ATSG GM HYDRA-MATIC 8L90 Automatic Transmission Rebuild Manual

This is the rebuild manual for the new Hydra-matic 8L90 (8 Speed RWD & 4WD).  It is a fully automatic eight speed rear wheel drive transmission that is available in both two and four wheel drive configurations. It features clutch to clutch shifting which provides eight forward and one reverse gear.

• Covers assembly, dis-assembly, diagnosis, troubleshooting, and electronic controls & operation.
• The 8L90 has undergone some parts changes from it’s inception until the present. Some of those changes are indicated in this manual and some are not.

The 8L90 transmission is a fully automatic eight speed rear wheel drive transmission that is available in both two and four wheel drive configurations. It features clutch to clutch shifting which provides eight forward and one reverse gear. It also uses a four element lockup torque converter, four planetary gear sets as well as five multiple disc and one mechanical clutch set. The 8L90 utilizes an off axis chain drive pump to maintain fluid volume and operating pressures. The externally located TCM controls the changing of gear ratios through the use of solenoids and also controls transmission line pressure through the use of a variable force motor. The TCM will also control converter clutch operation. The 8L90 has undergone some parts changes from it’s inception until the present. Many of those changes are indicated in this manual.The transmission in this manual was disassembled and reassembled without all factory tools.

Contents:

• General Description and Vehicle Application Chart
• Component Identification and Application Chart
• Shift Quadrant Operation
• Identification Tag Information and Specifications
• Transmission Fluid Requirement, Drain, Fill and Check Procedures
• Transmission Line Pressure Specifications
• Electronic Component Operation
• Solenoid Identification and Application Chart
• Manual Shift Shaft Position Switch Operation
• Transmission Speed Sensor Operation
• Transmission Fluid Temperature Sensor and Internal Main Harness ID
• Transmission Case Connector Terminal ID
• Wiring Diagram Example
• High Pressure Accumulator Stop / Start Operation
• Diagnostic Trouble Codes
• Solenoid Characterization Programming
• Transmission Disassemble
• Component Rebuild Section
• Transmission Assemble
• Transmission Final Assemble
• Air Check Locations
• Torque Specifications
• Special Tools

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