The Auburn Gear High Performance limited slip (cone type clutches) in my '05 F150HD requires a conventional gear oil (and let's not have that discussion again) with a friction modifier (FM) added 3 oz./qt. of gear oil. I had been running a 80W90 but wanted a better cold weather/warmup viscosity so went with the Valvoline conventional which has a better VI.
You can buy the Valvoline with or without the limited slip FM added and I bought the "with." The amount added is unknown. I wanted to see if the oil was adequately treated for my diff so I didn't add any FM. I can report that the Valvoline 75W90 conventional w/LS additive is INADEQUATELY treated with FM to forestall clutch chatter... at least in the Auburn gear LSD.
It took a while but clutch chatter gradually started. A total of six ounces of Auburn's LS additive, added two oz. at a time, was required to eliminate the chatter. With a Mag-Hytec cover my diff takes 5 quarts so according to Auburn's formula, I would need 15 oz of FM. If the elimination of chatter is an adequate measure of adequate FM treatment (according to Auburn Gear anyway), then the Valvoline oil was loaded with FM to about half or 2/3 of what is required for the Auburn. Other LSD may be different.
After looking at some Ford and GM manuals, it looks like the standard GM and Ford additive rate is around 2 oz/qt. but the manuals are quick to caveat, "or as required." I conclude that the Valvoline for limited slips might be "adequate" in for a plate type limited slip in many situations but an owner should be ready to add more FM as needed. It appears that the cone type clutches, which do not use plates or a friction material, need more FM than the more conventional plate-type LSD.
You can buy the Valvoline with or without the limited slip FM added and I bought the "with." The amount added is unknown. I wanted to see if the oil was adequately treated for my diff so I didn't add any FM. I can report that the Valvoline 75W90 conventional w/LS additive is INADEQUATELY treated with FM to forestall clutch chatter... at least in the Auburn gear LSD.
It took a while but clutch chatter gradually started. A total of six ounces of Auburn's LS additive, added two oz. at a time, was required to eliminate the chatter. With a Mag-Hytec cover my diff takes 5 quarts so according to Auburn's formula, I would need 15 oz of FM. If the elimination of chatter is an adequate measure of adequate FM treatment (according to Auburn Gear anyway), then the Valvoline oil was loaded with FM to about half or 2/3 of what is required for the Auburn. Other LSD may be different.
After looking at some Ford and GM manuals, it looks like the standard GM and Ford additive rate is around 2 oz/qt. but the manuals are quick to caveat, "or as required." I conclude that the Valvoline for limited slips might be "adequate" in for a plate type limited slip in many situations but an owner should be ready to add more FM as needed. It appears that the cone type clutches, which do not use plates or a friction material, need more FM than the more conventional plate-type LSD.
