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Massey Ferguson 6465, 6480, 6485 - Rear axle brake pistons

MF 6400 Series Tractors Service and Repair

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 (MF 6465, 6480 tractors); from a block/valves assembly (MF 6485, 6490 tractors).

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.

MF 6465, 6480 Tractors fitted with GTA-1040 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.

MF 6485, 6490 Tractors fitted with GTA-1540 transmission (50 kph)

For MF 6485, 6490 tractors fitted with GTA-1540 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: block/valves assembly (1) fitted to the front bulkhead of the cab and activated by the brake pedals; 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; return travel limit mechanism (3) for each brake piston.

Massey Ferguson 6465, 6480, 6485, 6490 - 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, 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) (MF 6465, 6480 tractors) or a block/valve assembly (MF 6485, 6490 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, 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

Massey Ferguson 6465, 6480, 6485, 6490 - Removing and refitting a brake piston

Brake piston removal

Remove the trumpet housing(s).

Disconnect the brake supply pipe (1) located above the centre housing that comes from the brake master cylinder. For tractors fitted with GTA1540 transmission (50 kph), the brake supply pipe (1) comes from the block/valves (1) fitted to the cab's front bulkhead.

Using a manual hydraulic pump connected to the union (3), drive out the piston (2) from the centre housing.

Remove the "O" rings (3) (4) fitted respectively on the centre housing and the differential support. "O" rings J, located between the differential supports and the centre housing, seal the brake piston chambers.

If seal(s) is/are to be replaced, remove the differential support(s).

Brake piston refitting

Clean and check all components. Replace those that are defective. In particular, check the wear on the brake plate, the sealed compartment or the spacer (depending on type of trumpet housing). If removed, refit the differential support(s) fitted with a new "O" ring J. Before the final refitting of the piston (2), test fit the piston in the centre housing, temporarily excluding the "O" rings (3) (4). This temporary fitting allows you to check that the piston can move freely in its bore and on its stop pins. During fitting, any friction points must be eliminated and problem parts must be identified. Remove all impurities from the piston chamber. Definitively refit the piston, but only after a satisfactory test fitting has been carried out.

Lubricate the new "O" rings (3) (4) with clean transmission oil. Fit them into their respective grooves (centre housing and differential support). If possible, turn the brake piston so that the majority of the lubricating ports around its rim are facing upwards (depending on piston type). Fit the piston into the centre housing by aligning its pin housings with the stop pins (6). Fit the piston (2) using a makeshift tool and two screws V of suitable length. These two screws are tightened gradually and alternately during the fitting process. For tractors fitted with GTA1540 transmission (50 kph), carefully monitor the fitting of the piston inside its return travel limit mechanism (3).

If necessary, fit by gently tapping with a plastic hammer in diametrically opposed positions around the piston rim. The return travel limit mechanism (3) means you have to push the brake pistons right back to the bottom of their cavity (pushing the brake pistons is made easier by gently unscrewing the centre housing and the bleed valves or pipes coming from the block/valve assembly). In this way, the mechanism (3) can once again return the brake pistons correctly if one or more of the following components has been replaced: brake discs; brake plates, compartment (single or sealed) or spacer (depending on the type of trumpet housing); brake pistons and/or "O" rings (3) (4). Remove the tool. Check that there are no seal fragments on the piston circumference.

MF 6465, 6480, 6485, 6490 - Brake piston leak test

The brake piston leak test can only be carried out correctly if the pressure gauge and compressed air supply line are completely sealed. Figure shows a simplified pressure gauge design. Other more complex pressure gauges can also be used. Fit the tool used to retain the piston (2) against the centre housing. Connect the pressure gauge to the union (3). Supply the brake piston with compressed air at approximately 3 bar to position the seals (3) (4) in their respective groove. Close the valve. Disconnect the compressed air source. Open the valve.

Supply the system again at approximately 0.3-0.4 bar to test the tightness of the seals (3) (4). Close the valve. Check that the pressure gauge needle remains still for approximately one minute. Shut the compressed air inlet when the test proves satisfactory. Remove: pressure gauge; piston retaining tool. Reconnect the brake supply pipe. Refit the trumpet housing (s). Thoroughly bleed the brake system. Road test the main brakes. Check tightness of: trumpet housing seals; unions and the pipes (brake supply and lubrication pipes).

Massey Ferguson 6485, 6490 - Disassembling, reassembling and adjusting the return travel limit mechanism of the brake piston

On MF 6485, 6490 tractor each brake piston (2) is assisted by a return travel limit mechanism. This mechanism, which comprises three assemblies (3), allows: piston to release itself from the brake disc by approx. 0.7 mm when the brakes are inactive; "drag" effect to be minimised.

The three assemblies (3) occupy an equidistant position on each differential support S. An assembly comprises: M6 x 40 screw (7); flat washer (6); spring (5); Mecanindus pin (4); shouldered nut with flat sections (1); locking screw (8).

Return travel limit mechanism disassembly

The differential support(s) must be removed in order to disassemble the brake piston's return travel limit mechanism. Remove: brake piston(s) (2); differential support(s) S. Place the differential support(s) on a workbench.

On faces F and F1 of differential support(s) S, remove an assembly (3) including: locking screw (8); shouldered nut with flat sections (1) (support the M6 screw (7)); Mecanindus pin (4); M6 screw (7); flat washer (6); spring (5). Repeat step for the other two assemblies (3).

Return travel limit mechanism reassembly

Clean and check all components. Replace those that are defective.

On faces F and F1 of differential support(s) S, refit: M6 screw (7); flat washer (6); spring (5); Mecanindus pin (4); shouldered nut with flat sections (1), with its thread lightly smeared with Loctite 243 or equivalent.

Settings

Adjust each assembly (3) of the brake piston's return travel limit mechanism, proceeding as follows for each assembly: Tighten the shouldered nut (1) with flat sections (M6, 100 pitch) to a torque of approximately 1 Nm (spring coils almost joined).

Slacken off this nut between approximately half and three quarters of a turn: this corresponds to an anti-clockwise rotation of 216° to 234° or 60% to 65% of a turn. By adjusting each assembly (3) of the return travel limit mechanism in this way, a gap E of approx. 0.60 to 0.65 mm is achieved between the piston (2) and the brake disc (35) when the main brake is inactive.

MF TRACTORS TROUBLESHOOTING
1652	1749	2620	2725	2805
3050	3120	3640	3709	4245
4455	5320	5455	5613	6150
6280	6480	6615	7618	7720