Manual Transmission/Transaxle: Description and Operation

Manual Transmissions

The manual transmission and final drive assembly fitted to the MINI COOPER S has been specifically manufactured by Get rag for this application. This transmission has 6 forward speeds and is rated for a maximum torque input of 210 Nm, enough to handle the output of the supercharged engine.

The gearshift pattern has reverse to the left of 1st gear. 6th gear is opposite 5th gear. The neutral position is in the 3rd /4th gear plane.

The gearbox uses the reference code "285".

Features of the Getrag 285 Transmission include:
- Three shaft design with four fixed gears on the input shaft.
- Seven gears on two output shafts.
- Overall length of 322 mm including the clutch housing.
- All gears have synchromesh.
- Aluminum die cast housings.
- All housings sealed with liquid sealer.

Primary components of the 285 transmission are:
- Gears and Shafts.
- Clutch Housing.
- Gearbox Housing.
- Gear Change Housing.
- Shift Mechanism.

System Components

Gears and Shafts

The 285 Transmission contains two output shafts in addition to the one input shaft. The input shaft is supported on a roller bearing in the clutch housing and a sealed ball bearing race in the gear case. The output shafts are both supported by roller bearings in the clutch housing and sealed ball bearing races in the gear case. All speed gears with the exception of first are supported on needle roller bearings. First gear is supported on a roller bearing. The differential assembly is supported on a pair of tapered roller bearings.

Output shaft 1 provides Reverse, 3rd and 4th gears. Output shaft 2 contains 1 st, 2nd, 5th and 6th gears. Both Output shafts are meshed with the final drive output gear.

Gear Box Housing
The gearbox assembly is constructed from four die casts aluminum housings.

Shift Mechanism



The shift mechanism consists of a single shift shaft and four shift rods. The shift shaft is supported by roller bearings. The shift forks are manufactured from die cast aluminum.

Principle of Operation

First Gear Power Flow

The first gear synchromesh hub is fixed to the output shaft "C", the hub synchronizes the speed of the hub (output shaft "C") and the speed of the first gear. The hub then locks the first gear to the output shaft "C" and drive is transmitted out through the final drive "D".


Second Gear Power Flow

The second gear synchromesh hub is fixed to the output shaft "C", the hub synchronizes the speed of the hub (output shaft "C") and the speed of the second gear. The hub then locks the second gear to the output shaft "C" and drive is transmitted out "D".


Third Gear Power Flow

The third gear synchromesh hub is fixed to the output shaft "B", the hub synchronizes the speed of the hub (output shaft "B") and the speed of the third gear. The hub then locks the third gear to the output shaft "B" and drive is transmitted out through the final drive "D".
Note:
Output shaft "B" is in mesh with the final drive output drive "D".


Fourth Gear Power Flow

The fourth gear synchromesh hub is fixed to the output shaft "B", the hub synchronizes the speed of the hub (output shaft "B") and the speed of the fourth gear. The hub then locks the fourth gear to the output shaft "B" and drive is transmitted out through the final drive "D".
Note:
Output shaft "B" is in mesh with the final drive output drive "D".


Fifth Power Flow




The fifth gear synchromesh hub is fixed to the output shaft "C", the hub synchronizes the speed of the hub (output shaft "C") and the speed of the fifth gear. The hub then locks the fifth gear to the output shaft "C" and drive is transmitted out through the final drive "D".


Sixth Gear Power Flow

The sixth gear synchromesh hub is fixed to the output shaft "C", the hub synchronizes the speed of the hub (output shaft "C") and the speed of the sixth gear. The hub then locks the sixth gear to the output shaft "C" and drive is transmitted out through the final drive "D".


Reverse Gear Power Flow

The reverse gear is meshed with and is driven by the first gear which rotates freely around the output shaft "C". The reverse gear synchromesh hub is fixed to the output shaft "B", the hub synchronizes the speed of the hub (output shaft "B") and the speed of the reverse gear and first gear. The hub then locks the reverse gear to the output shaft "B" and drive is transmitted out through the final drive "D".

Note: Output shaft "B" is in mesh with the final drive output drive "D".

Service Information Getrag 285
The oil drain and filler level plugs on the Getrag "285" are both positioned in the differential housing on the main gearbox casing. Both plugs have an 8 mm Allen key. There is no requirement for maintenance at any of the service intervals.