This Meritor technical instruction manual (TP-96181) provides guidelines for identifying and adjusting gear tooth contact patterns and backlash for Generoid and conventional hypoid and Amboid gearsets used in Meritor drive axles.

1. Identifying Gearset Types

Proper identification is critical because Generoid and conventional gears require different contact patterns and locations.

Conventional Gearsets: Identified by part numbers on the ring gear and drive pinion (e.g., 36786 and 36787).
Generoid Gearsets: Identified by similar part numbers but include a suffix letter (e.g., 36786 K and 36787 K).

2. Backlash Settings

Meritor provides specific backlash ranges based on the carrier type and pinion mounting:

Carrier Type	Pinion Mounting	Range (inches)	Initial Setting (New)
Single Reduction (< 17″ Pitch Dia.)	Straddle or Overhung	$0.008″ – 0.018″$	$0.012″$
Amboid Single Reduction	Overhung Only	$0.010″ – 0.020″$	$0.015″$
Single Reduction (17″+ Pitch Dia.)	Straddle or Overhung	$0.010″ – 0.020″$	$0.015″$
Double Reduction	Through Shaft	$0.008″ – 0.018″$	$0.012″$
Double Reduction	Overhung	$0.016″ – 0.026″$	$0.020″$

3. Tooth Contact Adjustments

Patterns are adjusted by moving the lengthwise position toward the “toe” or “heel” of the ring gear teeth.

Ideal Hand Rolled Pattern: Contact should favor the toe end and be centered between the top and bottom of the tooth. Under load, this pattern spreads to cover almost the full length of the tooth.
High Patterns: Indicates the pinion is not deep enough. Correct this by removing shims from under the pinion cage.
Low Patterns: Indicates the pinion is too deep. Correct this by adding shims under the pinion cage.
Backlash Effects: Decreasing backlash moves contact toward the toe on hypoid gears (heel on Amboid), while increasing backlash moves it toward the heel on hypoid gears (toe on Amboid).

4. Ring Gear Installation

For interference fit ring gears, Meritor recommends heating the gear in water to 160°–180°F (71°–82°C) for ten minutes before assembly. This ensures an easier fit over the differential case pilot without using a press, which can cause metal pick-up and resulting gear runout.