Transmission Rebuild - Automatic

Complete removal, disassembly, rebuild, and reinstallation of the 8L90 8-speed automatic transmission including replacement of clutches, seals, bands, and internal hard parts.

Warnings

Tools required

Parts

• 8L90 transmission rebuild kit (includes clutches, steels, seals, gaskets) × 1 — Use OEM or Sonnax/Transgo equivalent
• Transmission filter kit × 1 — ACDelco 24277652 or equivalent
• Torque converter (if damaged or contaminated) × 1 — Verify stall speed matches application
• Transmission pan gasket × 1 — ACDelco or rubber composite
• Transmission drain plug washer × 1 — Use new crush washer
• Front pump seal × 1 — Included in rebuild kit
• Rear output shaft seal × 1 — Included in rebuild kit
• Valve body separator plate and gaskets × 1 — Included in rebuild kit
• Bushings (as needed per inspection) × 1 — Use OEM specification
• Thrust washers/bearings (as needed) × 1 — Measure for wear, included in rebuild kit
• Wave plate and springs × 1 — Included in rebuild kit

Fluids

• ACDelco Dexron VI ATF — 11.5 qt

Preparation

1. Park vehicle on level surface, engage parking brake, and place wheel chocks at rear wheels
2. Disconnect negative battery cable and wait 2 minutes for airbag system to discharge
3. Raise vehicle on lift to working height and verify secure engagement on frame lift points
4. Remove transmission skid plate if equipped
5. Place drain pan under transmission pan and drain fluid via drain plug if equipped, otherwise remove pan bolts
6. Mark driveshaft-to-pinion flange relationship for reinstallation alignment
7. Prepare clean workspace with transmission holding fixture for bench work
8. Organize parts storage containers and label for each clutch pack and component location
9. Review service manual for specific 8L90 assembly clearances and specifications

Procedure

1. 1

   Remove transmission from vehicle
   Disconnect electrical connectors at transmission (range sensor, solenoids, speed sensors). Remove transmission cooler lines at radiator connections and cap lines. Disconnect shift linkage at transmission lever. Support engine with fixture or hoist. Remove crossmember mounting bolts. Support transmission with transmission jack. Remove bellhousing-to-engine mounting bolts. Mark torque converter-to-flexplate position, then remove torque converter bolts through starter opening. Carefully slide transmission rearward off dowel pins and lower from vehicle while supporting torque converter to prevent dropping.
   Torque spec

   Mounting Bolts76 Nm (56 lb-ft)

   Flywheel Bolts95 Nm (70 lb-ft)
2. 2

   Mount transmission and remove external components
   Secure transmission to holding fixture in vertical position (bell housing up). Remove torque converter and inspect for debris, bearing wear, and hub damage. Remove transmission pan bolts in cross pattern and remove pan. Remove transmission filter. Remove valve body bolts (note varying lengths and positions) and carefully lower valve body assembly. Mark and remove all external sensors, wiring harness, and park pawl components. Remove pump bolts and extract front pump assembly using slide hammers or pry evenly.
   Torque spec

   Pan Bolts20 Nm (15 lb-ft)

   Sensor Bolts14 Nm (10 lb-ft)
3. 3

   Disassemble transmission case and measure end play
   With pump removed, install dial indicator on input shaft. Measure input shaft end play by lifting and pushing shaft while reading dial indicator. Record measurement (specification typically 0.010-0.030 inch). Remove retaining ring for input clutch assembly. Remove input clutch drum assembly by lifting straight up. Tag and photograph clutch pack arrangement. Remove intermediate clutch assembly, noting thrust washer locations and orientations. Continue disassembly of clutch packs, documenting each component position.
4. 4

   Remove output shaft and planetary assemblies
   Remove output shaft retaining ring. Slide output shaft assembly forward and out of case. Remove planetary gear sets, noting which set goes in which position (front/rear). Remove sun gear shells and inspect splines for wear. Extract reaction carrier assembly. Remove all remaining snap rings, thrust washers, and bearings, keeping them organized by location. Inspect case for cracks, porosity, or damage to clutch apply passages.
5. 5

