Transmission Rebuild - Automatic

Complete removal, disassembly, inspection, rebuilding, and reinstallation of the Powerglide or Turbo Hydra-Matic automatic transmission in a 1966 Chevrolet Corvette with 327ci V8.

Warnings

Tools required

Parts

• Automatic transmission master rebuild kit (Powerglide or TH400 specific) × 1 — Use OEM specification or Borg Warner/ATP rebuild kit
• Transmission filter × 1 — GM 8630204 or equivalent
• Transmission oil pan gasket × 1 — Fel-Pro TOS18621 or equivalent
• Rear transmission seal × 1 — National 223015 or equivalent
• Front pump seal × 1 — National 222470 or equivalent
• Modulator valve (if applicable) × 1 — GM 8630206 or equivalent
• Torque converter (if damaged or worn) × 1 — Use OEM specification for stall speed
• Transmission mount × 1 — GM 3858403 or equivalent
• Driveshaft U-joint straps × 1 — Use OEM specification
• Throttle valve cable or linkage bushings × 1 — Use OEM specification
• Thread sealant (non-hardening) × 1 — Permatex 59214 or equivalent

Fluids

• Dexron III ATF — 11.5 qt

Preparation

1. Verify transmission type (Powerglide or TH400) by checking ID tag on transmission case right side
2. Obtain correct rebuild kit and service manual specific to your transmission model
3. Prepare clean, well-lit workspace with adequate room for transmission disassembly
4. Disconnect negative battery cable at battery
5. Raise vehicle on lift or jack stands at all four corners to working height, ensuring vehicle is level and secure
6. Place drain pan under transmission and drain fluid by removing pan bolts
7. Mark driveshaft and rear axle flange with paint for installation reference
8. Remove torque converter cover/inspection plate from bellhousing
9. Mark torque converter to flexplate relationship with paint before separation

Procedure

1. 1

   Disconnect external transmission connections
   Disconnect shift linkage at transmission lever and remove linkage rod. Disconnect throttle valve cable or kickdown linkage at transmission. Disconnect vacuum modulator line (if equipped) at modulator valve on right side of transmission case. Disconnect speedometer cable at transmission by unscrewing retaining clip. Disconnect neutral safety switch electrical connector. Disconnect transmission cooler lines at transmission fittings using flare nut wrench; plug open lines to prevent fluid loss.
2. 2

   Remove driveshaft
   Remove 4 U-joint bearing cap straps at rear axle pinion flange. Slide driveshaft rearward to disengage slip yoke from transmission output shaft. Lower driveshaft and remove from vehicle. Install transmission output shaft plug or tape over opening to prevent fluid leakage during removal.
3. 3

   Separate torque converter from flexplate
   Rotate crankshaft using breaker bar on harmonic balancer bolt to access each torque converter to flexplate bolt through inspection opening. Remove 3 torque converter mounting bolts. Push torque converter fully into transmission bellhousing to disengage from crankshaft pilot. Verify converter is fully seated in pump by measuring distance from bellhousing face to converter mounting pad; should be approximately 1/2 inch recessed.
4. 4

   Support engine and remove transmission mount
   Install engine support fixture across engine compartment or support engine from above using hoist with load leveler. Remove 2 transmission mount to crossmember bolts. Remove crossmember to frame bolts and remove crossmember from vehicle.
5. 5

   Remove transmission to bellhousing bolts
   Position transmission jack under transmission oil pan with safety chains. Remove bellhousing to transmission case bolts. On Powerglide, remove 6 bellhousing bolts; on TH400, remove 6 bellhousing bolts. Support transmission weight on jack and remove upper bellhousing bolts using extension and universal joint.
6. 6

   Remove transmission from vehicle
   Slide transmission rearward away from engine approximately 2 inches to disengage input shaft from engine crankshaft pilot. Ensure torque converter remains fully seated in transmission pump during removal. Carefully lower transmission on jack and roll out from under vehicle. Tilt transmission nose-up slightly to prevent torque converter from sliding out of pump during handling.
7. 7

   Remove external components
   Mount transmission securely on work stand or holding fixture. Remove vacuum modulator (if equipped) by unscrewing from case. Remove speedometer driven gear housing and gear. Remove manual shift lever and shaft. Remove neutral safety switch. Remove throttle valve lever and shaft assembly. Remove torque converter by pulling straight out of pump; drain converter fluid into pan.
8. 8

   Remove oil pan and valve body
   Remove oil pan bolts and remove pan; discard gasket. Remove transmission filter by pulling downward; discard filter. Remove valve body mounting bolts in correct sequence (note locations of different length bolts). Carefully lower valve body while disconnecting detent cable or throttle valve linkage. Remove valve body from case. Remove separator plate and gaskets; note orientation and condition.
9. 9

