Article 1299 - 4 Speed Transmission Noise Diagnosis

TSB #86 - February 23, 1968
(All Trucks with 4 Speed Transmissions)

The following article describes types of noises, originating sources, road test procedures and acceptable gear tooth wear and defect patterns.

Noise Description and Affected Area:
The following are noise definitions which apply to the transmission area:

Gear RattleA "Clanging" noise or "Rattle" type noise appearing to come from the transmission generally when the vehicle is under load or being lugged in third or fourth gear at road speeds of 15-30 M.P.H., engine speeds of 1000-2000 RPM. Noise more pronounced when engine/transmission is hot. Also may be evidenced by a driveshaft ringing noise noted at the same road speeds/engine speeds. Reference TSB 382 and 439 - New Process Transmission; TSB 898 - Warner Gear Transmissions.
Gear NoiseA "Growl" type of noise noted in low or reverse gear on a "vehicle" coast-down when the vehicle is decelerated using the engine as a braking source. A "Whine" type of noise noted in second, third, or fourth gear under all load conditions. Pitch and intensity varies with road speed.
Bearing NoiseA "Grinding, Grating, or Rumble" type noise noted in all speeds and under all load conditions. Intensity increases in proportion to road speeds.
Torsional Vibration"Moan" or "Groan" noise usually evidenced (8 cylinder vehicles) on pull or drive, at road speeds of 25-50 M.P.H. On 6 cylinder vehicles, it is usually noted at road speeds of 30-50-30 M.P.H. being more pronounced on a coast-down (50-30 M.P.H.).
Driveline VibrationThis is "Rumble" or vibration emanating from the floor pan area being evident at road speeds of 50-85 M.P.H., engine speeds of 3000 R.P.M. and up. Noise or vibration comes in and stays in throughout a definite road speed/engine speed span on drive, float, or coast-down.
Clutch Chatter/ ShudderA vehicle shake or shudder noted when clutch is partially engaged on initial starts in low or reverse under light throttle. Reference TSB 1113 and 1149.
Engine NoiseA "Hoot" type of noise, more noticeable on acceleration, is usually attributed to an air cleaner resonance or an induction type noise. Can be verified by accelerating vehicle 10 M.P.H. faster than the road speed span where noise is noted and coasting down with a wide open throttle and the ignition turned off. Note: A metallic "whine" or "knock" type of noise can be defined as "engine originating" if, by speeding up the engine with the transmission in 'neutral" and/or the clutch depressed, the noise is evidenced.

Road Test and Defect Area:
Transmission noise can be isolated to gear or bearings by using the following road test procedures:
Prior to a problem defining road test of the vehicle, it is suggested that the following areas be checked and adjusted if necessary:
  • Check engine performance, set engine timing to specifications.
  • Check wheels and tires for excessive runout. Inflate tires to specifications.
  • Check alignment of engine, clutch linkage components, and engine mounts.
  • Inspect exhaust system for leaks, improper routing, or interference conditions ("grounding" to frame or body). Make all necessary corrective repairs.
  • Check transmission floor pan cover, shift lever boot attaching screws, and transmission weather pad retaining plate for interference or "grounding-out" conditions. See TSB 75, Article 1156. Road test vehicle to define problem.
Note: The truck should be road tested until the engine, clutch components, transmission, and rear axle are up to the normal operating temperatures before diagnosing any customer complaint. It is suggested that a tachometer be used to correlate engine/transmission speeds to road speeds.

1. With engine at idle speed, clutch disengaged, transmission in neutral, and the vehicle not moving.Isolate noise to engine and/or clutch areas.
2. With engine running, clutch engaged, transmission in neutral, and the vehicle not moving.Indicates noise to be emanating from input shaft, cluster gear, second or third speed gears or idler gear or idler shaft areas.
3. With the engine running, clutch engaged, vehicle moving, evaluate each gear at road speeds equivalent to engine speeds of 1100-1500 R.P.M., road speeds of 10-30-40 M.P.H.Indicates a specific gear area.
4. With vehicle traveling approximately 30 M.P.H., disengage clutch, allowing the vehicle to "coast-down" with the transmission evaluated in fourth, third, and second gears.Indicates a specific gear area with a gear noise. Coast side of gear most probable area.
5. With transmission in low gear, drive vehicle to attain 15 M.P.H., disengage clutch, allowing the the vehicle to coast-down.Indicates a specific gear area with a gear noise. Coast side of gear most probable area.
6. Evaluate transmission, as in step #4 and 5, except drive vehicle to attain specified road speeds; then disengage the clutch and shut off the engine allowing the vehicle to coast-down in each gear.Indicates noise area is not connected with or induced by the engine. However, this step may indicate a noise condition that may be induced by the transmission, drive-shaft and/or coupling shaft, rear axle, or wheel bearings

Acceptable Transmission Gear Tooth Patterns
Evaluation of returned 4 speed transmission gears indicates that many non-defective gears have been replaced to correct noise problems. Acceptable vendor tool, machining, and nick repair marks are shown in the following charts. Vendor repair is allowed only on constant meshed gears. No repair is authorized on the low speed slider gear or the reverse idler gear.

Figure 10 - Transmission Gear Tooth Contact Pattern Chart
NOTE: Because of Manufacturing Tolerances and discrepancies, the above gear contact patterns can result from combinations of certain acceptable manufacturing errors.

Figure 11 - Normal Tool Marks - Transmission Gear Teeth

Figure 12 - Approved Transmission Gear Tooth Chip/Nick Removal Procedure