GM Full Size Vans 1967-1986 Repair Guide

Rear Main Oil Seal



Gasoline Engines

See Figures 1, 2, 3, 4, 5, 6 and 7

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Fig. Fig. 1: Remove the seal half from the bearing cap without scratching the cap

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Fig. Fig. 2: Removing the upper half of the seal from the block

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Fig. Fig. 3: A common half of a rear main seal

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Fig. Fig. 4: Make a rear main bearing seal packing tool from a wooden dowel

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Fig. Fig. 5: Packing the oil seal

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Fig. Fig. 6: Cutting the lower (bearing cap) seal ends

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Fig. Fig. 7: Sealing the bearing cap before the final tightening. Apply a bit of oil to the crank journal just before installing the cap

Both halves of the rear main oil seal can be replaced without removing the crankshaft. Always replace the upper and lower seal together. The lip should face the front of the engine. Be very careful that you do not break the sealing bead in the channel on the outside portion of the seal while installing it. An installation tool can be fabricated to protect the seal bead.

  1. Remove the oil pan, oil pump and rear main bearing cap.
  3. Remove the oil seal from the bearing cap by prying it out with a suitable tool.
  5. Remove the upper half of the seal with a small punch. Drive it around far enough to be gripped with pliers.
  7. Clean the crankshaft and bearing cap.
  9. Coat the lips and bead of the seal with light engine oil, keeping oil from the ends of the seal.
  11. Position the fabricated tool between the crankshaft and seal seat.
  13. Position the seal between the crankshaft and tip of the tool so that the seal bead contacts the tip of the tool. The oil seal lip should face forward.
  15. Roll the seal around the crankshaft using the tool to protect the seal bead from the sharp corners of the crankcase.
  17. The installation tool should be left installed until the seal is properly positioned with both ends flush with the block.
  19. Remove the tool.
  21. Install the other half of the seal in the bearing cap using the tool in the same manner as before. Light thumb pressure should install the seal.
  23. Install the bearing cap with sealant applied to the mating areas of the cap and block. Keep sealant from the ends of the seal.
  25. Torque the main bearing cap retaining bolts to 10-12 ft. lbs. (13-16 Nm). Tap the end of the crankshaft first rearward, then forward with a lead hammer. This will line up the rear main bearing and the crankshaft thrust surfaces. Tighten the main bearing cap to specification.
  27. Further installation is the reverse of removal.

Diesel Engines

The crankshaft need not be removed to replace the rear main bearing upper oil seal. The lower seal is installed in the bearing cap.

  1. Drain the crankcase oil and remove the oil pan and rear main bearing cap.
  3. Using a special main seal tool or a tool that can be made from a dowel (see illustration), drive the upper seal into its groove on each side until it is tightly packed. This is usually 1 / 4 - 3 / 4 in. (6.35-19.05mm).
  5. Measure the amount the seal was driven up on one side. Add 1 / 16 in. (1.5875mm) and cut another length from the old seal. Use the main bearing cap as a holding fixture when cutting the seal as illustrated. Carefully trim protruding seal.
  7. Work these two pieces of seal up into the cylinder block on each side with two nailsets or small screwdrivers. Using the packing tool again, pack these pieces into the block, then trim the flush with a razor blade or hobby knife as shown. Do not scratch the bearing surface with the razor.