Full Floater Posted May 10, 2016 Share Posted May 10, 2016 Hi fellas! I am about to change the tranny oil in my 1978 RS600l with a 12 speed. Question is, what viscosity of gear oil do I use? Are any additives worth putting in to? Thanks a bunch, Kevin Quote Link to comment https://www.bigmacktrucks.com/topic/45149-12-speed-gear-lube/ Share on other sites More sharing options...
j hancock Posted May 10, 2016 Share Posted May 10, 2016 Mack allows for 90, 80W-90, 80W-140, 85W-140, 140 weights of gear oil. SAE grade of GO-G or GO-H. Shouldn't need to add anything to it. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/45149-12-speed-gear-lube/#findComment-332846 Share on other sites More sharing options...
jkruss82 Posted May 10, 2016 Share Posted May 10, 2016 Lots of oils acceptable, see attached list of Engine and Transmission approved oils. Best not to use additives. Mack approved oils.pdf Quote Link to comment https://www.bigmacktrucks.com/topic/45149-12-speed-gear-lube/#findComment-332858 Share on other sites More sharing options...
Full Floater Posted May 14, 2016 Author Share Posted May 14, 2016 Thank you guys. I will put it 80-90 as that's what I have a lot of. Quote Link to comment https://www.bigmacktrucks.com/topic/45149-12-speed-gear-lube/#findComment-333246 Share on other sites More sharing options...
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