Morris Minor Owners Club

Good question, so I measured my car which is in a pretty good state.
With the car in Neutral and hand brake on the movement at the rear flange
(to omit any movement in the UJs) is exactly 10 mm. This is the cumulative
amount of free play between the Crown Wheel and Pinion and the planet
wheels on a diff which has done under 50,000 miles.(allegedly).

I suspect that mine has a lot more than 10mm. If it stops raining I'll have a go at measuring it accurately. Sounds a bit like a new diff to me.

Sure the noise is not just the natural Minor 'rasp' from the exhaust on over-run ?

Sadly, it's not the exhaust.
There is a physical element to the noise, you can feel it quite clearly.

Is it still there if you knock it out of gear and 'drift' down a hill ?

While you are under there measuring it see if you can move the pinion flange
towards the front of the car with a stout lever. If it moves forward then it is
most likely that the pinion nut is loose. You will see this nut if you unbolt the
prop shaft and it should be done up to 140 ft lbs(it has just a spring washer
to hold it, there is no locking plate).

Maybe check the oil level in the diff too!

I have been out in the rain checking (rain is cumbrian for snow). The flange does not want to move forwards, and has a little over 10mm of rotational backlash, but not much, the UJs seem fine. I will check the oil in the diff, when it really isn't raining. So I'm left to think that it might well be the gearbox with the sound going along the prop so that it only sounds like the problem is at the back. I'll let you know in due course.
Thanks for the help, please keep the advice coming.
The car will be off the road till the weekend as the brakes need sorting.

Gearbox would normally be noisy when driving, not when on over-run. Also worth checking gearbox oil of course. Not just exhaust system bumping against body? - or even brakes dragging ? And are the wheel nuts all tight!

Willie wrote:While you are under there measuring it see if you can move the pinion flange
towards the front of the car with a stout lever. If it moves forward then it is
most likely that the pinion nut is loose. You will see this nut if you unbolt the
prop shaft and it should be done up to 140 ft lbs(it has just a spring washer
to hold it, there is no locking plate).

When mine had a loose pinion nut it was the up/down movement of the flange that was most noticeable.

Just a thought about the "loud grating noise", it's not the fan hitting the radiator is it? More likely under heavy braking if the gearbox restraining cable's gone really. Worth checking anyway, along with the mounting rubbers.

the diff can make all kinds of unpleasant noises if it is dry!
However the Minor gearbox doesn't last forever and is therefore also a common cause of issues.
Whilsty you're rolling around and checking levels it is a good opportunity to grease the UJs and top all the oil levels.
The gearbox oil is worth changing every few years - this helps to reduce the amount of metal particles flowing around the gearbox.

I would suspect the needle roller bearings or the front ball bearing in the gearbox.

To start with I would drain the gearbox oil with the intention of replacing it. Examine the old oil very carefully for any sign of bits of old bearings in it.

If the needle bearings have gone the layshaft may be worn as well.

I still think gearbox would be noisy when driving under power - less so when on over-run. And there would be other symptoms such as jumping out of gear!

Which oils would you reccomend for the diff and gearbox.

The diff is traditionally EP90 - these days I use EP80/90 'cos that's what my local motorfactor stocks.

The gearbox should take normal engine oil - i.e. multigrade 20W50 (I think, it's a while since I've bought mog oil as opposed to ital oil). I still change the gearbox oil regularly - it generally comes out much like it went in, but I feel better for knowing it's clean and good oil in there.

Gearbox needs stsndard engine oil, axle EP 90

How come that wasn't there when I posted, Kate?
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EP - 90 for the diff, 20w50 engine oil for the gearbox

I'm not entirely sure Andrew. It definately *should* have been there. Perhaps it was hiding.