Transmission (M56; 2004-2010): Design: Synchronization

The synchronizing units are positioned on the shafts in the transmission as follows:

• The synchronizing unit for 1st - 2nd gear is on the lower output (secondary) shaft (output shaft for gears 1, 2, 3, 4)
• The synchronizing unit for 3rd - 4th gear is on the primary shaft
• The synchronizing unit for 5th/back-up (reverse) gear is on the upper output (secondary) shaft (output shaft for 5th and back-up (reverse) gear).

The synchronizing hub assembly consists of a coupling sleeve, flange and the hub. Each synchronizing hub is joined to its shaft by splines and rotates with it.

There are idler wheels on both sides of each synchronizing hub. The idler wheels rotate freely on the shaft. Each idler wheel is constantly engaged in its gear.

The synchronizing rings expand when heated by the same amount as the components they are in contact with. As a result no safety margin is required to counter expansion.

The idler wheels for single and double synchronization have no cones. An inner ring on the synchronizer unit performs this function instead.

The synchronizer unit is a modular system. This makes it easy to upgrade from a single synchronizer to double synchronization by replacing the synchronizer kit.

Single synchronization  , which has one friction surface, is on:

• back-up (reverse) gear
• 4th gear
• 5th gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The inner ring is pressed steel and the friction surface is coated with sintered brass.

Double synchronization  , two friction surfaces, is on:

• 3rd gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The sealing ring is pressed steel and the friction surfaces are coated with sintered brass. The inner ring is machined steel.

Triple synchronization  , three friction surfaces, is on:

• 1st gear
• 2nd gear.

The outer ring (to the left in the illustration) is manufactured in pressed steel. The sealing ring is pressed steel and the friction surfaces are coated with sintered brass. The inner ring is pressed steel and the inner friction surface is coated with sintered brass.