Symptoms
A hub low on oil, or oil spraying on the inner wheel or dripping from the portal. On the front axle, a differential that's overfull while its hub is low means the breather is pumping oil across. If one hub runs hotter than its partner on an infrared check, investigate.
The fix, step by step
- Drain the portal and differential and note how much comes out.
- Remove the wheel and portal cover, then replace the lower outer hub seal and the upper input seal.
- Many 6-lug axles use a 140 mm lower seal, but late SBU axles take a different upper inner seal, so check your axle number first.
- Fit a new wear ring if the old one is grooved.
- Clear or separate the hub and diff breathers so the hub can't pump into the axle; some owners fit independent breathers or auxiliary reservoirs.
- Refill each portal with about 300 ml of GL-5 gear oil and the differential to its plug.
- Recheck the levels after a few hundred kilometres.
Tools & part numbers
- Large sockets and breaker bar
- seal driver
- infrared thermometer
- clean drain pan
- 435 repair manual for torque values
- seal numbers depend on axle serial
Where to buy the parts
SBU upper inner portal box seal, late (front axle from U011485, rear from U014896)Expedition Imports ↗Amazon ↗
Lower outer portal hub seal, 140 mm (6-bolt diesel axles, incl. 1300)Expedition Imports ↗Amazon ↗
Hub reduction wear ring 4353370851 (later axles incl. U1300L)Expedition Imports ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Mercedes-Benz Unimog U1300L (435) parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.