Rear end fluid

[wordy1]

What rear end fluid should I use? Do I need to go to the dealer for the posi additive? And do I need to use 2 bottles of it. Car is a mid 11 second car so I don't want to mess up the gears. Also, should I replace the pin?

 

[Lynn D. Brown]

Rear fluid

I guess the 1st decision is whether to go synthetic or not. I have previously tended to go synthetic or all fluids, but have since concluded that I don't want it in the trans because it may be too slippery there, and I think U need some friction for the band surfaces to hold ? I think either will work in the rear, and I went ½ & ½ on my last fill just because that's what I had on hand. Come to think of it we also have clutches there in the Ltd Slip, so maybe U want some friction there also.

I have a new Eaton ready to go in (no hurry-that's another story), and I noticed that they said NOT to use synthetic. Maybe that's because of the limited slip ? For pure lubrication, like the engine, synthetic should definitely be better. Another thing, I think synthetic is more prone to leak.

So, I guess my conclusion is a good quality petroleum based fluid like Castrol, etc. and check the label to see if it passes the GL-5 test. One mechanic told me to get the specific GM additive rather than store brands, so I bought some from GM for ~ $5./bottle.

 

[wordy1]

I too have an eaton posi unit, I talked to the technical support line there and they recommended GM or comparable GOOD quality 80w90 with 2 bottles of GM posi additive. A single bottle is ok, but under higher temperatures the extra bottle of additive helps against wear of the posi unit. With a stock posi unit 1 bottle is fine. AutoZone rear end fluid will just not cut it at higher temperatures. The Parts Plus 80w90 is rated at the same standard as the GM rear end fluid as is their posi fluid and cost me $2.79 a bottle. Total cost was $18 for the fluid and additive, thanks for your input.