Just for fun I thought I would go to the horses mouth for a recommendation.
There has been a lot of talk on the lists as to which type of oil to put in a
gearbox, differential, and lever shocks, so I wrote a letter (Yes, snail
mail!) to Red line. I asked them to tell me what to use in my 1977 MG Midget.
(All standard 1500cc stuff.) In their own words:
"...In the transmission, I would recommend Red Line 75W90NS.
In the differential, I would recommend 75W90.
The difference between the two fluids is the friction modifier in the 75W90,
this helps reduce the temperature of the fluid and on the gear face as well as
reducing chatter if a clutch type limited slip is installed. While this fluid
works well in a differential, it can be too slippery to work well with the
syncros that need friction to work properly.
"In your shocks I would recommend the Heavy Suspension Fluid as the closest to
a '20W' fluid. Different 20W suspension fluids can vary in viscosity, so you
may need to blend the Medium with the Heavy to achieve the desired viscosity."
This was in the letter from Dave Granquist at Red Line. He sent along a lot
of literature on Red Line products, and a sticker. I was surprised that
"Different 20W suspension fluids can vary in viscosity..." I thought that the
"20W" was a way of indicating the viscosity across manufacturers so you can
always buy the right product for an application.
Anyway, that's what Red Line has to say about gear oils, FWIW. Remember that
this is for a late Midget 1500. YMMV.
'92 Mitsubishi Expo LRV Sport