   Disassemble front pump assembly
   Remove front pump retaining bolts from inside transmission case. Use slide hammer or pump puller to remove pump assembly from case; pump is interference fit. Remove pump O-ring seal and discard. Disassemble pump by removing 5 pump cover bolts. Separate pump halves and remove driven and drive gears. Remove pump bushing using bushing driver if worn or damaged.
10. 10

    Remove clutch assemblies and bands
    Remove input shaft and forward clutch assembly as unit by pulling straight out of case. Remove direct clutch drum assembly. Remove intermediate clutch pack components. Remove band adjusting screw locknut and screw, then remove band and struts. Remove servo covers by compressing with spring compressor tool and removing snap rings; remove servo pistons and springs. Keep all components separated and labeled by position.
11. 11

    Remove output shaft and planetary gear set
    Remove output shaft snap ring from rear of case. Remove complete output shaft assembly including planetary gear sets, sun gear, and internal components as single unit. Remove thrust washers and bearings, noting exact position and orientation of each. Remove governor assembly from output shaft by removing snap ring and sliding governor off shaft.
12. 12

    Clean and inspect all components
    Thoroughly clean all metal components in solvent and dry with compressed air. Do not soak clutch plates or seals in solvent. Inspect all clutch plates for burning, scoring, or warping; measure thickness with micrometer and compare to service specifications. Inspect clutch drums for scoring, cracks, or wear. Inspect bands for lining condition and breakage. Inspect all bushings for wear using telescoping gauges; replace if clearances exceed specifications. Inspect planetary gear sets for tooth damage, bearing wear, or shaft scoring. Inspect case for cracks, porosity, or stripped threads. Inspect pump gears for scoring or excessive clearance.
13. 13

    Measure critical clearances and end play
    Measure all clutch pack clearances using feeler gauges against specifications in rebuild kit instructions. Measure pump gear clearances using feeler gauge between gear teeth and crescent, and gear face to housing. Measure servo bore diameter and piston diameter to verify clearances. Check all snap ring grooves for wear or damage. Document all measurements for comparison to specifications.
14. 14

    Replace seals, gaskets, and wear components
    Install new bushings in pump housing, clutch drums, and case using correct size bushing drivers. Install new front pump seal using seal installer; seal lip faces toward transmission. Install new rear output shaft seal into extension housing with seal lip facing forward. Replace all O-rings, seals, and gaskets from rebuild kit. Soak new clutch plates in Dexron III ATF for 30 minutes before installation. Replace any worn thrust washers or bearings with components from rebuild kit.
15. 15

    Reassemble pump assembly
    Lubricate pump gears with transmission assembly lube and install in pump housing with alignment marks matched. Install pump cover with new gasket or O-ring. Torque pump cover bolts in criss-cross pattern. Install new pump O-ring seal on outside diameter of pump body. Verify pump rotates freely by hand without binding.
16. 16

    Reassemble planetary gear sets and output shaft
    Install governor assembly onto output shaft with new seals; secure with snap ring. Lubricate all thrust washers with assembly lube and install on output shaft in correct positions per service manual diagram. Install planetary gear sets onto output shaft in correct order. Install complete output shaft assembly into case; ensure all components seat properly. Install output shaft snap ring.
17. 17

    Assemble clutch packs and bands
    Assemble forward clutch pack by installing new seals on piston, lubricating with ATF, and carefully installing piston into drum using twisting motion to prevent seal damage. Install clutch pack starting with waved steel plate, alternating friction and steel plates per specifications. Install pressure plate and snap ring. Measure clutch pack clearance with feeler gauge and verify against specifications. Repeat process for direct and intermediate clutch assemblies. Install bands and struts in case. Install servo pistons with new seals, springs, and covers; compress springs and install snap rings.
18. 18

    Air pressure test clutch packs and servos
    Apply 25-30 psi compressed air to each clutch pack apply passage through transmission case to verify piston movement and seal integrity. Listen for air leaks and watch for piston application. Test each servo by applying air pressure to apply passage; verify piston travels smoothly and band tightens. If any assembly fails air test, disassemble and inspect for seal damage or improper installation.
19. 19

    Install front pump assembly
    Lubricate pump O-ring with ATF and carefully install pump into case bore; pump should press in with moderate hand pressure until fully seated against case shoulder. Align pump bolt holes and install pump retaining bolts. Torque pump bolts to specification in criss-cross pattern. Verify input shaft rotates freely with pump installed.
20. 20

    Install valve body assembly
    Install new separator plate gaskets on both sides of separator plate; verify all holes align correctly. Position separator plate and gaskets onto case. Connect throttle valve linkage or detent cable to valve body as applicable. Carefully position valve body onto case and separator plate, ensuring manual valve aligns with shift lever pin. Install valve body mounting bolts in correct locations (note different lengths) and torque in sequence from center outward. Do not overtighten valve body bolts as case is aluminum and threads strip easily.
21. 21

