Auburns site calls for a GL-5 oil with their posi units. Royal purple states that it is a GL-5 oil and one of the better ones.

http://www.royalpurple.com/prodsa/mgeara.html

 

Auburn's site says to use 80W90 GL-5 non-synthetic. Royal Purple is syntetic.
What year is your car?

 

98 Z28

 

I see nothing in the '98 owners manual saying to use synthetic. I will say I used synthetic in my '95 when I had an Auburn with no ill effects. Currently have an Eaton and use non-synthetic.

 

When installed correctly, gears should not whine.

 

Look at page 6-26 of the 98 camaro owners manuel. It clearly states 75w 90 synthetic fluid.

 

I did my gears and was careful as I could be. They now whine on the coast side above 30 mph. Kinda disappointing but it's not bad enough to put me through the work again. BTW, certain gears are more prone to whine because of the composition; or so I've been told....

 

https://www.mygmlink.com/pdf/go2cont...1998camaro.pdf

Here's the manual I'm reading. Don't see the word synthetic on page 6-26.

Do you mean GL-5? I believe the GL stands for gear lubricant.

API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.

 

I'm talking about the actual owners manual that came with the car of the lot.

 

Not sure what you mean, that's what these are.

http://shbox.com/pdf/manuals.html

My '95 owners manual is the same as the '95 in the above link.

 

No, theres a blue book that comes with the car from the dealership when the car was bought brand new. I'd trust what came originally with the car when it was made more than anything else.

 

Go to the blue one, the sixth one down on the left. go to 6-26

 

I see. Don't know about that book. Whatever you're comfortable with.

 

I read what auburn suggest for thier posi units which is a 80w 90 nonsynthetic. I just bought two bottles of valvoline 80w 90 and two bottles of additive. Thier site says to use 3 oz of additive per quart, each bottle is 4 oz so ill use about 1 1/2 bottle of additive. I'll give this a try.

 

Unless they get the gears set right the first time there will be noise. Once the gears have been broken in they will have a wear pattern and reshimming will not get rid of the noise. There are some gear lubes that will help reduce noise because they will stick on the gear better than others even the same viscosity.