Start with the manual, not with this list
Gearboxes differ widely: helical, worm, planetary, shaft-mounted, oil-bath, circulating-oil and grease-lubricated designs all have different requirements. The manual for your unit gives the approved oil grade, fill quantity, change interval, torque values and permitted operating temperature. What follows is a general order of work that most routines share. Where it disagrees with the manufacturer’s instructions, the manufacturer wins.
This is general information, not engineering advice. Work on powered equipment should be done by trained, authorized people following your site’s procedures and local regulations.
Step 1: Plan the job and gather information
Before touching the machine, collect what you will need:
- The manual and the equipment data plates, which show the model, ratio and serial information needed to order the right parts and oil.
- The last service record, so you know what was done and what was noticed.
- The correct lubricant, clean containers, new gaskets or seals if they are due, and suitable cleaning materials.
- A way to catch and dispose of used oil according to local rules.
Good records make every later step easier. Writing clear instructions is a skill in its own right, and work order quality often decides whether the next person can repeat the job correctly.
Step 2: Make the machine safe
Isolate the drive from every energy source, including the motor, any connected process that could back-drive the gearbox, and stored energy such as raised loads or tensioned belts. Apply your lockout tagout procedure, verify the isolation, and let hot surfaces cool. Gearbox casings and oil can be hot enough to cause burns, and a machine that coasts to a stop is still moving. If you are unsure whether the equipment is truly isolated, stop and ask.
Step 3: Clean and look at the outside
Clean the casing, especially around the breather, the fill and drain plugs, and the oil level indicator. Dirt left in these areas ends up in the oil when plugs are opened. A clean casing also makes leaks easy to spot later.
With it clean, look for:
- Oil weeping from joints, plugs and shaft seals
- Cracks, dents or corrosion on the housing
- Loose, missing or damaged guards
- Discolored paint, which can suggest past overheating
- Blocked cooling fins or a clogged fan cover, if fitted
Step 4: Check mounting and the connected drive
A gearbox is only as healthy as its installation. Check that mounting bolts are present and tight to the specified torque, that the base is not cracked or shifted, and that torque arms or bushings on shaft-mounted units are in good condition. Look at the coupling or drive element: worn flexible couplings and poor shaft alignment push extra load into bearings and seals, and are common root causes of repeat problems. If alignment must be checked or corrected, follow the method recommended for your coupling type.
Step 5: Check the oil
Oil is usually the most important item on a gearbox routine.
- Check the level at the sight glass, dipstick or level plug, with the unit stopped and level, and in the condition the manual specifies (some call for a cool, settled gearbox).
- Look at the oil. Milky or cloudy oil can indicate water, very dark or burned-smelling oil can indicate overheating or age, and a glittering or gritty appearance may point to metal particles.
- Take a sample if your plant uses oil analysis. A sample drawn the same way each time is more useful for spotting trends than a one-off result.
- Change or top up as the manual directs, using only the specified type. Do not mix oil types unless the manufacturer says it is acceptable, and do not overfill, since too much oil can cause churning, heat and leaks.
Details on oil type, breathers and contamination are covered in the separate article on gearbox lubrication.
Step 6: Service breathers, seals and filters
The breather lets the casing “breathe” as the oil heats and cools. A blocked breather can build pressure and push oil past the seals, while a worn one can draw in moisture and dust. Clean or replace it according to the manual. If the unit has an oil filter or a cooling circuit, service these at the stated interval. Replace any shaft seal that is leaking or hardened, and take care not to scratch the shaft or install the seal crooked, which is a frequent reason seals fail early; the common reasons shaft seals leak are worth understanding before you replace one.
Step 7: Reassemble, restart and listen
Refit guards, check that plugs are tightened correctly with good seals, and clean up any spilled oil. Remove locks and tags only through your site’s procedure, and make sure everyone nearby knows the machine is about to restart. At startup, observe:
- Any unusual noise, such as grinding, knocking or a high whine
- Rising temperature in the first hour or so of running
- Oil weeping at the plugs and seals you just touched
- Vibration that was not there before
If the readings are different from last time, treat that as information. Where the plant has the capability, vibration analysis on the input and output ends can give an early picture of bearing and gear condition.
Step 8: Record and set the next interval
Write down what you found, what you changed, the oil quantity added or drained, and anything that needs follow-up. Notes like “slight weep at output seal, recheck in two weeks” are exactly the details that prevent surprises. Over time, your records show whether the interval you chose is too short, too long, or about right. This is the logic behind preventive maintenance: intervals are a starting assumption that records can refine.
When the routine finds a problem
A routine is also a screening tool. If you find metal in the oil, repeated overheating, a cracked housing, loud or changing noise, or leaks you cannot stop with a normal seal change, escalate rather than continuing to run the unit. A structured root cause analysis after a failure is usually more valuable than repeating the same repair. Whether to repair or replace depends on cost, downtime and age, and it is covered in a separate decision guide.
A simple summary of the order
Plan, isolate, clean, inspect the outside, check mounting and drive, check and service the oil, service the breather and seals, reassemble and restart, then record. The order matters because each step protects the next: isolation protects people, cleaning protects the oil, and records protect the following service.