Which Gear Oil or Differential Oil should I use? Personal Conclusions and discussion. Molybdenum additive use?

General discussion about our beloved Tercel 4WD cars
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Toyotise
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Joined: Thu Mar 04, 2021 9:16 pm
My tercel:: 1983 4WD DLX. 1986 4WD SR5
Location: Arizona

Re: Which Gear Oil or Differential Oil should I use? Personal Conclusions and discussion. Molybdenum additive use?

Post by Toyotise »

The Professor wrote: Mon Nov 29, 2021 3:10 pm If you're going to run ATF, I'd suggest supplementing it with a thicker gear oil.
Professor: that’s about the same conclusion I came to when considering using ATF in any of my manual transmissions

I finally got around to wrenching on the new to me 1983 DLX this weekend. Here’s the transmission plug.
18D4CFFB-67CE-4A04-BC40-FA6007F2B668.jpeg
Very dark and oxidized I’d say that’s never been changed in its lifetime. A decent bit of magnetic fuzz and pretty noticeable glitter of brass flake in the oil pan, but nothing abnormally so if it was never changed. The transmission was about 1 quart low, which is not too bad considering. This is the blend I refilled it with:

2.5 quarts STP 80W 90 GL-5 Conventional

0.5 quarts STP 75W 140 GL-5 Conventional

1.0 quart AMS Oil Synthetic OE ATF Fluid

Drives and shifts good the same as it did before. Pretty amazing it drove so well on how old the fluid looked.

Rear differential was similar old fluid. Refilled with 0.5 quarts of STP 75W 140 GL-5 Conventional
And
0.5 quarts Pennzoil 80w 90 GL-5 Conventional I had laying around along with a squeezy bottle of the Liqui Moly MOS2 for Gears

I think I’ll run all that for a while to get things warmed up and cleaned out. See where I go from there. I’ll keep the thread updated.
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User avatar
Toyotise
Advanced Member
Posts: 79
Joined: Thu Mar 04, 2021 9:16 pm
My tercel:: 1983 4WD DLX. 1986 4WD SR5
Location: Arizona

Re: Which Gear Oil or Differential Oil should I use? Personal Conclusions and discussion. Molybdenum additive use?

Post by Toyotise »

Well it’s been a couple years and 5000 miles since I did a drain and fill on the transaxle with Sta-Lube 85w90 GL4 Hypoid rated oil and added the liqui-moly molybdenum additive for gears to the ‘86.
Observations are as follows:

-Molybdenum additive seems to have worked-in to the bearing races and gears sets based on auditory observations.

-The initial synchronizer reluctance observed after adding the Liqui-Moly Molybdenum additive for gears seems to have dissipated. Synchros are working at least as good as when I originally acquired the vehicle, maybe even slightly better. Into second gear is now the only gear change that necessitates a slightly longer pause for smooth change up.

My latest conclusion are:
1) The Molybdenum additive is very effective as advertised.
2) With out an empirical before and after disassembly experiment I cannot completely overlook its potential effect on synchronizers.
3) It requires some run-in time before it’s full effectiveness is realized.
4) Even if it has a moderate effect on synchronizer performance I believe it is indispensable in high mileage or high wear stressed transaxles.

I endorse its conservative usage in Tercel4WD Manual Transaxle and wholeheartedly endorse its use in rear differential.

https://www.liqui-moly.com/en/us/mos2-a ... tion-title
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