NOISE DIAGNOSIS SHOP MANUAL SUPPLEMENT

BULLETIN COVERS:

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 cr 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 Torque converter Torque converter circuit internally damaged

(A whine which may With foot on brake and be RPM or load gear selector in drive, sensitive and/or depress accelerator to stops when the approximately 1200 RPM 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 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 Bearing race or roller and seal assembly (354). surfaces rough or Refer to Figure 89L. pitted.

For pump cavitation.

(A"popping" noise Fluid level indicator similar to popcorn for bubbles. popping.) Transmission oil strainer Blocked screen (33). Refer to figure 5. Filter seam leak

Transmission oil strainer Mispositioned or cut seal (32) Refer to Figure 5.

For pressure buzz

(A buss or high frequency rattle Verified by a needle sound.) vibration on a pressure gage. (road test may be necessary.)

Pressure regulator valve Calibration (Valve (363) Refer to 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 The noise will stop as under light throttle the transaxle engages acceleration.) drive range.

Drive link (chain) assembly Stretched (A slipping chain (101) refer to Figure 78. will cause a loud rattle during heavy Drive sprocket (103) acceleration.) Refer to Figure 78. Teeth broken or sheared

Bearing surface nicked or scored

Drive sprocket support Bearing outer race (109) Refer to Figure 45. support rough or nicked.

Drive sprocket support Bearing race or roller bearing assembly (108). surfaces rough or pitted. Refer to Figure 41.

Driven sprocket (122) Teeth broken or sheared Refer to Figure 78. Bearing surfaces nicked or Driven sprocket support scored (602) Refer to Figure 76. Bearing outer race support rough or nicked

Driven sprocket support Bearing race or roller bearing assembly (601) surfaces rough or pitted Refer to Figure 76.

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 Valve body spacer Assembly circuit plate (20) (2.8L models only) (Buzz will cause Refer to Figure 96. Calibraiton (spacer plate) a 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 Speedometer driven Lack of lubrication when transmission gear shaft seal is hot).

Noise in first or reverse

Input gear set

(A whine which is Input internal gear (637) most noticeable in Refer to Figure 65. first or reverse Gears worn, pitted and is related to vehicle speed. The Thrust washer mating whine may diminish surfaces rough or pitted. to go away after an upshift.)

Input carrier assembly Gears worn, pitted, (640) Refer to Figure 65. Pinions tilting

Thrust washer mating surfaces rough or pitted

Input sun gear (642) Gears worn, pitted Refer to figure 65. 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/ Final Drive gear set or during turns

Noise in second

Input gear set

Refer to:

Noise in first Input gear set or reverse

Reaction gear set

(A whine which is Reaction Sun Gear Gears worn, pitted most noticeable in (646) Refer to second gear and is Figure 56. Thrust washer or thrust related to vehicle mating surface rough or speed. The whine pitted. may diminish or go away after an Reaction carrier assy. Gears worn, pitted, upshift.) (665) Refer to figure 56. pinions tilting

Thrust washer mating surfaces rough or pitted

Reaction sun gear to reaction internal gear Bearing race or roller thrust bearing (667). surfaces rough or pitted refer to Figure 56. Gears worn, pitted Reaction internal gear (668) refer to Thrust washer or thrust Figure 56. bearing mating surface rough or pitted

Lo an reverse clutch Lo and reverse clutch Steel plates not flat (A light metallic pack rattle noise most Clutch pack clearance noticeable in second or third between 25 MPH and 40 MPH under coast or drive operation.)

Final drive gear set

Refer to:

Noise in third Final Drive Gear Set and/or during turns

Noise in third and/ or during turns

Final drive gear set

(A hum that may be Final drive internal Gears worn, pitted noticeable in first gear (673) refer second and third, to Figure 49. Thrust washer or thrust under light throttle bearing mating surface acceleration, rough or pitted and/or during turns).

Final drive sun gear Bearing race or roller to final drive internal surfaces rough or pitted gear thrust bearin (674) refer to figure 49. Gears worn, pitted

Final drive sun gear Thrust Washer or thrust (675) Refer to figure 49. bearing mating surface rough or pitted

Final drive sun gear Bearing race or roller to differential carrier surfaces rough or thrust bearing (676) pitted Refer to Figure 49.

Differential carrier Gears worn, pitted, (678) Refer to figure 49. pinions tilting

Thrust washer or thrust bearing mating surfaces rough or pitted

Differential carrier to Bearing race or roller case thrust bearing (681) surfaces rough or Refer to figure 49. pitted

Differential pinions (685) Gears worn, pitted Refer to figure 49. Thrust washer mating surfaces rough or pitted

Differential side gears Gears worn, pitted (687) Refer to 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 Hub and bearing assembly. Ruptured seal or dented scraping noise which Refer to service manual race. may increase or Section 3C. become noticeable when 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.