gearbox oil

[Powertruck31T]

Just wondering what engine oil is everyone running in there gearboxes? I'm running a Total product at the moment Rubia 7400 which is a 15W-40. Its the same oil I run in the engine. I find in the gearbox it's still quite crunchy. Has anyone had any good results off any particular oil that seems to suit these gearboxes?

Jarrad

[geeves]

Modern engine oils have friction modifiers that are great for bearings and rings but they coat synchro rings making then nice and slippery which isnt what you want.
I saw an advertising display that quoted Total as having the best friction modifiers.
3 options for gearboxes
Isuzu quote same grade oil as engine But use the cheapest oil you can find The $10 special will work better than the $60 synthetic
ATF is excelent option but can cause leaks
Several cos make oil for 5 speed boxes Dont worry about the fact that it says 70/90 or similar. They are gl4 oils and use a different viscosity scale

[Powertruck31T]

Hi Geeves thanks yea the Total oil works really well have run it in my engines for the past 12 years it's good stuff. I spoke to the Total rep yesterday and he recommend I go to the cheaper grade oil with less friction modifiers just like you said. They have come across this problem before in these trucks. I've got some coming for Monday so will switch it over and see how it goes. What do you run in the transfer same oil?

[geeves]

same