Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Diff ratio

Ok, in the past I have expressed the belief on the BBS that my '58 Frogeye has a 4.55 ratio diff (as per original spec). I have been corrected and informed that it was fitted with a 4.22.
Whilst looking at the Morris Minor Owners Club website I saw the attached table which states that the Sprite midget 948 was fitted with a 4.55. What is the truth?

3.727 11/41 BTA 551 RILEY 1500
3.9 10/39 BTA 1222 WOLSLEY 1500
4.22 9/38 ATA7326 MINOR 1098
4.55 9/41 ATA 7093 MINOR 948 AND VAN
4.875 8/39 2A7320 A35 VAN
5.375 8/43 ATA 7073 MORRIS GPO VAN
3.727 11/41 BTA 551 MK 2 RILEY /WOLSELEY
3.9 10/39 BTA 1222 1275 MIDGET/SPRITE
4.22 9/38 BTA 550 MINOR/SPRITE/MIDGET 1098
4.55 9/41 ATA 7093 SPRITE MIDGET 948 MINOR 1098 VAN/PICKUP

Neil (K series)

Neil... Good to chat on F/B.. :-)

I think that the above list is incorrect. I don't think the 948 cars ever came as std with a 4.5:1 diff.

M T Boldry

As far as i know the 4.22 was used from the frist (what is in 101 Mark?) until the early MKIII (my 67 MKIII had one)
But then again my MKII has a 3.9 ;)
Onno Könemann


I seem to remember the ratio is also stamped on the edge of the alloy casing flange where it bolts into the case.
You can also check ratio by jacking up a wheel and turning the prop steadily by hand and count the revs for one turn of the roadwheel.

Onno is correct my first 1275 had a 4.22 it changed at the face lift.

Also the split screen minors 803cc also had a 5.375.

richard boobier

Full circle! - that list came from me, compiled from a variety of sources, workshop manuals, service books, road reports, web references etc etc over a lengthy period about 15 years ago when I was doing classic trials and wanted to know where to locate low ratio diffs. A such it may well contain wrong information, it's probably a good example of how mistakes get perpetuated ad infinitum. I've just dug out an Autobooks manual for Morris Minors '52-'71 which states 800cc (the sidevalve models) had either a 5.286 or 5.375 ratio, the 948cc had the 4.55 and the 1098s had the 4.22. I've never owned a Frog, or a manual for one, so couldn't say where I might have picked up on it sharing the 4.55 with it's heavier relative, but if I got it wrong all those years ago it was bound to come back to haunt me, sorry chaps ;-)
(BTW the typo of Wolseley in line 2 is not down to me)
David Smith

I think there may be a few other errors in there ;o)

A35 vans came in 3 flavours - 948, 1098 and 848. Did anyone know they made an 848cc in-line engine?

The 948 had a 4.55, 1098 a 4.22 and I think the 848 had a 4.875

and AFAIK Spridgets never had the 4.55, as previously stated.
Dave O'Neill 2


The early minors 'up to Jan 54 ran a different axle,
not the interchangeable diff, 3/4 floating we now have, Jan 54 was the start of the 5.375 8/43 units.

It was my first car and i swopped it out for a 4.55 when I started to tune it up - memories, memories LOL.

Now how many engines did I blow up ????

richard boobier

My little A35 has an 848cc Van engine in it. I've driven from Yorkshire to Goodwood, Avimore, East and West coasts with it and even to Zanvoort with three of us (Tarquin, Harington and me). I've given it serious pain wherever I've gone and I still can't kill that little engine.... it still lives :-)

M T Boldry

BTW I'm looking for a 5.125 diff, if anyone should have one?
Dave O'Neill 2

This thread was discussed between 19/11/2010 and 20/11/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.