Join Date: Sep 2007
Location: Livonia, Michigan
Fix the vent hose first. If the vent hole is blocked, it will cause a pressure build-up in the differential when it gets warm. That's what the vent is there for -- to equalize the pressure in a hot differential. The end fitting that was shown above is the correct one, and you can get them a lot of places. However, I know a bunch of people that just attach the hose to the diff vent and run the hose up as high as they can get it. Just be aware that if you enter water that is deep enough to cover the open end of the vent hose, then you'll suck water into the diff and you'll have to drain, flush, and refill it. BTW, your front diff and your t-case should also have vent hoses attached to them. I run my vent hoses up to the passenger-side grill brace in the engine compartment. Once you have the new vent hose attacked, blow into the hose and make sure it's clear to the diff.
Don't worry about changing the seals until you have fixed the vent hose and have drained the excess gear lube out of the diff. Yes, do that on level ground, and with a COLD diff.
If, after you've done that, the seals sstill leak, then replace them.
BTW, if you do decide to go to one-opiece axles (such as Superior or Moser), you won't be changing the AMC 20 diff -- you'll just be changing the axle shafts, the outer bearings, and the outer seals.
1977 CJ7, AMC360 V8 w/ headers, DUI HEI, Edelbrock intake, Holley 4150 carb, , TF999, D300, D30 front and AMC20 rear with 4.56 gears and lockers both ends, 4" susp lift, 2.5" body lift, 35" BFGs, ARG steering, 8000-lb winch, etc.