Driveline Snap
A snap or clunk noise when the vehicle is shifted into gear (or the clutch engaged) can be caused by:
- High engine idle speed.
- Transmission shift operation.
- Loose engine/transmission/transfer case mounts.
- Worn U-joints or CV.
- Loose spring mounts.
- Loose pinion gear nut and flange.
- Excessive ring gear backlash.
- Excessive side gear to case clearance.
The source of a snap or a clunk noise can be determined with the assistance of a helper. Raise the vehicle on a hoist with the wheels free to rotate. Instruct the helper to shift the transmission into gear. Listen for the noise, a mechanics stethoscope is helpful in isolating the source of a noise.
DIAGNOSTIC CHART
| Condition | Possible Causes | Correction |
|---|---|---|
| Wheel Noise | 1. Wheel loose. | 1. Tighten loose nuts. |
| 2. Faulty, brindled wheel bearing. | 2. Replace bearing. | |
| Axle Shaft Noise | 1. Misaligned axle tube. | 1. Inspect axle tube alignment. Correct as necessary. |
| 2. Bent or sprung axle shaft. | 2. Inspect and correct as necessary. | |
| 3. End play in pinion bearings. | 3. Refer to pinion pre-load information and correct as necessary. | |
| 4. Excessive ring and pinion gear backlash. | 4. Check and adjustment ring and pinion gear backlash. | |
| 5. Improper pinion bearing adjustments. | 5. Adjust the pinion bearings pre-load. | |
| 6. Loose pinion flange nut. | 6. Tighten pinion flange nut to specifications. | |
| 7. Scuffed gear tooth contact surfaces. | 7. Inspect and replace as necessary. | |
| Axle Shaft Broke | 1. Misaligned axle tube. | 1. Replace broken shaft after correcting tube mis-alignment. |
| 2 Vehicle overloaded. | 2. Replace broken shaft and avoid excessive weight on vehicle. | |
| 3. Erratic clutch operation. | 3. Replace broken shaft and avoid or correct erratic clutch operation. | |
| 4. Grabbing clutch. | 4. Replace broken shaft and inspect and repair clutch as necessary. | |
| Differential Cracked | 1. Improper differential bearing adjustment. | 1. Replace case, inspect gears and bearings for further damage. Set differential bearing pre-load properly. |
| 2. Excessive ring gear backlash. | 2. Replace case and inspect gears and bearings for further damage. Set ring gear backlash. | |
| 3. Vehicle overloaded. | 3. Replace case and inspect gears and bearings for further damage. Avoid excessive vehicle weight. | |
| 4. Erratic clutch operation. | 4. Replace case and inspect gears and bearings for further damage. Avoid erratic use of clutch. | |
| Differential Gears Scored | 1. Insufficient lubrication. | 1. Replace scored gears. Fill differential with the correct fluid type and quantity. |
| 2. Improper grade of lubricant. | 2. Replace scored gears. Fill differential with the correct fluid type and quantity. | |
| 3. Excessive spinning of one wheel/tire. | 3. Replace scored gears. Inspect all gears, pinion bores, and shaft for damage. Service as necessary. | |
| Loss Of Lubricant | 1. Lubricant level too high. | 1. Drain lubricant to the correct level. |
| 2. Worn axle shaft seals. | 2. Replace seals. | |
| 3. Cracked differential housing. | 3. Repair as necessary. | |
| 4. Worn pinion seal. | 4. Replace seal. | |
| 5. Worn/scored flange. | 5. Replace flange and seal. | |
| 6. Differential cover not sealed. | 6. Remove, clean, and seal cover. | |
| Axle Overheating | 1. Lubricant level low. | 1. Fill differential to correct level. |
| 2. Improper grade of lubricant. | 2. Fill differential with the correct fluid type and quantity. | |
| 3. Bearing pre-loads too high. | 3. Adjust bearing pre-loads. | |
| 4. Insufficient ring gear backlash. | 4. Adjust ring gear backlash. | |
| Gear Teeth Broke | 1. Overloading. | 1. Replace gears. Examine other gears and bearings for possible damage. |
| 2. Erratic clutch operation. | 2. Replace gears and examine the remaining parts for damage. Avoid erratic clutch operation. | |
| 3. Ice-spotted pavement. | 3. Replace gears and examine remaining parts for damage. | |
| 4. Improper adjustments. | 4. Replace gears and examine remaining parts for damage. Ensure ring gear backlash is correct. | |
| Axle Noise | 1. Insufficient lubricant. | 1. Fill differential with the correct fluid type and quantity. |
| 2. Improper ring and pinion gear adjustment. | 2. Check ring and pinion gear contact pattern. | |
| 3. Unmatched ring gear and pinion. | 3. Replace gears with a matched ring gear and pinion. | |
| 4. Worn teeth on ring and pinion gears. | 4. Replace ring and pinion gears. | |
| 5. Loose pinion bearings. | 5. Adjust pinion bearing pre-load. | |
| 6. Loose differential bearings. | 6. Adjust differential bearing pre-load. | |
| 7. Loose or sprung ring gear. | 7. Measure ring gear run-out. Replace components as necessary. | |
| 8. Loose differential bearing cap bolts. | 8. Inspect differential components and replace as necessary. Ensure bearing caps are torqued to the proper specification. | |
| 9. Housing not machined properly. | 9. Replace housing. |