Mercedes-Benz W123 rear axle and gearbox oil
What oil does the W123 rear axle and manual gearbox use?
The rear axle takes hypoid oil of class GL-5 and viscosity 85W-90. Multigrade 10W/30 oil does not meet the requirements. The manual gearbox takes ATF transmission fluid, not ordinary manual gearbox oil, which can damage the bearings and synchromesh.
How do you check the rear axle oil level and change the oil on the W123?
The level can only be checked through the filler hole, which is on the left side above the drive shaft. On the 240 D, a 14 mm hex socket key is needed for the hole's plug. For a change, the lower plug is opened, the old oil is drained and the new oil is poured in through the filler hole with a hose. If your finger does not fit in the hole, the level can be checked with a piece of wire.
Why does the W123 rear axle leak oil from the propshaft side?
The cause can be the seal between the rear axle and the propshaft or a clogged breather. If the breather is blocked, pressure builds up in the axle and the oil is forced past the seals even if the seal is new. The breather is at the back of the axle, and it is cleaned thoroughly. The seal type varies by model year.
Where else can a W123 rear axle oil leak come from?
The leak can also come from a broken axle shaft bearing, which takes the seal with it. If the bearings are suspect, they are cleaned and checked before the seal is replaced.