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Copyright © ATSG 2004

ENERAL MOTORS125C (3T40)

AUTOMATIC TRANSMISSION SERVICE GROUP18639 SW 107TH AVENUEMIAMI, FLORIDA 33157

(305) 670-4161

MAINTENANCE AND ADJUSTMENTS.................................................................................................

ON CAR SERVICE.....................................................................................................................................

DIAGNOSIS AND REPAIR.......................................................................................................................

DISASSEMBLY..........................................................................................................................................

VALVE BODY.............................................................................................................................................

TECHNICAL BULLETINS.......................................................................................................................

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INTRODUCTIONTHM 125C (3T40)

AUTOMATIC TRANSMISSION SERVICE GROUP18639 SW 107TH AVENUEMIAMI, FLORIDA 33157

(305) 670-4161

ED KRUSETECHNICAL CONSULTANT

WAYNE COLONNATECHNICAL SUPERVISOR

PETER LUBANTECHNICAL CONSULTANT

JIM DIALTECHNICAL CONSULTANT

GREGORY LIPNICKTECHNICAL CONSULTANT

JERRY GOTTTECHNICAL CONSULTANT

JON GLATSTEINTECHNICAL CONSULTANT

DAVID CHALKERTECHNICAL CONSULTANT

ROLAND ALVAREZTECHNICAL CONSULTANT

GERALD CAMPBELLTECHNICAL CONSULTANT

1

No part of any ATSG publication may be reproduced, stored in any retrieval system or transmitted in any form or by any means, including but not limited to electronic, mechanical, photocopying, recording or otherwise, without written permission of Automatic Transmission Service Group. This includes all text illustrations, tables and charts.

"Portions of materials contained herein have been reprinted underlicense from General Motors Corporation, Service & Parts Operations

License Agreement #0510718."

The information and part numbers contained in this booklet havebeen carefully compiled from industry sources known for their

reliability, but ATSG does not guarantee its accuracy.

UpdatedOctober, 2002

We wish to thank General Motors Corporation for the information and illustrations that have made this booklet possible. This booklet contains the general description, diagnosis and overhaul procedures necessary to repair, overhaul or service the THM 125C (3T40) transaxle. In addition to this booklet for the assembly and disassembly procedures, the Green "Update Handbook" available from ATSG is also necessary to inform you of the many engineering changes that have occured over the years. The THM 125C transaxle represents the addition of a converter clutch to the THM 125 transaxle that was introduced in 1980. The Torque Converter Clutch was added to increase fuel economy by eliminating the fluid coupling of the transmission at road load conditions, replacing it with a direct mechanical connection. The torque converter smoothly couples the engine to the planetary gear system through three multiple disc clutch packs, one roller clutch and one band, to produce three forward speeds and reverse. Changing of the gear ratios and application of the converter clutch is controlled automatically.

DALE ENGLAND TECHNICAL CONSULTANT

MIKE SOUZATECHNICAL CONSULTANT

NOTES----NOTES----NOTES