Gear Oil

[Oldfireguy]

Been told about using only a specific gear oil for T90/D18. Anyone out there know of a GL4 rated oil that is not rated "extreme pressure" as well? Thanks!

[LarrBeard]

Bmorgil - this one's for you ...

[bmorgil]

https://willysjeepforum.kaiserwillys.com/showthread.php?2371-The-correct-lube-for-a-Jeep-synchronized-transmission

Yes you are correct. You are doing that old tranny a favor by looking for the right stuff. LarrBeard and I have written each other on this subject. Unfortunately, I lost what I wrote! Anyway, I use Redline MT90. https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil

I will tell you that in the 60's and 70's and into the early 80's, it was not uncommon to find straight 40 weight engine oil in Heavy Duty Class 8 Semi Transmissions. In a pinch I would definitely use Straight 40 weight engine oil over any unknown. I rebuilt many Spicer 14 speeds, 16 speed and 20+ speed transmissions, that ran 1,000,000 or more miles, on Straight 40 weight Engine Oil.

[LarrBeard]

Here is your last essay on grease - we were talking grease for light and heavy duty Zerk fittings:

The "Zerk Lube" has two categories.

1) Zerk's that need High temp, E.P grease. (U-Joints and Wheel Bearings) "Spicer U-Joints" and all Wheel bearings require an NLGI grade 2 grease. I use Chevron Ultra Duty NLGI 2 EP Grease. We tested it severely on the U-Joints. It was the best we could find.

2) Those Zerk's that can use anything (Low Temp, Chassis Lube) The Chassis points do not require High Temp or E.P.. Here a NLGI Grade 0 or 1 will work. I like NLGI 1 because it is thicker and stays put. I like a good name NLGI grade 1 White lithium.

The study of grease can be mind boggling and misleading. For instance the Universal Service Manual calls for the wrong grease in the U-Joints. U-Joints MUST have an EP additive. This is probably a miss print or, left over from long ago.I can show you what a U-Joint looks like when you use the wrong stuff. I also found several spots on the Internet with incorrect information. No matter what you read I can assure you I spent many years promoting NLGI Grade 2 EP ONLY in Spicer U-Joints. The most common cause of failure in a U-Joint is "Lack Of Lube". The second most common is "Wrong Lube".

Many manufactures specify different greases for different reasons. There is a lot of stuff written that's for sure! Sticking to the above will keep all out of trouble.

Maybe this one clarification will save a U-Joint.

[bmorgil]

Oh yeah that's it! I deleted my PM's by accident. We also went on about the trans lube didn't we?

The thing to remember is that the GL rating is actually a thickness indicator so to speak, just for gear boxes. GL-4 is very similar in viscosity to 40 weight motor oil. You can get GL-4 with EP in it. It is important to really dig deep to be sure. It is actually getting difficult to find the right stuff that is compatible with the old Brass or Bronze cone clutch style synchro.

[okiemark]

I put Rotella HD in mine. It is the same stuff I use in my tractors. I looked up in the specs and it is non corrosive to copper and brass.

[LarrBeard]

I put Rotella HD in mine. It is the same stuff I use in my tractors. I looked up in the specs and it is non corrosive to copper and brass.

This ties back to BMorgil's comment about million-mile super heavy duty gearboxes using straight 40W oil. No sulfur based additives, therefore no brass issues. But 40W and Rotella seem to be one of the lesser known secrets - probably because there isn't a lot of glamour or magic to them - they just get into things and work.

[bmorgil]

Very true. Not many people realized that the big truck fleets of the day learned that one motor oil would do a lot. It definitely reduced their inventory of maintenance items.

The thing to remember is there are MANY combinations of additives in lubricants for MANY different reasons. What we know as an Extreme Pressure Additive, is something designed with sliding friction involved. All lubricants must maintain film strength in a given situation. In motor oil these additives that protect and maintain strength are referred to as Friction Modifiers. Combinations of this stuff make up lubricants for different applications. A good example is Rotella. A motor oil that will perform in a transmission with synchronizers indicates the correct lubricity. If it were an EP, the syncros would have difficulty because of the EP additive. Even if it had an EP that was compatible with brass, it still would have the wrong properties. Again Rotella does not contain EP as we think of it. Rotella also has Friction Modifiers that make it compatible with the clutch facings in the auto trans axles and the brakes that are submerged in some cases.

It comes down to economy. You don't need the high detergent of a motor oil, but it doesn't hurt. You don't need Friction Modifiers for facing materials, but it doesn't hurt. The most important things are the correct viscosity, additives and compatibility with the internal components. Sometimes you can find something that though it has more than you need, it is cheaper because of how much of it is available.

Finally if you are looking for something that is application specific, you are going to pay more for it. I don't know what to think about that. The Red Line is made specifically for the trans. I do know how it performs "under the gun". Would a good motor oil do just as well? Probably! It just comes down to what you want to trust or, like.

[Oldfireguy]

The 40 wt oil would be great...and cheap! Is'nt it a little thin; as opposed to the recommendation for 80-90wt?

[bmorgil]

Engine oil and gear oils are rated differently hence the GL ratings. GL-4 SAE 80 wt Gear Oil is very similar to 40 weight Motor Oil in flow.

[okiemark]

The hydraulic oil like the Rotella HD I mentioned is probably no more than 30 wt. but it is used in heavy equipment with ring gear and pinions, power shift transmissions, etc with extended continuous use under high temperature conditions. I think it would work in a jeep tranny.

[bmorgil]

The real trick here is to match the EP ability of the oil/lube to the application. Here it is important to remember to much EP capability (as intended for use in sliding hypoid applications), inhibits the synchro's ability to engage the next gear and "clutch". This causes more gear clash than normal and wears the clutching gear teeth faster. In addition the shift will be "stiffer" and slower than it was designed. The brass facings will become glazed making things worse. Most will never hear the excessive gear clash, there is usually to much other noise. This damage is subtle.

GL-4 gear oil does have some EP. It is not so excessive that it causes shift issues. GL-5 is tops on the EP additives list, and is intended for the high sliding friction of a Hypoid gear set. The reverse error of putting a low EP in a Hypoid gear set is obvious and happens quickly. It is a total failure. The failure analysis in the Tech Section has some good pic's. If you make a mistake and use a high EP in a cone style synchro, life isn't over. Many have done it. Some don't notice. A sharp transmission re-builder familiar with old school synchro's, would know immediately.

[Oldfireguy]

Thanks ya'll for your wisdom. I'll try the 40 wt oil.