I have a 2000 Standard C 5 Convertible. I will be changing the rear gear oil in the near future and I find many brands available with and without friction modifier included ( LS designation usually). Has anyone found it necessary to add additional friction modifier to the likes of Royal Purple, AMSOIL or Mobile 1 that all state the friction modifier is included? Also can there be too much modifier in the oil? Thanks in advance.

 

I did 2 quarts of Amsoil and one tube of their friction modifier last diff fill

 

I have just used the GL-5 lube with it own modifier and did NOT have to add any. Go that direction.
Do some lube/clutch break in tight figure 8 turns and if the clutchs chatter, add some more modifier till your diff is happy.

The modifier allows the clutches to slip against each other the proper amount in tight turns.

IF,,,,,, YOU add to much, YES, it could adversely the limited slip clutch operation. I would rather add not enough then blindly dump in a load of modifier. Adding not enough will only cause the clutches to chatter against each other in tight turns. It will not damage the differential to figure out if you need to add more.

RECOMMENDATIONS: Before you change the rear end lube, check to see if your clutches are working correctly!

Jack ONE rear wheel off the ground. Trans in N, park brake off. Attempt to ROTATE that one wheel. It will take some force as you are slipping the limited slip clutches. If you have a 33mm deep well socket and a torque wrench, you can get an exact Torque that it takes to break the wheel free. If you don't, you will just need to get a good guesstimate on what it feels like and then do that same procedure to the other wheel.
They should both be about the same torque. If one wheel has really light break away torque, its likely that you have a broken Belleview Clutch Pack Spring.

Another note!
1. ALWAYS remove the Diff FILL PLUG first and then the drain plug!
2. The drain plug has a small metal ring washer on it. It normally sticks to the diff housing and falls off during the drain procedure. You wont find it until you dump the old lube into the waste container . You will have to remove the drain again to reinstall the seal washer. If the diff has been refilled, well, you know where this is going!

Bill

 

I've always used Amsoil 75w-90 which includes limited slip friction modifier. I have never found that I needed more modifier. If you add too much you'll just turn your limited slip into an open diff.

Good tip from Bill about checking the torque. Our diffs have a bad habit of snapping that spring washer and it eventually takes out the whole diff.

 

I have used AMSOIL Severe Gear 75W-90 in several C5 diffs without additional friction modifier and never had issues.

https://www.amsoil.com/shop/by-produ...-EA?zo=1934716

 

As stated above, if it's included there's no need to add more.

 

My 03 Z06 just turned 6K miles should I change the trans and diff fluid?

 

If it's never been done before then yes, the factory fluid does break down with age.

Steve

 

Thanks than I shall getter done!

 

I’ve put 8,000 miles on since I serviced the rearend with redline product, no additional additives and no problems.
cruzbox

 

I've used OEM, amsoil, and valvoline products for LS diffs. When I change my Z06's fluid I'll use Amsoil. (It seemed to have more consistent performance over time vs others I've used)

 

Just use oem. It’s what the manufacturer recommends and switching products only causes more headaches. Here’s a wheel. Don’t reinvent it.