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MG MGB Technical - Crownwheel & Pinion Question

My problem is that in some cases Hardy-Spicer made the same ratio crownwheel & pinion for different size rear axles. For example, both the Spridget and the MGA/MGB rear axles were made in a 3.909:1 ratio, but used different crownwheel & pinion parts which, naturally had different part numbers in order to distinguish them from each other. They are not interchangeable.

Perhaps the simplest way to put my question is: Did Hardy-Spicer ever produce 5.125:1 or 3.545:1 crownwheel & pinion gearsets that would install onto the differential carrier of the Hardy-Spicer differential that was used in the MGA/MGB? If so, what were the BMC part numbers?
Stephen Strange

Steve
The lowest one I have a list of is 4.55 --- 88G284
cheers willy
William Revit

Steve
On further hunting I came accross this list
Looks like 5.125 is the lowest and 3.727 the high
I can't find it but I'm sure that the 3.727 was fitted to early automatic MGBs
Hope this helps - no part nos though sorry
willy

1956 - 1965 Medium Axle
Wolseley 15/50 late 4.875 39/8
Wolseley 15/60 4.556 41/9
Wolseley 16/60 4.300 43/10
Austin A50, A55 4.875 39/8
Austin A55 van 5.125 41/8
Austin A55 Mk II 4.556 41/9
Austin A60 4.300 43/10
Austin A60 Traveller 4.556 41/9
Austin 10cwt, 15cwt van 5.125 41/8
Morris JU J2 van 5.125 41/8
Morris Oxford S4 4.875 39/8
Morris Oxford S5 4.556 41/9
Morris Oxford S6 4.300 43/10
Morris Oxford S6 Traveller 4.556 41/9
MG Magnette ZA 4.875 39/8
MG Magnette ZB, ZBV 4.556 41/9
MG Magnette Mk 3, Mk 4 4.300 43/10
MGA 1500, 1600 Mk I 4.300 43/10
MGA 1600 Mk II 3.909 43/11
MGA 1600 Mk II 3.727 41/11
mgb roadster 3.909 43/11
MGB Roadster 3.727 41/11
Riley 4/68, 4/72 4.300 43/10
William Revit

To the above list add:
Wolseley 1500, Morris Major, Austin Lancer and possible Riley 1.5 at 3.727 41/11

IIRC the Morris Minor had a 5.something to 1 diff and the MGB V8 had 3.07.

Herb
Herb Adler

William & Herb-
Thanks for that!

William-
You mentioned the term "Medium Axle". I know that Hard-Spicer produced three ranges of axles for BMC. Do you by any chance know what the terms were for the other two, that is, the lighter-duty ones for use in the smaller cars, and the one for the larger cars such as the Austin Westminster?

Herb-
In the Moris Minor it was 5.125:1, the gearset number should start with ATB followed by (?).
Stephen Strange

The Wolseley/Riley 1500 used the light duty diff. I believe the Morris Major/Austin Lancer was possibly ther same car, so would be the same.

MGB automatics used the Salisbury type axle, as did the V8.
Dave O'Neill 2

Willy, good list. The BMC parts book lists the MGA1600 Mk2 as 41/10.
Paul Walbran

Hi Paul
Yeah I remember getting a 4.1 out of an A to fit up to a B
Steve
I'l see if I can copy the whole page

willy
William Revit

The whole page
This is 1956 - 1965 so won't include things like MGC and MGBv8 Salisbury type diffs

Unique diff titles small medium large
I wonder how long it took them to come up with them

===============================


The amalgamation of the Nuffield Group with Austin in 1956 to create the BMC, brought with it a rationisation of drive line components. The rear axle was one of these and now consisted of a three-quarter floating hypoid gear 'banjo' type, with a cast aluminium differential housing casing. It was available in three sizes - small, medium and large, with the following ratios:

