Gear / Tranny Oil

[TallBoy441]

I have a 2004 T800 log truck and it’s time to change the tranny & rear fluids. I know it calls for 50w tranny & 75w90. I was thinking of just going with 80w 90 in all three. Does the 80w90 meet manufactures requirements ? What’s the pros & cons. I’m in south Ga so don’t have a lot of cold weather here. TIA

[Waterloo]

That is what I run in my Eaton 18 speed, the gear oil, same as the rear boxes, no issues up here in Michigan.

[TallBoy441]

(11-29-2019 )Waterloo Wrote:  That is what I run in my Eaton 18 speed, the gear oil, same as the rear boxes, no issues up here in Michigan.

Waterloo, does it need to be 80w90 synthetic, or regular ? Someone told me once synthetic can’t go back to regular, it won’t stick or something. Just trying to learn here, because don’t have any knowledge on the subject.

[Waterloo]

It was semi-syn, and it was Mobil One, had Speedco down at Rawze's place in Jackson GA change the transmission fluid out. I run the same in the boxes. No issues.

[HES]

I've heard that is an old wives tale that once you go synthetic you can't go back. I would just shrug and tell these broads you'll never replace the real deal lol.

[Rawze]

(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.

[smorgan87]

{post removed by Rawze: more bulls#it}!

[Curtisj28]

"They" say film strength is better in synthetic. But "they" say alot of things. I use mobile synthetic 50 in trans and 75-90 in rears. I change it every 150-200k. Probably overkill but haul heavy. Also can check for metal bits that way. 1.3 on truck and everything is original. As long as you regularly service I wouldn't see an issue running either. But in my application I prefer synthetic. Extreme cold and heat heavy 95% of the time 90-100k lbs. Probably just peace of mind.

[Mattman]

About to service my transmission. Did I see something that was put out by Eaton about gear oil being just as good as the sae 50 transmission fluid? I can't find it now but know I saw the right up.

What is everyone running in front hubs on steer axle?