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 into 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.
Materials/tools needed:
- 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, as listed above, 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 in the bulleted list above this paragraph. 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
$56 (Using mid-priced Mobil 1 synthetic gear oil. If you do not have a bottle pump, add about $10.)
Smokey the Jeep 
Did you know, Jeep has built a commemorative, one-of-a-kind Wrangler 75th Salute concept vehicle to mark the 75th anniversary of the Willys MB. They’ve created this unique vehicle in celebration of the brand’s legendary history, 75 years later,
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Yes, it’s a nice nod to the Wrangler’s Willys MB heritage. Here’s a link to a video I shared on this concept last week: https://smokeythejeep.wordpress.com/2016/07/19/military-concept-wrangler-pays-tribute-to-75-years-of-jeep-greatness/
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I just did this last week. What a difference indeed. I put 80W-90 Castrol Limited Slip Gear Oil in my 2013 JKU Sahara, and no more annoying ticking from the LSD. The dealership wanted almost $200 to do it. I couldn’t believe it. 45 bucks (including the cost of the drain pan). Easy and effective. I’ll probably switch to synthetic at 100,000 miles. I might redo the rear in 15,000 miles just because I would prefer having pure synthetic in the rear.
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Once you start doing things yourself, you’ll never pay shop prices again! 👍🏻
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Is this different than the regular differential fluid? For the 1997 jeep Cherokee?
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I use a synthetic oil with a friction modifier for my Jeep’s limited-slip rear. I’m not intimately familiar with your XJ, but if you, too, have a limited-slip rear, this should fit within what I can find on your specs. If you do a lot of towing, you may consider a heavier oil. When in doubt, refer to your owner’s manual. Good luck!
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What about replacing the gasket?
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When just draining and replacing the gear oil like this, it isn’t necessary to remove the diff cover, which would require a new gasket. It is a wise habit, though, to remove the cover every so often (say, every three or four fluid changes) so you can visually inspect the gears for chipping, etc.
If you discover metal fragments when doing a simple fluid change like this, it’s advisable to go ahead and remove the cover for such an inspection. Hope this helps!
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