TRACK AR 3841716 - Caterpillar

Caterpillar Off-Highway Trucks and TractorsReference: Guideline For Reusable Parts, "Differential Components for Wheel Loaders, Off-Highway Trucks and Tractors, Articulated Dump Trucks, Wheel Tractors, Compactors, and Integrated Toolcarriers", Form SEBF8119.Reference: "Analyzing Gear Failures", Form SEBD0520The problem of noise (differential gear whine) is often reported and may be difficult to remove. In these cases, critical attention to pinion bearing preload and gear backlash can have a positive effect.
There is no information showing the expected contact pattern required when installing the bevel gear and pinion in the differential carrier on a Caterpillar Off-Highway Truck.
A "straddle mounted" differential is used in the off-highway trucks. The straddle mounted pinion minimizes the pinion bending. The pinion location is held by carrier dimensions to 0.05 mm (.002 in). This does not effect the pattern. A straddle mounted pinion also requires less overall length for bearing design.
The differential carrier, gears and bearings have tight tolerances to make sure that the pinion teeth are positioned correctly to give the desired tooth contact pattern under load. The load during machine operation can cause the gear teeth to deflect which explains why checking the contact pattern during assembly may not give a "centered" pattern.
The shimming and preload adjustment of the pinion bearings is critical for achieving satisfactory differential service life. When shimming the pinion bearings, it is advisable to adjust the shim pack to give a rotational torque value that is either equal to, or slightly higher than, the specified valve. Some relaxing of the preload may occur in the first few hours of operation. This may allow the pinion to move towards the transmission under the loads exerted during machine operation.
If the pinion is allowed to move toward the transmission only a small amount, the tooth contact pattern moves down into the root of the pinion teeth. This can cause pitting in the "start of active profile" area. The pitting can lead to spalling and eventual pinion tooth failure.
When setting gear backlash, differences of up to 0.15 mm (.006 in) can be obtained when measurements are taken at points around the gears. These variations may occur due to some slight bevel gear warping during the heat treat process. The measurement values should be averaged together and compared to the specified value. An average backlash equal to, or slightly tighter than the specified value is desirable.