Join Date: Apr 2008
Location: Central Florida
For the AMC-20 the important thing is using a "GL-5" 75+/- to 90+/-W oil. The GL-5 classification means the oils has the correct Extreme Pressure" (EP) lubricants for the ring and pinion gears.
Choose your favorite flavor of oil, and change it regularly- 10,000 miles or less, or after any "under water events". The reason we change the gear oil is to remove accumulated dirt and water.
If you have a "track-lock" clutch type posi differential, be SURE to use the "track-lock" additive in the oil...
IGNORE any discussion of "extended drain intervials", "Synthetics are good for 500,000 miles", etc. Any gear oil that you use will last forever. The problem and the reason for short change intervials is the oil gets dirt and water in it, from the way most Jeeps are driven. Remember, the AMC-20 has an unfiltered vent line that allows air (with dirt and moisture) to move in and out of the differential.
Oh, don't use the GL-5 gear oil in your transmission....
Last edited by halpeters; 01-23-2011 at 07:29 AM.
Reason: added comment about additive in the oil