I have a couple 10 bolt Posi's I'm refilling.
How many bottles of additive do I need and what is the recommended gear oil...80w90?
I'd like to go synthetic if possible.
Thanks.

 

Well, for volume that's in your owners manual - it takes 4.25 pints. 80-90 weight should be fine. Just add the posi lube first, then top up your gear oil until its at the top of the fill plug hole. You can get a fill tube adapter to screw onto the posi fluid and gear oil top so it's easier to fill. Far as I know you should be able to use synthetic without any problems. Might even be better in cold temps because of the way the molecules are spaced.

 

I don't see a spec anywhere for the ratio of posi additive...one 4 Oz bottle per refill?
Thanks.

 

1 should be lots. If you're going to synthetic (like Mobil1 75W 90 LS) it's supposed to have the additive already in it. http://www.mobiloil.com/USA-English/..._75W-90LS.aspx
I haven't used it, but I use synthetic motor oil and it will find any weakness in seals and leak out. If you have any issues with leaking pinion or axle seals, synthetic will likely find them and create seepage. O'Reillys has it for around 11.00 qt. You could probably get the bigger 5 gallon size if you're doing a lot of pumpkins and want to save by using bulk.

 

Thanks for the tip on the 5 gallon bucket...should last me a while...a good excuse to change out all the rears...most guys forget all about them.

 

GM recommends using only one bottle of additive. More could cause it to slip too much.

 

A lot of guys will add only 2 oz of the stuff and see how it runs, you can always add the remaining 2 oz if you need it.

 

One bottle or tube or additive.Do NOT use synthetics with a clutch style posi unit.It is more harm than good. 80/90 is the norm,but I put 85/140 in all of my rears.

 

I bought a gallon of 85-140,but was thinking I should mix it with some 80-90.
The pour point is quite high for the 85-140.
3 qts gear lube and one bottle of posi additive did the trick...