Troubleshooting Tips

Improper lubrication causes a high percentage of gear reduction unit failures. Too frequently, speed reducers are started up without any lubricant at all. Conversely, units are sometimes filled to a higher oil level than specified in the mistaken belief that better lubrication is obtained. This higher oil level usually results in more of the input power going into churning the oil, creating excessive temperatures with detrimental results to the bearings and gearing. Insufficient lubrication gives the same results.

Gear failure due to overload is a broad and varied area of misapplication. The nature of the load (input torque, output torque, duration of operating cycle, shocks, speed, acceleration, and so on) determines the gear unit size and other design criteria. Frequently, a gear drive must be larger than the torque output capability of the severity of application conditions by providing a higher nominal power that in effect increases the size of the gear unit. If there is any question in the user's mind that the actual service conditions may be more severe than originally anticipated, it is recommended that this information be communicated to the gear manufacturer before start-up. Often there are remedies that can be suggested before a gear unit is damaged by overload, but none are effective after severe damage.

Motors and other prime movers should be analyzed while driving the gear unit under fully loaded conditions to determine that the prime mover is not overloaded and thus putting out more than the rated torque. If it is determined that overload does exist, the unit should be stopped and steps taken either to remove the overload or to contact the manufacturer to determine suitability of the gear drive under the observed conditions.

Table 2 is an extensive troubleshooting chart that should be consulted whenever necessary.

TABLE 2 Troubleshooting chart


What to inspect Action

Overheating 1. Unit overload

2. Oil-cooler operation

3. Oil level

4. Bearings adjustment

5. Oil seals or stuffing box

6. Breather

7. Grade of oil

8. Condition of oil

9. Forced-feed lubrication system

10. Coupling alignment

11. Coupling lateral float

12. Speed of unit

Reduce loading or replace with drive of sufficient capacity.

check coolant and oil flow. Vent system of air. Oil temperatures into unit should be approximately 110°F (43°C). Check cooler internally for buildup of deposits from coolant water.

Check oil level indicator to see that housing is accurately filled with lubricant to the specified level.

Bearings must not be pinched. Adjustable tapered bearings must be set at proper bearing lateral clearance. All shafts should spin freely when disconnected from load.

Oil seals should be greased on those units having grease fitting for this purpose. Otherwise, apply small quantity of oil externally at the lip until seal is run in. Stuffing box should be gradually tightened to avoid overheating. Packing should be self-lubricating braided-type.

Breather should be open and clean. Clean breather regularly in a solvent.

Oil must be of grade specified in lubrication instructions. If not, clean unit and refill with correct grade.

Check to see if oil is oxidized, dirty, or of high sludge content; change oil and clean filter.

Make sure oil pump is functioning. Check that oil passages are clear and permit free flow of lubricant. Inspect oil line pressure regulators, nozzles, and filters to be sure they are free of obstructions. Make sure pump suction is not sucking air.

Disconnect couplings and check alignment. Realign as required.

Adjust spacing between drive motor, and so on, to eliminate end pressure on shafts. Replace flexible coupling with type allowing required lateral float.

Reduce speed or replace with drive suitable for speed.


What to inspect Action

Shaft failure

Bearing failure

1. Type of coupling used

2. Coupling alignment

3. Overhung load

4. Unit overload

5. Presence of high-energy loads or extreme repetitive shocks

6. Torsional or lateral vibration condition

7. Alignment of outboard bearing 1. Unit overload

2. Overhung load

3. Bearing speed

4. Coupling alignment

5. Coupling lateral float

6. Bearings adjustment

7. Bearings lubrication

8. Rust formation due to entrance of water or humidity

Rigid couplings can cause shaft failure. Replace with coupling that provides required flexibility and lateral float.

Realign equipment as required.

Reduce overhung load. Use outboard bearing or replace with unit having sufficient capacity.

Reduce loading or replace with drive of sufficient capacity.

Apply couplings capable of absorbing shocks and, if necessary, replace with drive of sufficient capacity to withstand shock loads.

These vibrations can occur through a particular speed range. Reduce speed to at least 25% below critical speed. System mass elastic characteristics can be adjusted to control critical speed location. If necessary, adjust coupling weight, as well as shaft stiffness, length, and diameter. For specific recommendations, contact factory.

Realign bearing as required.

See "Overheating" (item 1). Abnormal loading results in flaking, cracks, and fractures of the bearing.

See "Shaft Failures" (item 3).

See "Overheating" (item 12).

See "Overheating" (item 10).

See "Overheating" (item 11).

See "Overheating" (item 4). If bearing is too free or not square with axis, erratic wear pattern will appear in bearing races.

See "Overheating" (items 2, 3, 7, 8, 9). Improper lubrication causes excessive wear and discoloration of bearing.

Make necessary provisions to prevent entrance of water. Use lubricant with good rust-inhibiting properties. Make sure bearings are covered with sufficient lubricant. Turn over gear unit more frequently during prolonged shutdown periods.


What to inspect Action

Gear wear

9. Bearing exposure to abrasive substance

10. Damage due to improper storage or prolonged shutdown

Oil leakage 1. Oil

2. Open breather

3. Open oil drains

4. Oil seals

5. Stuffing boxes

6. Force-feed lubrication to bearing

7. Plugs at drains, levels, and so on, and standard

8. Compression-type pipe fittings

9. Housing and caps

1. Backlash

2. Misalignment of gears

3. Twisted or distorted housing

Abrasive substance will cause excessive wear, evidenced by dulled balls, rollers, and raceways. Make necessary provision to prevent entrance of abrasive substance. Clean and flush drive thoroughly and add new oil.

Prolonged periods of storage in moist air and at ambient temperatures will cause destructive rusting of bearings and gears. When these conditions are found to have existed, the unit must be disassembled and inspected and damaged parts either thoroughly cleaned of rust or replaced.

Check through level indicator that oil level is precisely at level indicated on housing.

Breather should be open and clean.

Check that all oil drain locations are clean and permit free flow. Drains are normally drilled in the housing between bearings and bearing cap where shafts extend through caps.

Check oil seals and replace if worn. Check condition of shaft under seal and polish if necessary. Slight leakage normal, required to minimize friction and heat.

Adjust or replace packing. Tighten packing gradually to break in. Check condition of shaft and polish if necessary.

Reduce flow of lubricant to bearing by adjusting orifices. Refer to factory.

Apply pipe joint sealant and tighten fittings.

Tighten fitting or disassemble and check that collar is properly gripping tube.

Tighten cap screws or bolts. If not entirely effective, remove housing cover and caps. Clean mating surfaces and apply new sealing compound (Permatex #2 or equal). Reassemble. Check compression joints by tightening fasteners firmly.

Gear set must be adjusted to give proper backlash. Refer to factory.

Make sure that contact pattern is above approximately 75% of race, preferably in center area. Check condition of bearings.

Check shimming and stiffness of foundation.

Trouble What to inspect Action
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Survival Treasure

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