Measuring backlash in a differential is a crucial step for ensuring proper gear mesh and preventing premature wear. Backlash refers to the amount of play or free movement between the teeth of the ring gear and the pinion gear.
To measure backlash accurately, you need to prevent the pinion gear from rotating and then check the movement of the ring gear.
Steps to Measure Differential Backlash
Here is a straightforward guide on how to measure the backlash in your differential:
- Prepare the Differential: Ensure the differential assembly is accessible. It's often done with the differential removed from the vehicle, but can sometimes be checked in place.
- Prevent Pinion Rotation: This is a critical step. You must prevent the pinion gear from rotating. This can be done using a special tool that holds the pinion flange or shaft stationary, or by applying resistance to the input shaft.
- Mount a Dial Indicator: Securely mount a dial indicator with its tip resting perpendicularly against the tooth face of the ring gear. Position it near the outer diameter of the ring gear, halfway between the root and the top of the tooth.
- Rotate the Ring Gear: With the pinion held still, rotate the ring gear back and forth as far as it will move without the pinion turning.
- Read the Dial Indicator: The amount the dial indicator moves (the amount of play) indicates the amount of backlash. The amount the ring gear can move (the amount of play) determines the amount of backlash. Note this reading.
- Check Multiple Points: Rotate the ring gear to several different positions (e.g., 3 or 4 spots evenly spaced around the ring gear) and repeat the measurement. Backlash can vary slightly around the gear.
Understanding Backlash Values
The acceptable range for differential backlash varies depending on the specific axle and manufacturer. Always consult your vehicle's service manual or the axle manufacturer's specifications for the correct range. Typical values are often between 0.006 inches and 0.010 inches, but this is just a general guideline.
Adjusting Backlash
If your measured backlash is outside the specified range, it needs adjustment. Adjusting backlash typically involves moving the ring gear carrier assembly side-to-side using shims or adjusters.
- Moving the carrier assembly closer to the pinion gear decreases backlash.
- Moving the carrier assembly away from the pinion gear increases backlash.
Keep in mind a key detail from the reference: When changing the backlash bear in mind that the backlash setting changes about 0.007” for each 0.010” that the carrier moves. This insight helps understand the sensitivity of the adjustment process.
Summary Table: Measuring Backlash
| Step | Action | Key Point |
|---|---|---|
| 1. Preparation | Ensure differential is accessible. | Often done out of vehicle. |
| 2. Pinion Restraint | Prevent the pinion gear from rotating. | Use a holding tool or resistance. |
| 3. Mount Dial Indicator | Attach indicator with tip perpendicular to ring gear tooth face. | Position correctly for accurate reading. |
| 4. Rotate Ring Gear | Rotate the ring gear back and forth while holding pinion still. | Check free play. |
| 5. Read Measurement | Note the movement on the dial indicator. | The amount of play determines the backlash. |
| 6. Check Multiple Spots | Repeat measurement at different points on the ring gear. | Accounts for potential runout or variation. |
Measuring backlash is essential for proper differential setup and longevity. Always follow the specific procedures and specifications for your particular differential.
