Robin dual line braking system

Service Bulletin - January 1979............. number 1979/3


Robin dual line braking system

A dual line braking system has been introduced on all R.H.D. Robin Saloon and Estate vehicles. The introductory chassis points for the two vehicles are as follows:

Robin Estate: 8K6/12124056

Robin Saloon: 8K6/13224090

General Description

The dual line braking system operates drum brakes both front and rear. A tandem master cylinder and pressure differential warning actuator (PDWA) are fitted for use with the dual line braking system (figure 1).

The tandem master cylinder is designed to operate dual line hydraulic brake systems. It consists of two independent cylinders in a single casting and should one cylinder, or system, develop a fault the other remains operative.

The dual line system also incorporates a pressure differential warning actuator (figure 2). This is a device which is incorporated in dual line hydraulic systems and is, in effect, two opposed cylinders with a common piston which is connected between the two separate systems. As long as both systems are functioning correctly the piston is maintained in balance. The piston is made in two parts and the longer piston of the two has a machined radiused groove acting as a ramp for the plunger of an electrical switch assembly. Providing the pistons remain in balance the switch plunger is in the ‘at rest’ position, but if a failure of one system occurred the pistons would be forced from the central position and the switch plunger would be depressed. This would result in illumination of the brake failure warning light situated centrally between the main instruments on the fascia. The warning light will remain on until the pistons are reset to allow the switch plunger to resume its normal extended position. Movement of the piston in the event of a failure of any one part of the system is limited by the end plug and adaptor which act as stops. The re-setting of the pistons is achieved hydraulically whilst bleeding the system after the fault has been corrected. The PDWA should not be dismantled except to fit a new switch. If a fault occurs it must be replaced as a complete unit.

Warning light switch renewal

1. Check switch operation with 12v test lamp connected to battery.

2. If faulty, disconnect harness leads and unscrew switch from PDWA. Fit a new switch and reconnect harness leads. To check the warning light circuit, switch on the ignition and press the brake circuit test switch/brake failure warning light situated centrally between the main instruments on the fascia. The warning light will illuminate indicating the circuit is operative. Torque tighten switch to 2 - 2.5lb.ft (0.27 - 0.34kg.m) (2.71 - 3.38 Nm)

Master cylinder removal

1. Drain the system by attaching a bleed tube to the brake bleed valve. Unscrew valve one half turn and pump fluid into container by operating brake pedal. Discard used fluid.

2. From within the engine compartment prise out the rubber blanking plug located on top of the driver’s footwell to gain access to the split pin, clevis pin and washer securing the master cylinder clevis to the brake pedal.

3. From inside the footwell, remove the split pin and washer, withdraw the clevis pin and disconnect the master cylinder from the brake pedal.

4. Disconnect the two hydraulic fluid pipes from the master cylinder ports and plug.

5. Remove the top locknut and washer and the bottom set-screw and lock-washer securing the brake master cylinder and pedal mounting bracket to the body.

6. Remove the master cylinder from the vehicle. Replace in reverse order. Bleed brakes. (see figure 1).

Fluid reservoir renewal

To remove

1. With the master cylinder removed from the vehicle unscrew the filler cap and drain the reservoir of fluid through the filler orifice.

2. Remove the reservoir fixing pin retaining clips. Withdraw the reservoir fixing pins and pull the reservoir away from the master cylinder body.

To replace

1. Ensure that the fluid reservoir is perfectly clean and fit on to the master cylinder body. Refit the reservoir retaining pins and secure in position with the retaining clips. Re-fill the fluid reservoir with new fluid to the correct level and screw on the filler cap.

Pressure Differential Warning Actuator (PDWA)

To remove

1. Disconnect the four hydraulic fluid pipes at the PDWA ports and plug to prevent loss of fluid and ingress of dirt.

2. Disconnect the black/white harness leads connected to the PDWA warning switch.

3. Disconnect the yellow/white harness leads and white harness lead from the ballast resistor.

4. Remove the two bolts, coachwashers and nuts securing the PDWA to the main body and remove from the vehicle. NOTE One bolt, coachwasher and nut also secures the ballast resistor to the PDWA. Ensure it is refitted when mounting the PDWA to the body.

5. Replace in reverse order.

Bleeding the hydraulic dual line braking system

The apparatus required for bleeding the system consists of a bleed screw spanner, a clean glass jar containing some brake fluid, and a length of rubber tubing of sufficiently small bore to fit tightly over the bleed screw nipples.

Please Note Because of the PDWA incorporated in the dual line system, only a light pedal effort is required and the pedal must not be pushed through at the end of the stroke. In addition never ‘try’ the pedal until all air has been dispelled and the system has been fully bled, otherwise the action will cause the PDWA piston to move thereby operating the warning switch.

If during the bleeding procedure the plunger operates the switch and the warning light is on, the bleedscrew must be closed and the bleedscrew at the other end of the system opened (i.e. if bleeding the front brake, open a bleedscrew on the rear brake and vice-versa).

A steady pressure must then be applied to the pedal until the light goes out, when the pressure must be released immediately and the bleedscrew closed, otherwise the piston will move too far in the opposite direction and require re-setting again.

When the light goes out a ‘click’ will be felt on the pedal as the piston moves back.

During the process ensure that the level in the reservoir is maintained with fresh fluid, not that which has been bled from the system. Scrupulous cleanliness must be observed at all times. Always remove the floor mat or any other object which may obstruct the full movement of the pedal.

Bleeding procedure

1. Remove the RH rear bleed nipple rubber dust cover, fit the tube over the bleed nipple and unscrew it half a turn.

2. Immerse the free end of the tube in the fluid in the glass jar.

3. Using only a light effort depress the pedal, do not push the pedal through at the end of the stroke. Allow the pedal to return slowly. There should be a pause of 3 or 4 seconds and the action repeated until expelled fluid is free from air bubbles. Tighten the bleed screw immediately after the last downward stroke of the pedal.

4. Remove the bleed tube and replace the rubber dust cover.

5. Repeat the above procedure to bleed the LH rear brake and front brake.

6. Top up fluid reservoir with approved fluid to the correct level and replace filler cap after checking that vent hole is clear.

7. Check brakes on road test.

Brake circuit test switch/failure warning light

The test switch is situated centrally between the two main instruments and incorporates a red warning light. The warning light is illuminated on application of the brakes when either the front or rear brakes have failed as a result of a failure in the hydraulic braking system. The fault should be investigated immediately and any necessary repairs carried out by an authorised Reliant dealer. The electrical circuit and bulb function can be tested at any time, with the ignition switched on by pressing the switch which will illuminate the warning light, indicating the circuit is operative.

Figure 1

fig 1

Identification number reference table
1. Master cylinder 11. Coach washer 21. Bundy
2. Pin 12. Nut 22. Rear flexible hose
3. Clip 13. Bundy primary 23. Locknut
4. Set-screw 14. Bundy secondary 24. Lockwasher
5. Lock washer 15. Bundy 25. Bundy
6. Nut 16. Front flexible hose 26. Bundy
7. P.D.W.A 17. Locknut 27. Clip
8. Switch 18. Lockwasher 28. Clip
9. Bleed screw 19. Grommet 29. Clip
10. Set-screw 20. Bundy



Figure 2

fig 2