NOISE DIAGNOSIS SHOP MANUAL SUPPLEMENT

6000, SUNBIRD, GRAND AM AND FIERO MODELS EQUIPPED WITH THM 125C TRANSAXLE

Noise diagnosis supplement for the 1987 THM 125C Automatic Transaxle Service Manual, Hydraulic Diagnosis Section.

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 Figure 46. Broken, Mispositioned, 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 the Depress Accelerator to Torque Converter Clutch Approximately 1200 RPM engages.) for no more than 6 Seconds (Stall Test).A Torque Converter Noise Increases Under Load. Oil Pump System Oil Pump Assembly Oil Pump Rotor/ Slide Thickness Refer to Figure 91

(A high pitch whine An increase in Line 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 Assembly(354). Bearing Race or Roller Refer to Figure 89L. Surfaces Rough or Pitted.

For Pump Cavitation

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

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 frequency rattle Vibration on a Pressure sound.) Gage. (Road test May Be Necessary.)

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

Drive Link System

(A whine or growl With Engine Running and increases and fades with Foot on Brake, Move the vehicle speed, most Gear Selector to Drive. noticeable under light The Noise Will Stop as the throttle acceleration.) Transaxle Engages Drive Range.

Drive Link (Chain) Assembly (A slipping chain will (101) Refer to Figure 78. Stretched cause a loud rattle during heavy accelera- Drive Sprocket (103) tion.) Refer to Figure 78. Teeth Broken or Sheared

Bearing Surfaces Nicked or Scored

NOISE IN ALL RANGES 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 Support or Scored (602) Refer to Figure 76. Bearing Outer Race Support 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 Gear Lack of Lubrication transmission is hot.) 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 Figure Gears Worn, Pitted reverse and is related 65. to vehicle speed. The Thrust Washer Mating whine may diminish or go Surfaces Rough or away after an upshift.) Pitted

Input Carrier Assembly (640)Refer to Figure 65. Gears Worn, Pitted, 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 most Reaction Sun Gear(646) noticeable in second Refer to Figure 56. Gears Worn, Pitted gear and is related to vehicle speed. The whine Thrust Washer or Thrust may diminish or go away Bearing Mating Surface after an upshift.) Rough or Pitted Reaction Carrier Assembly (665)Refer Gears Worn, Pitted, to Figure 56. Pinions Tilting

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 Figure 56. Gears Worn, Pitted

Thrust Washer or Thrust Bearing Mating Surface Rough or Pitted

Lo and Reverse Clutch

(A light metallic rattle Lo and Reverse Clutch Steel Plates Not Flat noise most noticeable in Pack second or third between Clutch Pack Clearance 25 MPH and 40 MPH 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, under Figure 49. light throttle accelera- Thrust Washer or Thrust tion, and/or during turns.) Bearing Mating Surface

Final Drive Sun Gear to Final Drive Internal Gear Thrust Bearing (674) Refer to Figure 49. Bearing Race or Roller Surfaces Rough or Pitted Final Drive Sun Gear (675)Refer to Figure 49. Gears Worn, Pitted

Thrust Washer or Thrust Bearing Mating Surface Rough or Pitted

Final Drive Sun Gear to Differential Carrier Thrust Bearing (676) Refer to Bearing Race or Roller Figure 49. Surfaces Rough or Pitted

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

Differential Carrier to Case Thrust Bearing (681).Bearing Race or Roller Refer to Figure 49. Surfaces Rough or Pitted

Differential Pinions (685)Refer to Figure 49. Gears Worn, Pitted

Thrust Washer Mating Surfaces Rough or Pitted

Differential Side Gears (687)Refer to Figure 49. Gears Worn, Pitted

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 Assembly. noise which may increase Refer to Service Manual Ruptured Seal or or become noticeable when Section 3C. Dented Race turning.)

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.