According to Jeep, the gear oil in Smokey’s front and rear differentials should be changed about every 15,000 miles, based on the “heavy driving” maintenance schedule. (Here’s a helpful hint: Unless your vehicle only leaves the garage for a weekly Sunday afternoon drive around the block, you should be following the heavy-use schedule.) Based on that schedule, I was more than 15,000 miles overdue for this maintenance and wanted to get it done in advance of a planned summer highway trip.
After a recent unplanned venture in to some deep mud, I decided to be safe rather than sorry. There was no evidence my breather tubes had become dislodged, allowing in the muck, but, at less than $60, the necessary four quarts of gear oil were simply cheap insurance.
- Four quarts, 80W90 gear oil (A full-synthetic 75W90 is an acceptable substitute and contains the friction modifier that otherwise would have to be added to the limited-slip rear differential. Use a heavier grade for towing.)
- Fluid pump
- 3/8-inch ratchet
- Ratchet extension
- Torque wrench
- Fluid drain pan
- Shop towels
OEM fluid capacities
- Dana 30 front: 1 quart (approx.)
- Dana 44 front: 1.4 quarts (approx.)
- Dana 44 rear: 2 quarts (approx.)
Jeep claims the differentials will hold 1.2, 1.4 and 2.4 quarts, respectively. Even with Smokey’s stock covers in place, I found these figures to be completely unrealistic, as fluid was pouring out of the fill holes at the capacities listed above. Based on Internet research, it appears there’s several tenths of a quart difference from Jeep to Jeep. Use your best judgment.
Step 1: Drain old oil
Place the drain pan below your differential. Attach the ratchet extension to the 3/8-inch ratchet and insert the head of the extension into the bolt hole on the front of the differential cover. Turn counter-clockwise to loosen and remove the bolt. Repeat the process for the drain bolt, located on the bottom right side of each differential. Allow the fluid to completely drain before proceeding.
Step 2: Refill the differential
Use a couple of shop towels to wipe clean the drain plug, which will be covered with a gritty, dark grey mass. This is normal. The magnetic drain plug catches tiny metallic filings floating in the fluid. If noticeably larger shavings are present, consider removing the differential cover to give your gears a thorough visual inspection.
Replace the cleaned drain plug and tighten to about 25-30 ft. lbs. Attach the pump to the bottle of gear oil and route the length of hose into a secure location inside the fill port. Begin pumping oil into the hole. If your pump will not completely empty the bottle, it may be necessary to transition to a second bottle, eventually pouring the remains of the first bottle into the second.
If you have stock differential covers like Smokey, you’ll know the differential is full when fluid begins to overflow the fill port. Replace the fill plug, tightening to 25-30 ft. lbs., and wipe clean the cover.
NOTE: Do not attempt to overfill the differentials, as doing so may force excess fluid out of the axle’s breather tube.
Total time to complete
About 45 minutes
Total project cost
$58 (Using mid-priced Mobil 1 synthetic gear oil. If you do not have a bottle pump, add about $10.)