Reference: Manual Transmission Oil

[Wayne Hingley]

Having recently changed the transmission lubricant in my M38A1, I realized I hadn't considered whether my oil had EP additive in it or not, as I wasn't aware most newer oils (GL 4 & 5 certifications) contained EP. Its not well identified on some containers, so you need to look at the specifications to see what additives are in the oil and what compatibility notes are outlined by the manufacturer.

Sure enough the oil I used contained an EP additive. I have now drained my transmission and transfer case (along with my steering box and PTO/winch), and flushed them out, and refilled with a non-EP yellow metal compatible oil.

My jeep had less than 100 miles on the EP oil, and I already had signs of breakdown of some brass components (see photos below). The first photo is the oil that I drained, and the second is the "flush". You can see the brass on the bottom of the drain pan.

I hope others will check their systems, and avoid the types of failures noted by Robert and Lynn.

My transmission is still working perfectly, so I think I was lucky to take action before too much damage was caused.

[rob love]

Thanks for the posts Wayne.

I have been trying to do a little research into the gear oil question, and it would seem that if the GL5 has an MT1 designation, it may be OK for the yellow metals.

I also may start a program of changing the gear oils in most of the museum's vehicles, as well as my own. Pretty sure I have been using off the shelf 80W90 in most of my older transmissions, including my Jeep.

Perhaps we can post what oils are available at Cdn tire/NAPA/Walmart that are reasonably priced and fully compatible.

Barry mentioned using straight weight 50 motor oil in the transmissions. On one forum I looked at, they mentioned even going to as low as 30W oil and having satisfactory results.

[Wayne Hingley]

Rob, I have a few documents in my oil resources folder that I still need to go through. Below is one excerpt from a 215 page Petro Can document that generally outlines the API Classifications. I have another similar manual from Shell that I haven't looked at yet. The correct lubes are out there, but the ones we want are more "specialized" than in the past. I will post any that I come up with too.

The second image (API descriptions) is from a Shell Lubricants Handbook.

Im not 100% sure, but it appears the API classes are more related to the application and type of service, and are independent of the additive package(s) that each manufacturer may include in each specific product.

[Wayne Hingley]

Below is an example of a product that specifically mentions being compatible with yellow metals...

[Jordan Baker]

Thanks Wayne, this subject is probably best on its own thread so as not to get lost in my restoration thread. Ill now be checking my Willys MB

[Wayne Hingley]

Originally Posted by Jordan Baker

Thanks Wayne, this subject is probably best on its own thread so as not to get lost in my restoration thread. Ill now be checking my Willys MB

Yes I thought we hijacked your thread enough, Jordan...