Gear / Tranny Oil

[tree98]

I run 75/90 synthetic in my rears and steers.

[david24]

(11-29-2019 )Rawze Wrote:  

(11-29-2019 )TallBoy441 Wrote:  ... Someone told me once synthetic can’t go back to regular
...

I would say to stop listening to the droves of idiots on social media.

NEXT: You should be changing your oil in the gearboxes every 2 years or 250k miles (whatever comes first) if you value your equipment long term. The oil in gearboxes separates (also known as "additive precipitation") long before it goes bad, and when it does, it accelerates wear.

ALSO: there is absolutely no significant difference in wear protection on those gear boxes in mineral oils and synthetic oils if your not going into extreme environments all the time. - Synthetic's only advantage over mineral oils is the fact that it does not get thicker in extreme cold weather nearly as badly. (or thinner if your hauling heavy stuff above 80,000 lbs) You being form GA, and not from northern canada, regular oil should be just fine for most people.

AND: its perfectly fine to run 75/90 or 80/90 in the tranny. The lubricated components will actually last longer with the slightly higher viscosity oil in it. I have run it on mine for the last 1.3 million miles and tranny is still running strong, never been rebuilt yet. Passed inspection of all gears for wear, etc. at 1.03 million. -- I also get 9+ mpg in my truck average, so the horse-garbage that it makes for poor fuel mileage is nothing but that. It will have slight effect, only tenths or so unless ur running 70+ mph everywhere.

-- That is my own experience, I am sticking to it.

I have an automatic. Does that change anything or can I use what you suggested?

[Lonestar10]

Unless it has a torque converter its automated which means it's just a manual with an air controlled clutch and shifter. So yes all still apply

[Mattman]

Changed my transmission and rear ends today. Used 80w90 GL-5 in all three. About $45 a bucket at local oil and fuel distributor.

Transmission had fine metal shavings on drain plug.

Rear ends had larger metal shavings. Didn't see anything to be worried about. Hopefully can get lots more miles out of them.

[Tony]

Is it ok to use a 75w90 if its GL-5 rated?
(Eaton 18 speed for reference)

[Rawze]

(10-31-2025 )Tony Wrote:  Is it ok to use a 75w90 if its GL-5 rated?
(Eaton 18 speed for reference)

what does the tranny call for?.

if it is a typical RTLO tranny the yes, the 75/90 is preferred over the 50-wt trash.

[4ways]

(02-06-2020 )david24 Wrote:  ...
I have an automatic. Does that change anything or can I use what you suggested?

Match your transmission with the Eaton recommended oil.


https://www.eaton.com/content/dam/eaton/...mt0021.pdf

And use a good oil coalescing air dryer filter to protect the sensitive sensors in the automated transmission. They’re pricey but probably cheaper than transmission problems.

[Tony]

So I know MY eaton requires PS-386. But about all the 75w90 oils I find are GL5 rated which have EP (extreme pressure). Which is where my lack of knowledge comes in.

Eaton doesn't recommend EP oils. But I know some people use 75w90. So thats why I was trying to confirm the GL5 rating

[Rawze]

(Yesterday )Tony Wrote:  So I know MY eaton requires PS-386. But about all the 75w90 oils I find are GL5 rated which have EP (extreme pressure). Which is where my lack of knowledge comes in.

Eaton doesn't recommend EP oils. But I know some people use 75w90. So thats why I was trying to confirm the GL5 rating

You might be confusing auto-trannies with stick trannies?., - They are very different from each other ...

If it is an automatic tranny, or an auto-shifter, use what is recommended only. Otherwise, you will likely have issues. they are simply built different than stick trannies.

If it is a manual tranny,.. like an an RTLO, etc... then 57/90 is the recommended wt oil for highway use,.. (and the 50-wt for lighter duty stuffs / line-haul),.. although I would never run mine with 50-wt, as I have seen more wear inside trannies with only 50-wt used in them.

here is mine (a typical eaton, RTLO style manual tranny) after 1.4 million miles of running 75/90 in it, with pictures ...
https://rawze.com/forums/showthread.php?...6#pid52116