Reference · Manual gearboxDraftv0.1

Gearbox Identification

Which gearbox is this? The gear change, the casing number, the gears inside and the final drive of the manual gearboxes under the A and A+ Series engines.

Compiled from the published references listed under Sources, not from factory records. Where those references disagree the disagreement is noted. Gearboxes are rebuilt with whatever is to hand, so the casing, the gears and the final drive each have to be identified on their own. Automatic gearboxes are not covered.

What to check, in order

1. Gear change. Visible from the driver's seat, and enough to place the gearbox in one of three generations. See Gear change.
2. Casing number. Narrows the generation to a few years. Type it into the casting above, or see Casing numbers.
3. Gears. Only with the gearbox off the engine: the tooth shape gives the type, a tooth count gives the ratio set. See Gears.
4. Final drive. Count the teeth of the crown wheel and the pinion. See Final drive.
5. Speedometer drive. With the speedometer housing off, the two small gears in it say which final drive the gearbox was built with. See Speedometer drive.

Gear change

Three ways of moving the gears were used, and they cannot be confused.

The magic wand, also called the direct change or the pudding stirrer, and the remote change share the selectors inside the gearbox. The rod change does not: its three selector shafts became one. That makes the rod-change gearbox a separate design, although the gears in it stayed the same at first.

Until late 1968 the magic wand had its own differential housing with a small tower for the lever. On the four-synchromesh gearbox it shares the remote housing and the lever sits on a pressed-steel adaptor plate.

Generations

First gear had no synchromesh until late 1968. Before that the gears changed twice, afterwards once more, for the A+.

A and B type gears are not interchangeable and have to be fitted as complete sets. The one exception is the early Cooper S, whose laygear (22G204) was made to take B type first and reverse gears. About 1984 the retainer of the centre mainshaft bearing went from four bolts to three, because the casing cracked at one of the four holes.

Mini Spares and Calver both date the A+ gears to about 1982; the Guess-Works list puts the change at 1984.

Casing numbers

The casing has its number cast into it. None of the sources consulted says where on the casing to look. A casing was sold under a different part number, given in brackets.

The casing does not fix what is in it: 22G68 and 22G190 were built with both A and B type gears, and 22G1128 was used with every engine size. The 1100 and 1300 saloons (ADO16) used the same casings, so a casing number alone does not say the gearbox came from a Mini.

Gears

Six sets of ratios were fitted as standard. Top gear is direct in all of them.

The ratios are those of the Guess-Works list; Calver gives the same sets to two decimals. A seventh set, with a 4.004 first gear, belongs to the economy Metro and is marked by a double groove in the teeth.

The close-ratio set of the Cooper S Mk3 and the 1275GT can only be told with the gearbox off the engine. Its first, second and third gears are those of the standard gearbox; the difference is in the first motion shaft gear, the smallest gear at the clutch end, which has 18 teeth where the standard one has 17. The laygear is usually stamped 22G1040. A few A+ gearboxes were built the same way, with first motion shaft DAM3167 and laygear DAM3168.

Final drive

The only certain way to know the final drive is to count teeth: those of the crown wheel, the large gear in the differential housing, divided by those of the pinion, the small gear on the end of the mainshaft. A higher number is a lower gear.

An A+ crown wheel has a number stamped into it that is not its part number; the column gives it. The two ratios without one (4.267 and 4.133) were made before the A+ only, and the four highest gears (3.211, 3.105, 2.95 and 2.76) for the A+ only.

A+ and earlier final drive gears have different tooth profiles and are not interchangeable, and neither are gears of different ratios that happen to share a tooth count. An A+ pinion is machined flat on both sides; an earlier one has a shoulder on one side.

Speedometer drive

The speedometer is driven by a spindle and a plastic pinion in a housing on the gearbox. From 1988 one speedometer served every model, and the pair of gears was chosen to suit the final drive and the wheel size, so the pair says what the gearbox was built for. The colours are the factory's own codes.

As a rule of thumb from the same article: before 1990 a Mini had a 6-tooth spindle and a 17-tooth pinion, except the City E and the cars built on 12 inch wheels from 1985, which had a 7-tooth spindle.