GPA20 rear axle

The tractor rear axle comprises four main housings:
- the centre housing which contains the crow nwheel and pinion, the power take-off transmission in all variants as well as the 4-wheel drive tractor transmission, the hand brake control mechanism and the main brakes. It also supports the two trumpet housings, the linkage cover plate, and the side cover plates.
- the right and left-hand trumpet housings fixed to each side of the centre housing, acting as a housing for the rear wheel drive system.
- The linkage cover plate fitted to the top of the centre housing supports the linkage arms, which are connected to the tractor hitch.

Centre housing assembly

The pinion is driven by the gearbox output shaft, attached to the connecting shaft by splined sleeves. The helical crown wheel and pinion assembly transmits the drive to the trumpet final drive units. A differential lock system with a dog clutch and activated by hydraulic pressure is incorporated into the unit. The differential lock is controlled either by the Autotronic 5 for models fitted with a Power Shuttle, or by an electrical circuit for models fitted with a mechanical reverse shuttle.

4-wheel drive clutch
A driving gear attached to the pinion drives the counter driven gear of the 4WD clutch assembly. Drive is then transmitted via the Belleville washers to the clutch output shaft. The 4WD clutch is hydraulically activated. There is therefore no possibility of accidental disengagement of the 4WD clutch in the event of hydraulic failure.

Power take-off drive line
The rotation of the shaft passing through the gearbox, proportional to engine speed, is transmitted to the hydraulic clutch located at the front of the centre housing. In the clutch engaged position, drive is transmitted by an intermediate shaft and a set of driving and driven gears to the 540 or 1000 rpm PTO shaft. Speeds are selected by a system of interchangeable shafts or by shifting. A hydraulic brake mechanism stops the rotation of the PTO shaft in the disengaged position. Two additional options are offered:
- 4 speed economy PTO.

Hand brake assembly
A brake assembly comprising three discs and an expanding mechanism is fitted to the pinion.

Main brakes
Two pistons fitted laterally into two cavities in the centre housing act on two discs attached to the trumpet housing input sun gears. The brake pistons are activated hydraulically.

J Clearance
P Preload
E Taper distance
E = Z + T - (X + Y)
E = 184.955 + T - (X +90.520). where:
Z: Nominal dimension of the pinion = 184.955 mm.
T: Correction of the nominal dimension engraved on the end of the pinion; this may be a positive or a negative value.
X: Dimension of the centre housing stamped on the rear right-hand side of the housing, behind the lift ram.
Y: Dimension of the pinion with bearing = 90.520