gear oil

[rtkjmk]

I am in the process of draining and refilling the diffs ,trans and transfer case in my 1953 M37. What weight and type of gear oil should I use? straight 90W or 85/90W ? I am also replacing all the seals and using ready seals on the trans and transfer cases . Does anyone know the NAPA # for the axle seals ?

[Lifer]

I'd say it pretty much depends on what you plan to do with your truck. It's lasted somewhere around 50 years with the original spec lubricants, so they must work "okay." Some experts who are more knowledgeable about modern oils than I am prefer more modern lubricants for varying applications (daily driver, mudding, rock crawling, etc.) and their recommendations are all over the map. If you're a die-hard purist doing a restoration, the original spec stuff is the only way to go. Otherwise, you have to decide how you plan to use your truck, do your homework, and take your choice.

[cuz]

Cabell's web site has a nice cross reference
http://www.garbee.net/~cabell/PartsCross.PDF

[Josh]

I always just put 75-90 in mine, and never had an issue.

[Nickathome]

I've heard people say not to use gear oil in the trans, but to use straight 50W instead. I've used the same NAPA brand 85W-90 gear oil in both the diff's and trans since I've had the truck, and have experienced no problems. I take Lifer's approach to this. Its 50 years old and had God knows what oil used in it, so anything I use can only be an improvement.

[mikkelborg]

That cross reference is out of date,Napa must have reorganized beause most of those numbers don't do anything anymore. I ussually have to find a civiallian truck with the same parts and order those, A WM300 oil pan gasket for instance.

You will probably want to check my facts, I am going off my memory and I'm suposed to be too young to have trouble with it, but school is stressful...

I think the 50 weight oil was the origional manufacture specification for the transmission, but as a cost reduction the military put standard gear lube in the transmission instead. The theory is that 50 weight will make the transmission shift easier and run cooler. If you do try 50 weight be sure to use a non-detergent oil only because I have read detergent oils have a bad habit of foaming in transmissions and become ineffective. Also, it has to be yellow metal safe or it will attack the syncros and other yellow metal parts in there. I'm running Cennex brand agracultural grade 50 weight heavy duty non-detergent oil in my truck's transmission and transfer case and have run over 1000 miles since the switch without heat or leakage problems.

Collin

[MSeriesRebuild]

Today's recommendation for the transmission and t/case is actually a heavy duty engine oil in a straight grade 30, 40, or 50 weight, depending on the ambient temps you operate in. 30 weight for cold climate. We have used Synergen synthetic 50 weight trans lube for several years in all our rebuilt gear boxes. It has been a huge success, shift easier, run significantly cooler, especially the t/case which tends to run warm, and never the first problem issue. Since this product is formulated for transmission use, the ingredients that attack brass components used in synchronizers have not been used in the additive package.

[Lifer]

Napa must have reorganized beause most of those numbers don't do anything anymore.

I don't think NAPA has reorganized, but they do change part numbers from time to time for some reason than not even my dealer can fathom. My guess is that they just toss a bunch of parts in a bin and a bunch of numbers in a hat, some guy pulls a part from the bin with his left hand, pulls a number out of the hat with his right hand, and VOILA! The part is assigned a number!

[MSeriesRebuild]

Napa must have reorganized beause most of those numbers don't do anything anymore.

I don't think NAPA has reorganized, but they do change part numbers from time to time for some reason than not even my dealer can fathom. My guess is that they just toss a bunch of parts in a bin and a bunch of numbers in a hat, some guy pulls a part from the bin with his left hand, pulls a number out of the hat with his right hand, and VOILA! The part is assigned a number!

NAPA's #'s change when ever the parts sources change. Like most, they are constantly looking at how to stay competitive. One way to do that is to change sources if another source will sell to NAPA at a cheaper price. Sometimes the changes are for the worst if you are seeking quality, but that doesn't seem to matter to most these days. Some fairly recent changes have been from National Seals to CR seals, precision u-joints to a Chinese line, Victor gaskets to Fel-Pro, Timken bearings to Chinese brands, and so on.

[CREEPING DEATH]

It isn't the weight that's important so much as the GL spec. I don't remember exactly, but you should use GL3 and not GL4, or maybe use GL4 and not GL5. If you go one number too high it DESTROYS the brass that's very common in the older gearboxes.

CD

[steved]

While this was a concern in the old days, modern gear oils have the sulfur locked in compounds so that it doesn't attack yellow metals...

Most synthetics are multi-rated...and won't bother yellow metals.

[MSeriesRebuild]

It isn't the weight that's important so much as the GL spec. I don't remember exactly, but you should use GL3 and not GL4, or maybe use GL4 and not GL5. If you go one number too high it DESTROYS the brass that's very common in the older gearboxes.

CD

This is but a partial truth, you will need to read more fine print in the spec sheets. The fact of the matter is all in the ingredients that are used in the additive packages that various blending facilities use are not the same. One Co may use a certain ingredient in order to meet a given spec while another may use a totally different ingredient in their package to meet the same spec. I recall a few years ago, Chevron offered an 80-90 weight product with a GL5 rating that was compatible for use with brass components, while other's GL5 rated products were not suitable. Just because you may find one Co who plainly states not to use their product if brass components are present, others who's product may carry the exact same GL rating are compatible with brass. We have asked for and studied thoroughly oil spec sheets on every lubrication product we use. It keeps you out of trouble and increases the operating life of any equipment. Lubricant suppliers have become very generalized with their products, all in the name of saying oh yeh we have just what you need. They are selling out of ignorance for lack of better words, there to make $$ instead of be certain they are furnishing what you really need. Don't be fooled CD, you may be searching out a GL4 rated oil thinking it is brass compatible because of the rating, when all the time the very same ingredient is in your brand of GL4 that will kill the brass. I'll bet you can go to several dealers and ask the brass question. Most will tell you straight out that their product is great for your need, and all the time they don't have a clue about how to answer your question, some use that age old line, oh yeh everybody is using that with 0 problems.

Bottom line, if you don't insist on getting the spec sheets so you can know for sure, you will be the loser when issues occur simply because you did not check up and know better. The only way you can know for sure is like anything else, do it yourself and have piece of mind.