To Gear Oil Freaks,

I've tried about all the different gear oils out there, and I totally believe there are advantages of going synthetic. One thing I've noticed though, is that not all synthetics are created equal. Nissan trannys do not like overly light viscosity gear oils. I had no luck with "ultra-light" stuff like ATF, or even Redline MTL. I believe you need some thickness(cling) to keep lubrication of all the gears and synchros.  Also, extra thickness helps to absorb the shock-loading of aburupt engagement or hard acceleration over rough pavement. 240's have an inherant sloppiness in the driveline, and those qualities are magnified(sound) with thinner gear oils.  I have had excellent results with Redline Synthetic Products over the years. From my experience with their products, the recommendation I have for all 240 owners is:

Redline 75w-140NS for the transmission (excellent for old synchros)
Redline 80w-140 for the rear differentials

I have used this combo on my car for many years. Even with lightning fast shifting and occasional mishaps, my tranny showed no signs of fatigue or wear. (I cracked it open to check and change seals.) I am currently testing the REDLINE Heavy Weight Shockproof Gear Oil in the transmission, because it offers additional shock-loading resistance.  So far so good... I hope this information helps.

Simon Kim. S13