Rear Main Seal

Replace the rear main crankshaft seal on a 1970 AMC Rebel Machine with 390ci V8 engine by removing the transmission and flywheel to access the seal.

Warnings

Tools required

Parts

• Rear main crankshaft seal × 1 — Use OEM specification for AMC 390 V8
• Transmission pan gasket × 1 — Specific to transmission type (automatic or 4-speed manual)
• Transmission fluid × 1 — As required for refill
• Engine oil × 1 — As required for refill

Fluids

• Engine oil (10W-30 or 10W-40) — 5 qt
• Transmission fluid (Dexron II/III for automatic or gear oil for manual) — 4 qt

Preparation

1. Disconnect negative battery cable
2. Raise vehicle on lift or securely support on jack stands at appropriate lift points
3. Place oil drain pan under engine and drain engine oil completely
4. Remove starter motor to provide clearance for bellhousing bolts and flywheel access
5. Mark driveshaft-to-rear axle flange position with paint or punch marks for proper realignment
6. Disconnect exhaust system at manifolds or remove exhaust crossover pipe if needed for clearance

Procedure

1. 1

   Remove driveshaft
   Remove the four bolts securing the driveshaft U-joint to the rear axle pinion flange. Support the driveshaft and slide it rearward out of the transmission tailshaft. Plug the transmission extension housing with a rag or old yoke to prevent fluid loss.
2. 2

   Disconnect transmission linkage and components
   Disconnect the speedometer cable from the transmission. Disconnect shift linkage (column or floor shift depending on transmission type). For automatic transmissions, disconnect vacuum modulator line and kickdown linkage. Disconnect neutral safety switch or backup light switch electrical connectors.
3. 3

   Support and remove transmission crossmember
   Position transmission jack under transmission pan and secure transmission with safety chain. Remove the bolts securing the rear transmission mount to the crossmember, then remove the bolts securing the crossmember to the frame rails. Remove the crossmember from the vehicle.
4. 4

   Remove bellhousing-to-engine bolts
   Remove all bellhousing-to-engine block bolts. On AMC 390 engines, there are typically 6-8 bolts depending on transmission type. Note bolt locations as they may be different lengths. For automatic transmissions, also remove the inspection cover and mark torque converter-to-flexplate position, then remove torque converter bolts by rotating engine with socket on crankshaft bolt.
5. 5

   Remove transmission
   Carefully slide transmission straight back away from engine, ensuring torque converter (if automatic) stays with transmission. Lower transmission on jack and remove from under vehicle. For manual transmissions, support clutch disc as transmission is withdrawn to prevent it from falling.
6. 6

   Remove clutch and pressure plate (manual transmission)
   If equipped with manual transmission, mark pressure plate-to-flywheel orientation. Remove the six pressure plate bolts in a crisscross pattern, loosening gradually to release spring pressure evenly. Remove pressure plate and clutch disc.
7. 7

   Remove flywheel or flexplate
   Use flywheel holding tool or large screwdriver wedged against ring gear and block to prevent crankshaft rotation. Remove the six flywheel (manual) or flexplate (automatic) bolts. Note orientation of flywheel for correct balance during reinstallation. Remove flywheel/flexplate from crankshaft flange.
8. 8

   Remove rear main seal
   Inspect the two-piece rope-style rear main seal typical of AMC 390 engines. Use seal pick or small screwdriver to carefully pry out the lower seal half from the rear main bearing cap. The upper seal half is located in the block and can be removed by rotating it out with needle-nose pliers or by carefully driving a brass drift into one end to push it around and out the other side of the block.
9. 9

   Clean seal surfaces
   Thoroughly clean the rear main bearing cap seal groove and block seal groove using a wire brush and clean rags. Remove all old seal material, dirt, and oil residue. Inspect crankshaft seal surface for grooves or damage that may cause new seal to leak. Light polishing with fine emery cloth is acceptable if minor imperfections exist.
10. 10

    Install new rear main seal
    Lightly oil the new seal with engine oil. For rope-style seals: Install upper seal half into block groove by carefully working it into place, ensuring it seats fully in the groove and is centered. Use seal installation tool or wooden dowel to press seal into groove. Install lower seal half into rear main cap groove, ensuring proper seating. Seals should protrude slightly above parting surface. Trim any excess with razor blade flush to parting surface.
11. 11

    Install flywheel or flexplate
    Clean crankshaft flange and flywheel/flexplate mating surfaces. Install flywheel or flexplate in original orientation (use marks from removal). Install flywheel bolts with thread locker if specified. Hold flywheel with holding tool and torque bolts in a star pattern. Typical specification is 95-105 ft-lbs for AMC 390, verify with service manual.
12. 12

    Install clutch assembly (manual transmission)
    If equipped with manual transmission, install clutch disc and pressure plate. Use clutch alignment tool to center disc on flywheel pilot bearing. Install pressure plate aligned with marks made during removal. Install and tighten pressure plate bolts in crisscross pattern gradually and evenly.
13. 13

    Reinstall transmission
    Guide transmission into position using transmission jack. For automatic transmissions, ensure torque converter is fully seated in pump (should be recessed approximately 1/2 inch from bellhousing face). Align transmission input shaft with clutch disc (manual) or torque converter with flexplate (automatic). Slide transmission forward until bellhousing seats against engine block. Do not force transmission or use bolts to draw it in.
14. 14

    Install bellhousing bolts and reconnect components
    Install all bellhousing-to-engine bolts and tighten securely. For automatic transmissions, rotate engine to access torque converter bolt holes and install converter-to-flexplate bolts aligned with marks made during removal. Reinstall transmission crossmember and mounting bolts. Remove transmission jack. Reconnect all shift linkage, electrical connectors, vacuum lines, and speedometer cable.
15. 15

    Reinstall driveshaft and complete assembly
    Install driveshaft by sliding front yoke into transmission extension housing, then align marks on rear U-joint and pinion flange. Install and tighten U-joint strap bolts. Reinstall starter motor. Reconnect exhaust system if disconnected. Lower vehicle and reconnect negative battery cable.

Reassembly

1. Torque all fasteners to manufacturer specifications using service manual
2. Ensure all electrical connectors and linkages are properly reconnected and adjusted
3. Verify transmission crossmember and mounts are secure before removing jack
4. Double-check driveshaft alignment marks match to prevent vibration

Verification

• Fill engine with appropriate quantity and grade of engine oil
• Fill transmission with appropriate fluid to correct level (check with dipstick for automatic or fill plug for manual)
• Start engine and check for oil leaks at rear main seal area
• Allow engine to reach operating temperature and verify no leaks
• Test drive vehicle and verify proper transmission operation and no unusual vibrations
• Recheck fluid levels after test drive and inspect for leaks again

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