NOISE DIAGNOSIS SHOP MANUAL SUPPLEMENT

MODEL AND YEAR: VEHICLES EQUIPPED WITH THM 125C TRANSAXLES

This bulletin provides noise diagnosis information for the 1987 THM 125C Transaxle Service Manual, Hydraulic Diagnosis section.

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.

A check for loose or misaligned components within the engine compartment which could contact the engine or transaxle during engine roll (engine torque movement) should also be made.

Follow the preliminary check procedure as outlined in the oil pressure chart included in the THM 125C hydraulic diagnosis section.

- Transaxle fluid level

- Condition of fluid (including presence of bubbles or contaminants on fluid level indicators)

- 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) Broken, Mispositioned, Refer to Figure 46. or Missing.

NOISE IN ALL RANGES

Torque Converter Circuit Torque Converter Torque Converter Internally Damaged.

(A whine which may by 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 pressure which gets louder as will vary an Oil Pump noise. engine RPM increases or (Note during preliminary is pressure sensitive. check procedure)

Pump Shaft Roller Bearing Bearing Race or and seal assembly (354). roller surfaces Refer to Figure 89L. rough or pitted.

For pump cavitation.

(A "popping" noise Fluid level indicator for bubbles. similar 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 Verified by a needle frequency rattle vibration on a pressure sound. gage. (Road test may be necessary.

Pressure Regulator Valve Calibration (Valve (365) 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) Stretched assembly (101) Refer to Figure 78.

Drive sprocket (103) Teeth broken or Refer to Figure 78. sheared.

Bearing surfaces nicked or scored

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

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

Driven sprocket (122) Teeth broken or Refer to Figure 78. sheared

Bearing surfaces nicked or scored

Driven sprocket support Bearing outer race (602) Refer to Figure 76. support rough or nicked.

Driven sprocket support Bearing race or bearing assembly (601) roller surfaces Refer to Figure 76. 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 Valve body spacer plate Calibration (spacer Circuit (20) (2.8L models only) plate) refer to Figure 96. (buzz will cause a pulsation in the accelerator pedal.)

External cooler lines Transaxle Cooler Pipes Vibrating together or against other vehicle components

SQUEAL AT LOW SPEED

Input Gear Set

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

Input carrier assembly Gears worn, pitted (640) Refer to figure pinions tilting 65. 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/or Final Drive gear set during turns

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 Gears worn, pitted most noticeable in (646) Refer to second gear and is Figure 56. Thrust washer or related to vehicle thrust bearing mating speed. The whine surface rough or mau diminish or go pitted away after an upshift) Reaction carrier Gears worn, pitted assembly (665) pinions tilting Refer to Figure 56. Thrust washer mating surfaces rough or pitted Reaction Sun Gear to reaction internal Bearing race or gear thrust bearing roller surfaces (667). Refer to rough or pitted figure 56.

Reaction internal gear Gears worn, pitted (668) Refer to Figure 56. Thrust washer or thrust bearing mating surface rough or pittted

Lo and Reverse Clutch

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

Final drive gear set

Refer to:

Noise in third and/or Final drive gear set 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 under light throttle thrust bearing mating acceleration, and/or surface rough or during turns.) pitted.

Final drive sun gear Bearing race or to final drive internal roller surfaces gear thrust bearing rough or pitted (674) Refer to figure 49.

Final drive sun gear Gears worn, pitted (675) Refer to Figure 49. Thrust washer or thrust bearing mating surface rough or pitted.

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

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

Thrust washer or thrust bearing mating surfaces rough or pitted

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

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

Differential side gears(687) Gears worn, pitted Refer to figure 49. Thrust washer or thrust bearing mating surface 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 scraping noise which Refer to service manual dented race. may increase or become section 3C. 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.