For 1990-2009 cars

# NOISE DIAGNOSIS SHOP MANUAL SUPPLEMENT

#### MODELS AFFECTED: All 1987 SKYHAWKS, SOMERSETS/SKYLARKS, AND CENTURYS EQUIPPED WITH THM 125C (MD9) TRANSAXLES

Use the following information to update the THM 125C Automatic Transaxle section of the 1987 Buick Chassis Service Manual.

SERVICE ACTION

Before diagnosing the transaxle for a noise related condition, verify presence of noise in relation to drive range, vehicle speed, and engine RPM. Make certain the noise condition is not external to the transaxle. Refer to the noise and vibration analysis procedure, Section 7A, of the Service Manual.

Check for loose or misaligned components within the engine compartment which could contact the engine or transaxle during engine roll (engine torque movement).

Follow the preliminary check procedure as outlined in the oil pressure chart included in the THM 125C Hydraulic Diagnosis Section. Carefully note:

- Transaxle fluid level. - Condition of fluid (including presence of bubbles or contaminants on fluid level indicator). - Oil pressures as listed.

THM 125C NOISE DIAGNOSIS

#### NOTE: FOR ALL FIGURE REFERENCES, REFER TO THE THM 125C UNIT REPAIR SECTION OF THE 1987 SERVICE MANUAL

CONDITION/ Circuit or System (General Description) Inspect For Cause --------------------- ------- ---------- RATCHETING ---------- Park System Parking Pawl Spring (707) Refer to Broken, Mispositioned, Figure 46. or Missing. NOISE IN ALL RANGES ------------------- Torque Converter Circuit Torque Converter Torque Converter Internally Damaged. (A whine which may be With Foot on Brake and RPM or load sensitive Gear Selector in Drive, and/or stops when Depress Accelerator to Approximately 1200 RPM the Torque Converter for No More than 6 Seconds Clutch engages.) (Stall Test).A Torque Converter Noise increases Under Load.

Oil Pump System Oil Pump Assembly Oil Pump Rotor/Slide Thickness Refer to (A high pitch whine An increase in Line Figure 91 which gets louder as pressure will Vary an engine RPM increases Oil Pump Noise.(Note or is pressure During Preliminary Check sensitive.) Procedure)

Pump Shaft Roller Bearing and Seal Bearing Race or Roller Assembly(354). Surfaces Rough or Pitted. Refer to Figure 89L.

For Pump Cavitation

(A "popping"noise Fluid Level indicator for similar to popcorn Bubbles. popping.) Transmission Oil Strainer(33). Refer Blocked Screen to Figure 5.

Filter Seam Leak

Transmission Oil Strainer Seal (32) Refer to Mispositioned or Cut Figure 5.

For Pressure Buzz

(A buzz or high Verified by a Needle Vibration frequency rattle on a Pressure Gage. (Road test sound.) May Be Necessary.)

Pressure Regulator Valve (365) Refer to Calibration (Valve Figure 89L. Shuttling)

#### Drive Link System

(A whine or growl With Engine Running and increases and fades Foot on Brake, Move the with vehicle speed, Gear Selector to Drive. most noticeable under The Noise Will Stop as the light throttle accelera- Transaxle Engages Drive Range. tion.) Drive Link (Chain) Assembly (101) Refer to Figure 78. (A slipping chain Stretched will cause a loud rattle during heavy Drive Sprocket (103) acceleration.) Refer to Figure 78. Teeth Broken or Sheared

Bearing Surfaces Nicked or Scored

Drive Sprocket Support (109)Refer to Figure Bearing Outer Race 45. Support Rough or Nicked.

Drive Sprocket Support Bearing Assembly (108). Bearing Race or Roller Refer to Figure 41. Surfaces Rough or Pitted.

Driven Sprocket (122) Refer to Figure 78. Teeth Broken or Sheared

Bearing Surfaces Nicked Driven Sprocket or Scored Support(602) Refer to Bearing Outer Race Support Figure 76. Rough or Nicked

Driven Sprocket Support Bearing Assembly (601) Refer to Figure 76. Bearing Race or Roller Surfaces Rough or Pitted

#### NOISE DURING ACCELERATION

Drive Link System

#### Refer to:

Noise in All Ranges Drive Link Assembly

Torque Converter Circuit

#### Refer to:

Noise in All Ranges Torque Converter For Pressure Buzz

Control Valve Assembly Circuit Valve Body Spacer Plate (20)(2.8L Models Only) (Buzz will cause a Refer to Figure 96. Calibration(Spacer Plate) pulsation in the accelerator pedal.)

