Rear Main Seal

Replace the rear main crankshaft seal on a 1966 Corvette 327ci V8 by removing the transmission and flywheel to access the seal at the back of the engine block.

Warnings

Tools required

Parts

• Rear main crankshaft seal × 1 — Use OEM specification
• Transmission pan gasket × 1 — Use OEM specification or cork gasket
• Transmission filter (if applicable) × 1 — Use OEM specification
• Oil pan gasket (if disturbed) × 1 — Use OEM specification or cork gasket
• RTV silicone gasket maker × 1 — High-temp red RTV

Fluids

• 5W-30 Conventional engine oil — 5 qt
• Dexron III ATF — 11.5 qt
• 75W-90 GL-5 Gear Oil — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake.
2. Disconnect negative battery cable to prevent accidental starter engagement.
3. Allow engine and exhaust system to cool completely.
4. Raise vehicle and support securely on jack stands at frame rails.
5. Remove both rear wheels for better working clearance if equipped with side exhaust.
6. Place drain pan under engine oil pan and drain engine oil completely.
7. Place drain pan under transmission pan and drain transmission fluid.
8. Remove transmission inspection cover to access flywheel bolts.

Procedure

1. 1

   Disconnect driveshaft
   Mark the relationship between the rear axle pinion flange and driveshaft yoke with paint or a scribe for reinstallation alignment. Remove the 4 U-bolt nuts securing the rear U-joint to the differential pinion flange. Slide the driveshaft rearward to disengage from the transmission output shaft, then lower and remove from vehicle. Inspect the rear U-joint for wear while accessible.
2. 2

   Disconnect exhaust system
   Disconnect the exhaust system at the front collector or header flanges. On side-pipe equipped vehicles, support the exhaust with wire or remove completely for clearance. Remove any exhaust hangers that will interfere with transmission removal. Set exhaust components aside safely.
3. 3

   Disconnect shift linkage and cables
   Disconnect the shift linkage from the transmission. On Powerglide automatic transmissions, disconnect the throttle valve cable and kickdown linkage at the transmission. On manual transmissions, disconnect the clutch fork return spring and clutch cross-shaft. Label all connections for proper reassembly.
4. 4

   Disconnect electrical and speedometer connections
   Disconnect electrical connectors at the transmission, including neutral safety switch (automatic) and backup light switch (manual). Remove the speedometer cable by unscrewing the retaining ferrule at the transmission. Mark connector positions for reinstallation.
5. 5

   Disconnect transmission cooler lines (automatic only)
   If equipped with automatic transmission, place a drain pan under the transmission cooler lines. Use a flare nut wrench to disconnect both cooler lines from the transmission case. Cap or plug the lines and transmission ports to prevent contamination. Expect additional fluid drainage.
6. 6

   Support transmission and remove crossmember
   Position a transmission jack under the transmission pan with a wood block to distribute load. Raise jack slightly to take weight off the crossmember. Remove the 4 bolts securing the transmission mount to the crossmember. Remove the crossmember mounting bolts (typically 2 per side) and remove the crossmember from the vehicle.
7. 7

   Remove bellhousing-to-engine bolts
   Remove all bellhousing-to-engine block bolts. On automatic transmissions, there are typically 6 bolts securing the bellhousing to the engine. On manual transmissions, there are 4 main bellhousing bolts. Note the location of any different length bolts for proper reinstallation. Support the rear of the engine with a jack stand and wood block if needed.
8. 8

   Remove transmission
   With an assistant or using secure transmission jack straps, carefully slide the transmission rearward away from the engine. Keep the transmission level to prevent binding on the input shaft or clutch disc. On automatic transmissions, ensure the torque converter remains with the transmission and does not fall. Lower the transmission jack and remove transmission from under the vehicle.
9. 9

   Remove clutch and pressure plate (manual) or flexplate (automatic)
   For manual transmissions: Mark the pressure plate relationship to the flywheel. Use a flywheel holding tool to prevent rotation. Remove the 6 pressure plate bolts in a crisscross pattern, loosening gradually to prevent warping. Remove pressure plate and clutch disc. For automatic transmissions: Mark the flexplate-to-torque converter relationship. Remove the flexplate-to-crankshaft bolts while holding the flywheel. Remove flexplate from crankshaft.
10. 10

