Flexplate

This procedure covers removal and replacement of the flexplate on a 1970 AMC Rebel Machine with 390ci V8, requiring transmission removal to access the flexplate between engine and torque converter.

Warnings

Tools required

Parts

• Flexplate × 1 — Use OEM specification for 390ci V8 automatic transmission
• Flexplate bolts × 1 — Replace all crankshaft-to-flexplate bolts
• Torque converter bolts × 1 — Replace if damaged or stripped
• Transmission pan gasket × 1 — Use OEM specification
• Rear transmission mount × 1 — Replace if deteriorated

Fluids

• Automatic transmission fluid (Type A suffix A or Dexron) — 6 qt

Preparation

1. Park vehicle on level surface and set parking brake firmly
2. Disconnect negative battery cable
3. Raise vehicle and support securely on jack stands at frame rails
4. Remove exhaust crossover pipe from exhaust manifolds to provide clearance
5. Mark driveshaft-to-differential yoke orientation for proper reinstallation
6. Remove driveshaft and plug transmission tailshaft to prevent fluid loss
7. Disconnect transmission cooler lines at transmission and cap openings
8. Disconnect shift linkage and throttle valve linkage from transmission
9. Disconnect speedometer cable from transmission
10. Disconnect electrical connectors from neutral safety switch and any other transmission sensors
11. Place drain pan under transmission pan and drain transmission fluid

Procedure

1. 1

   Remove transmission inspection cover
   Locate and remove the stamped steel inspection cover on the bellhousing that provides access to the torque converter and flexplate bolts. This cover is typically held by 2-4 bolts on the lower bellhousing area.
2. 2

   Mark torque converter to flexplate relationship
   Using a paint marker or scribe, mark one torque converter bolt location relative to the flexplate to ensure reinstallation in the same position. Rotate crankshaft using a socket on the front crankshaft bolt to access each torque converter bolt through the inspection opening.
3. 3

   Remove torque converter bolts
   Remove all torque converter-to-flexplate bolts (typically 4 bolts). Use flywheel holding tool or have assistant hold crankshaft from rotating. Rotate engine incrementally to access each bolt through inspection cover. Push torque converter back into transmission slightly after bolts are removed.
4. 4

   Support transmission with transmission jack
   Position transmission jack under transmission oil pan with a wood block to distribute load. Raise jack until it just contacts transmission, taking slight weight but not lifting. Secure transmission to jack with safety chain or strap.
5. 5

   Remove transmission crossmember
   Remove bolts securing transmission mount to crossmember, then remove bolts securing crossmember to frame rails. Lower transmission jack slightly and remove crossmember from vehicle. Inspect transmission mount for damage and replace if necessary.
6. 6

   Remove bellhousing bolts
   Remove all bellhousing-to-engine block bolts (typically 4-6 bolts of various lengths). Note location of different length bolts for proper reinstallation. There may be bolts accessible from above and below the vehicle.
7. 7

   Separate and lower transmission
   Carefully pull transmission straight back on jack to disengage input shaft from crankshaft pilot bushing. Ensure torque converter remains fully seated in transmission pump (should be recessed approximately 1/2 inch from bellhousing face). Lower transmission on jack and roll out from under vehicle with helper assistance.
8. 8

   Mark and remove flexplate
   Mark flexplate position relative to crankshaft flange using paint marker. Use flywheel holding tool wedged between flexplate teeth and block to prevent rotation. Remove all flexplate-to-crankshaft bolts working in a cross pattern. Carefully remove flexplate from crankshaft, noting location of any shims or spacers behind flexplate.
9. 9

   Inspect and clean mating surfaces
   Thoroughly inspect crankshaft flange for cracks, damage, or excessive runout. Clean all mating surfaces on crankshaft flange and inside pilot bushing bore using solvent and clean rag. Inspect pilot bushing in crankshaft for wear and replace if necessary. Clean all old thread locker from bolt holes.
10. 10

    Install new flexplate
    Position new flexplate on crankshaft flange aligning with marks made during disassembly to maintain engine balance. Install new flexplate bolts with thread locker, starting all bolts by hand. Torque bolts in a cross pattern per manufacturer specifications (typically 95-105 ft-lbs for AMC 390). Verify flexplate rotates freely without binding or excessive runout.
11. 11

    Reinstall transmission
    With helper, position transmission on jack and roll under vehicle. Ensure torque converter is fully seated in pump before attempting to mate transmission to engine. Carefully align transmission to engine block dowel pins and slide forward, ensuring input shaft enters crankshaft pilot bushing. Install all bellhousing bolts and tighten evenly.
12. 12

    Install crossmember and mount
    Raise transmission into position with jack. Install crossmember to frame rails and tighten bolts. Install transmission mount to crossmember and transmission, ensuring proper alignment before final tightening. Remove transmission jack once mount is secured.
13. 13

    Install torque converter bolts
    Rotate flexplate to align with marks made during disassembly. Install torque converter bolts through inspection cover opening, rotating crankshaft to access each bolt location. Torque bolts to specification (typically 35-45 ft-lbs). Verify torque converter pulls tight to flexplate with no gap.

Reassembly

1. Install transmission inspection cover with all bolts
2. Reconnect all electrical connectors to neutral safety switch and sensors
3. Reconnect speedometer cable
4. Reconnect shift linkage and throttle valve linkage, adjusting per factory specifications
5. Reconnect transmission cooler lines and tighten fittings securely
6. Install driveshaft aligning marks made during disassembly
7. Install exhaust crossover pipe with new gaskets if needed
8. Fill transmission with proper type and quantity of automatic transmission fluid
9. Reconnect negative battery cable

Verification

• Start engine and verify no unusual noises from bellhousing area
• Check for transmission fluid leaks around pan, cooler lines, and all connections
• With engine at operating temperature, check transmission fluid level and add as needed
• Test drive vehicle and verify smooth engagement in all gears with no slippage
• Listen for any abnormal starter engagement noises that could indicate flexplate/ring gear problems
• Verify no vibration that could indicate improper flexplate balance or installation
• Recheck all fastener torques after test drive

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