    Install filter and oil pan
    Install new transmission filter onto valve body intake port; press firmly until seated. Clean oil pan thoroughly and install new gasket. Position oil pan onto case and install pan bolts. Torque pan bolts in criss-cross pattern starting from center to specification; do not overtighten as pan will distort.
22. 22

    Install external components
    Install manual shift lever and shaft with new seal; torque retaining nut to specification. Install throttle valve lever and shaft with new seal. Install neutral safety switch with new seal; adjust per specifications. Install speedometer driven gear and housing with new O-ring. Install vacuum modulator with new O-ring if equipped.
23. 23

    Install torque converter
    Inspect torque converter for damaged hub, cracked welds, or loose fins by shaking and listening for rattles. If converter shows damage or excessive wear, replace with new unit. Fill new or reused converter with 2 quarts Dexron III ATF before installation. Install converter into front pump by rotating and pushing inward; converter will engage in three stages (pump drive gear, forward clutch splines, input shaft). Verify converter is fully seated by measuring distance from bellhousing mating surface to converter mounting pad; should be approximately 1/2 inch recessed minimum.
24. 24

    Install transmission into vehicle
    Apply thin coat of high-temperature grease to torque converter pilot hub. Position transmission on transmission jack and raise into position under vehicle. Align transmission input shaft with engine crankshaft pilot and torque converter pilot with crankshaft register. Slide transmission forward carefully; input shaft should engage engine crankshaft pilot smoothly without forcing. If resistance is felt, rotate torque converter slightly to align splines. Once transmission contacts bellhousing, verify torque converter remains fully seated before installing bolts.
25. 25

    Install transmission mounting hardware
    Install bellhousing to transmission case bolts and torque to specification. Rotate crankshaft to access torque converter to flexplate bolt holes through inspection cover. Align torque converter and flexplate using marks made during disassembly. Install 3 torque converter to flexplate bolts and torque to specification. Install transmission crossmember and mount; torque crossmember bolts and mount bolts to specifications. Remove engine support fixture.
26. 26

    Connect external components and driveshaft
    Connect transmission cooler lines at transmission fittings; torque fittings to specification using flare nut wrench. Connect speedometer cable and secure retaining clip. Connect neutral safety switch electrical connector. Connect vacuum modulator line if equipped. Connect throttle valve cable or kickdown linkage and adjust per specifications. Connect shift linkage and adjust per specifications. Install driveshaft by aligning marks on driveshaft and pinion flange; install 4 U-joint straps and torque bolts to specification. Install torque converter inspection cover.
27. 27

    Fill transmission with fluid and initial startup
    Add 6 quarts Dexron III ATF through dipstick tube. Start engine and allow to idle. With parking brake applied and foot on brake pedal, shift transmission through all gear ranges slowly, pausing 3 seconds in each position. Return to Park. Check fluid level with engine running at idle and transmission at operating temperature (160-180°F); add fluid as needed to bring level to COLD mark on dipstick. After test drive, recheck fluid level at operating temperature; level should be between ADD and FULL marks on dipstick.
28. 28

    Perform road test and adjustments
    Road test vehicle and verify proper operation through all gear ranges. Check for smooth shifts under light throttle, positive 1-2 and 2-3 upshifts, and proper downshifts. Verify no slipping, harsh engagement, or delayed shifts. Check for proper kickdown operation under full throttle. After road test, check transmission for leaks at all external seals and connections. Adjust shift linkage if necessary to ensure proper gate position. Adjust throttle valve cable or kickdown linkage per specifications if shift points are incorrect. Recheck fluid level and condition; fluid should be clean red color without burnt smell.

Reassembly

1. Transmission rebuild requires precise reassembly in reverse order of disassembly with all new seals, gaskets, and friction materials from rebuild kit
2. Critical clearances including clutch pack clearance, end play, and gear backlash must be measured and verified against specifications during reassembly
3. All internal components must be lubricated with Dexron III ATF or transmission assembly lube during installation
4. Air pressure testing of all clutch packs and servos must be performed before final assembly to verify seal integrity
5. Valve body bolt torque sequence and specifications are critical to prevent case damage and ensure proper hydraulic circuit operation

Verification

• Verify transmission shifts smoothly through all gears without slipping or harsh engagement
• Verify no external fluid leaks at pan gasket, cooler lines, modulator, speedometer housing, or output shaft seal
• Verify proper fluid level at operating temperature with transmission in Park and engine idling
• Verify shift linkage operates correctly with proper gate alignment in all positions
• Verify throttle valve cable or kickdown linkage provides proper shift timing under various throttle positions
• Verify torque converter does not exhibit shudder, excessive noise, or vibration
• Verify transmission operates quietly without whining, grinding, or rattling noises
• Verify proper operation of neutral safety switch (engine starts only in Park or Neutral)

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