Noise In Differential Or Copper In Power-Train Oil Caterpillar

Problem:

Questions continue concerning allowable wear limits for copper (CU), samples with high copper levels, interpretation of samples, and customer concerns about copper readings, and also about noise in the differential.

Solution:

Problems stem from the fact there are several potential sources of measured copper readings and noise. All these sources must be considered when evaluating a sample or considering a repair.

Copper can come from:

A. Actual wear of copper or bronze components within the differential or transmission system.

B. The oil formulation or additive package itself.

C. Chemical reaction between the oil and copper or bronze components within the system.

In the H series differential, copper sources are the spider sleeve bearings, two thrust washers (one for each side gear), and spacers behind each spider pinion. In the transmission, there is one sleeve bearing on each side of the number 4, 5, and 6 clutches, and two sleeve bearings on each of the number 7 and 8 clutches. Also, there are four sleeve bearings in the transmission pump and copper tubes in the cooler.

An increase in copper SOS or copper in the filters doesn't necessarily indicate a pending problem. Copper is a soft malleable metal which is not abrasive and in itself, doesn't cause wear of other components. A potential problem is suspected if copper and another element increase simultaneously.

Since high copper readings can be present in the oil from non-failure sources, Caterpillar has recommended for some time the interpreter NOT suggest a repair action on the basis of copper readings ALONE.

Copper readings, in conjunction with other test results (e.g. iron, aluminum), can be an indicator of real system distress however, especially when the readings are trended over several samples for the same compartment.

NOTE: It is important to verify the oil has been changed per the recommended interval (1000 hours) because normal wear of copper based bearings and washers will continue to raise the level of copper. In addition, if the oil is not changed for extended periods, the lubrication additives break down and can cause accelerated wear.

NOISE: If noise is heard in the differential (grinding, growling, clunking) it can be caused by different factors. These are listed below and must be investigated before deciding on repairs:

Before evaluating, determine if the noise is heard with the differential locked or unlocked. When the differential is locked the differential pinion gears on the spider are not rotating but are locked up through the action of the differential lock package. When the differential is unlocked the differential pinion gears on the spider may rotate which allows easier steering and wheel spin on one side when there is loss of traction.

1. If the noise is heard when the differential is locked, the pre-load on the differential deflection stop inside the case may have changed. Remove the right hand tandem and verify the pre-load setting. If not in specification, make the necessary adjustment, install the tandem and check the noise level.

2. If the pre-load is within specification, verify the pinion backlash with the ring gear. Adjust if necessary.

3. Verify the pre-load on the side bearings and inspect for side bearing failure.

If the noise is heard only when the differential is unlocked, investigate the following for failure:

1. Clutch discs or plates for excessive wear.

2. Clutch piston or piston housing for damage.

3. Thrust spacer or thrust washer failure.

4. Pinion gear failure.

5. Pinion sleeve bearing failure.

6. Thrust plate behind pinions for damage.

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