Trans Lube

[RocketScott]

Cummins 444xt (ish), 0 miles
Eaton Fuller 18 speed RTO, 550K miles (?) unknown history

I got my truck out of the shop on Wednesday. Six months after going in. I'll update my 'moving home' thread when I get a chance...

Driving back to my shop I noticed the trans was noisier than before. More noise when in OD but both that and direct were louder than I remember. Could be that I forgot what it sounded like in six months but I doubt it. The noise wasn't bad at the right RPM, if I let off the pedal or gave it a little too much it got worse

The shop refilled the trans with synthetic. I'm pretty sure it's always had conventional. Should I drain that out and go back to conventional or if it's normal to get more gear noise with synthetic? Possibly there are other issues?

[Rawze]

use synthetic if you have temperature extremes, like in cold northern climates. Otherwise, it is not necessary. That choice is dependant upon application.

use 75/90 or 80/90 instead of 50wt too.. 50wt is not nearly as protective for a truck tranny than a decent 75/90 is.