GPA20 rear axle - Hand brake unit and control


The hand brake assembly is fitted on the pinion. It consists of a mechanism placed between three friction discs splined to the pinion. The mechanism comprises two cast iron plates held by springs and separated by ball bearings housed in rails. The three discs are fitted to the pinion as follows:
- two discs separated by an intermediate plate between the thrust plate (29) and the mechanism,
- a disc between the mechanism and the cover plate (24).

Operation

When the hand brake lever in the cab is pulled, the cam (14) is moved via the pin (20). The cam pushes the rod (13) which causes the plates of the mechanism (31) to rotate and move apart. The discs (30) are then compressed between the moving plates (31), the intermediate plate (34), the cover plate (24) and the thrust plate (29), preventing the pinion from rotating. When the hand brake lever is released, the spring (17) brings the cam (14) back to the rest position and the mechanism is returned by its springs.


Parts list
(1) Circlip (2) Gear (3) Stud (4) Nut (5) Gear plate (6) Pin (7) Clevis (8) Pin (9) Pin (10) Left-hand cover plate (11) Plug (12) Seal (13) Rod (14) Cam (15) Circlip (16) Finger (17) Spring (18) Centring pin (19) Seal
(20) Control pin (21) Snap ring (22) Washer (23) Finger (24) Cover plate (25) Screw (26) Pinion (27) Shim(s) (28) Screw (29) Thrust plate (30) Discs (31) Mechanism (32) "O" ring (33) Retaining ring (34) Intermediate plate


Disassembly
Drain the rear axle housing.
Chock:
- the front wheels of the tractor
- between the frame and the front axle
Raise the tractor using a jack.
Place axle stands in position.
Remove the rear wheels.
Remove the right and left-hand hydraulic cover plates.

Tractor with no creeper unit
Drive out the double pins (2) (4) from the coupling sleeves (1) (5). Slide the sleeves towards each other on the shaft (3) linking the pinion (26) and the gearbox output shaft. Remove the shaft and sleeve assembly. On 4WD tractors: If the pins are not accessible, disconnect the front axle shaft by sliding the rear sleeve and manually turning the front axle clutch shaft to position the shaft (3). Remove the circlip (1).
Remove the gear (2) (if fitted).

Tractor with creeper unit
Remove the creeper gear fork and the sleeve assembly (connecting shaft and coupler).


 Tractors with or without creeper unit
If necessary, remove the cab screws. Raise and chock the cab. Check the space between the bonnet and the windscreen (if the space is too narrow, remove the body). Disconnect the cable (3). Take out the pin (1) and remove the control rod (2).


Remove the retaining ring (33) and remove the seal (19).
Release the spring (17) using a pair of pliers.
Loosen the nut (4) to release the rod (13) from the cam (14).
Remove the circlip (15). Remove the cam (14) with the finger (16).
Remove the screw (25). Remove the cover plate (24) and the control pin (20). Keep the mechanism (31) and the brake discs (30) towards the rear. Extract the cover plate (24), tilting it to disengage it from the pin (18), the finger (23) and the pinion (26) and to release the pin (20) from the housing.


Remove the spring (17) and the washer (22).
Remove the snap ring (21) (if necessary) on the control pin (20).
Remove the discs (30) and the mechanism (31).

If replacing the mechanism
Unscrew the nut (4) and remove the plate (5) and the pin (6).
Take out the pin (9) and remove the pin (8) and the clevis (7). The stud (3) is smeared with Loctite 270 and locked in the clevis (7).

If replacing the thrust plate (29)


Remove two diametrically opposed screws (28) and screw in two guide studs (A). The purpose of this operation is to hold the shims (27).


Unscrew the two remaining screws.
Remove the thrust plate (29). Check that the shims have all remained on the housing. The finger (16) smeared with Loctite 270 is screwed onto the cam (14). The finger (23) smeared with Loctite 270 is screwed onto the thrust plate. The centring pin (18) is fitted home on the shoulder of the cover plate (24). Check and clean the components. Replace any defective parts.

If replacing the thrust plate (29)
Reinstall the plate. Smear the two screws (28) with Loctite 270 and then tighten them to a torque of 90 - 120 Nm.

If replacing the mechanism
Reinstall the clevis (7) prepared with the stud (3) and the pin (8). Reinstall the pin (9). Install the rod (13) with its pin (6) on the stud (3) of the clevis.
Reinstall the plate (5) and screw on the nut (4). The plate (5) is rectangular. It must be positioned horizontally so that the pin (6) Install correctly on the rod (13).


Reinstall the discs (30), placing the mechanism (31) between them. Insert the rod (13) on the finger (23). Check that the discs slide freely on the shaft of the pinion (26). Install the snap ring (21) (if removed) on the pin (20).
Install the pin (20) in the cover plate (24) with the washer (22), the spring (17) and the seal (32). Check that the discs (30) and the mechanism (31) are correctly positioned. Install and tighten the screws (25) to a torque of 90 - 120 Nm. Install the cam (14) with its finger (16).


Position the circlip (15). Re-tension the spring (17), while positioning its ends E as indicatedLightly smear the pin (20) with AS 767 Anti-Seize grease or equivalent. Install the seal (19) on the housing and compress it to 5.8 ± -0.15 mm using a retaining ring (33).


Reinstall the gear (2) (if fitted). Position the circlip (1).

Depending on the model:
- with creeper unit: refit the sleeve assembly (connecting shaft and coupler) and the creeper gear fork. Turn the groove on the pinion sleeve towards the rear of the tractor. Replace the pins. Adjust the forks.
- without creeper unit: refit the sleeve assembly (connecting shaft and coupler). Turn the groove on the pinion sleeve towards the rear of the tractor. Replace the pins. Reinstall the left-hand cover plate.


Position the rod (2) with the cam (14) in contact with the rod (13) to obtain a distance of 315 mm ± 12 mm between the cable attachment axis and the support (3). Install the pin (1).


Adjust the mechanism (31) with the adjustment nut, so that the cam displacement from rest position "a" to maximum position "b" is 60°. The adjustment nut (4) is accessed via the plug port (3) on the left-hand cover plateReconnect the control.

Adjust the hand brake control reverse.
Reinstall the right-hand hydraulic cover plate.
Raise the tractor using a jack. Install the wheels.
Remove the axle stands and the jack.
Tighten the wheels to a torque of 400 - 450 Nm.
Remove the chocks at the front of the tractor between the frame and the front axle. Top up the rear axle housing oil level.
Check the operation of the electrical circuits, the low pressure switch, the solenoid valves and the blockage indicator.
Check the operation of the linkage and the hand brake.
Check the tightness of the mating faces, cover plates and hydraulic unions.

Assembling and adjusting the control

Introduce the cable (1) from below towards the cab interior and fasten with the clip (2)Fix the clevis (7) on the brake lever (4) with the pin (5), the washer (6) and the pin (3). Check that the cable is not pinched.
Install the sheath end (2) in the attachment support (1).


Attach the end of the cable (7) to the lever (6).
Place the hand brake lever in the released position. Make essential adjustments to obtain a distance of 315 mm ± 12 mm between the nut (5) and the centreline of the cable end (7).
Tighten the nut (3) on the washer (4).


Check the operation of the control.
- Tighten the lever. Initial brake travel should be approximately 8 notches. The indicator light on the instrument panel should come on and the buzzer should sound if a gear is engaged.
- Release the lever. The control should return freely to the rest position. In this position, the buzzer stops and the indicator light on the instrument panel should go out.