Sprite, Midget, and Minor Parts & Accessories

Mini Automatic to Manual Conversion

Basic Information

            The following is an overview of the necessary steps to convert a Mini from an automatic transmission to one with a manual transmission/gearbox.

Assumptions Made and Areas Not Discussed In Detail.

1.         The entire power unit for a manual gearbox car is to be swapped into the engine compartment of a Mini originally equipped with an automatic transmission. The engine blocks of an automatic Mini and a manual gearbox Mini are not interchangeable. An automatic block can be modified to fit a manual gearbox, but it is skilled work and beyond the scope of this write up.

2.         The power units being swapped are both of the same capacity; e.g. both are 1275cc units. There are some differences between, for instance, 998 and 1275 power units that have to be dealt with in any engine swap, regardless of the transmission type; e.g., upper radiator hose and bracket are not the same for 998s and 1275s.

3.         The power units are from the same generation. Early automatics used Hardy Spicer U-joints and later ones inner CV (“Pot”) joints. Mixing would require axle changes. There is also the issue of installing rod change gearbox shift linkage into a pre-rod change body and visa versa. And there are issues between A and A+ engines regarding starters, generators/alternators, and distributors.

4.         The front subframe for the automatic car is to be retained when the power unit swap is made. The two types of subframes are different. A manual subframe could be installed directly into the automatic car as long as it is of the same type (single bolt r two bolt).

Changes To Make

1.         Subframe and Motor Mounts

            The automatic front subframe is slightly wider to accommodate the automatic transmission and both motor mounts are different. To install a manual gearbox power unit, the following are necessary.

            Obtain two manual gearbox motor mounts.

            Make two spacers that will be used between the front and rear motor mounts and their mounting points on the replacement power unit. This widens the mounting base of the manual gearbox power unit to fit into the automatic subframe. The spacers should be 9 – 10mm or 3/8” thick with three holes for the mounting bolts to pass through. New mounting bolts will be needed. The front three are fine thread and the rear three are coarse.

             The front, manual motor mount has narrower spaced mounting holes than the automatic mount it replaces. Line the new mount up with the rearmost hole in the subframe and use the front mount hole to drill a new hole in the subframe.

2.         Clutch Hydraulics

            Obtain a clutch master cylinder.

            Obtain a clutch slave cylinder and hose appropriate for the manual gearbox power unit. If an A+ power unit, you might need the mounting platform for the clutch slave if it doesn’t come with the power unit.

            A clutch pipe will need to be obtained/fabricated to go from the clutch master cylinder to the mounting point for the clutch slave cylinder hose on the firewall.

            A clutch pedal will need to be installed on the pedal box, or a pedal box from a manual gearbox car can be swapped in.

3.         Shift Mechanism

            If not supplied with the manual gearbox power unit, all the shift linkage, the lever, the boot, and the boot retainer applicable to the gearbox must be obtained.

4.         Electrics and Speedometer

            Automatics had an inhibitor switch that would not let the engine start if the car was in gear. The switch will not be used with the manual gearbox so the wires involved need to be located and joined together; otherwise, the starting circuit will not allow the car to be started. Look for the switch near the automatic shift lever; although there may be other locations more easily accessed.

            It is unlikely that the final drive ratio for the manual gearbox will be the same as the one from the automatic. If not, either the speedometer will have to be recalibrated, or speedometer drive gears will need to be installed to match the final drive and speedometer.

Chuck Heleker
Article Date: Feb 10, 2010
Car Accociations: MINI
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