CHAMP NEWS
Austin Champ, Checking a back axle unit

CHECKING A REAR DIFFERENTIAL UNIT
The ultimate test of a rear differential unit (diff unit) is to fit it into an Austin Champ and try it. But the situation can arise where a diff unit is for sale in unknown condition. The crucial parts of the unit are the crown wheel and pinion, can these be checked off the vehicle? They can, and in one of two ways: one, using a boroscope - a small camera on a flexible stalk connected to a screen and recording equipment - and put into the diff unit via the oil drain plug hole; two, by taking the nosing off the axle and then the crownwheel and pinion can be clearly seen.

Boroscope method: the first picture is of a Boroscope unit and the following ones are the pictures taken by it of the inside of a diff unit - the photos were taken of the boroscope's screen so the actual pictures seen on the screen and reproduced by the machine would be of a higher quality. The downside of the Boroscope is this unit cost £30,000! I think there are cheaper units available. Thanks to Nick Wolsey for the Boroscope information and photos.

Boroscope

Inside the diff unit 1

Inside the diff unit 2

Inside the diff unit 3

Nosing removed method: clean the diff unit; drain any oil; take off the power take off cover (blue arrow); remove the ring of bolts (red arrow shows separation point and bolts); from memory there is one or more screws on the side of the case on the nosing to be removed; pull off the nosing.
Perhaps, surprisingly, taking off the nosing does not need any special tools and does not alter any settings, the nosing can be easily replaced.
Time, to remove and replace the nosing should take no more than half an hour or so. Whether a seller will allow a prospecive purchaser to remove the nosing is another matter.
The crownwheel and pinion are the two major components in the back axle unit but there can be other faults. The casing can be damaged, that is, cracked or other physical damage, more likely, there could be very bad wear or pitting at the Tracta joint position on the driver's side, the nearside is a separate piece but would be hard to find as a spare part. Bearings could be worn, etc.

General view of the axle

The photos below show a damaged crownwheel and pinion, most likely through lack of oil.

A damaged diff unit 1

A damaged diff unit 2