Red Line gear oil for Toyota transfer case

[batook]

Last fall I replaced the gear oil in my 91 Toyota Previa 5MT AWD. The manual calls for "multipurpose gear oil GL-4 or GL-5 75W-90" for both the manual gearbox and the transfer. I had a hard time finding many 75W-90 options locally, and none were GL-4. I ending up going with Coastal dino 75W-90 GL-5 from Autozone. I hate this oil in the MT, the trans feels a lot more notchy than before, and I'm replacing it this weekend with Red Line MT-90 which is a true synthetic GL-4 75W-90 and has been highly recommended by several people.

My question is, what should I use in the transfer? In the past, I tried Supertech synthetic 75W90 GL-5, but it leaked, so I switched back to the dino and it stopped. Never had a problem with the transfer, but would like to use better (synthetic) oil in there. I'm seeing a few options on the Red Line site for 75W-90:

(1) 75W-90 GL-5 gear oil (57904)- Says this is OK for most LSDs...might be too slippery for a transfer case or open diffs?

(2) 75W-85 GL-5 gear oil (50104) - Red Line says "Popular in many Toyota light truck differentials and transfer cases"

(3) The same MT-90 75W90 GL-4 Gear Oil (50304) I'm planning to use in the 5MT, or

(4) 75W90 NS ("non-slip") GL-5 Gear Oil (58304), which says "Contains extreme pressure additives like our 75W90 GL-5 oil, but lacks friction modifiers to balance slipperiness".

While I'm at it, which of these would be best in the Diffs, which call for hypoid gear oil GL-5 80W-90 (although I've spoken with many different Toyota dealers who just use dino 75W-90 in everything). I don't see any 80W-90 specifically made by Red Line, but their application guide for this vehicle says the following:

MT-90 75W90 GL-4 Gear Oil
•For use in manual transmission

75W90 GL-5 Gear Oil
•For use in front differential with AWD
•For use in rear differential

But they don't mention the transfer case...

Thanks for any advice.

 

[hate2work]

Call Dave at Red Line and ask him what to use, he will set you straight-

 

[SLCraig]

Allow me to suggest Amsoil MTG 75w90 GL-4 fluid.
Best GL-4 around.

Best thing I ever did when I had my Maxima 6 speed was dump the MT-90 and go with the MTG. The shift quality improved immediately.

I feel that this would probably be your best bet.

 

[batook]

What is Dave's #?

I'm sure either RL or Amsoil would be a dramatic improvement over the dino GL-5 I have in my 5MT now. I'll probably try both eventually. I think the previous oil (which was fine) was just a dino GL-4, but I can only find synth GL-4 from these boutique brands now it seems.

My focus now is primarily on the transfer, and I hope to hear from someone having experience with a Toyota transfer case and synth gear oil recommendations in that regard. The viscous coupling is what tends to wear out in them, and I'm not sure how much impact the oil selection even has on reducing that problem, but I'd still like to put the correct/optimal oil in if possible.

 

[batook]

Originally Posted By: hate2work

Call Dave at Red Line and ask him what to use, he will set you straight-


This is what Dave had to say:

Originally Posted By: Dave

1) The 75W90 would be suitable for use in your transfer case and recommended to simplify selection with an automatic transmission.
2) The 75W90NS would certainly be an option.
3) The 75W85 used in many Toyota truck differentials from 2003 for CAFE improvements.
4) The MT-90 our recommendation for your transfer case with a manual transmission, as any fluid exchanged across the seal is the same.

Any number of fluids are suitable for the transfer case, in yours the MT-90 would be the first choice.

Regards, Dave
Red Line Oil


He makes a good point about fluid crossover, so I'll definitely be using the same fluid in both the transmission and the transfer, since it also simplifies product selection in my case.