1992 Toyota Pickup 5 Speed Manual Transmission Fluid Change
 

When trying to decide which fluid to use in my pickup the owners manual is only slightly helpful in narrowing it down. It gives me the option for the following:
GL-5 75W-90
GL-5 80W-90
GL-4 75W-90
GL-4 80W-90
Out of the four choices (not accounting for multiple brands) there should be one that provides the best performance and protection, although, I realize the difference may be so negligible that I wouldn't be able to discern which one. However, I don't want to do four fluid changes to find the right one. The only easy decision was to go with a full synthetic.

After reading many other threads on this topic as well as a few outside articles I'll link or attach below the top three contenders are:
1) Redline MT-90 (50304)
2) AMSOIL 75W-90 (MTGQT-EA)
3) Royal Purple 75W-90 (01300)
Honorable Mention: Ravenol VSG SAE 75W-90

I was ready to buy the Redline MT-90 until I read the product description of the Royal Purple which claimed it met both GL-4 and GL-5 requirements as well as being safe for yellow metals. What are everyone's experience with one or more of these products specifically in 1994 and older Toyota 5-speed manual transmissions? Did I miss any other options that should be considered? If you favor one over another tell me why! If one gave you horrible results please explain that as well. My goal is to provide others with as much info in one place as possible as well as figure out which fluid I should go with too. Thanks in advance.

For a little background info my pickup is a 22R-E 2wd with 150,000 to 180,000 miles on it (broken odometer). I live in the PNW therefore the summers as well as winters are mild. Likely only to get below freezing a few weeks a year and maybe a handful of days over 100 F. I've read somewhere that the GL-5 oils of today no longer are corrosive to brass metals, but, I don't know that to be true for them all.

https://cimg8.ibsrv.net/gimg/www.yot...ff239c28da.jpg
Also one should check out https://www.bobistheoilguy.com/forum...22Gear_oil_API

The purported corrosiveness of GL-5 lubricants is probably not a issue now; if it ever was..

It is the increased slipperyness of them over the GL-4 spec gear oils that might be problematic.

While the GL-5, or GL-4-GL-5 multi oils are best for differentials, the plain GL-4 spec oils often give better results in trannys where worn syncro action is further weakened by the extra slippery GL-5 oil.

It's really up to you. Many use GL-5 oils with no complaint. I do use GL-4 oils in my own trannys.

I use Amsoil GL-4 in the tranny & transfer case & Amsoil GL-5 in the diffs. 75W-90 in all

GL-4: https://www.amsoil.com/shop/by-produ...?code=MTGQT-EA

GL-5: https://www.amsoil.com/shop/by-produ...?code=FGRQT-EA

Yeah the only real question I think I have now is to choose between Amsoil and Redline. The owner's manual says to use GL-5 90W in the rear differential. I think I will end up using a synthetic GL-5 75W-90, however.

1992 Toyota Pickup 2WD

Amsoil is cheaper by a couple $. For me MT-90 is easier to come by so that's what I always use. Never used anything else but never replaced a trans before either so I'm sticking with MT-90. It's helped fix neglected transmissions that I've purchased. I'm sure the same can be said for Amsoil.

Redline mt-90. I wont use anything else in my trans now. I made the mistake of putting GL5 in for about 3000 miles and it was notchy and just not smooth to shift. Drained it filled with mt-90 and it was smooth and shifted better all around.

Mine had gl-5 in it when I bought it. Shifted smooth when I got it. After about year it started to get hard to shift. Eventually to the point where it almost couldn't be shifted without a good double clutch. I drained the synchros out with the oil.

While being on a budget to find something that would help, I tried a trick the jeep guys would do with their ax15 transmissions. I filled mine with valvoline full synthetic 10w30 motor oil. Slightly over full. It brought my gears back. Still a tad notchy. Can't usually float between gears but shifts good otherwise.

The thinner oil helps get the synchros working. Synthetic oil holds up to all the sheering forces better than conventional. I overfilled it because there are a few guys on here that claimed their trans shifted better about a pint over full. I filled mine correctly first then added some more about 1k later and it did smooth out a little more.

I'm sure theres plenty of people that will despise what I done, but it certainly worked for me. But because it worked well for me, doesn't mean it'll work good for you. If your trans still shifts pretty good then I would probably go with the tried and trued mt90.

MT-90 here and replace you shifter seat bushings while you at it. Marlin has them cheap.

The YouTube vids I watched made that shifter bushing look pretty straight forward which is great because last summer it was randomly popping out of 3rd unless I held it in there. It mysteriously "fixed" itself for now but I suspect replacing those bushings will fix it properly.