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STEP 1
Verify that the rear main seal is leaking. If it is, oil will originate from inside the flywheel housing. This should not be confused with an oil pan leak or other engine leaks, which end up dripping from outside the flywheel housing. A fluorescent dye can be added to the engine oil to help easily pinpoint the source of any oil leak.
STEP 2
Disconnect and remove the transmission, clutch, and flywheel.
STEP 3
Ensure that the flywheel and bell housing are centered by performing the “Reinstalling a Flywheel Housing” Skill Drill in Chapter 8: Cylinder Blocks, Crankshafts, and Engine Bearings. An improperly centered flywheel or bell housing will cause premature wear on one side of the seal. Correct any flywheel runout before removing or reinstalling the new rear main seal.
STEP 4
Remove the old seal using a heel bar to pry on a self-tapping screw installed in the seal.
STEP 5
Remove any seal wear ring installed on the crankshaft, which most manufacturers use on HD diesels.
STEP 6
Inspect the crank sealing surface for damage and clean up the seal surface with crocus cloth.
STEP 7
Clean the seal bore in the bell housing.
STEP 8
Place a pry bar between the crankshaft and the bell housing to gently pry up on the crankshaft to observe whether there is any visible movement of the crankshaft that would indicate excessive bearing wear. There should be no movement detected. Take special precautions to prevent damaging the crankshaft with the pry bar. Any detectable vertical movement of the crankshaft requires a main bearing replacement and further investigation regarding the remaining service life of the engine. Any movement causes the seal to prematurely wear and leak.
STEP 9
Mount the seal on the seal driver using the OEM-prescribed seal installation tool and follow any special instructions recommended by the OEM.
STEP 10
Center the seal driver on the end of the crankshaft and set the seal to the correct depth required by the OEM. (This is usually achieved as a feature of the installation tool’s design.) Install a wear ring at the same time as the seal. Use special care to drive the seal into the bore squarely because gravity will tilt the driver and seal and cause damage to both if the seal is misaligned while tightening it into the bore.
STEP 11
Clean, reinstall, and torque the flywheel. Run the engine and check for oil leakage from the rear main oil seal.
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