Originally Posted by 4 Jaw Chuck
It is not commonly known in many circles but the original posi trac additive used in rear axles is an extract of fish oils, normally called a friction modifier on the bottle.
Yes, the old school GM friction modifiers used to be made from whale oil. For obvious reasons todays GM friction modifier is synthetic. These modifiers usually dont smell very nice.
A buddy has an 85 IROC-Z and he changed the fluid and didnt rpleace the friction modifier. He did some slow speed figure 8's in a parking lots and teh clutch plates grabbed and chattered. Got one of those small bottles of GM friction modifier and 1 slow speed figure 8, the posi plates slipped with nary a single chatter.