Rear Main Seal

Replace the rear main crankshaft seal on a 1972 Ford F-100 with 302ci V8 engine by removing the transmission and flywheel to access the seal housing.

Warnings

Tools required

Parts

• Rear main crankshaft seal × 1 — Use OEM specification or Fel-Pro BS 40036
• Oil pan gasket × 1 — Use OEM specification or Fel-Pro OS 30148 R
• Oil pan drain plug gasket × 1 — Use OEM specification
• Transmission pan gasket (if automatic) × 1 — Use OEM specification
• RTV silicone gasket maker × 1 — High-temp red or black RTV

Fluids

• 10W-30 or 10W-40 conventional engine oil — 5 qt
• Type F ATF (if automatic transmission) — 11 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable
3. Allow engine to cool completely if recently operated
4. Raise vehicle and support securely on jack stands at the frame rails
5. Remove the rear wheels to improve access to the driveline (optional but recommended)
6. Place drain pans under engine oil pan and transmission pan

Procedure

1. 1

   Drain fluids
   Remove the engine oil drain plug and drain the crankcase completely into a drain pan. If equipped with automatic transmission, remove the transmission pan bolts and carefully lower the pan to drain the fluid. For manual transmission, locate and remove the transmission drain plug if equipped.
2. 2

   Disconnect driveshaft
   Mark the relationship between the driveshaft yoke and rear axle pinion flange with paint or a scribe for proper reinstallation. Remove the four U-bolt nuts securing the rear U-joint to the pinion flange. Slide the driveshaft rearward to disengage the slip yoke from the transmission output shaft. Cap or plug the transmission extension housing to prevent fluid spillage.
3. 3

   Disconnect transmission linkage and electrical connections
   For automatic transmission: disconnect the shift linkage rod from the transmission lever, disconnect the throttle valve (TV) linkage or kickdown rod, and disconnect the neutral safety switch connector. For manual transmission: disconnect the clutch linkage and/or hydraulic line at the bellhousing. Disconnect the speedometer cable at the transmission.
4. 4

   Remove exhaust crossover pipe or Y-pipe
   Support the exhaust system with a jack or wire. Remove the two flange bolts connecting the exhaust pipes to the exhaust manifolds. Remove any exhaust hangers or clamps that will interfere with transmission removal. Lower or move the exhaust aside to provide clearance for transmission removal.
5. 5

   Support transmission and remove crossmember
   Position a transmission jack under the transmission pan and secure the transmission to the jack with a chain or strap. Remove the two crossmember-to-frame bolts on each side (four bolts total). Remove the two transmission mount-to-crossmember nuts. Lower the transmission jack slightly and remove the crossmember from the vehicle.
6. 6

   Remove bellhousing-to-engine bolts
   Remove the starter motor (two mounting bolts). Remove all bellhousing-to-engine block bolts. For automatic transmission (C4 or C6), there are typically six bellhousing bolts. For manual transmission (3-speed or 4-speed), there are typically four to six bellhousing bolts depending on configuration. Support the rear of the engine with a block of wood and a floor jack under the oil pan to prevent the engine from tilting when the transmission is removed.
7. 7

   Remove transmission
   With the transmission supported on the transmission jack, carefully slide the transmission rearward away from the engine, ensuring the torque converter (automatic) or input shaft (manual) fully disengages from the engine. For automatic transmission, hold the torque converter in place as you pull the transmission back to prevent it from falling. Lower the transmission and remove from under the vehicle.
8. 8

   Remove flexplate or flywheel
   For automatic transmission: remove the four flexplate-to-torque converter bolts (access through starter opening) if not already done, then remove the six flexplate-to-crankshaft bolts. For manual transmission: remove the pressure plate and clutch disc, then remove the six flywheel-to-crankshaft bolts. Use a flywheel holding tool or have an assistant hold the crankshaft from rotating via the front pulley bolt. Mark the orientation of the flexplate/flywheel to the crankshaft for proper reinstallation.
9. 9

   Remove oil pan
   Remove all oil pan bolts (typically 16-20 bolts around the perimeter). Carefully break the gasket seal using a plastic gasket scraper or putty knife. Lower the oil pan and remove from the vehicle. On some installations, you may need to raise the engine slightly to gain additional clearance for oil pan removal.
10. 10

    Remove rear main seal and cap
    The 1972 302 uses a two-piece rope-style rear main seal design. Remove the two rear main bearing cap bolts and carefully remove the bearing cap. Remove the lower half of the old seal from the bearing cap groove using a seal pick or screwdriver. For the upper half, use a seal removal tool or carefully rotate the crankshaft while gently prying the seal out with a blunt pick, working it around until it can be pulled free. Avoid scratching the crankshaft journal surface. Verified detail (The 302 (Windsor small block) uses a two-piece rear main seal, which is correct, but the standard 302 main bearing caps use two bolts per cap so that part is fine. The bigger issue is describing it as 'rope-style or split rubber' — the 302 factory used a two-piece lip-type (rubber) seal, not a rope seal. Rope seals were used on older/other engines; stating rope-style may mislead part selection.): The 302 uses a two-piece split rubber (lip-type) rear main seal design. Remove the two rear main bearing cap bolts and carefully remove the bearing cap.
11. 11

