Hydraulic System: Service and Repair
Hydraulic System, Bleeding
• Description covers bleeding of hydraulic system using the brake filler and bleeder tool (VAS 5234).
• A positive pressure of 2 bar required to bleed the ABS hydraulic unit (N55).
Special tools, testers and auxiliary items required
• Brake filler/bleeder unit (VAS 5234)
• Brake filler/bleeder unit suction adapter (V.A.G 1869/4)
• Tool set for brake bleeding (VAS 6564)
Pre-Bleeding
• One chamber in the brake fluid reservoir is completely empty on a vehicle with EDL, EDL/ASR or EDL/ASR/ESP This will happen if there are leaks in the brake system.
- Connect the (VAS 5234).
Bleeding sequence:
1 - Bleed the left front and right front brake calipers simultaneously
2 - Bleed left rear and right rear brake caliper together simultaneously
- With bleeder bottle hoses attached, leave bleeder valves open long enough that brake fluid exits without bubbles.
- Afterward, bleed the brake system normally.
Bleeding
• On vehicles with ABS/ASR or ABS/EDS/ASR/ESP, the brake system must be pre-bled when a chamber in the brake fluid reservoir is completely empty.
Adhere strictly to work sequence when bleeding brake system.
- Connect the (VAS 5234).
- Open bleeder valves in the prescribed sequence and bleed brake caliper.
1- Front left brake caliper
2 - Right front brake caliper
3 - Left rear brake caliper
4 - Right rear brake caliper
• Use suitable bleeder hose. It must fit tightly on bleeder valve so that no air gets into brake system.
- With bleeder bottle hose attached, leave bleeder valve open long enough that brake fluid exits without bubbles.
Post-Bleeding
Perform a post-bleeding when:
• The brake pedal travel is too long, or the so-called soft brake pedal.
A second technician is required during the post-bleeding.
- Press brake pedal forcefully and hold.
- Open bleeder valve at brake caliper.
- Press brake pedal down onto stop.
- Close bleeder valve with the pedal assembly pressed.
- Release brake pedal slowly.
• This bleeding procedure must be performed 5 times per brake caliper.
Bleeding sequence:
1- Front left brake caliper
2 - Right front brake caliper
3 - Left rear brake caliper
4 - Right rear brake caliper
• A road test must be performed after bleeding. During this, at least one ABS regulation must be performed!