Hydraulic Unit, Brake Booster/Master Cylinder, Overview

Hydraulic unit, brake booster/master cylinder, overview

Note: Complete brake master cylinders and brake boosters can be replaced separately.

1. Brake Booster
- For gasoline engines vacuum is taken from the intake manifold
- Diesel engines have a vacuum pump to create the required vacuum
- Functional check:
- With engine switched off, depress brake pedal firmly several times (to exhaust vacuum in the unit)
- Hold brake pedal with average foot pressure in brake position and start engine. If brake booster is functioning properly, brake pedal should give noticeably underfoot.
- If pedal does not give, replace brake booster
- Check valve (in vacuum hose)
Functional check
- Separating from brake pedal.
- Removing and installing
2. Cap
3. Brake fluid reservoir
4. Plug
- Coat with brake fluid and press into reservoir
5. Retaining pin
- Insert through brake master cylinder
6. Brake master cylinder
- Cannot be repaired. If faulty, replace as complete unit
7. Hex nut, self-locking 20 Nm (15 ft. lbs.)
8. Bolt, 8 Nm (70 inch lbs.)
9. Cap nut, 20 Nm (15 ft. lbs.)
10. ABS/EDL hydraulic unit
11. ABS control module
- Control module connector is not disconnected before On Board Diagnostic (OBD)
12. Connection for brake line
- Hydraulic unit to left front brake caliper
13. Connection for brake line
- Hydraulic unit to right rear wheel cylinder/ brake caliper
14. Connection for brake line
- Hydraulic unit to left rear wheel cylinder/ brake caliper
15. Connection for brake line
- Hydraulic unit to right front brake caliper
16. Brake line
- Brake master cylinder/pressure rod piston circuit to hydraulic unit
17. Brake line
- Brake master cylinder/floating piston circuit to hydraulic unit
18. Hex nut, self-locking, 20 Nm (15 ft. lbs.)
19. Hex nut, self-locking, 20 Nm (15 ft. lbs.)
20. Seal
- Always replace
21. Vacuum hose
- Install in brake booster
22. Sealing plug
23. Hex nut, self-locking, 20 Nm (15 ft. lbs.)
24. Seal
- For brake booster
25. Boot
- Make sure boot is properly seated or suction noises may be noticed
26. Bracket

Brake lines from brake master cylinder to hydraulic unit, connecting

Fig. 1 Vehicles with ABS





A - Secondary piston circuit
B - Primary piston circuit
1. Hydraulic unit to right front brake caliper
2. Hydraulic unit to left rear wheel cylinder/brake caliper
3. Hydraulic unit to right rear wheel cylinder/brake caliper
4. Hydraulic unit to left front brake caliper

Fig. 2 Vehicles with ABS/EDL





A - Secondary piston circuit
B - Primary piston circuit