Unassisted brake master cylinder


The tractor brake master cylinder are attached to the pedal console and are housed to the right of the cab front bulkhead (single system). They act on the tractor main brake located in the centre housing. Depending on user requirements, the master cylinder can be activated separately or together in locked mode via a pedal latch. The master cylinder have different specifications depending on the option fitted on the tractor:
Tractor without trailer brake
Single  master cylinder assembly
Tractor with trailer brake
Double master cylinder assembly

The brake master cylinder are kept at a constant level by a residual oil flow coming from hose. This hose is connected to the lubrication and charge system by a multi-connector located at the front left-hand side of the gearbox.

Layout of hydraulic lines

Hydraulic lines with single master cylinder

Parts list 
(2) Charge tank (3) Main brake supply lines (right and left) (4) Pressure balancing junction line (5) Brake master cylinders (10) Connector to assist bleeding (11) Inlet port (charge oil)

Hydraulic lines with double master cylinder (trailer brake)

Parts list 
(1) Brake spool valve control line (2) Charge tank (3) Main brake supply lines (right and left) (4) Pressure balancing junction line (5) Brake master cylinders (6) Trailer brake spool valve (7) Trailer brake quick coupling (10) Connector to assist bleeding (11) Inlet port (charge oil)

Practical maintenance advice

Repair kits
Repair kits for brake master cylinders are listed in the spare parts catalogue.

Disassembly
If it is necessary to disassemble the brake master cylinder, carry out the operation on a clean workbench free of dirt and shavings. Carefully clean all components. Replace any components found to be scratched or damaged.

After disassembling or replacing
After disassembling or replacing the brake master cylinder:
- bleed the main brake system and trailer brake system (if fitted);
- check, if necessary, pedal adjustment and the operation of the locking latch.

Single-system master cylinders (without trailer brake)

Operation

Pedals uncoupled 
The force applied to a pedal is transmitted by the rod (5) to the piston (4) which moves in the bore of the active master cylinder. The valve (1) closes the supply port. The balance valve (3) is opened by the piston (4) and ball bearing (2). Oil under pressure is directed to the main brake ports (C) and the pressure balancing junction (D). Via the balancing junction, the pressure closes the valve (3) of the passive master cylinder.

Pedals coupled
Braking and pressure balancing
The force applied to the two pedals is transmitted by the rods (5) to the pistons (4) which move in the bores of the two master cylinders. The two valves (1) close the supply ports. The two balance valves (3) are opened by the pistons (4) and ball bearings (2). Pressure balancing is ensured in the two master cylinders by the balancing junction (D). Oil under pressure is also directed to the ports (C) and (C’) of the main brake system.

Legend 
B Master cylinder level kept constant by the lubrication and charge system
C Supply to main brake
D Pressure balancing junction


Pedals coupled
Braking and pressure balancing
The force applied to the two pedals is transmitted by the rods (5) to the pistons (4) which move in the bores of the two master cylinders. The two valves (1) close the supply ports. The two balance valves (3) are opened by the pistons (4) and ball bearings (2). Pressure balancing is ensured in the two master cylinders by the balancing junction (D). Oil under pressure is also directed to the ports (C) and (C’) of the main brake system.
Trailer braking
The continuous movement of the pistons (4) and (6) closes the valves (F) and (F’). The pressurised chambers (E) and (E’) supply the trailer brake control valve via ports (A) and (A’).

Adjusting brake pedals

Preparing for adjusting
If the pins (5) and (6) are removed, smear them lightly with molybdenum disulphide or AS767 grease or equivalent.
Screw the counter-nut (8) and clevis (1) onto the rod (2).
Install the return spring (3).


Settings
Adjust clevis (1) to obtain dimension X = 115 - 0.5 mm between the support (4) and the attachment pin. Lock the counter-nut.
Carry out the same procedure on the second clevis and ensure that the locking latch (1) operates smoothly.
Check pedals for correct operation. Ensure they are at the same height when not activated and that they return freely to their initial position.

Bleeding the main brake system

Installation
A male quick connector (3) is fitted as standard on the 5 bar line of the left-hand hydraulic cover plate. It facilitates the bleeding of the tractor brake system under pressure.
Join the connector (3) to the connector (10) with a makeshift hose (2) fitted at each end with a female connector ref. 3582045M1.
Connect a transparent pipe to the right and left-hand bleed screws (1) of the centre housing.
Immerse the ends of the two pipes into a container partially filled with transmission oil.
Using a clamp fitted with protective jaws, pinch the return hose (1) without flattening it excessively. Some hoses may be difficult to pinch due to their rigid structure. Consequently, it will be necessary to disconnect the hose from the connector (10) and temporarily replace it with a plug.

Legend 
D Movement of pressurised fluid through brake master cylinders during bleeding

Bleeding procedure
Run the engine at approximately 1300 rpm and heat the oil to operating temperature.
Open the two bleed screws by one turn and wait 5 minutes.
• Pedals coupled:
Fully press down and slowly release the pedals 8 times until the oil flows free of air bubbles.
• Pedals uncoupled:
Fully press down and slowly release each pedal 8 times until the oil flows free of air bubbles.
• Pedals coupled:
Fully press down and slowly release the pedals 5 times until the oil flows free of air bubbles. First close the left-hand bleed screw and then the right-hand bleed screw. Remove:
- the clamp placed on the hose (1).

Check
Press very hard (approximately 60 to 80 kg) on each pedal to correctly position the brake pistons.
Check the hardness under force of each pedal. Coupled pedals should not travel more than 120 mm for the force stated above. Stop the engine.

In case of operating problems
If an operating problem emerges, carry out the bleed sequence a second time. If the problem remains, check tightness of:
- the system;
- master cylinders;
- piston seals.

Bleeding the trailer brake system

If the tractor is fitted with a trailer brake, it is strongly recommended to bleed the main brake and trailer brake systems simultaneously. To carry out this bleeding procedure for  the bleeding of the main brake system and follow these additional points:
• Open:
- the two bleed screws (1) of the main brake;
- the trailer brake screw.
• When the bleeding is complete, tighten in the following order:
- the left-hand brake bleed screw;
- the right-hand brake bleed screw;
- the trailer brake bleed screw.
• Check the trailer brake pressure on the quick coupling located at the rear of the tractor. If this pressure is not correct, eliminate any air entering in the system and repeat the bleeding procedure.
• Carry out a road test.