GPA40 rear axle - Brake pistons


The brake pistons (2) are housed in two cavities formed by the centre housing and the left and right-hand differential supports. They are:
- concentric with the mating face of each trumpet housing;
- guided by three stop pins (6) force fitted into the centre housing.
Each brake piston has two ring faces F and F1, which have different cross sections.


Face F is under hydraulic pressure:
- from the master cylinders (tractors fitted with GTA1040 and GTA1540 transmission (40 kph));
- from a block/valves assembly (tractors fitted with GTA1540 transmission (50 kph).


Face F1 compresses the brake disc, which is splined to the input sun gear of the trumpet housing, against the compartment or spacer, depending on the trumpet housing type. The compartment or spacer also acts as a brake plate. The pistons are sealed by "O"rings (3) (4) mounted respectively into the grooves of the centre housing and the differential supports. A seal J placed in the angle of each support prevents the pressure in the piston chamber from escaping into the centre housing.

Tractors fitted with GTA1040 or GTA1540 transmission (40 kph)
Each brake piston is controlled by a master-cylinder assisted hydraulically by the 21 bar low-pressure system (pressure P). When the brake is released, minimal clearance is ensured between the brake piston and disc. The brakes are self-adjusting. They maintain constant pedal clearance.

Tractors fitted with GTA1540 transmission (50 kph)


For tractors fitted with GTA1540 transmission (50 kph) and depending on the legal requirements of certain countries where the tractor is registered with a maximum speed of 50 kph, the hydraulic control of the brakes is fitted with:
- a block/valves assembly (1) fitted to the front bulkhead of the cab and activated by the brake pedals;
- an electronically controlled 50 kph accumulator and a hydraulic braking unit (5) located on the right-hand side of the transmission;
- brake pistons (2) and discs (35) fitted in the centre housing cavities and designed with a greater braking surface S than that of the brake pistons and discs on 40 kph tractors;
- a return travel limit mechanism (3) for each brake piston.

Operation of the return travel limit mechanism of the brake pistons

Brakes active 


When the brake pistons (2) are pressurised by the block/valves assembly (1) and the 50 kph hydraulic braking unit (5), they compress the brake discs and drive the elements (4) (1) (7) and (6) of the return travel limit mechanism. At the same time, the springs (5) compress by 0.60 to 0.65 mm depending on space E in order to fit the flat washers (6) against the differential supports. Any wear to the brake discs (35) is automatically corrected by the "tight" sliding of the brake discs (2) on the Mecanindus pins (4).

Brakes inactive 


When the brake pedal is released and the hydraulic pressure drops in the brake piston chamber (2), the springs (5) decompress to the limit of E (0.60 to 0.65 mm), thus separating the pistons (2) of the brake discs by the same value.

Lubrication


The brake discs are cooled during use by a flow of oil coming from the lubrication system and flowing towards the hydraulic manifold (1) and port O via the right-hand hydraulic cover plate. Oil flows between the brake discs and pistons and lubricates their braking surfaces when they are not in use.
On Normal Duty trumpet housings, the brake discs are lubricated by union R screwed directly onto each trumpet housing.

Parts list 
(2) Brake piston (3) "O" ring (4) "O" ring (6) Stop pins
(30) Compartment or spacer (depending on type of trumpet housing) (35) Brake disc

Legend
A - Brake mechanism without compartment (the trumpet housing is thrust directly against the centre housing)
B - Brake mechanism with single compartment
C - Brake mechanism with sealed compartment
D - Brake mechanism with spacer
J Seals
O Port for lubrication of brake discs
P Pressure emitted by the master cylinder(s) (40 kph tractors) or a block/valve assembly 50 kph tractors)
R Union

Parts list 
(2) Brake piston (3) "O" ring (4) "O" ring (6) Stop pins
(30) Compartment or spacer (depending on type of trumpet housing)
(32) Hub (Heavy Duty sealed trumpet housing versions and trumpet housings with composite final drive) (35) Brake disc

Legend
A - Brake mechanism without compartment (the trumpet housing is thrust directly against the
centre housing)
B - Brake mechanism with single compartment
C - Brake mechanism with sealed compartment
D - Brake mechanism with spacer