Hydraulic Control Assembly - Antilock Brakes: Service and Repair

NOTE:
Hydraulic unit must be replaced as a complete unit. Hydraulic unit must not be opened under any circumstances. Reassembling it requires special equipment and facilities.

The hydraulic unit, reducing valve and control module are on the same bracket in the engine compartment. It hydraulic unit has to be changed, the whole bracket must be removed first before the hydraulic unit can be removed from its mounting.

Preparations [NE1]
- Ignition off.
- Remove battery negative lead.

Removing bracket [NE2]





- Drain system of brake fluid.
- Clean brake hose and pipe connections on hydraulic unit and master cylinder.
- Put rags under hydraulic unit to protect painted surfaces in the event of a brake fluid spillage.
- Remove complete air filter casing.

In turbo models:

- Remove inlet pipe between filter casing and turbocharger unit.

[NE3]
- Remove the two brake pipes to the reducing valve from the master cylinder.
- Remove the three brake pipes (cars with TRACS have a fourth brake pipe from the reducing valve) from the side of the hydraulic unit. Seal off the brake pipes and connectors on hydraulic unit immediately to prevent dirt getting into the system.

[NE4]





- Remove the 15-pin connector between hydraulic unit and engine leads (on top of shock absorber turret).
- Remove the two bolts holding the connector to the mounting.
- Twist the leads to this connector together with the lead to the control module 55-pin connector to avoid confusion.

[NE5]
- Remove combination relay from mounting.
- Remove the 4-pin connector connecting the hydraulic unit and combination relay.
- Hang combinations relay up to prevent it coming into contact with brake fluid.

[NE6]





- Remove nut holding hydraulic unit to bracket by shock absorber turret.
- Undo the two nuts on the shock absorber turret and lift that mounting enough to allow the hydraulic unit bracket to be removed.

[NE7]
- Remove the two brake hoses running to the brake fluid reservoir. One hose is difficult to get at, so it may be easier to remove it when lifting the bracket out.
- Lift bracket carefully out of the engine compartment, together with the suspended hydraulic unit, reducing valve and control module.

Removing hydraulic unit [NE8]





- Cut tie band and remove coiled lead from bracket.
- Remove the two brake pipes to the reducing valve.
- Remove the four mounting bolts from the hydraulic unit.
- Remove hydraulic unit.

NOTE: Hydraulic unit must be replaced as a complete unit. Never open hydraulic unit under any circumstances. Reassembling it calls for special equipment and facilities.

Installing hydraulic unit [NE9]





- Install the new hydraulic unit on bracket and tighten the four mounting bolts.
- Install the two brake pipes from to reducing valve to their respective connectors.
- Tighten to 14 Nm (10 ft.lb.).
- Attach the coiled lead to the bracket with insulating tape.

Installing bracket [NE10]





- Install bracket carefully in car.
- Install the two brake hoses from the brake fluid reservoir

NOTE: Use only glycerine for greasing hoses.

- Lift shock absorber turret mounting over nut on hydraulic unit bracket.
- Tighten the two nuts on shock absorber turret.
- Install and tighten nut at top of hydraulic unit bracket.

[NE11]
- Install combination relay connector and attach to bracket.
- Install connector to motor leads and attach up on shock absorber turret with the two bolts.
- Install the three brake pipes (four brake pipes in cars with TRACS) in their respective connections on the side of the hydraulic unit.
- Install the two brake pipes on master cylinder.
- Tighten to 14 Nm (10 ft.lb).

[NE12]





- install control module connector.
- Install air filler casing.

Turbo models:

- Install inlet pipe between air filter casing and turbocharger.

Finishing [ND13]
- install battery negative lead.
- Bleed brake system as per LK. Bleeding brakes. Then continue as below.
- Clean off any spilled brake fluid with lukewarm water and car wash shampoo.

Operational checks [NE14]





- Read off any DTCs posted in control module and erase them.
- Quit DTM by switching off ignition.





- Test drive car, check that brakes work and that ABS warning indicator goes out.
- Read off DTCs and check that code 1-1-1 appears.
- Quit DTM by switching off ignition.