Rear Axle Noise

[Kevin]

I was in a friends Minor last night and I noticed a slight hum coming from the back axle (no he had not been aware of it) I had not noticed it at first just after a few miles and it sounded like it might be bearing related, a sort of faint whirring sound not much but there all the same, and when put into neutral while going along it was more noticeable, not having had this problem myself before I was not sure of what to advise, do you think it can be left until it becomes it becomes much worse, and do you think it sounds more wheel bearing related rather than the axle itself

[Cam]

It sound like a worn crownwheel & pinion. After high mileage these tend to get a bit noisy.

It should also be noisy when using the engine to 'engine brake'.

If it is OK when accelerating then only one side of the gears are worn.

It should not be a problem, more of an annoyance. A knackered bearing would be more of a rumble then a whine.

[Willie]

Lo, if the noise starts above a certain speed and is audible at all
times when you are above that speed it is a bearing noise. Could
be wheel bearing or diff bearing. If the noise is ONLY when 'pulling'
or ONLY on overrun then it is the crown wheel and pinion producing
it and it could go on like that for thousands of miles. The last three
allegedly rebuilt diffs I have used all started to whine after less than
a hundred miles! In other words it is difficult to obtain a unit which
have been expertly set up so that it is quiet.

[Cam]

The last three
allegedly rebuilt diffs I have used all started to whine after less than
a hundred miles!

Same here, with my MK2 Escort axle with a (supposed) new 4.4:1 crown wheel and pinion. The first time they did it the pinion bearing collapsed which caused a lot of grinding and squealing (as well as a lot of lost oil!) - and the need for a new crown wheel and pinion.

Makes you wonder........