External Cooler Lines

Transaxle Cooler Pipes Vibrating Together or Against other Vehicle Components. SQUEAL AT LOW SPEED

Speedometer Assembly

(Most noticeable when Speedometer Driven Lack of Lubrication transmission is hot.) Gear Shaft Seal

NOISE IN FIRST OR REVERSE

Input Gear Set

(A whine which is most Input Internal Gear noticeable in first or (637)Refer to Gears Worn, Pitted reverse and is related Figure 65. to vehicle speed. The Thrust Washer Mating whine may diminish or Surfaces Rough or Pitted go away after anupshift.)

Input Carrier Assembly (640) Refer to Gears Worn, Pitted, Figure 65. Pinions Tilting Thrust Washer Mating Surfaces Rough or Pitted Input Sun Gear (642) Refer to Figure 65. Gears Worn, Pitted

Thrust Washer Mating Surfaces Rough or Pitted Reaction Gear Set

#### Refer to:

Noise in Second Reaction Gear Set

Final Drive Gear Set

#### Refer to:

Noise in Third and/or During Turns Final Drive Gear Set

NOISE IN SECOND

Input Gear Set

#### Refer to:

Noise in First or Input Gear Set Reverse

Reaction Gear Set

(A whine which is Reaction Sun Gear (646) most noticeable in Refer to Figure 56. Gears Worn, Pitted second gear and is related to vehicle Thrust Washer or Thrust speed. The whine may Bearing Mating Surface diminish or go away Rough or Pitted after an upshift.) Reaction Carrier Assembly (665)Refer Gears Worn, Pitted, to Figure 56. Pinions Tilting Thrust Washer Mating Surfaces Rough or Pitted Reaction Sun Gear to Reaction Internal Gear Thrust Bearing (667). Bearing Race or Roller Refer to Figure 56. Surfaces Rough or Pitted Reaction Internal Gear (668) Refer to Gears Worn, Pitted Figure 56. Thrust Washer or Thrust Bearing Mating Surface Rough or Pitted

Lo and Reverse Clutch

(A light metallic rattle Lo and Reverse Steel Plates Not Flat noise most noticeable Clutch Pack in second or third between Clutch Pack Clearance 25 MPH and 40MPH under coast or drive operation.)

Final Drive Gear Set

#### Refer to:

Noise in Third and/or During Turns Final Drive Gear Set

NOISE IN THIRD AND/OR DURING TURNS

Final Drive Gear Set

(A hum that may be Final Drive Internal noticeable in first, Gear (673)Refer to Gears Worn, Pitted second and third, Figure 49. under light throttle Thrust Washer or Thrust acceleration, and/or Bearing Mating Surface during turns.) Rough or Pitted Final Drive Sun Gear to Final Drive Internal Gear Thrust Bearing Bearing Race or Roller (674) Refer to Surfaces Rough or Pitted Figure 49.

Final Drive Sun Gear (675) Refer to Gears Worn, Pitted Figure 49. Thrust Washer or Thrust Bearing Mating Surface Rough or Pitted Final Drive Sun Gear to Differential Carrier Thrust Bearing Race or Roller Bearing (676) Surfaces Rough or Pitted Refer to Figure 49.

Differential Carrier (678) Refer to Gears Worn, Pitted, Figure 49. Pinions Tilting Thrust Washer or Thrust Bearing Mating Surfaces Rough or Pitted Differential Carrier to Case Thrust Bearing Bearing Race or Roller (681). Refer to Surfaces Rough or Pitted Figure 49.

Differential Pinions (685) Refer to Gears Worn, Pitted Figure 49. Thrust Washer Mating Surfaces Rough or Pitted Differential Side Gears (687)Refer to Gears Worn, Pitted Figure 49. Thrust Washer or Thrust Bearing Mating Surfaces Rough or Pitted

Lo and Reverse Clutch

#### Refer to:

Noise in Second Lo and Reverse Clutch

Wheel Bearing System

(Scratching or scraping Hub and Bearing noise which may increase Assembly. Refer to Ruptured Seal or or become noticeable when Service Manual Dented Race turning.) Section 3C.

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.