W59 Transmission Fluid

I did a search but am still confused over what type of trans oil I should run in my W59 manual transmission. 1996 Toyota Tacoma 2wd. What is the difference between GL-4 or GL-5 fluid, and will the GL-5 hurt brass (or bronze, whatever this tranny has) synchros?

 

Put Redline MT-90 in this transmission. It's GL-4 and will make it shift smooth.

 

Here’s a good read to settle the subject:
http://www.widman.biz/uploads/Transaxle_oil.pdf
Basically GL5 oils have a more corrosive phosphorus which is harmful for soft metals (brass synchros) and a GL4 oil has a way smaller concentration of said elements.

 

I second this. Just did this not too long ago, finally replaced the fluid from the factory at 170k miles (oops!) with Redline MT-90 and shifting feels much nicer. Also did the rear diff at the same time with Mobil 1 and it feels like I picked up (regained??) like 10-15 horsepower. I even added a couple MPGs (5 lug 2WD, YMMV).

 

Either redline or amsoil makes a great syn gl4 for our tucks i run amsoil gl4 in my w59

 

Redline MT90 all the way. I normally don’t buy into snake oil hype but it really did shift smoother with MT90 instead of regular gear oil