Rear Main Seal

Replace the rear main crankshaft seal by removing the transmission, flexplate/flywheel, and rear seal housing to prevent oil leaks at the rear of the engine block.

Warnings

Tools required

Parts

• Rear main crankshaft seal × 1 — GM 12669602 or equivalent
• Rear seal housing gasket × 1 — Use OEM specification
• Oil pan rear gasket section (if damaged) × 1 — Use OEM specification
• Oil drain plug crush washer × 1 — GM 12610877 or equivalent
• Transmission fluid (if servicing) × 1 — ACDelco Dexron VI
• RTV silicone sealant (GM approved) × 1 — GM 12378521 or equivalent

Fluids

• ACDelco dexos1 0W-20 — 8.5 qt
• ACDelco Dexron VI ATF — 11.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable and secure away from terminal
3. Raise vehicle and support securely on jack stands at frame points
4. Remove skid plate or belly pan if equipped
5. Drain engine oil completely and install drain plug with new crush washer
6. Remove starter motor and secure out of the way
7. Mark driveshaft-to-differential flange orientation with paint pen for proper alignment during reassembly

Procedure

1. 1

   Support engine and prepare for transmission removal
   Install engine support fixture across engine bay or attach engine hoist to lifting eyes on cylinder heads. Take up slight tension to support engine weight. The transmission crossmember will be removed and engine must be independently supported.
2. 2

   Disconnect transmission connections
   Disconnect transmission cooler lines at transmission and plug openings. Disconnect shift linkage at transmission. Remove electrical connectors from transmission (park/neutral switch, vehicle speed sensor, solenoid harness). Label all connections for reassembly.
   Torque spec

   Electrical Connector Bolts8 Nm (6 lb-ft)
3. 3

   Remove driveshaft
   Remove four driveshaft flange bolts at rear differential. Support driveshaft and slide rearward to separate from transmission output shaft. Lower driveshaft and remove from vehicle. Avoid damaging slip yoke seal.
4. 4

   Remove transmission crossmember and mount
   Support transmission with transmission jack positioned at center of transmission pan. Remove transmission crossmember mounting bolts from frame. Remove transmission mount bolts. Carefully lower transmission jack slightly to allow clearance for crossmember removal. Remove crossmember from vehicle.
   Torque spec

   Mounting Bolts60 Nm (44 lb-ft)
5. 5

   Remove transmission-to-engine bolts
   Remove all transmission bellhousing bolts securing transmission to engine block. On this L83 engine, there are typically 6-8 bolts around the bellhousing perimeter. Ensure all bolts are removed before attempting to separate transmission.
   Torque spec

   Transmission-to-Engine Bolts55 Nm (41 lb-ft)
6. 6

   Separate and remove transmission
   Verify all connections, bolts, and brackets are disconnected. Carefully slide transmission rearward on transmission jack, keeping it level. Transmission must slide straight back approximately 2-3 inches to clear alignment dowels and separate from engine. Once separated, lower transmission jack and remove transmission from under vehicle. Have assistant help guide and stabilize.
   ⚠Transmission weighs approximately 180 lbs for 6L80/6L90 automatic. Ensure transmission jack is secure and use assistance.
7. 7

   Remove flexplate or flywheel
   Insert flywheel holding tool or large screwdriver through flexplate opening to lock crankshaft rotation. For automatic transmission, remove six flexplate bolts in star pattern. For manual transmission, remove flywheel bolts (typically TTY and not reusable). Mark flexplate/flywheel orientation to crankshaft before removal for balanced reassembly.
   ℹ️Flywheel bolts on manual transmissions are often torque-to-yield (TTY) and must be replaced with new bolts.
   Torque spec

   Flexplate Bolts85 Nm (63 lb-ft)

   Flywheel Bolts95 Nm (70 lb-ft)
8. 8

   Remove rear oil pan section if necessary
   On the L83 engine, the rear oil pan section may need to be loosened or removed for seal housing access. Remove rear oil pan bolts. Gently tap oil pan loose with rubber mallet if stuck. Leave oil pan hanging or remove completely based on access needed.
   Torque spec

