSION THEY WILL DESTROY IT.

Since I use the same transmission in my Dodge - I will tell you to go use Amsoil.

Not only does it come recommended very highly from my friends, it does not cost $24.95 per quart from the dealer as the Dodge stuff does.

Well then, disregard any comment I may have made.... I know little to nothing about the dodge trannys.... gee... wait a minute... Last time I changed my 5speed Tranny oil in my 2000 Jeep wrangler, i used standard gear oil from napa... maybe that was a mistake? Should I flush it out with Amsoil?

Use a 70W/80 gear oil. It is a near equivalent to your 15W40 engine oil in viscosity and a better gear lubricant. There are synthetics as well but for general automotive use drop in the 70W/80 it is not as expensive. I've always used it in my manual transmissions.

Additives in standard gear and axle lubes will etch the bronze synchronizers and 80W oil will not properly flow into the NV3500 bearings.

http://www.autosmanual.com/614/synthetic-manual-transmission-transaxle-gear-lube.html

My wife's 1979 Chevy NP 203 transfer case: 30W oil. My 1989 S-10 5 speed manual: automatic transmission fluid. Would not surprise me at all that 15-40 is called out.

I think you have confused (or mis-read) the viscosity requirements for engine and transmission oil. The 15W-40 is a common viscosity for truck diesel engines but I have never heard it used in transmissions. I recommend that you contact a GM dealer and ask for the factory viscosity recommendations for transmission oil. It is foolish to guess. Note that transmission oil is formulated with a very different additive package than engine oil. Transmission oil usually contains large amounts of EP additives (usually compounds containing zinc, clorine of phosphorus) and moderate amounts of viscosity index improvers which will temporarily lose viscosity under high pressure. Multi-viscosity engine oil has larger amounts of viscosity index improver and very little EP additives because they will poison the catalyst.

Note the viscosity scale for engine oil and transmission oil is different

Dennis Waller

The synthetic requirements of viscosity are low.

Go to a quick lube shop. They have all the pertinent shop manuals and will look it up. It wont cost you much to have them do it and you wont have to worry about putting the correct fluid in. Now a days they use everything from GL4/GL5 gear oil, motor oil, ATF and special dealer only fluids. I would suspect that the truck actually calls for ATF but could call for any of the oils mentioned above. If you want to do it yourself call the dealership and have the Vin# and model year and they would probably look it up for you. The 15w/40 oil mentioned in his owners manual is most likely talking about the engine oil required and usually lists several weights/options depending on temperature. Remove the check plug on the side of the transmission and see if it is full. Make sure you remove the correct plug or you could inadvertenly mess something up inside. If it's red it is ATF. If it is clear/yellow or dark colored it could be anything. Just take it to the quick lube shop. Quick, Easy and cheap.

From my 1989 Chevrolet Shop overhaul manual;

Borg Warner and New Process transmissions use Dextron II transmission fluid.

The HM-117 (option M20) Is a 4 speed heavy duty model uses a separate bell housing. This transmission uses SAE 80W or SAE 80W90.

And just to make sure you are confused, there is the HM-290 5 speed transmission. It is option MG5. It uses Manual Transmission Fluid 5W-30. GM P/N 1052031. Good luck.