Manual Transmission fluid

[JimT]

So it's about time for the next fluid replacement for my transmission and rear ends. The rears are pretty straight forward gear lube. But the trans has me wondering about different options.

Currently it's filled with the nicely expensive ”mobile delvac 1 synthetic transmission fluid 50”. Only real reason for that is it's what TA used when they did the last drain and fill and so it's what I've been using to top off what leaks out. But it's currently $54/gal or $250-300/pail and with the leak it's really just an experience way to oil coat the underside of the tractor.

The leak is getting worse, but still only requires a top off every 2-3 months (bought a pail 2 years ago and it's just under half empty). I'm wondering if a thicker fluid might help reduce the leak, but not sure what would be a safe option. It's an Eaton Fuller 9-speed converted to 13-speed. In the past I looked up the manufacturer recommendations and they basically said to use what I currently have, but I'm wondering what my fellow real world users suggest?

I operate mainly in New England with temps typically ranging from low teens in the winter to 80s-90s in the summer. Most of my loads are light roofing insulation (about 7-8k on the deck), but sometimes I load up with rolled asphalt (40-45k) or rolled rubber (35-40k). No overweight, usually top out around 65-70k gross, though about 70% of the time I'm grossing high 30's. Half my miles are deadhead. Typically drive around 58-60mph, but when I'm busy I might bump up to about 68mph to stay within drive time limits. Drops the fuel mileage a little, but the extra loads per week more than make up for it.

So what fluids AND brands do you fine folks recommend? I've been using Traveller brand gear lube for engine oil additive. Long winded as always, but I tried to paint a complete picture and hopefully anticipate any questions. And no, I don't personally care whether it's synthetic or dino, just looking to maybe save a little money while maintaining proper performance

[Pigpen 2869]

I have been using Swepco 202 80w90 in the transmission and both rear ends. Havent bought any in 3 years no idea on price. Last time it was 275 a pail

[hookliftpete]

I use 80w90 on axles, 50wt in the trans.

[amermextrucker]

Jim ,

Check out Sinopec , it says on there page its approved by eaton road ranger.

[Rawze]

The gear sizes and clearances calls for 75/90 as being the proper weight for the trans. 50wt is the thinnest you can get away with, and you end up with a bit more wear over the million miles. - 75/90 or 80/90 for the rears too.

Here is a fine example: https://rawze.com/forums/showthread.php?...6#pid52116

[Volvo8873]

I run the upper Midwest mainly and have always ran 80W-90 in the trans and rear ends for years. I change the fluids out every spring and this time around I’m gonna switch to 75W-90 synthetic to help out a little more in the below zero weather. Either Mobil Delvac or Valvoline.

[JimT]

Thanks guys. I was thinking of trying 75/90 but didn't want to go too heavy. I'm no expert on gear lube and the different weights but I do remember reading that the trans needed a lighter weight than the rears. The rears are currently using either 75/90 or 80/90, whatever TA used years ago. 80/90 was what i intended to refill them with.

What's the difference between 75/90 and 80/90? Is it significant? For some reason I had it in my head that 75/90 is synthetic and 80/90 is conventional and otherwise they are interchangeable. But my lack of knowledge here is why I ask first.

[Pigpen 2869]

Everything will work fine with gear lube. Then you have one fluid for all 3 components.

[amermextrucker]

(04-10-2025 )Pigpen 2869 Wrote:  Everything will work fine with gear lube. Then you have one fluid for all 3 components.

eBay.


Regardless of transmission year? I like the idea of 1 fluid for both. I have 2019 LT with manual.