Model Ratio Crownwheel/Pinion
1956 - 1965 Small Axle
Wolseley 1500 early 3.909 43/11
Wolseley 1500 late 3.727 41/11
Riley 1.5 early 3.909 43/11
Riley 1.5 late 3.727 41/11
Austin A30 4.556 41/9
Austin A35, A40 4.300 43/10
Morris Minor 4.556 41/9
Morris 1000 4.300 43/10
Morris 5cwt, 7cwt van 5.125 41/8
MG midget early 4.300 43/10
MG Midget late 3.909 43/11
MG Midget some 3.727 41/11
1956 - 1965 Medium Axle
Wolseley 15/50 late 4.875 39/8
Wolseley 15/60 4.556 41/9
Wolseley 16/60 4.300 43/10
Austin A50, A55 4.875 39/8
Austin A55 van 5.125 41/8
Austin A55 Mk II 4.556 41/9
Austin A60 4.300 43/10
Austin A60 Traveller 4.556 41/9
Austin 10cwt, 15cwt van 5.125 41/8
Morris JU J2 van 5.125 41/8
Morris Oxford S4 4.875 39/8
Morris Oxford S5 4.556 41/9
Morris Oxford S6 4.300 43/10
Morris Oxford S6 Traveller 4.556 41/9
MG Magnette ZA 4.875 39/8
MG Magnette ZB, ZBV 4.556 41/9
MG Magnette Mk 3, Mk 4 4.300 43/10
MGA 1500, 1600 Mk I 4.300 43/10
MGA 1600 Mk II 3.909 43/11
MGA 1600 Mk II 3.727 41/11
MGB Roadster 3.909 43/11
MGB Roadster 3.727 41/11
Riley 4/68, 4/72 4.300 43/10
1956 - 1965 Large Axle
Wolseley 6/90 4.100 41/10
Wolseley 6/99 3.909 43/11
Wolseley 6/99 Auto 3.545 39/11
Wolseley 6/110 3.909 43/11
Wolseley 6/110 Auto 3.545 39/11
Riley Pathfinder 4.100 41/10
Austin A99 3.909 43/11
Austin A110 3.909 43/11
Austin-Healey 100-6 4.100 41/10
Austin-Healey 100-S 3.667 33/9
Austi-Healey 3000 3.545 39/11
William Revit

I remember being told years ago by someone who worked at Abingdon that some 1275 Midgets with the 3.727 ratio final drive had been fitted with left over Riley 1.5 rear axles following the cessation of Riley production. Good old BL, never ones to waste materials!
J Barnacott

Willy

Where did the list come from. There are a number of errors in there.
Dave O'Neill 2

Dave
Old fella that lived near my parents years ago had it He was into Wolseleys
Feel free to add any corrections
I would imagine in all fairness that it's old and there were probably more/less options for each or some cars even back then
I put it up here for Steve so that he might be able to find something to suit his needs
I'm not saying it's perfect but

cheers willy
William Revit

A few corrections on the small axles, plus MGA/MGB

Austin A30 (early) 5.125 8/41
Austin A30 (late) 4.875 8/39
Austin A30 van 5.375 8/43
Austin A35 saloon 4.55 9/41
Austin A40 Mk1 4.55 9/41
Austin A40 Mk2 4.22 9/38
Sprite/Midget 948 4.22 9/38
Sprite/Midget 1098 4.22 9/38
Sprite/Midget 1275 4.22 9/38
Sprite/Midget 1275 3.9 10/39
Midget 1500 (early)3.9 10/39
Midget 1500 (late) 3.727 11/41
Morris Minor 948 4.55 9/41
Morris Minor 1098 4.22 9/38

Morris Minor commercials used a shorter ratio than saloons, either 4.55, 4.875 or 5.375

MGA were only fitted with 4.1 or 4.3 AFAIK

MGB (banjo) were only 3.909, although 4.1, 4.3 and 4.55 were available from Special Tuning.

I can't comment on the accuracy of the figures for other vehicles in the list, as I don't have any experience of them.

HTH
Dave O'Neill 2

Steve

Did you see my posts on the Midget/Sprite BBS, where you also posted?
Dave O'Neill 2

William-
Wow! Now, that's an effort!

Dave-
Yep, I spotted it! Useful.

Now, does anybody out there know the BMC Part number for the 5.125:1 crownwheel & pinion gearset?
Stephen Strange

This thread was discussed between 14/12/2014 and 17/12/2014

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