A/T - Noise Diagnosis Update
Bulletin 87-7125-1Date Feb. '87
Ref. No. 87-065-7125
Corp. Ref. No. 777109
SUBJECT: 1987 SERVICE MANUAL UPDATE NOISE DIAGNOSIS
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 Figure 46. - Broken, Mispositioned, or Missing.
NOISE IN ALL RANGES
Torque Converter Circuit
^ Torque Converter - Torque Converter Internally Damaged.
(A whine which may be RPM With Foot on Brake and Gear Selec-
or load sensitive and/or stops tor in Drive, Depress Accelerator to
when the Torque Converter Approximately 1200 RPM for No
Clutch engages.) More than 6 Seconds (Stall Test),
A Torque Converter Noise Increases Under Load.
Oil Pump System
^ Oil Pump Assembly - Oil Pump Rotor/Slide Thickness
(A high pitch whine which An Increase in Line Pressure will Refer to Figure 91
gets louder as engine RPM Vary an Oil Pump Noise.
increases or is pressure (Note During Preliminary Check
sensitive.) Procedure)
^ Pump Shaft Roller Bearing and Seal
Assembly (354). Refer to Figure 89L. - Bearing Race or Roller surfaces Rough or Pitted.
^ For Pump Cavitation
(A "popping" noise similar - Fluid Level Indicator for Bubbles.
to popcorn popping.)
^ Transmission Oil Strainer (33). Refer to Figure 5. - Blocked Screen
- Filter Seam Leak
^ Transmission Oil Strainer Seal (32)
Refer to Figure 5. - Mispositioned or Cut
^ For Pressure Buzz
(A buzz or high frequency - Verified by a Needle Vibration
rattle sound.) on a Pressure Gage. (Road test
May Be Necessary.)
^ Pressure Regulator Valve (365)
Refer to Figure 89L. - Calibration (Valve Shuttling)
Drive Link System
(A whine or growl increases With Engine Running and Foot on
and fades with vehicle Brake, Move the Gear Selector to
speed, most noticeable Drive. The Noise Will Stop as the
under light throttle accelera- Transaxle Engages Drive Range.
tion.)
^ Drive Link (Chain) Assembly (101)
(A slipping chain will cause Refer to Figure 78. - Stretched
a loud rattle during heavy
acceleration.) ^ Drive Sprocket (103)
Refer to Figure 78. - Teeth Broken or Sheared
- Bearing Surfaces Nicked or Scored
CONDITION/ Circuit or System
(General Description) Inspect For Cause
NOISE IN ALL RANGES
Drive Link System (Cont.)
^ Drive Sprocket Support (109)
Refer to Figure 45. - Bearing Outer Race Support Rough or Nicked.
^ Drive Sprocket Support Bearing
Assembly (108). Refer to Figure 41. - Bearing Race or Roller Surfaces Rough or Pitted.
^ Driven Sprocket (122)
Refer to Figure 78. - Teeth Broken or Sheared
- Bearing Surfaces Nicked or Scored
^ Driven Sprocket Support (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 pulsation Refer to Figure 96. - Calibration (Spacer Plate)
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 Shaft Seal Lack of Lubrication
transmission is hot.)
NOISE IN FIRST OR REVERSE
Input Gear Set
(A whine which is most ^ Input Internal Gear (637)
noticeable in first or reverse Refer to Figure 65. - Gears Worn, Pitted
and is related to vehicle
speed. The whine may di- - Thrust Washer Mating Surfaces Rough or Pitted
minish or go away after an upshift.)
CONDITION
Circuit or System For Cause
(General Description) Inspect
NOISE IN FIRST OR REVERSE
Input Gear Set
(Cont.) ^ 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 Reverse ^ Input Gear Set
Reaction Gear Set
(A whine which is most ^ Reaction Sun Gear (646)
noticeable in second gear Refer to Figure 56. - Gears Worn, Pitted
and is related to vehicle
speed. The whine may di- - Thrust Washer or Thrust Bearing Mating Surface
minish or go away after an Rough or Pitted
upshift.)
^ Reaction Carrier Assembly (665)
Refer to Figure 56. - Gears Worn, Pitted, Pinions Tilting
- Thrust Washer Mating Surfaces Rough or Pitted
^ Reaction Sun Gear to Reaction Internal Gear Thrust Bearing (667). Refer to Figure 56. - Bearing Race or Roller 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 noise ^ Lo and Reverse Clutch Pack - Steel Plates Not Flat
most noticeable in second
or third between 25 MPH - Clutch Pack Clearance
and 40 MPH under coast or drive operation.)
CONDITION/ Circuit or System
(General Description) Inspect For Cause
NOISE IN SECOND (Cont.)
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 notice- ^ Final Drive Internal Gear (673)
able in first, second and Refer to Figure 49. - Gears Worn, Pitted
third, under light throttle
acceleration, and/or during - Thrust Washer or Thrust Bearing Mating Surface
turns.) Rough or Pitted
^ 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 Figure 49. - Bearing Race or Roller 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). Refer to Figure 49. - Bearing Race or Roller 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 noise ^ Hub and Bearing Assembly.
which may increase or be- Refer to Service Manual Section 3C. - Ruptured Seal or Dented Race
come noticeable when turning.)