Question about transmission and rear differential oil
 

This is for the 2015 Manual Transmission BRZ Limited


I thought there was only transmission oil and rear differential oil? But upon reviewing the manual and their website for maintenance, there’s a lot of different names for them. Are they all the same or are they actually different oils that need to be maintenanced? Also, I've heard the term manual transmission oil, is that another type of oil is is it the same thing as rear differential oil/differential oil?

48k miles service- inspect transmission gear oil
60k- inspect ATF/transmission fluid
72k- inspect transmission gear oil

48k- inspect rear differential gear oil
60k- inspect rear differential fluid

60k- replace rear differential gear oil



https://imgur.com/a/ZafpqP3https://imgur.com/a/ZafpqP3

You are correct, the components are a transmission and a rear differential. In this case the terms, "fluid" and "gear oil" are interchangeable, however, that's not to say that the fluid/gearoil itself is necessarily interchangeable between the components.

Motul claims their 300 Gear Oil can be used both in the transmission (manual) and the differential. Most just use Subaru's Differential Oil without any issues.

This has been covered a lot before, and in conflicting ways. Based one the spec called for in the owners manual I went with the below products.

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I know many people will sell the Motul as being suitable for both the transmission and differential, but if you ever have a warranty issue with the transmission then the dealer may not be able to get Toyota to cover it unless you can prove you used the proper spec fluid.


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Motul 300 is a proper spec fluid.

Here is the research I did before delving deeper into the meaning and spec of GL-3, 4, and 5:
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https://uploads.tapatalk-cdn.com/201...ca06a4e233.jpg
https://uploads.tapatalk-cdn.com/201...c3dc79f431.jpg


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My decision as well. I don't trust that it's truly safe for the brass. There's no harm in using a straight GL-4, especially when the gearbox requires only GL-3.

It's safe for brass in an environment where the brass components are not synchronizer rings. The buffer that coats the yellow metals and protects them will flake off by the inherent action of syncros and in the process, it brings a small layer of the substrate brass itself with it. Just use the correct GL3/4 from the get-go, instead of something that has a bandaid applied to it in an attempt to make it work in the wrong environment.

GL5 in a hypoid gear environment like the rear diff is perfect.

Yes, thanks for expressing that distinction. This is exactly my understanding of the accelerated-wear mechanism. Crispy crust over a soft center is good for M&Ms but not for synchro clutches.

It doesn't help that Motul is both tight-lipped about their formula and use weasel words in their application info. If they were truly confident in their product, I would expect them to use big bold font instead of burying it in small print.

For what it's worth, I dropped the trans and diff oils at 12000km and they were very soiled from the break-in period.

I went amsoil synchromesh in the trans because 2nd was tough to get in in cold weather and 75w140 gl5 in the diff.

I just changed again today, 11000km later, went to amsoil 75w90 gl4 in the trans, synchromesh was a bit too thin and brought out the noisy side of the gearbox, the gl4 shifts much smoother and quieted down the box. For the same reason, I went back to dinosaur gl5 in the diff, but what I had on hand was a bit thicker than stock at 80w90. That should hardly make a difference.

https://uploads.tapatalk-cdn.com/201...e1ae40a86f.jpg
This is what the differential drain plug looked like with 20k miles on the OEM fluid.


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Pentosin MTF2 in the trans. 75w-80
Motul 300 in the diff 75w90

I did mine at 40k. Didnt even look dirty. Im now around 53k, trans feels great.

https://s.yimg.com/aah/rodi/pentosin...l-liter-23.png