   Disassemble and inspect clutch packs
   For each clutch pack assembly: compress springs using clutch spring compressor tool and remove retaining ring. Remove pressure plate, springs, and backing plate. Remove friction clutches and steel separator plates, counting each. Measure friction clutch thickness with micrometer (compare to service limit). Inspect steel plates for heat discoloration, scoring, or warping using straightedge. Check piston for cracks and seal grooves for damage. Remove and discard all seals. Inspect clutch drum splines and bushings for wear. Air check each clutch apply circuit in case for blockage.
6. 6

   Clean and inspect all components
   Thoroughly clean all hard parts in solvent tank or parts washer. Dry with compressed air, blowing out all oil passages in case, drums, and shafts. Inspect all bushings for scoring or excessive wear using telescoping gauge. Check all bearing surfaces for damage. Inspect all gear teeth for chips, excessive wear, or cracks. Measure planetary pinion end play using feeler gauges (typically 0.009-0.032 inch depending on set). Inspect thrust washers and races for wear or grooving. Replace any worn bushings using bushing removal/installation tools. Verify all case oil passages are clear using compressed air.
7. 7

   Reassemble clutch packs with new components
   Install new seals on all pistons using seal installation tools, ensuring lips face correct direction per service manual. Lubricate seals with ATF. Install piston into drum, rotating and pressing evenly to seat seals. Install new wave plate and return springs. Install backing plate and compress springs with tool. Install new retaining ring, ensuring full seating in groove. Soak new friction clutches in Dexron VI for 30 minutes minimum. Install clutches and steels in correct order per rebuild kit instructions, alternating friction and steel. Install pressure plate and measure clutch pack clearance with feeler gauge (specification typically 0.025-0.055 inch, varies by clutch). Adjust clearance with selective backing plates if needed. Air check each clutch pack at 30 psi to verify piston apply and seal integrity.
8. 8

   Reassemble case with planetary and output components
   Install all new thrust washers and bearings in case using assembly lubricant to hold in place. Install reaction carrier assembly into case. Install sun gear shells in correct positions. Install planetary gear sets, verifying correct front/rear placement and engagement with sun gears. Install output shaft assembly, ensuring all splines engage properly. Verify output shaft rotates smoothly. Install retaining ring for output shaft. Check that all thrust bearings are still in position.
9. 9

   Install clutch assemblies and verify operation
   Install intermediate clutch assembly with new seals and gaskets, aligning with case passages. Install input clutch drum assembly, ensuring engagement with planetary components and proper alignment of thrust washers. Rotate input shaft to verify smooth operation. Install input clutch retaining ring. Verify ring is fully seated in groove. Apply compressed air to each clutch apply passage in case (one at a time) at 30 psi while rotating input/output shafts to verify clutch engagement and proper operation. Listen for air leaks indicating seal problems.
10. 10

    Install front pump and check end play
    Install new pump seal into pump body using seal driver. Install new pump-to-case gasket or seal. Carefully align pump with case, ensuring input shaft engages pump gears. Rotate pump while pressing to ensure full seating. Install pump bolts and tighten to specification in cross pattern. Reinstall dial indicator on input shaft and measure final end play. Compare to initial measurement and specification. If out of specification, select different thickness thrust washers to correct. End play is critical for transmission durability.
11. 11

    Rebuild and install valve body
    Disassemble valve body on clean workbench. Remove all solenoids, noting positions. Remove valve body cover screws and separate body halves. Remove all valves and springs, organizing in order. Clean all valves and bores thoroughly. Inspect valves for scoring or wear. Check valve springs for weakening or damage. Replace all valve body seals and gaskets per rebuild kit. Install updated separator plate and gaskets if included in kit. Reassemble valve body with new components, ensuring all check balls are in correct positions per service manual diagram. Install solenoids with new seals. Torque valve body cover screws. Install valve body into transmission case, aligning manual valve with shift lever. Install and torque valve body bolts (note varying lengths).
    Torque spec

