Rumbling from the back

[Davidmbe]

1952 morris minor convertible with a 1098 engine. When I get to 40mph there’s a rumbling sound coming from the rear can anyone help. I don’t know if it’s the prop shaft or the back axle it’s had an updated diff on it (good for cruising up the motorway)
David

[oliver90owner]

A bit more detail might be helpful.

You are sure it is one of those two, not body parts?

Accelerating, decelerating. cruising?

Only at 40mph?

When was this apparent? Recently or for a longer period?

Prop shaft only has universal joints and flange bolts that could be the culprit.

Diffs usually whine if worn, or not set up correctly. It’s not wheel bearings?

If differential gears, the back-lash when turning one wheel, with the other on the ground might provide a clue?

[rocco]

Most rumbles I've ever had tend to emanate from wheel bearings. If it's a sudden onset and they are a good few years old then perhaps they dry/worn? Raising the rear off the ground will allow you to check them.

[Davidmbe]

The rumbling from the back of the car starts from about 40mph then the faster I go it gets progressively worse
I will check the wheel bearings
David

[Davidmbe]

Wheel bearings okay
Bring me back to square one
David

[les]

I was surprised to find tyres to be the cause of a sound like worn wheel bearings, on a car I once had. If you’ve got a spare, maybe worth trying one rear at a time.

[Davidmbe]

No les it’s not tyres nor wheel bearings.

[rocco]

The only other things turning at the rear are the differential gears and the propshaft. How about the brake shoes, are they binding? Handbrake releasing fully? I'm not sure if the UJs would cause a rumble or just a knock when taking up drive?

If diff oil hasn't been changed for a while, opening the drain bolt (open the fill bolt first of course) will tell you if you at least have any in there. Maybe someone else has more/better suggestions for you to try?

[Bill_qaz]

Could it be the propshaft out of balance, vibration and noise are one and the same.
You could try putting a jubilee clip or two on the prop, this will change the balance, even unbalance it, to see if the balance effect is what you are hearing.
Then remove them, if it effects the noise then have the prop shaft balanced.