Latest on Diff. Fluid ???

[TX '90 ZR1]

OK. I stayed up way too late last night reading all the posts about using additive in our differentials. There are a lot of them, and the opinions seem to vary widely.
Using Mobil 1 75W-90 I saw everything from "It (additive) is not needed" to "Add 2 bottles" of the additive. One was "Use as needed".
My understanding is that the additive is formulated to reduce friction. On the surface this sounds good. BUT, if friction is reduced too much it could interfere with the function of the clutches. Too little and it could produce chatter.
Maybe there is not an answer that applies across the board. Amount needed could vary from car to car depending on mileage, type of use, etc.
So, after probably getting way too far into the weeds on this, the question.
WHAT DO YOU GUYS DO ?
Is the currently available additive still the same formula as it was when our cars were new?
Here we go !

[RussMcB]

"Use as needed". That's pretty straight forward, huh? :-)

[efnfast]

Amsoil says it's not needed unless you get chatter. I just did my fluid and added a little, less than recommended. I figured it was easier to add than try to remove some.

[WVZR-1]

I'd be inclined now to use the actual Spicer/Dana #43161 Additive and avoid likely all others. The GM additive like any other other lubricant has undergone many refinements. The 'original' GM additive was actually a sperm whale derivative that was reformulated long before the '90 production. Reformulated since? I'd certainly think so. I've seen the 'original' used when assembling rockers on older 216/235 GM 6-cylinder, some of the very old Jeep OHC also.

I've never used synthetics for rear axle lube either. Spicer/Dana I don't believe ever spec'd synthetic for the Trac-Lok.

Conventional lube like the FSM and a change to the Spicer/Dana 43161. Spicer/Dana mentions 1 (4oz)

For the later Trac-Loc in the Jeep (Super 44) they spec'd 80W90, only in the Hydra-Loc did they change the spec to synthetic (2000/2001)

[TX '90 ZR1]

Thanks for the replys Guys.
I think I will go with the Mobil 1 straight & test it. If I get any chatter or premature lockup I'll add some of the Dana/Spicer.

[jss06c6]

I changed the oil in my '91 when I had the drivetrain down during my transmission rebuild and used Mobil 1 75-90. No additive. Have put about 750 miles on it and it remains dead quiet. Interesting analogy is that the Gen V Camaro SS I just bought for a daily driver was chattering like hell when cold. TSB called for change to AC Delco LS Gear Oil. After the swap, and 500 miles, the clutches are quiet.

Sent from my QTAIR7 using ZR-1 Net Registry mobile app

[Dynomite]

Originally Posted by jss06c6

I changed the oil in my '91 when I had the drivetrain down during my transmission rebuild and used Mobil 1 75-90. No additive. Have put about 750 miles on it and it remains dead quiet. Interesting analogy is that the Gen V Camaro SS I just bought for a daily driver was chattering like hell when cold. TSB called for change to AC Delco LS Gear Oil. After the swap, and 500 miles, the clutches are quiet.

Sent from my QTAIR7 using ZR-1 Net Registry mobile app

Yep........3.2 pints - Mobil 1 - 75W-90 Gear Lube Limited Slip