Complete removal and reinstallation of the Powerglide or Turbo Hydra-Matic 400 automatic transmission from a 1966 Corvette 327 V8, including driveshaft removal, torque converter separation, crossmember detachment, and all necessary disconnections.

Warnings

Tools required

Parts

• Transmission pan gasket × 1 — Use OEM specification
• Transmission filter × 1 — Use OEM specification
• Torque converter seal × 1 — Use OEM specification
• Rear transmission seal (extension housing seal) × 1 — Use OEM specification
• Transmission cooler lines (if damaged) × 1 — Use OEM specification
• Exhaust gaskets (if disturbed) × 1 — Use OEM specification
• U-joint straps/bolts (if replacing) × 1 — Use OEM specification

Fluids

• Dexron III ATF — 11.5 qt

Preparation

1. Disconnect negative battery cable at the battery.
2. Raise vehicle on a lift or securely support on jack stands at all four corners, providing adequate working clearance underneath.
3. Remove the transmission dipstick from the dipstick tube.
4. Mark the driveshaft-to-differential yoke orientation with paint or marker for proper reassembly alignment.
5. Place drain pan under transmission pan and drain transmission fluid by removing pan bolts (fluid will drain as pan is loosened).
6. Allow engine to cool completely if recently operated.

Procedure

1. 1

   Remove transmission inspection cover
   Remove the bellhousing inspection cover (lower dust shield) from the bottom of the bellhousing to access the torque converter bolts. This cover is typically held by 2 bolts on the lower bellhousing.
2. 2

   Mark and disconnect torque converter from flexplate
   Rotate the engine crankshaft using a breaker bar on the front harmonic balancer bolt to bring each torque converter-to-flexplate bolt into view through the inspection opening. Mark the converter-to-flexplate relationship with paint. Remove all 3 torque converter mounting bolts. Push the torque converter back slightly toward the transmission to disengage it from the crankshaft pilot.
3. 3

   Disconnect driveshaft from transmission
   Remove the 4 U-joint strap bolts at the differential yoke. Slide the driveshaft rearward to disengage the slip yoke from the transmission output shaft. Plug or cap the transmission extension housing to prevent fluid loss and contamination.
4. 4

   Disconnect transmission cooler lines
   Using a line wrench or flare nut wrench, disconnect the two transmission cooler lines from the transmission case fittings on the right side of the transmission. Cap or plug the lines and transmission ports immediately to prevent fluid loss and contamination. Note the routing for reinstallation.
5. 5

   Disconnect shift linkage
   Disconnect the shift linkage rod from the transmission shift lever. On column shift models, this is typically a clevis pin connection at the transmission lever. Remove the retaining clip and slide the pin out. Mark or note the linkage adjustment position if possible.
6. 6

   Disconnect vacuum modulator line
   Disconnect the vacuum line from the vacuum modulator valve on the right rear of the transmission. This line connects to the engine intake manifold and controls shift firmness based on engine vacuum. Note: Powerglide transmissions do not have a vacuum modulator; skip this step if equipped with Powerglide.
7. 7

   Disconnect electrical connections
   Disconnect any electrical connections to the transmission. This may include the backup light switch (neutral safety switch) connector located on the left side of the transmission case. Tag connections if necessary for proper reinstallation.
8. 8

   Disconnect speedometer cable
   Unscrew the speedometer cable from the speedometer driven gear housing on the right side of the transmission extension housing. The cable has a knurled nut that unscrews by hand or with pliers. Carefully pull the cable and driven gear assembly out of the transmission.
9. 9

   Support engine and transmission
   Position a transmission jack under the transmission pan with a block of wood to distribute load. Raise jack until it just contacts the transmission and provides slight support. Place a floor jack with a block of wood under the engine oil pan to support engine weight once the transmission mount is disconnected. Be careful not to dent the oil pan.
10. 10

    Remove transmission crossmember
    Remove the 2 transmission mount-to-crossmember bolts or nuts. Then remove the 4 crossmember-to-frame bolts (2 on each side). Lower and remove the crossmember from the vehicle. The transmission is now supported only by the transmission jack and the bellhousing bolts.
11. 11

    Remove bellhousing-to-engine bolts
    Remove the bellhousing-to-engine block bolts. There are typically 6 bolts securing the bellhousing to the engine block on the 327 V8. Note that some bolts may be accessed from above in the engine compartment while others are accessed from below. Keep track of bolt lengths and locations as they may vary.
12. 12

    Separate and lower transmission
    With all bolts removed and the transmission supported on the jack, carefully pull the transmission straight back away from the engine. Move slowly to ensure the torque converter remains seated in the transmission pump (it should stay with the transmission, not the engine). Once the input shaft clears the bellhousing, angle the transmission slightly nose-down and lower it carefully on the transmission jack. Secure the torque converter to the transmission with a C-clamp, safety wire, or converter holding strap so it doesn't slide out during handling.
13. 13

    Inspect and clean mating surfaces
    With the transmission removed, inspect the engine block bellhousing mounting surface, flexplate, torque converter pilot in the crankshaft, and rear main seal for damage, wear, or leaks. Clean all mating surfaces with a wire brush and brake cleaner. Replace the rear transmission seal in the extension housing and the torque converter front seal before reinstallation.

Reassembly

1. Before installing transmission, verify the torque converter is fully seated in the transmission pump by measuring the distance from the bellhousing face to the converter mounting lugs - it should be approximately 1/2 inch to 3/4 inch recessed, and the converter should rotate freely.
2. Apply a small amount of high-temperature grease to the torque converter pilot hub and the input shaft splines.
3. Ensure the torque converter rotates freely and is fully engaged with the pump drive and stator support before mating the transmission to the engine.
4. When reinstalling bellhousing bolts, thread all bolts in by hand first to ensure proper alignment before tightening.
5. After bolting transmission to engine, verify that the torque converter rotates freely before installing the converter-to-flexplate bolts.
6. When reconnecting the driveshaft, align the marks made during disassembly to maintain driveline balance.
7. Install new transmission filter and pan gasket before filling with fluid.
8. Refill transmission with 11.5 quarts of Dexron III ATF through the dipstick tube, then check level with engine running in Park after reaching operating temperature.
9. Adjust shift linkage per factory specifications after installation to ensure proper gate selection and Park/Neutral safety switch operation.

Verification

• With engine running, verify transmission shifts smoothly through all gears (P-R-N-D-L for TH400 or P-R-N-D-L for Powerglide).
• Check for fluid leaks at the pan gasket, cooler line fittings, speedometer cable housing, extension housing seal, and torque converter seal.
• Verify backup lights illuminate in Reverse and engine starts only in Park and Neutral.
• Road test vehicle to verify smooth shifting under load, proper shift points, and no unusual noises or vibrations.
• Recheck transmission fluid level after road test with engine at operating temperature and running in Park.
• Verify no driveline vibration indicating driveshaft was installed out of phase.

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