Symptoms
Oil dripping from the joint between engine and transmission. Rule out the valve cover gasket, oil-pressure sender, oil-filter-adapter O-rings and (on distributor engines) the distributor gasket first.
The fix, step by step
- The 4.0 uses a two-piece seal, so it can be done with the engine in the truck and the transmission in place.
- Raise the Jeep high and support it, drain the oil and drop the pan.
- Remove the rear main bearing cap, pull the lower seal half, then work the upper half out by pushing one end around the crank.
- Clean everything, oil the new seal lips, install the upper half and then the lower half in the cap, fit the cap and torque it to spec.
- One NAXJA member quotes 80 ft-lb for a 1999 confirm in manual.
- Refit the pan with a new gasket, which is where most comebacks happen.
Tools & part numbers
- Jack and stands
- torque wrench
- seal pick
- RTV per seal instructions
- new pan gasket
Where to buy the parts
Crown 4778126 rear main seal kit, 1987–99 4.0LQuadratec ↗Amazon ↗
Crown 5018594 rear main seal, 2000–06 4.0LQuadratec ↗Amazon ↗
Crown 4713221 lower gasket set (pan), 1992–2000 4.0LQuadratec ↗Amazon ↗
Crown 5017432AC lower gasket set, 2001–06 4.0LQuadratec ↗Amazon ↗
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Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.