    Access and inspect rear main seal area
    With the flywheel or flexplate removed, the rear main seal is now visible in the back of the engine block. Inspect the crankshaft flange for wear, grooves, or damage. Check for excessive oil leakage patterns. Inspect the seal bore in the block for damage or distortion. Clean the area thoroughly with brake cleaner and shop rags.
11. 11

    Remove old rear main seal
    The 1966 327 uses a rope-style two-piece rear main seal. Remove the upper seal half by carefully prying it out of the groove in the block with a seal puller or brass pick, working from one end and rotating the crankshaft slightly if needed. Remove the lower seal half from the rear main bearing cap by prying carefully. Avoid damaging the seal surfaces in the block or cap.
12. 12

    Clean and prepare sealing surfaces
    Thoroughly clean the seal grooves in both the engine block and rear main bearing cap using a wire brush and brake cleaner. Remove all old seal material, RTV, and oil residue. Inspect the crankshaft sealing surface for scoring or grooves that could cause leaks. If minor imperfections exist, polish with fine emery cloth. Wipe all surfaces clean with a lint-free rag.
13. 13

    Install new rear main seal - upper half
    Lubricate the new upper rope seal lightly with engine oil. Insert the seal into the groove in the block with the lip facing forward (toward the front of the engine). Use a seal installation tool or large socket to carefully press the seal into the groove, ensuring it seats evenly. The seal should protrude slightly beyond the block parting surface. Some mechanics use a small amount of RTV on the seal ends where they meet the cap.
14. 14

    Install new rear main seal - lower half
    Lubricate the lower rope seal half with engine oil. Install it into the rear main bearing cap groove with the lip facing forward. Press the seal firmly into place ensuring even seating. The seal ends should protrude slightly beyond the cap surface to ensure proper compression when the cap is installed. Apply a thin bead of RTV silicone to the seal ends and cap parting surface.
15. 15

    Verify seal installation and reinstall flywheel/flexplate
    Verify both seal halves are properly seated and aligned. Rotate the crankshaft by hand to ensure smooth rotation without binding. Clean the flywheel or flexplate mounting surface and crankshaft flange with brake cleaner. Install the flywheel or flexplate, aligning marks made during disassembly. Install flywheel bolts and tighten in a star pattern. Note: Torque specifications should be verified for this application.

Reassembly

1. Reinstall clutch disc and pressure plate (manual) or verify flexplate runout is within specification (automatic).
2. Apply a light coat of high-temperature grease to the transmission input shaft spline and pilot bearing.
3. Ensure the torque converter is fully seated in the transmission pump before installing automatic transmission (should click 2-3 times when pushed in).
4. Carefully align transmission input shaft with clutch disc or flexplate and slide transmission forward onto engine, ensuring proper engagement.
5. Install all bellhousing-to-engine bolts and tighten in a crisscross pattern.
6. Reinstall transmission crossmember and mount, ensuring proper alignment before tightening bolts.
7. Reconnect all transmission cooler lines (automatic), electrical connections, speedometer cable, and shift linkage.
8. Reinstall driveshaft, aligning marks made during disassembly, and torque U-bolt nuts.
9. Reconnect exhaust system at header flanges or collectors.
10. Refill rear differential with 2.0 quarts of 75W-90 GL-5 gear oil if drained.
11. Refill transmission with 11.5 quarts of Dexron III ATF (automatic) or appropriate fluid (manual).
12. Refill engine with 5.0 quarts of 5W-30 conventional engine oil.
13. Reinstall transmission inspection cover.
14. Reconnect negative battery cable.

Verification

• Start engine and verify oil pressure registers immediately on gauge.
• Check for oil leaks at rear main seal area while engine is running at idle.
• Allow engine to reach operating temperature and recheck for leaks.
• Test drive vehicle and verify proper transmission operation and smooth shifting.
• Check transmission fluid level when hot and in Park (automatic) or neutral (manual) and adjust if necessary.
• Recheck for leaks after test drive, inspecting rear main seal area, transmission pan, and all connection points.
• Verify no abnormal noises or vibrations from driveline during operation.
• Monitor oil consumption and check for leaks again after 50-100 miles of driving.

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