Spitfires had three (3) different clutches, three (3) different gearboxes and basically one (1) diff, but with variations to the ratios, flange and stub axle sizes.
The original clutch was finger type with a diameter of 61/4". At the beginning of the MKII a diaphragm type clutch was introduced of the same diameter 61/4" this was continued through the MKIII and MKIV. The next change was with the 1500. To cope with the extra torque of the bigger motor a 71/4" diaphragm clutch was used.
All three (3) variations had different flywheels. The three (3) different gearboxes were as follows:
- MKI, MKII, MKIII had basically the same gearbox with no syncromesh on first gear.
- MKIV had syncromesh on all gears and slightly closer ratios.
- 1500 had a stronger single rail box which is also interchangeable with earlier cars with small changes to the clutch plate and tailshaft.
The diff was basically the same with all models and interchangeable, the ratios were as follows:
- 4.11-1 in the MKI, MKII and MKIII
- 3.89-1 and 4.11-1 in the MKIV
- 3.63-1 and 3.89-1 in the 1500
The variation in ratios was noting to do with the optional overdrive, but what country the car was built for.
There are also three (3) different tailshafts, because Leyland couldn’t make up their mind, probably the early type was the best being just the spline type. The last type being the same as the TR7 and not serviceable.