Jack the rear of the vehicle up, put in neutral and turn the wheel. If the other wheel turns in the same direction it is a posi-traction or limited slip, if the opposite wheel turns in the opposite direction it is not a posi. These rear ends give many problems though. I doubt friction modifier will solve your problem unless it makes a slight popping noise in very slow turns like in a parking lot.
Rear diff does require friction modifier.
75w90 or 80w90. If limited slip it will require 4 ounces of friction modifier.
FRONT AXLE ± 0.3 L (2 oz.) C200F 1.7 L (57.5 oz.) C200FE 1.7 L (57.5 oz.) REAR AXLE ± 0.3 L (2 oz.) C213R 2.07 L (70 oz.)* C213RE 2.24L (75.5 oz.) *Vari-Lok, add 0.07 L (2.5 oz.) of Friction Modifier.
Trac-Loc axles require a friction modifier to be added. Crawl under your GC and look for a metal tag under one of the bolt heads that says to use the friction modifier. You will likely have to wipe the tag off to read it. My tag was at about the 4 o-clock position on the rear of the differential. Do you have the factory tow package? I believe limited slip diffs were part of this package. You can also go to http://www.jeep.com/wccsapp/universal/J/index.jsp?appStr=wccs&titleStr=Contact+Jeep&familyStr=brand&franchise=J&actionURL=%2Fwccs%2Fbrand_forms%2Fus%2Fwebform.jsp&promotion=null&category=U and request your 'build sheet' which they will email you in a few days. It will tell you if the GC left the factory with the Trac-Loc differential.
75w90 Gear Oil, preferably high-end synthetic (not just Mobil 1, but Redline or Royal Purple). Non 'open' differentials may require a friction modifier.
You can purchase a friction modifier from your local auto parts store. It is used as an additive to the gear oil in a positraction differential.
2.5L and friction modifier additive
Rear diff does require friction modifier.
80w90, does not need to be synthetic. If limited slip it will require friction modifier additive.
75w90 or 80w90. If limited slip it will require 4 ounces of friction modifier.
Almost 4 quarts 80w90 If posi. it requires 7 ounces of friction modifier.
i believe its 2.1 quarts to be exact and if you have a trac lock (cop cars etc.) it needs the friction modifier.
In a 1997 Ford Aerostar ( REAR differential ) With the 7.5 " ring gear ( 3.5 U.S. pints ) With the 8.8 " ring gear ( 5.0 ) * traction lok , add 4 ounces of friction modifier
The 1995 Chevrolet C1500 PU came equipped with multiple differential sizes. However all can use 80W90 GL5 gear oils. If the differential is limited slip a bottle of friction modifier may also be needed.
90w ======================================================== According to the 1996 Ford Explorer Owner Guide ( 80W90 ) for the REAR differential * if you have a Ford Traction-Lok add 4 ounces of friction modifier
On a 1995 Ford Explorer : According to my owners manual : Rear differential ( 5.5 U.S. pints ) plus ( 4 ounces of friction modifier if it is a Ford Traction-Lok ) of Motorcraft Premium Rear Axle Lubricant
According to the owners manual for a 1999 Ford Ranger ( all applications ) the rear differential takes 5.0 - 5.3 pints ( 2.4 - 2.5 liters ) of Motorcraft SAE 80 w 90 Premium Rear Axle Lubricant . If it is a Traction - Lok differential include 4 ounces ( 118 ml ) friction modifier for a complete refill.