If your gearbox is leaking oil, don’t replace the oil seal right away. Before doing that, go through these checks — otherwise, the new seal will likely leak again.
Several customers have recently asked us about output shaft leakage — even after replacing the seal. The truth is, leakage isn’t always the seal’s fault. Check these areas in order:
- Inspect the oil seal first
Remove the end cover and examine the seal lip. If it’s hardened or cracked, replace it — that’s straightforward. Standard seals are typically made of FKM (fluororubber) or NBR (nitrile rubber), both of which are suitable for normal operating conditions.
- Check the shaft’s seal journal
If the seal itself looks fine, inspect the shaft surface where the seal rides. If it’s worn, the shaft needs to be repaired or fitted with a repair sleeve.
- Measure radial runout
If the seal journal is not worn, the most likely cause is bearing wear. Check whether radial runout exceeds the allowable limit — if it does, the seal can’t hold. Use a dial gauge to measure the runout value. If it’s out of spec, the bearings are likely worn or damaged and need replacement. Catching this early prevents more serious damage to the gearbox.
- Don’t forget the breather plug
Still leaking after checking all the above? Look at the breather plug — it’s often overlooked. If it’s clogged, internal pressure builds up and forces oil out through gaps. Clean it or replace it with a new one.
Ongoing preventive maintenance
After repairs, we recommend inspecting the seal every 2,000 operating hours and measuring radial runout every 4,000 hours. This basic routine will effectively prevent recurrence.
Also, keep the seal lip area clean at all times — it significantly extends the service life of both the seal and the seal journal.