Quick question here guys. I have an '89 Trans-Am with the posi rear diff. Can I just use synthetic Valvoline 75/90 gear oil or do I still need the posi additive with the synthetic. On Jeeps with Dana rears, I think we had a synthetic at the dealership that didnt use the additive. Might have been in the oil we used though. Anyway, thanks in advance.

 

look at what it says on the bottle. Usually it will tell you if you will need the posi additive or not.

 

Well, the bottle says it is recommended for all standard and limited slip hypoid differentials. But is it recommended so logn as you put the additive or does that mean it can replace the additive. I just dont want to mess up the rear end on this car as it already has enough miles without being put through any extra strain of incorrect gear oil. Thanks again.

 

you shouldn't have to put the additive in. But I guess if your paranoid about it you can put it in too.

 

this is a debatable subject...

if your car has the 9 bolt rear end, its a cone type differential in which it needs friction to act like a posi. if you add a posi additive, it will cause the posi to slip and act like a peg leg.


now some ppl have added additives and have had great success with it.

so some say dont add it, some say do. i'm leaning toward dont add it if its a 9 bolt rear.

 

It has the 3.27 "aussie" rear end...so Ive heard anyway. Im not exactly sure when it comes to driveline stuff beyond the engine and tranny. From what I have gathered, the aussie diff. is a 9 bolt right? Anyway, right now it is filled with only the Valvoline synthetic gear oil. If I had to add the additive, I would just syphen out a little and add the additive. Its not that I'm paranoid about it, just not sure and thought I would ask. Wouldnt want to find out through driveline noise if you know what i mean. High miles and extra strain generally result in costing me money...especially me hehe. Thanks again.