Peugeot 404 - rear axle transmission

"pont a vis"

From the Peugeot 203 to the 404 the rear axle transmission uses a special plant-based oil ("huile de recin" in French).

As T. Brandtner notes :

404's do need a special oil for the rear axle transmission, but it's definitely not motor oil ! A special plant-based oil (not a mineral oil!) called VT-oil is used in the rear axle, because of the bronze wheel. Production for this VT-oil in Europe was stopped a few years ago. I don't know whether it was ever available in America.

rear axle

Many rear axles were ruined by people who exchanged the rear axle oil and put in standard motor or gear oil. The problem was not the motor or gear oil, but the remaining VT-oil reacts with the mineral oils and builds a sticky substance which messes up the whole thing and can hardly be removed afterwards. The problem is that it's getting close to impossible to get VT-oil on the market, because the remaining stocks of VT-oil deteriorate (goes bad, like food). If you are forced to switch to mineral oil, this should be done only after taking the whole rear axle transmission apart and cleaning it carefully, so absolutely no remainders of the VT-oil are left in there. There is little known how long a rear axle transmission lasts with the wrong (mineral) oil, but it's supposed to work out more or less fine for some time.

Any mixture of a mineral oil or even a semi-synthetic oil will polymerize the existing oil resulting in a broken transmission !

To replace the oil it is necessary to clean the rear axle with a mixture of 50% toluene and 50% isopropyl alcohol. Once cleaned it is possible to use an gear oil "pont à vis" like the Esso gear oil VT (mineral) or the Castrol R40 (synthetic).

So, to clean the transmission just add the mixture and pick up and shake the car a lot (don't drive with this mixture!) or, gasp!, unmount the rear-axle transmission to clean it. As I've never done this, I won't give the instructions here; suffice to say that this is not to be done as a 'light' project!