Morris Minor Owners Club

Is there a way to identify the differences in terms of ratios?

Other than removing the cover and counting teeth, the only difference I can think of, between 1098cc diff and 948cc diff, unless changes have been made, is the position of the fill/level plug. 1098cc it's on the rear cover, 948cc it's on the casing front side.
Maybe there's a part identifier somewhere on the casing or cover?
Possibly mark a rear wheel and the propshaft and with the rear wheels off the ground count the number of propshaft turns to a full turn of a rear wheel?

The diff ratio is marked on the top of the diff alloy carrier mounting flange.

As Phil says, right up on the top.
It's stamped on there but not necessarily the clearest of markings.
Took me a bit of cleaning and several phone photos to get one at the right angle to read. Eventually confirmed it as an 8/43.

As I recall, it's on the top surface just above where the Brake Pipe junction is.
.

See also:-
viewtopic.php?t=71823

Thank you very helpful

Whatever number you find, the ratio will definitely not be an integer. The ratio will be such that the crown-wheel and pinion do not use just one set of tooth contacts. There will be a a prime number in there, somewhere, I expect.

oliver90owner wrote: ↑Tue Mar 05, 2024 8:54 pm Whatever number you find, the ratio will definitely not be an integer. The ratio will be such that the crown-wheel and pinion do not use just one set of tooth contacts. There will be a a prime number in there, somewhere, I expect.

What do you mean?
The ratio is simply total number of crown wheel teeth vs total number of pinion teeth, how many are in contact at any given point is irrelevant to the ratio calculation.
How many revolutions of the pinion to achieve one revolution of the crown wheel.

Here are the two I have....any thoughts? The top photo looks like 9/?8

The bottom looks like 9/41

minorissues135 wrote: ↑Wed Mar 06, 2024 3:56 pm Here are the two I have....any thoughts?IMG_6262.JPGIMG_6265.JPG

The top photo looks like 9/?8

The bottom looks like 9/41

9/38 = 4.22 : 1 ratio
9/41 = 4.55 : 1 ratio

Top diff - 9/38 teeth - 4.22 ratio - 1098cc rear axle.

Bottom diff - 9/41 teeth - 4.55 ratio - 948cc rear axle.

minorissues135 wrote: ↑Wed Mar 06, 2024 3:56 pm Here are the two I have....any thoughts?IMG_6262.JPGIMG_6265.JPG

The top photo looks like 9/?8

The bottom looks like 9/41

As I said previously, it can take some cleaning and photos at different angles. At least yours look to be off the car, I was working under the car to get my photos...
Given the options available, Phil is undoubtedly correct.

What do you mean?
The ratio is simply total number of crown wheel teeth vs total number of pinion teeth, how many are in contact at any given point is irrelevant to the ratio calculation.
How many revolutions of the pinion to achieve one revolution of the crown wheel.
[/quote]


I mean exactly what I wrote. The ratio most certainly has nothing at all to do with the very few teeth in actual contact at any point in time - and I never even suggested anything such as your claim.

Anyone actually understanding my post would realise that the particular tooth counts of crownwheel and pinion will mean that for every revolution of the crownwheel a different pinion tooth will be driving each individual tooth - so that all of the pinion teeth will be driving any one crownwheel tooth in sequence - not the same pinion tooth bearing on that tooth every crownwheel revolution. Got it?

For instance, no sensible drive would have even numbers of teeth for both gears as half of the teeth would never come in contact - possibly leading to uneven wear. Simple engineering pracice.