SUMMARY OF SHUDDER THM 440-T4 DIAGNOSIS-POTENTIAL CAUSES

Model and Year: 1984-1986 ALL MODELS WITH THM 440-T4 TRANSMISSIONS

TO: ALL CHEVROLET DEALERS

This bulletin provides additional diagnosis information, and a new Part Number, cancelling and superceding Chevrolet Dealer Service Bulletin 86-41 (Section 7A) dated March 1986 which should be destroyed. This bulletin also supplements Chevrolet Dealer Service Bulletin 85-34 (Section 7A) dated February, 1985.

A vehicle equipped with a 1984 through 1986 THM 440-T4 transaxle may experience a shudder condition which could be described as similar to driving over rough pavement. This condition may be the result of various engine and/or transaxle-related causes.

Before diagnosing for a transaxle-related shudder condition, make sure the condition is not engine-related.

Refer to the chart for trouble shooting procedures.

When performing any Service procedure, refer to the appropriate service Manual.

CONDITION INSPECT COMPONENT FOR CAUSE --------- ----------------- --------- ENGINE-RELATED SHUDDER, Engine Fuel Delivery System Restriction or OR "CHUGGLE" imbalance. For Engine Ignition System example,fouled fuel injectors due to deposits.

Improper operation. Includes items such as fouled or broken spark plugs.

TCC APPLY SHUDDER Torque Converter Cover Dimpling caused by too-long bolts(Max. Torque Converter length 15 mm).

TCC APPLY SHUDDER OR Turbine Shaft Seals See NOTE, following CROWD SHUDDER (Crowd chart. shudder occurs after TCC Accumulator Piston Seal TCC apply, when Missing or damaged. accelerator is depressed) Cut or rolled. Refer to Bulletin HM 85-17. TCC Solenoid O-Ring Cut or broken.

Valve Body Gasket Torn or mis- positioned. TCC CROWD SHUDDER Downshift Delay Module Improper operation. (Canadian 2.8 LE2 Only)

1-2 SHIFT SHUDDER 2nd Clutch Plates Replace steel and fiber plates(soak in transaxle fluid for 30 mins. prior to installation).

2-3 SHIFT SHUDDER Servo Release Pipe Seals Cut seals. Refer to Bulletin HM SHUDDER UNDER LOAD OR Right Rear Engine Mount 86-07. Engine ACCELERATION (1986 3.8L H-Body Only) grounding out.

NO TCC APPLY, DELAYED TCC TCC Solenoid Apply Valve, Sticking in valve RELEASE, OR TCC APPLY AND/ TCC Pressure Regulator body. (At start OR RELEASE SHUDDER Valve Or Spring of production 1986, the TCC regulator valve spring was eliminated on the following models: AAH,ACH,ADH,AFH, AMH,ARH,BHH,CFH, CHH, CMH, CNH,HBH, and HJH.) SHUDDER IN REVERSE Right Rear Engine Mount Engine grounding (1986 E-Body) out. Figure 2

A 1986 THM 440-T4 transaxle built before March 10, 1986 (Julian Date 069) may exhibit a torque converter clutch apply shudder at 45-55 mph.

Refer to Figure 1 for transaxle identification.

The shudder condition may be caused by the damper plate not fully seating.

If the TCC apply shudder condition is exhibited, and all diagnostic procedures have been performed, replace the torque converter with a service converter as indicated below.

MODEL TORQUE CONVERTER PART NUMBER ----- ---------------------------- 4CW, 5CM, 5CN, 5CP, 8656920 5CW, 5HA, 5HJ, 5HT, 6CFH, 6CMH, 6CNH

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.