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Transfer case and diff oil


Well-Known Member
Mar 1, 2010
I will be rebuilding my hubs soon and i am wondering what viscosity oil to use in the diffs/TC. I have heard that some of you use the same oil in the TC as in the diffs. I will be putting some expensive fully synthetic toyota oil in the manual gearbox as i have read on the other forum that this was the only oil that cured the sticky/clunky gear shift.

User manual says:
75w90 for the gearbox and TC (gl4 or gl5)
90 above -18deg c and 80w90 or 80w below -18deg c for the diffs. (hypoid gl5)

If i were to use the same oil in both should i go for 75w90 or 80w90? It will have to be gl5 as diff can only take gl5.
I had it on good advice that I should use ep80/90 oil. So I did.

Thanks paul, does anyone use 75w90 for both?

A different way of looking at this is to ask what would be worse, running an oil which is too viscous at low temps in the TC or running an oil which is not viscous enough at low temps in the diff? My guess would be that the later is a better solution what do you guys think?
Not viscous enough is what you want to avoid. But I can't see you coming to this point - those oil ranges are so close that they will hardly make a difference unless you're running in very cold temps. Do you know something about climate change that we don't? :mrgreen:
If the oil is in fact not viscous enough, then the gears will wear more quickly - as you're unlikely to be way out of the temperature range, the additional rate of wear is likely to be low. If the oil is too viscous (to the extent that it possibly could be in the oil specs you've given), the oil might be a bit slow to coat the gear surfaces but I would think if you take it gently at first, the oil should warm after a while and you'd be ok. Obviously going straight into a heavy load while the oil is way below -18 would not be a good thing.

Beyond using the oil grades that Toy recommends for the 80, I think there is a danger of over-thinking this :mrgreen: Chuck in good quality oil of the recommend specs and call it good!
Andrew Prince said:
Beyond using the oil grades that Toy recommends for the 80, I think there is a danger of over-thinking this :mrgreen: Chuck in good quality oil of the recommend specs and call it good!

I want to reduce the amount of different oils i will need to carry on overland expeditions. If i need expensive oil in the manual gearbox for smooth gear changes then i could either go with what i mentioned above or run the TC on the expensive stuff as well and having a different oil in the diffs. I will enquire as to how much the toyota fully synthetic 75w90 gearbox oil costs and make my decision.
Fair enough, Rob - point taken. Are you talking about carrying spare oil to do routine oil changes (which would be a LONG overland trip) or are you talking about having the oil there for emergencies?

If the latter, then I think the T/case oil would be ok for the diffs if it meets the grade specs. Same story if the gearbox oil specs match those for the t/case & diffs. It also comes down to how much oil you're going to carry - off the top of my head, the t/case holds around 3-3.5l, which is pretty similar to each of the diffs, so are you planning to carry 3-4l to cover a diff or the t/case? If you're going to carry 6l, then you could go for t/case plus a batch for 1 diff. The bottles seem to come in 0.5l or 1l sizes mostly, so quite easy to mix and match and they're easy to pack in nooks & crannies. The likeliest case is topping up if you have a leak so you wouldn't use your whole reserve anyway.

I'm pretty sure I'm using a higher viscosity oil in my t/case (EP80/90 like Paul) and something different for my diffs (I think a straight 90 grade) and mine is an auto, so the gearbox oil doesn't cover anything else really. :twisted:

Hope that helps in some way :mrgreen:

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I've always used an EP80/90 in the TC and diffs or our 80's and now the 100 Rob and it hasn't caused any issues I'm aware of. About a week ago though I decided to pamper the 100 a bit and put some synthetic 75W-90 in the TC :) The TC oil capacity is quite small and (obviously) transmits all the power so I thought I'd have the extra protection of a quality synthetic in there but the diffs have half the power to deal with and much higher oil capacity so I think the ordinary EP80/90 is more than up to the job.
I have just changed my transfer box oil with this stuff, cost an arm & a leg & hope that it's suitable as its all I could get on a Saturday afternoon, the numbers all seem to be correct, it's just that it's fully synthetic, any thoughts?

I have 100series 4.2lrt diesel 1 hz motor 2002 just need to now best way change My front and rear diff oil and what oil to use and how many ltrs of oil to buy be great if u respond thanks