GPA40 rear axle - Hand brake unit and control


The mechanical hand brake control assembly (secondary brake) is fitted to the pinion (9), located in the centre housing. It consists of six discs (11) and four intermediate plates (26) distributed equally on the mechanism (16). The mechanism is composed of two cast-iron plates that can be expanded thanks to balls fitted in rails. The discs are splined to the pinion. The intermediate plates are fixed to the unit by lugs. The mechanism is controlled by a rod (3) which acts on an actuator lever (24) connected to the mechanism’s adjustable tie rod (23). The mechanism is adjusted via a nut (21). This nut can be reached by removing the hexagon socket plug (2) located above the centre housing.

Lubrication 
The lubrication pipe (57) carries the oil from the hydraulic manifold above the centre housing to the central channel and the radial holes in the pinion, in order to lubricate the discs and the intermediate plates of the hand brake mechanism.

Operation 
When the hand brake lever in the cab is pulled, the cable activates the rod (3). This pivots and pulls the actuator lever (24), separating the mechanism plates (16). This, in turn, compresses the discs in the unit (13) (15) and locks the pinion. When the hand brake lever is released, the mechanism is at rest and the discs and intermediate plates are free.

Sealing 
The tightness between the cam (22) pin and the centre housing is ensured by two "O" rings (1).

Parts list 
(1) "O" rings (2) Plug and seal (3) Control rod (4) Support (5) Screw (6) Washer (7) Cotter pin (8) Spacer (9) Pinion (11) Discs (12) Snap ring (13) Unit cover plate (15) Hand brake unit (16) Mechanism
(17) Washer (20) Pin (21) Adjustment nut (22) Cam (23) Tie rod (24) Actuator lever (25) Pin (26) Intermediate plates (32) Spring (57) Lubrication pipe

Legend
B Shaft and bearing for 4WD tractors fitted with GTA1040 transmission
C Shaft and bearing for 4WD tractors fitted with GTA1540 transmission
L Lubrication

Parts list 
(1) "O" rings (2) Plug and seal (3) Control rod (4) Support (5) Screw (6) Washer (7) Cotter pin (8) Spacer (9) Pinion (11) Discs (12) Snap ring (13) Unit cover plate (15) Hand brake unit (16) Mechanism (17) Washer (20) Pin (21) Adjustment nut (22) Cam (23) Tie rod (24) Actuator lever (25) Pin
(26) Intermediate plates (32) Spring (58) ParkLock device (if fitted) (59) Support (tractors without ParkLock device)

Removing and refitting, disassembling and reassembling the hand brake unit and its control

Removing and disassembling the hand brake mechanism involves splitting the tractor between the gearbox and the rear axle. Disconnect the tractor between the gearbox and the rear axle. Remove:
- the right-hand hydraulic cover plate;
- the left-hand hydraulic cover plate;
- the power take-off clutch;
- the 4WD clutch;
- the creeper unit control mechanism (if fitted).


Remove:
- the circlip (5);
- the thrust washer (2);
- the shim(s) (6).
Remove the 4WD driving gear (17)Mechanically disengage the Park Lock function (if fitted) using the special screw.


Remove:
- the nut (21);
- the push rod (10);
- the M20 screw (5);
- the washer (6);
- the actuator lever (24).

Removing the hand brake unit
Remove the pinion/hand brake unit assembly.


Completely unscrew the nut (18) using socket ref. 3378118M1 and special socket ref. 3378119M1. Remove the following parts, making a note of their position:
- the tapered roller bearing cone (1);
- the shim(s) (3);
- the thrust washer (4).

Disassembling the hand brake unit
Place the pinion/hand brake unit assembly on a workbench. Remove the cover plate (13) from the hand brake unit (15)Visually note the hand brake unit components and remove:
- the mechanism assembly (16);
- the actuator lever (24);
- the discs (11);
- the intermediate plates (26).

Disassembling the control 
Note the angular position of the rod (3) in relation to the splined pin on the cam (22). Remove:
- the cotter pin (7);
- the control rod (3);
- the spring (32);
- the snap ring (12);
- the spacer (8);
- the washer (17).
Pull the cam (22) downwards to release it from the centre housing.
Discard the "O" rings (1).

Reassembling the control
Clean and check all components. Replace those that are defective.
Lightly smear the pin and the cam (22) with AS767 graphite grease or equivalent. Fit a new "O" ring (1) into the groove on the centre housing.
Refit the cam (22) inside the centre housing. Slide the second "O" ring onto its pin (1). Refit:
- the washer (17);
- the spacer (8);
- the new snap ring (12).
Manually check the movement of the cam (22).

Reassembling the hand brake unit
Clean and check all components. Replace those that are defective. If the unit (15) and the cover plate (13) display any faults such as discoloration due to abnormal overheating or wear to the friction surface areas, a new unit/cover plate assembly should be fitted. In this case, it is necessary to shim the tapered roller bearings again and to re-adjust the position of the pinion/hand brake unit assembly.


Place the hand brake unit, fitted with its pinion, vertically on a makeshift support SInsert three discs and two intermediate plates into the unit, starting with a disc. Position the mechanism. Insert the three other discs and the two other intermediate plates, first placing a disc against the mechanism.

Check that the locating pin for the cover plate (13) is present on the unit (15). Refit the cover plate, fitted with its tapered roller bearing cup, onto the hand brake unit. Temporarily tighten the cover plate (13) using the two locally obtained short screws (M16). The discs and intermediate plates must not be under load. Finish assembling the unit/cover plate assembly by refitting the following:
- the thrust washer (4);
- the shim(s) (3) used to preload the pinion tapered roller bearings;
- the front tapered roller bearing cone (1).
Partially screw on the nut (18) (see chapter 6) using wrench ref. 3378118M1 and special socket ref. 3378119M1. The final tightening torque for the pinion nut (18) will be applied after the pinion/hand brake unit assembly has been refitted in the centre housing.

Refitting the hand brake unit
Refit the pinion/unit assembly in the centre housing complete with its hand brake mechanism. At the same time, guide the actuator lever (24) onto its pin. The actuator lever pin is fitted tightly onto the centre housing.
Fix the pinion/hand brake unit assembly to the centre housing compartment. Tighten the screws to the appropriate torque. Lightly smear the thread of the pinion nut (18) with Loctite 270 or equivalent. Tighten the nut to the
appropriate torque.

Final steps
Lightly smear the thread of the M20 screw (5) with Loctite 270 or equivalent. Fit the washer (6) onto the screw and slide the screw into the hollow actuator lever pin. Tighten the screw to 230-250 Nm.


Refit:
- the push rod (10) (tractors fitted with a Park Lock device);
- the nut (21).
Align the 4WD gear (17) as required and slide it onto the pinion splines.


In the following order, fit:
- the shim(s) (6);
- the thrust washer (2);
- the circlip (5).
Adjust the hand brake mechanism and control.

Refit:
- depending on the option, the creeper unit control mechanism;
- the 4WD clutch;
- the power take-off clutch;
- the left-hand hydraulic cover plate;
- the right-hand hydraulic cover plate.
Reconnect the tractor between the gearbox and the rear axle.
Check that the hand brake lever operates correctly.
Mechanically re-engage the Park Lock function (if fitted) using the special screw. Carry out a road test to check:
- engagement of the Park Lock device (if fitted);
- tractor movement with the hand brake off;
- creeper unit operation (if fitted);
- sealing of the hydraulic cover plate mating faces
(right-hand, left-hand and 4WD).