Transmission, Transfer, Differential Gear Oils - 3rz, Manual, No-Locker.

Specs from 2003 FSM:

Front diff 1.15L or 1.2qts of hypoid API GL5

$29 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90

Rear diff 2.5L or 2.6qts of hypoid API GL5 SAE90(+degF), 80w(-degF), or 80w-90(-degF)

Xmsn (W59) 2.5L or 2.6qts of API GL4 or GL5 75w-90

Xsfr 1.1L or 1.1qts of API GL4 or GL5 75w-90





Top 4 on the chart: Amsoil Severe Gear 75w-90, Red Line Synthetic 75w-90, Lucas 75/90 Synthetic, and Valvoline HP 80w-90. Lucas 75/90 Synthetic's initial high viscosity seems to be a bad idea to me (maybe better for tractors, lol).

After going nuts trying to find gear oil off the shelf, I am using Valvoline HP 80w-90 for all gearboxes that i found at AutoZone. It is sort-of comparable, cheaper (66$ for 2gallons), not synthetic, no limited slip modifier. Without the friction modifier the onset of oxidation should be less. There is only a 14degF difference on low temp threshold between 75w and 80w, it satisfies GL4 and GL5, I can buy in 1gallon containers, and I can buy locally-late night. On a side note I will not be using the friggin squeeze bagged quarts again, a friggin mess.

If you are starting off with dirty gearboxes, the Valvoline could be a flush before using the more expensive Amsoil or Red Line. IDK, maybe I'm justifying.

 

Soooo, Redline is now being missed for the xmsn. Valvoline is getting the job done. But the shifting is easier with Redline. Maybe 75w makes shifting easier too.

 

That's a whole lotta fancy numbers and graphs for "The best oil is the one changed on time".

I run Mobil 1 synthetic in everything except the auto transmission (MaxLife ATF). Everything gets changed on time, and haven't had any problems in ~22.5 years of ownership. The oil has never come out burnt, with metallic bits, or issues indicative of a larger issue.

 

Fancy numbers like 75w or 80w, and fancy charts like bar charts. And maybe "The best oil is the one available". It could be said that the manual transmission is the toughest player here, maybe the most finicky.

Really just wanted to post something simple for manual transmission-4x4 newbie and frugal guys and girls, like me, to look at while they make a decision at the shelf. Tried to work with the title to make the project easily searched. Maybe I'll add links to the stickies.

 

Redline MT-90 is the best for any manual trans.

 

I think so too. I have used it before and one can tell immediately with smoother shifting. You can also tell when you stop using it, lol. I will be ordering some shortly.

 

I always ran it and I forgot why, then I had my 88’ Runners transmission rebuilt and the local rebuilder, who only does standard transmissions, said to only ever use MT-90.

That being said, I use Amsoil Severe Gear in my Diffs. It’s relatively inexpensive.

 

I had to hit the road for work in slightly north California before I could think about MT-90. I stopped in a Napa store in Cloverdale, Ca, close to my Motel. It was a real Napa parts store, stuff packed all over, country boys trying to get stuff for their old trucks.

I went through the whole Tacoma spill with the counter man after looking at the gear oils they had, and they had options which was cool. Then the counter man said "I think I have some of that stuff". He had all sorts of Redline and MT-90 on a little stand sort of out of sight. 15$ a quart and he gave me a Vet discount, which might be a Redline thing. Going to order some

$29 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 for me, for next time.

Rare, old school, Napa