26.10.1997

Alfa 156: The gearboxes


Introduction
In order to make the most of the generous performance supplied by each of its six engines, the Alfa 156 offers a choice of two gearboxes. The 22 kgm unit goes with the 1.6, 1.8 and 2.0 Twin Spark 16-valve power plants. The 31 kgm, available in 5 and 6-speed versions, equips the range's most powerful engines: 5-speed on the 1.9 and 2.4 JTD diesels; 6-speed on the 2.5 V6 24V petrol version.

The 31 kgm unit
The 31 kgm transmission is a new generation gearbox that is less bulky in every direction and offers silky smooth gearshifts. It adopts a transverse configuration with two gearshafts in echelon and a differential. On the six-speed version, sixth is a 'power' speed for use when travelling at top speed. On this unit the tightly packed gear ratios allow for ultra-precise management of the 6-cylinder petrol engine's impressive revs, and a torque which peaks at a generous 22 kgm-plus in a way that adds zest to the car's performance and makes it easier, more enjoyable and more comfortable to drive.
In both its 5 and 6-speed versions, the new gearbox adopts a 'collar' that prevents any involuntary shift into reverse and also makes for more precise engagement in fifth.
It is for example, unusually quiet thanks to thickly-coated toothing and the special finish on second, fifth and final drive gear pairings.
Using the 31 kgm gear lever also demands 50% less effort than a traditional gearbox of the same size. This has been achieved by applying a Borg-Warner 'free-ring' type synchro on all gears. That is in addition to the triple-cone synchro on first and second and the twin-cone version on third, these being the gears most often used in town traffic.
Gear engagement is also easier when cold, thanks to dynamic lubrication with multigrade oil. Ultra-precise gear engagement is assisted by a four-step selection system (reverse is on the fourth level) and a gate that is set centrally on a bearing mount.
The clutch pedal is notably light, being hydraulically activated and equipped with super-efficient shaft bushings.
The gear lever neither shakes nor judders thanks to the double-acting gear stick. The latter, which appears on all Alfa 156s, is a high-tech model that employs ultra-strong technopolymers for significantly enhanced precision and low noise gearshifts.

The 22 kgm unit
The 22 kgm transmission mounted on the Alfa 156's three petrol engines (1.6, 1.8 and 2.0) features a new clutch release mechanism.
This is the first time this new coaxial hydraulic unit appears on a Fiat Group model and it offers the advantage of unvarying performance throughout the life-span of the car. It weighs about 2 kg less than a traditional hydraulic system and it eliminates all the couplings and consequent slippages that tend to cause problems as components age.
With the aid of this system the clutch pedal remains smoothly responsive and returns without a problem, while clutch action is less noisy than on conventional models and transmits no vibration of any kind.
The clutch pump has also been improved. Like the piston it adopts a plastic body and a steel cylinder and its coaxial system makes an excellent job of screening out engine noise and vibration.


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