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Motor Oil and Gear Oil have different SAE viscosity scales. 80/90 Gear Oil is about the same viscosity as 30/40 Motor Oil.

I'm aware of that. Perhaps I should have said the cling of the Hypoid oil leaves too thick a layer on the tranny gears and bearings/bushings. I and many others have had much better performance and wear characteristics with the 50 wt engine oil. Many will also note that many modern manual tranny's use ATF. With the investment folks make in their jeeps it would make sense to choose the best product for each component and not which product can satisfy the basic needs of as many components as possible.

Anyhoo both opinions are on the board. The folks can study further and make their choices.

Hi guys,
I've been watching this discussion for awhile now. Im at the point where I am going to put the tub on my jeep tomorrow, and want to fill all fluids BEFORE I put the tub on.
I'm going to go to NAPA tomorrow to get the fluids. Here's what I've gotten so far:
Engine: 30/40/50w (detergent, possibly high mileage), or 10w30/40/50 (5 quarts)
Tranny: 50w motor oil, or 90w gear oil (1 quart)
Transfer: 50w motor oil, or 90w gear oil (1 quart)
Diffs: SAE 90 EP, Rotella 85-90, or 90w Hypoid gear oil (5 quarts)
Steering gear: 90w gear oil (not much)

was looking at fluids the other day and noticed that Lucas makes 80-90 w gear oil. label says something to the effect of "great for transfer cases". Has anyone used or added this to their tranny/x-fer case?

Being as far south as you are I would not waste my time with the multigrade engine oils. Stay with the straight weights in the appropriate weight for your seasons which were 20 and 30 weights when I lived down there. Unless you have a tired engine or a slacker rebuild you should not need those racing heavy weights 40 or 50.

Make darn sure the Gear oil you elect to use in the tranny/transfer/steering is approved for use in gear boxes which contain non-ferous metals.

Got it - now what about the knuckles? I'm guessing just plain ol' 90w GO? How much do they use?

The steering knuckles are the most contested lube item on all the Willys closed knuckle jeeps.

The Army manuals and very early Willys manuals say #2 chassis grease. The later Willys/Kaiser manuals call out GL3 140 wt.

Unless you have factory new knuckles the gear oil doesn't work well. Also there is no oil slinger in there so the upper king pin (pivot) bearing gets no lube. Bottom line is the knuckles are suppose to be dis-assembled, cleaned and hand packed with #2 chassis lube every 12,000 miles. You check and add lube every 2,000 miles.

Now many folks dream up their own personal concoction called knuckle pudding. They mix GL3 with #1 chassis lube. Some use the old Ford 600 wt gear oil.

So it's up to you. If you want to review the 100's of opinions just use the web site's search function for "Knuckle Pudding".

I'll check out NAPA and O'reilly this morning to see what's available on the knuckle grease or Ford 600w GO. I think I have a complete list now - thanks all!

Matt

Hi there, if I could join this discussion I have a question.

Is it the hypoid part that is bad for the synchros or is it the GL-5? I found some 80-90 oil at ORiley that was GL-4 but also said it was hypoid. Is that ok for the transmission?

I also saw some products that claim to be GL3,GL4 and GL5 compliant. I presume that this is still not ok? A lot of the other oils only mention GL5.

The only oil I found that said anything about being ok for soft metals was Royal purple synchromax. But it says it is for manual transmissions that need automatic trans fluid. I can't find any viscosity specs on it.

I also found Sta-Lube 80-90 GL-4 Hypoid at NAPA. It says clearly on the back of the bottle that it will not harm soft metals, brass, bronze and is recommended as a replacement for GL-3, GL-4.

I imagine this day and age they are able to formulate the oil to be compatible with older running gear.

Unfortunately it is a matter of cost and demand. If there is not enough demand to make it worth while, none of the companies will make it.

I found some at O'Riellys. Can't remember if it was 80w90 or 85w90. It had GL-4 on the bottle front. On the back it had GL-4 and GL-5 service. I didn't buy it because of the GL-5 printed on it.
That throwed confusion into it.

Sta-Lube GL-4 is what I've been running in my M38A1 with good results. Went to buy some more to finish my M38 rebuild "first fill" and could not find any GL-4 of any brand in my area! So I drained the differentials of the clean gear lube I just put in, put that in the transmission/transaxle and bought GL-5 for the diffs. What next, order the stuff on the internet or meet some gun in a dark alley and buy out of the back of a truck or brew some up my self?! Might just have to go to engine oil.

Ha! back alley oil dealing.

We have an "off the beaten path" auto parts store out here and they are stocked up on the stuff. It's kinda pricey at 24.00 but I may buy an extra bottle just in case.

The Hypoid part of the equation is meant to survive the high gear face pressures that are not found in transmissions. So there is no need to pay more for a quart of any Hypoid type oil just for tranny use. The newer GL-5 Hypoid oil simply has sulfer additives in it that will harm non-ferrous metals.

50 and 60 weight engine oils that met the older standards will work just fine in the tranny.

The Army probably thought switching oil specs on the GI mechanic under the car in the middle of his job would cause confusion and since the old Hypoids back then would work ok in the tranny they just left all 5 chassis units using the same oil.

Before the multi-viscosity hypoid gear oils it was common practice in cold climates to switch to 50 weight engine oil in the tranny and transfer. Many folks that noticed the better/easier shifting they got with 50 weight oil stayed with it year round.

So the short of it all is:

1-Hypoid gear oils are only a necessity in the differentials.
2-The GL-5 hypoid gear oils have harmful to your tranny sulphers in them.
3-50 or 60 weight engine oil will work just fine in your tranny and transfer so long as it doesn't have any sulpher in it. If the lower weight worries you then try the 60 to 75 weight racing engine oils.

I was at NAPA today looking at their oils. Was talking to the counter person about manual transmission oils and the differences of GL4 & GL5.
I told her (the clerk) that I had read that some folks use motor oil in their manual trnasmissions. She was familiar with that and said she ordered some 50wt motor oil for a gentleman who wanted to use it in his transmission.

I said, order me 4qts and I'll pick up tomorrow. $8.00 cheaper than their gallon of StaLube.