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Gearbox oil - interesting result and good info...


Active Member
Apr 21, 2022
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Hello folks,
This is probably well known but i thought id pass this on -
I recently replaced my gearbox oil with a very well known brand 75W-90 GL4/GL5 and immediately found the gears were notchy at all temperatures - and when cold, selecting 2nd gear while even crawling was a fight.
Forget first unless totally stationary!

So, i dropped it out and refilled with Toyota genuine 75W-90 GL4 - and the gearchanges are silky smooth again - like night and day!!

The well known brand was a red colour and smelled spicy like gearbox oil does.... and the Toyota genuine oil was golden brown - with no real EP spicy smell to it.
I had to stop and triple check i hadnt missed something - and was pouring engine oil in!!

Anyway, im delighted and thought id pass this on!
I've always found with the weaker 2nd gear syncro issues on the 80 either 50% ATF or 100% ATF has helped the gearchange no end with no ill effects to the box.
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Don't keep us guessing, what is the well known brand?
Haha... I was just adding the element of suspenders... I mean suspense.
It was a Fuchs titan semi synthetic.. gear syn or some such.
I dont have the can anymore but I'm absolutely certain it was stated as GL4/GL5 (I won't bet my mortgage on that though)
Come to think of it, is there such a thing as a GL4/GL5?
It might say GL4/GL5 on the can but there is no such thing. GL4 does not attack synchro rings whereas GL5 does. GL5 AKA EP is for hypoid gears found in axles. Gearboxes need a different oil. GL5 is very slippery so if used in a synchro box the synchro may not work as well as GL4, and also the synchro rings will be dissolving. If it says GL4/GL5 avoid.