   Oil Pan Bolts12 Nm (9 lb-ft)
9. 9

   Remove rear main seal housing
   Remove all rear main seal housing bolts (typically 8-10 bolts around perimeter). Gently pry housing loose using plastic pry tool at designated pry points only. Do NOT pry against crankshaft or machined sealing surfaces. Remove housing and old gasket material.
   Torque spec

   Rear Main Seal Housing12 Nm (9 lb-ft)
10. 10

    Remove old rear main seal
    Using seal puller or pick, carefully extract old rear main seal from housing. Work around perimeter evenly to avoid cocking seal in bore. Clean housing bore thoroughly with brake cleaner and lint-free cloth. Inspect for scoring or damage.
    ⚠Do not scratch or gouge seal bore surface. Damage will prevent new seal from sealing properly.
11. 11

    Install new rear main seal
    Lightly coat seal outer diameter and lip with clean engine oil. Position new seal in housing bore with seal lip facing toward engine. Using seal driver or appropriately sized socket (slightly smaller than seal OD), drive seal squarely into housing until fully seated and flush. Verify seal is seated evenly around entire circumference.
12. 12

    Clean and prepare sealing surfaces
    Thoroughly clean engine block rear seal surface and seal housing mating surface using plastic razor blade scraper and brake cleaner. Remove all old gasket material and RTV. Surfaces must be completely clean and dry. Clean crankshaft flange and inspect for burrs or damage that could damage new seal.
13. 13

    Install seal housing with new gasket
    Install new housing gasket onto engine block or housing (per gasket design). Apply small bead of GM-approved RTV to corners where gasket meets oil pan surface if specified by service manual. Carefully position housing over crankshaft, ensuring seal lip does not fold or damage. Install all housing bolts finger tight, then torque in criss-cross pattern to specification.
    ⚠Ensure rear main seal lip is not folded under during installation. Carefully guide housing over crankshaft while observing seal edge.
    Torque spec

    Rear Main Seal Housing12 Nm (9 lb-ft)
14. 14

    Reinstall oil pan section
    If oil pan was removed or loosened, clean mating surfaces and install new gasket or apply RTV sealant as specified. Reinstall rear oil pan bolts and torque to specification. Allow RTV to cure per manufacturer instructions if used before adding oil.
    Torque spec

    Oil Pan Bolts12 Nm (9 lb-ft)
15. 15

    Reinstall flexplate or flywheel
    Align flexplate/flywheel to crankshaft using alignment marks made during removal. Install bolts finger tight. Lock crankshaft with holding tool. Torque flexplate or flywheel bolts in star pattern to specification. For manual transmission with TTY flywheel bolts, use new bolts and follow any additional angle torque specifications in service manual.
    Torque spec

    Flexplate Bolts85 Nm (63 lb-ft)

    Flywheel Bolts95 Nm (70 lb-ft)

Reassembly

1. Clean transmission input shaft and torque converter/pilot bearing contact surfaces
2. Apply thin layer of high-temp grease to transmission input shaft splines
3. Verify torque converter is fully seated in transmission pump (measure setback from bellhousing face per specifications)
4. Carefully align transmission to engine, ensuring alignment dowels engage properly
5. Install all transmission-to-engine bolts and torque in star pattern to 55 Nm (41 lb-ft)
6. Reinstall transmission crossmember and mount, torque mounting bolts to 60 Nm (44 lb-ft)
7. Remove engine support fixture or hoist once transmission is secured
8. Reinstall driveshaft, aligning marks made during removal, torque flange bolts evenly
9. Reconnect all transmission electrical connectors and torque connector bolts to 8 Nm (6 lb-ft)
10. Reconnect transmission cooler lines and shift linkage
11. Reinstall starter motor
12. Reinstall skid plate or belly pan if equipped
13. Lower vehicle from jack stands

Verification

• Fill engine with 8.5 quarts ACDelco dexos1 0W-20 engine oil
• Fill transmission with 11.5 quarts ACDelco Dexron VI ATF (check level per procedure in owner's manual)
• Reconnect negative battery cable
• Start engine and verify no leaks at rear main seal area while engine is at idle
• Check transmission fluid level with engine at operating temperature and verify proper operation through all gears
• Monitor for leaks during first 100 miles of operation
• Recheck engine oil and transmission fluid levels after initial test drive

More procedures for this vehicle