4.0L rear main is a one-piece lip seal. Leaks usually trace to clogged PCV or worn seal. Repair requires transmission removal.
The 4.0L rear main seal is a one-piece lip seal pressed into the rear of the block. Failure causes oil drips on the bellhousing inspection plate area and a slow loss of oil. Before condemning the seal, replace the PCV valve and check for cylinder blowby - excessive crankcase pressure forces oil out the rear main long before the seal itself fails. If you have clean PCV, no blowby past the oil-fill cap, and still leak, the seal is failed. Repair requires removing the transmission, flywheel/flex plate, and seal retainer. The seal is Fel-Pro BS40663 or Mopar 53020678. Critical: do not pry the old seal out with a screwdriver against the crank journal - even small scratches will leak. Use a slide-hammer style seal puller. Pre-lube the new seal with engine oil. While the trans is out, replace the pilot bushing (manual) and inspect the flywheel and clutch.
| Part | Vendor | Est. price |
|---|---|---|
| Rear main seal Fel-Pro | RockAuto | ~$25 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.