    Clean sealing surfaces
    Thoroughly clean the rear main bearing cap and engine block mating surfaces with brake cleaner and a wire brush. Clean the crankshaft seal journal surface with a clean rag and brake cleaner, inspecting for grooves or damage. Clean the oil pan rail surfaces on both the engine block and oil pan, removing all old gasket material and RTV residue. Inspect the crankshaft for scoring or wear in the seal contact area.
12. 12

    Install new rear main seal
    Do not pre-oil rope-style seals. Install them dry and allow them to absorb oil naturally during engine operation. Install the upper seal half into the engine block groove by carefully working it into position. Rope seals are non-directional. Use a blunt tool like a wooden dowel or the handle of a hammer to press the seal firmly into the groove, ensuring it seats completely around the crankshaft. Use a blunt tool like a wooden dowel or plastic tool to press the seal firmly into the groove, ensuring it seats completely around the crankshaft. Install the lower seal half into the rear main bearing cap groove, working it firmly into place with a blunt tool. Ensure both seal halves protrude approximately 1/32" to 1/16" above the block and cap parting surfaces. This protrusion is intentional and will be compressed when the bearing cap is installed and torqued, creating a proper seal.
13. 13

    Reinstall rear main bearing cap
    Apply a small amount of clean engine oil to the bearing cap bolt threads. Position the rear main bearing cap onto the engine block, ensuring proper orientation (the cap is marked for position). Install the two bearing cap bolts and tighten in a cross pattern. Since torque specifications are not provided in the database, tighten to the appropriate specification for the 302 engine (typically 60-70 ft-lbs for main bearing caps, but verify this specification before proceeding).
14. 14

    Reinstall oil pan
    Install a new oil pan gasket with a thin bead of RTV silicone on the front and rear seal areas where the timing cover and rear main cap meet the block. Position the oil pan and install all bolts finger-tight first. Tighten the oil pan bolts in a spiral pattern from the center outward to the appropriate specification (typically 9.0 lb-ft (12.0 Nm) for small block Ford oil pan bolts). Do not overtighten as this can distort the pan and cause leaks. Install a new drain plug gasket and reinstall the drain plug.
15. 15

    Reinstall flexplate or flywheel
    Clean the crankshaft flange and flexplate/flywheel mounting surface. Position the flexplate or flywheel onto the crankshaft, aligning the marks made during disassembly. Install the six crankshaft-to-flexplate/flywheel bolts and tighten in a star pattern. Torque specifications should be verified, but typical value is 75-85 ft-lbs for small block Ford applications. Apply thread locker to bolt threads before installation.
16. 16

    Reinstall transmission
    For automatic transmission, ensure the torque converter is fully seated in the transmission pump (should click into place at least twice as it engages the pump drive and stator support). Measure the distance from the bellhousing face to the torque converter mounting ear; it should be recessed approximately 1/2 inch. Position the transmission on the jack and carefully align with the engine. For manual transmission, ensure the clutch disc is properly aligned using a clutch alignment tool. Slide the transmission forward, ensuring the input shaft or torque converter pilot engages properly without forcing. Install all bellhousing-to-engine block bolts and tighten evenly.
17. 17

    Reinstall crossmember and mounts
    Raise the transmission into position and install the crossmember. Install the transmission mount-to-crossmember nuts and the four crossmember-to-frame bolts. Tighten all mounting hardware securely. Remove the transmission jack and engine support. Reinstall the starter motor with its two mounting bolts.
18. 18

    Reconnect driveshaft and linkages
    Remove the plug from the transmission extension housing. Lubricate the slip yoke splines with a small amount of transmission fluid or high-temp grease. Slide the driveshaft forward into the transmission, aligning the marks made during disassembly on the rear U-joint and pinion flange. Install the four U-bolt nuts and tighten securely (typically 12-15 ft-lbs). Reconnect all transmission linkages, electrical connectors, and speedometer cable.
19. 19

    Reconnect exhaust system
    Position the exhaust pipes back onto the exhaust manifold flanges, aligning the mounting holes. Install new exhaust flange gaskets if needed. Install the flange bolts and tighten securely. Reinstall any exhaust hangers or clamps that were removed.
20. 20

    Refill fluids and final checks
    Lower the vehicle to the ground. Refill the engine crankcase with 5 quarts of 10W-30 or 10W-40 conventional engine oil. For automatic transmission, add approximately 4-5 quarts of Type F ATF through the dipstick tube initially (the transmission will require full capacity after startup and cycling through gears). For manual transmission, refill through the fill plug on the side of the transmission case. Reconnect the negative battery cable.

Reassembly

1. Reassembly is covered in the main procedure steps
2. Ensure all fasteners are tightened to proper specifications
3. Double-check that all electrical connections and linkages are properly reconnected before starting the engine

Verification

• Start the engine and verify oil pressure registers on the gauge within 5-10 seconds
• Allow the engine to reach operating temperature while monitoring for leaks at the rear main seal area and oil pan
• For automatic transmission: with the engine idling and parking brake applied, cycle through all gear positions, then check transmission fluid level with the engine running in Park. Add Type F ATF as needed to bring level to the full mark
• For manual transmission: check for proper clutch operation and smooth shifting through all gears
• Test drive the vehicle and recheck all fluid levels after 50-100 miles of operation
• Inspect underneath the vehicle for any signs of oil or transmission fluid leaks after the test drive

More procedures for this vehicle