Gear Oil Recommendations

[ANDYS87]

I want to change the gear oil in the differential of my 87 GN. I want to use a synthetic, but what is a good brand? What weight to use? and do synthetics still need the anti-slip additive????? My car is a street driven garage queen, that will never see the track. But I am planning to make it a FAST street car, in the range of 11.5 to 12.0 sec....if I ever did take to the track to verify! Thanks

 

[Quick6'n'-K.C.]

3 quarts 80/90 royal purple synthetic from napa, 2 - 8oz full bottles of GM posi additive is the treatment your cars rearend needs...

Yes,all rear fluid including "posi" fluid needs 2 8oz full bottles of posi fluid, no matter regular 80/90 or synthetic... needs friction modification and that will cure any rear end chatter that may occur when turning a tight corner.

Also, i dont use a rear end gasket at all, just some sealant RTV black is fine if everything is clean.
BW

 

[ANDYS87]

Thanks for the reply.

I have 2 questions: 1. Doesn't that GM anti-slip additive only come in 4
ounce bottles? Or is there an 8 ouncer like you said?

2. I have an aftermarket rear end cover with a drain
plug. It looks deeper than the stocker. If it now takes
more than 3 quarts to fill, should I add another
bottle of anti-slip?

 

[mybuick]

just stick with the 2 quarts.

 

[Blown&Injected]

I would think that the level not the quantity would be the determining factor - why only 2 qts if the aftermarket cover alters the capacity?

I have always used conventional 80w90 and one 4oz bottle and managed to get about 300K of excellent operation.

 

[Quick6'n'-K.C.]

I was wrong, they are 4 oz bottles, totalling 8 oz for the rear....

I would add the posi additive and then start adding the fluid till it runs out.
BW

 

[turbopaul]

I would only add the posi additive if the rear chatters. You also need to check that the posi works at least 4 or 5 times a day

Paul

 

[fast eddie]

You wont need the additive with Royal Purple

Ed