A/T - Diagnosis Information LO-Reverse Clutch
89Chevy16Number: 89-154-7A
Section: 7A
Date: April, 1989
Subject: DIAGNOSIS INFORMATION - LO - REVERSE CLUTCH THM 125C/ HYDRAMATIC 3T40
Model and Year: 1980-89 A, J, L CARS WITH 125C/ HYDRA-MATIC 3T40 TRANSAXLES
TO: ALL CHEVROLET DEALERS
This bulletin provides diagnosis information for possible inoperative Lo-Reverse Clutch assemblies used in the THM 125C/HYDRA-MATIC 3T40 transaxle.
Causes for an inoperative Lo-Reverse assembly are as follows:
In the Direct Clutch area:
^ Direct Clutch Drum Center Seal that is rolled and/or cut.
This condition would cause a cross circuit leak that would apply (drag) the Lo-Reverse clutch each time the vehicle is driven in the third gear range.
^ Driven Sprocket Support Seals - check for improperly cut angles.
In Lo-Reverse Clutch area:
^ Rolled and/or cut Lo-Reverse clutch piston seals.
^ Cup Plug Seals (improperly installed) or cut.
^ Cut O-Ring Seal on Lo-Reverse Pipe.
^ Bent and/or Leaky Lo-Reverse Pipe.
^ Bent and/or Missing Lo-Reverse Pipe Bracket.
Parts Non Conformity:
^ Porosity in the # 4 and # 5 Check ball area of the case cover (cross channel leak during 3rd gear apply).
^ # 6 Check ball not seated during apply.
^ Stuck Boost Valve.
^ Backing plate out of location.
Whenever a suspect Lo-Reverse condition exists all of the previous items should be inspected and/or replaced if necessary.
SERVICE MANUAL REFERENCE:
Whenever service to the Lo-Reverse Clutch Assembly is necessary refer to the THM 125C/HYDRA-MATIC 3T40 Unit Repair Section of your Service Manual.
SERVICE NOTES:
The Direct Clutch in the THM 125C/HYDRA-MATIC 3T40 is only applied in 3rd gear and Reverse. The Reverse Clutch is on in the Manual Lo and Reverse gear ranges. If a Lo-Reverse condition exists, the Direct Clutch assembly should be inspected.