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 - Midget 1500 and spitfire 1500 speedometer

Hi all,

Just wondering if anyone can tell me if the midget 1500 and the spitfire 1500 speedometers are interchangeable? They have the same engine and gearbox, but I notice the spitfire one reads to 120 rather than 110 like my midget one...

Karl Bielby

They may have the same engine and - possibly - same gearbox, although some have overdrive.

They may not necessarily have the same speedo drive in the gearbox, and possibly not the same final drive ratio - bearing in mind that a 1500 Midget diff could be 3.9 or 3.7

Midget 1500 speedos also changed - as did all clocks/gauges - to Triumph style in the later models.
Dave O'Neill 2

the answer might be read the small print!
there's a type number in tiny letters on the face, and to the right there's a 4-digit number, this is the TPM (turns per mile) that the speedo is calibrated to, depending on the diff ratio fitted, 4.2 / 3.9 / 3.7.
1500s to August 1977 had the 3.9 and from then to end of production it was the 3.7.
IIRC the 3.9 is 1376 TPM, not sure what the 3.7 is.
Of course you can always use the Spit one and have it recalibrated, there's a couple of specialists who do this, Richard Jenkins in Redditch being often recommended.
David Smith

The presence or absence of overdrive makes no difference to the speedometer as the drive is taken off the output shaft after the o/d unit. If it were otherwise you would need to change the speedometer every time you went in or out of overdrive!!
But differential ratio and tyre size does, and depending on model, they are different speedo heads. As Dave says, look for the TPM figure on the dial.

OK great cheers chaps, il get my magnifying glass out and report back!
Karl Bielby

I think the 1376 is the tpm for the 1275 cars. I read recently that the 1500's have 1000 although I don't know which diff ratio that applies to.
Graeme Williams

Ah interesting, the spit one on the front says

SNT 6211/125 1000

I haven't been able to look at the one in my midget yet..

I'm unsure what diff ratio i have, all I know is that it's not long enough! It runs out of gears at 50 far too easily.
Karl Bielby

Graeme, the 1275 had two different ratios over it's production life. As did the 1500 also, which I explained in my previous post.

@Karl - what's your VIN number - the change point to the 3.7 was GAN6/ 200000
David Smith

OK good point, il see if I have it anywhere..

Edit confirm that my vin is GAN6 217***
Karl Bielby

meaning the diff is as long as possible..

Which TPM am I looking for on a speedo then?

Cheers guys
Karl Bielby

The 1376 is for the 3.9 and the 4.2 is marked 1472 (for the 1275 cars)
Graeme Williams

So 1000 should be good then?
Karl Bielby


Your car may have had a 3.7 when it left the factory, but it doesn't mean it still has.

It's not uncommon for a worn/broken 3.7 to be replaced with a 3.9 or 4.2
Dave O'Neill 2

<<The presence or absence of overdrive makes no difference to the speedometer >>

Very true, but certainly with the GT6, the O/D cars had a different diff ratio to the non-O/D versions.

I'm not that into Spits, so I don't know if the same applies.
Dave O'Neill 2

Maybe the o/d versions of the GT6 had some other change as well - to the diff ratio or tyre size? If you think about it a mechanical speedo drive has to be downstream of any gear or o/d that is changed as you drive. It cannot be otherwise! Of course the speedo might differ in some other way such as the top speed shown but this doesn't effect the ratio.

My point was that the GT6 with O/d would have had a different speedo as it had a different diff ratio.

The Spitfire may have also used a different diff ratio for O/D, therefore it would have a different speedo, also.
Dave O'Neill 2

Ah, sorry Dave. I missed the point you were making then.Apologies.

Numbers checked out. Speedo on its way! Cheers for the help chaps!
Karl Bielby

This thread was discussed between 11/04/2016 and 14/04/2016

MG Midget and Sprite Technical index

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