GM Full-Size Trucks 1970-1979 Repair Guide

Rear Main Oil Seal

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REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4 and 5



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Fig. Fig. 1: Using a small prytool, carefully remove the seal half from the bearing cap without scratching the cap



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Fig. Fig. 2: Remove the upper seal half from the engine block



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Fig. Fig. 3: View of a common rear main seal half, bearing cap side



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Fig. Fig. 4: Make a rear main bearing seal packing tool from a wooden dowel. The upper tool dimensions are for engines up to 400 cu. in.; the bottom dimensions are for the 454 cu. in. engine



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Fig. Fig. 5: Packing the oil seal into the groove

Inline 6-Cylinder Engines

The rear main bearing oil seal, both halves, can be removed without removal of the crankshaft. Always replace the upper and lower halves together.

  1. Remove the oil pan.
  2.  
  3. Remove the rear main bearing cap.
  4.  
  5. Remove the old oil seal from its groove in the cap, prying from the bottom using a small screwdriver.
  6.  
  7. Coat a new seal half completely with clean engine oil, and insert it into the bearing cap groove. Keep oil off of the parting line surface, as this surface is treated with glue. Gradually push the seal with a hammer handle until the seal is rolled into place.
  8.  
  9. To remove the upper half of the old seal, use a small hammer and a soft, blunt punch to tap one end of the oil seal out until it protrudes far enough to be removed with needlenosed pliers. Push the new seal into place with the lip toward the front of the engine.
  10.  
  11. Install the bearing cap and tighten the bolts to a loose fit, do not final torque. With the cap fitted loosely, move the crankshaft first to the rear and then to the front with a rubber mallet. This will properly position the thrust bearing. Tighten the bearing cap to a final torque of 65 ft. lbs. (88 Nm). Install the oil pan.
  12.  

V6 and V8 Gasoline Engines
  1. Refer to the Oil Pan Removal and Installation procedures in this section and remove the oil pan.
  2.  
  3. Remove the oil pump and the rear main bearing cap.
  4.  
  5. Using a small pry bar, pry the oil seal from the rear main bearing cap.
  6.  
  7. Using a small hammer and a brass pin punch, drive the top half of the oil seal from the rear main bearing. Drive it out far enough, so it may be removed with a pair of pliers.
  8.  
  9. Using a non-abrasive cleaner, clean the rear main bearing cap and the crankshaft.
  10.  
  11. Fabricate an oil seal installation tool from 0.004 in. shim stock.
  12.  
  13. Coat the new oil seal with engine oil; DO NOT coat the ends of the seal.
  14.  
  15. Position the fabricated tool between the crankshaft and the seal seat in the cylinder case.
  16.  
  17. Position the new half seal between the crankshaft and the top of the tool, so that the seal bead contacts the tip of the tool.
  18.  

Make sure that the seal lip is positioned toward the front of the engine.

  1. Using the fabricated tool as a shoe horn, to protect the seal's bead from the sharp edge of the seal seat surface in the cylinder case, roll the seal around the crankshaft. when the seal's ends are flush with the engine block, remove the installation.
  2.  
  3. Using the same manner of installation, install the lower half onto the lower half of the rear main bearing cap.
  4.  
  5. Apply sealant to the cap-to-case mating surfaces and install the lower rear main bearing half to the engine; keep the sealant off of the seal's mating line.
  6.  
  7. Install the rear main bearing cap bolts and tighten to 10-12 ft. lbs. (13.5-16 Nm). Using a lead hammer, tap the crankshaft forward and rearward, to line up the thrust surfaces. Tighten the main bearing bolts to 70-85 ft. lbs. (95-115 Nm) for V6 and V8 engines, or to 60-75 ft. lbs. (81-102 Nm) for inline 6-cylinder engines and reverse the removal procedures. Refill the crankcase.
  8.  

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.
  2.  
  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.
  4.  
  5. Measure the amount the seal was driven up on one side; add 1 / 16 in. then cut this length from the old seal that was removed from the main bearing cap. Use a single-edge razor blade. Measure the amount the seal was driven up on the other side, add 1 / 16 in. and cut another length from the old seal. Use the man bearing cap as a holding fixture when cutting the seal as illustrated. Carefully trim protruding seal.
  6.  
  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 them flush with a razor blade or hobby knife as shown. Do not scratch the bearing surface with the razor.
  8.  

It may help to use a bit of oil on the short pieces of the rope seal when packing it into the block.

  1. Apply Loctite® #496 sealer or equivalent to the rear main bearing cap and install the rope seal. Cut the ends of the seal flush with the cap.
  2.  
  3. Check to see if the rear main cap with the new seal will seat properly on the block. Place a piece of Plastigage® on the rear main journal, install the cap and tighten to 70 ft. lbs. (95 Nm). Remove the cap and check the Plastigage® against specifications. If out of specs, recheck the ends of the seal for fraying that may be preventing the cap from seating properly.
  4.  
  5. Make sure all traces of Plastigage® are removed from the crankshaft journal. Apply a thin film of sealer (GM part #1052357 or equivalent) to the bearing cap. Keep the sealant off of both the seal and bearing.
  6.  
  7. Just before assembly, apply a light coat of clean engine oil on the crankshaft surface that will contact the seal.
  8.  
  9. Install the bearing cap and tighten the bolts to specifications.
  10.  
  11. Install the oil pump and oil pan.
  12.  

 
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