72cutlassdog

I was wondering what is a good gear oil to use and weight? I have a 72 cs.

RandyS

80-90 weight gear oil.

72cutlassdog

should I use synthetic or not?

monzaz

Usually with Limited slip we use the NON synthetic and open (non posi) or torsen worm gear limited slip you can use the synthetic.
If you change your rear diff oil even every 20k-30k (common manufacture numbers are 30k -50k ) you really should never need synthetic. We have parted out 1000's of rears and none were synthetic back in the day and had been probably NEVER changed over 100K miles...lol. all looked good... Key is never let the oil go low or run out of oil....IT ONLY TAKES ONCE to screw up the gears.
weight really does not matter much...
rule here. thicker viscosity for the hotter southern states and thinner for the northern states OR depends on racing or not racing etc.
Thinner oil can give a slight advantage in drag racing etc. but for a road race car after 5 mins or a couple laps the oil is thin as water anyway. More oil changes / or frequency for towing vehicles... common sense really

Jim
JD Race