I am looking at putting a posi differential in my RS... Is it alright to use 85 140 plus posi additive when the differential calls for 80 90? Any input would be appreciated.

 

85-140 = wheel bearing grease, compared to 75W-90 or 80W-90 which is more like thick oil

No it is not alright.

Use the right stuff. It's cheeeeeeeeep eeeeeeeeeezzy and plentiful. Follow the recommendations of the mfr of the posi you end up with. Don't go out of your way and do extra work just to do damage.

 

Why would you want to use the thicker oil? There is no need to do that. It will run cooler with the correct oil.

You didn't say which differential you have. That makes a difference in what additive you need and how much. So what do you have?

 

Well, I believe It's a 10 bolt posi, and it's in an 87 Camaro. The differential works fine and both tires will spin, but I can hear the ring and pinion gear whine a little, so I thought about using heavy duty 80 140 to quiet it down till I can have them replaced.

 

If it's the original differential then it's probably an Auburn, but it could be a Governor Lock. The Auburn needs the oil additive, but the Gov Lock doesn't. If it's making noise then check the pinion nut to see if it's still tight. If the nut is tight then you probably have a bad bearing, or the gears are worn out.

 

Well, to my knowledge 80 140 is a thick differential gear oil, and not grease.

 

Relatively speaking, it is.

About like if your engine oil called for 0W-20, and instead you put 20W-50 in it.

It's the wrong thing for your car. Stick with the right stuff. Nothing to be gained by taking the extra risk, but everything to lose. Not a hard decision for a logical person.

 

Sofakingdom, I believe in what you are saying. It's what I don't understand is what's the issue is at hand, and that is; would it harm the differential in any way if I used the heavy duty lube?

 

Not in warm weather. When it gets cold it will take longer for the oil to start flowing and then it might cause a problem.