MANUAL GEARBOX 3
ASTRA HD8Ec SECTION 6
DESCRIPTION
The ZF 16S 1620 and ZF 16S 2320 TD version consist of:
-a central box containing the primary shaft, drive input shaft,
secondary shaft and the cogs of the four forward and one
reverse gear;
-a rear casing containing the Epicyclical Reducer Group
(G.R.E). The function of this is to double the number of
forward gears by means of epicyclical gears with helical
teeth.
This gives a range of gears that starting with four input
ratios permits eight different output ratios (four normal
ratio and four low ratio gears);
-a front casing containing the “splitter”, that gives a further
double selection for each of the eight forward gears and
for the reverse gear.
The “splitter” halves the difference between two
successive gears, effectively splitting each gear into a slow
ratio (L = slow ratio) and a fast ratio (S = fast ratio).
These gearboxes therefore have a total of sixteen forward
gears with finely scaled ratios, all engageable in succession, and
two reverse gears.
Thesynchronisersaresingleconetype.
Lubrication is by means of a gear pump.
The double H type gear shift control is equipped with a
pneumatically powered “servoshift” device to improve gear
selection and engagement.
The servoshift is a device consisting of a mechanical/pneumatic
functional unit and a dual action cylinder.
The advantages of this device are:
-gear selection and engagement more rapid and with less
effort;
-it dampens the vibration of the control linkages, reducing
noise;
-less strain to the synchronisers.
The device functions mechanically in case of pneumatic system
failure.
The gearboxes mounted of vehicles with F3B engines are fitted
with a synchro protection device.
This permits pneumatic power to the servoshift for gear
engagement only after the clutch pedal has completed 70% of
the disengagement stroke.
It consists of an electrovalve controlled by a proximity switch
mounted on the clutch disengage master cylinder.
Figure 1
1. Distributor – 2. Servoshift – 3. Servoclutch – 4. *Servoshift power electrovalve
* only for vehicles with F3B engine
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