    Cover Screws14 Nm (10 lb-ft)
12. 12

    Install filter, pan, and external components
    Install new transmission filter and seal, pressing firmly to seat. Clean transmission pan thoroughly and install new gasket. Position pan on case and start all bolts by hand. Torque pan bolts in criss-cross pattern starting from center. Install rear output shaft seal using seal driver. Install all external sensors with new seals/O-rings. Install park pawl components and linkage. Install transmission range sensor and adjust per specification (typically in Park position). Install wiring harness and secure all connectors.
    Torque spec

    Pan Bolts20 Nm (15 lb-ft)

    Sensor Bolts14 Nm (10 lb-ft)
13. 13

    Prepare torque converter and reinstall transmission
    Install new torque converter or verify used converter cleanliness. Check torque converter end play and bearing condition. Measure torque converter depth in bellhousing to verify proper seating (should be recessed minimum 0.5 inch from bellhousing face). Install new pilot bushing in crankshaft if needed. Apply small amount of grease to torque converter hub. Position transmission on transmission jack. Raise transmission to engine while supporting torque converter. Align transmission with dowel pins and slide forward until bellhousing contacts engine. Install and torque bellhousing mounting bolts. Rotate crankshaft to access torque converter bolt holes through starter opening. Align marks on flexplate and torque converter. Install and torque flywheel bolts in star pattern.
    Torque spec

    Mounting Bolts76 Nm (56 lb-ft)

    Flywheel Bolts95 Nm (70 lb-ft)
14. 14

    Reconnect all external connections and fill transmission
    Install crossmember and torque bolts to specification. Remove transmission jack and engine support. Reconnect transmission cooler lines, using new O-rings. Torque cooler line fittings to specification. Reconnect shift linkage and adjust if needed. Reconnect all electrical connectors to transmission sensors and solenoids. Verify park pawl operation by shifting into Park and attempting to rotate driveshaft. Install driveshaft, aligning reference marks. Torque driveshaft bolts to specification. Install skid plate if equipped. Lower vehicle. Fill transmission with 5 quarts Dexron VI through fill tube. Start engine and add fluid in 1 quart increments while cycling through gears.
    Torque spec

    Fill Plug42 Nm (31 lb-ft)
15. 15

    Perform initial startup and fluid level adjustment
    With engine at idle and transmission in Park, check for leaks at pan, cooler lines, and pump seal. Shift through all gear ranges with foot on brake, pausing 3 seconds in each range. Return to Park. Check fluid level on dipstick with engine running and transmission at operating temperature (195°F). Add fluid as needed to bring to proper level (between cross-hatched area on dipstick). Do not overfill. Recheck for leaks. Perform transmission relearn procedure using Tech 2 scan tool or equivalent by following prompts to allow TCM to learn new clutch characteristics.

Reassembly

1. All torque specifications must be followed precisely to prevent transmission failure
2. Ensure all thrust washers and bearings remain in position during assembly
3. Verify clutch pack clearances are within specification before final assembly
4. Air check all clutch circuits before installing valve body to verify seal integrity
5. End play measurement is critical - recheck if not within specification
6. Use only Dexron VI ATF - other fluids will cause transmission damage

Verification

• Check transmission fluid level at operating temperature with engine running in Park
• Verify no fluid leaks at pan, cooler lines, pump seal, or output shaft seal
• Test drive vehicle and verify all gear changes are smooth with no slipping or harsh engagement
• Verify proper engagement in all gears including manual mode if equipped
• Check for abnormal noises during gear changes or at idle in gear
• Verify transmission does not slip under load in any gear
• Confirm Park pawl holds vehicle on incline
• Monitor transmission temperature during test drive - should stabilize at 195-210°F
• Scan for diagnostic trouble codes using scan tool - address any codes present
• Recheck fluid level after test drive and top off if needed

Related trouble codes on this vehicle

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