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)
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. lb)
8- Bolt, 8 Nm (70 in. lb)





9- Cap nut, 20 Nm (15 ft. lb)
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. lb)
19- Hex nut, self-locking, 20 Nm (15 ft. lb)
20- Seal
^ Always replace
21- Vacuum hose
^ Install in brake booster
22- Sealing plug
23- Hex nut, self-locking, 20 Nm (15 ft. lb)
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