Bleeding the brakes vacuum brake booster

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Caution: The description below applies only to vehicles with vacuum brake booster.

Important notes about brake fluid

Use only new brake fluid DOT 4. Observe brake-fluid quality.

The brake fluid DOT 4 Type 200 used until now (change interval 3 years) is no longer available via the Porsche Parts Servie.

"Super DOT 4" brake fluid will be delivered instead. The change interval for this brake

Vehicles with brake systems filled with the previous brake fluid must be filled with Super DOT 4 at the next scheduled brake-fluid

This brake fluid is available under the

Container volume 1 litre = 000.043.203.66 Container volume 30 litres = 000.043.203.67

Miscibility of the brake fluids:

The brake fluid DOT 4 Type 200 used until now is miscible with Super DOT 4. This means that, until the next scheduled brake-fluid change, vehicles with brake systems filled with the previous brake fluid can be topped up with Super DOT 4. Both brake fluids are coloured amber.

Note about water absorption:

As little as 2% water content in the brake fluid reduces the boiling point by approx. 60° C.

Procedure for bleeding

Fill reservoir to its top edge with new brake fluid. Attach bleeding-devie to the reservoir.

Clamp the overflow hose / bleeding hose shut with a hose clamp. The overflow hose / bleeding hose has been omitted as of October 1995; refer to Technical Information, Group 4, No. 16/95. Switch on the bleeding device. Bleed pressure approximately 1.5 bar.

Proceed with bleeding the brake calipers. Sequence: RH rear / LH rear / RH front /

Open each bleeding valve until clear, bubble-free brake fluid escapes. Make sure that both bleeder valves are bled at each

Use a recipient bottle to be able to check the escaping brake fluid for cleanliness, freedom from air bubbles and to check the quantity of brake fluid used.

Observe the following details when bleeding the brakes after fitting a new brake master cylinder: Open right-hand rear bleeder valves, then depress brake pedal several times. After depressing the pedal, keep it in the bottom position for 2 to 3 seconds and release pedal slowly. Repeat this procedure two or three times on the left rear / right front / right rear wheels. This causes all air bubbles to be removed from the brake master cylinder.

Note

Also carry out this operation if the hydraulic brake system has been drained virtually completely or if air is found to remain trapped in the system after bleeding (e.g. if pedal travel is excessive). Caution: Double the pumping cycles on high-mileage vehicles or older vehicles but use only half the brake master cylinder stroke in these cases (to avoid damage to the master cylinder, i.e. primary cups).

Switch off and disconnect bleeding device. Top up brake fluid if required.

Vacuum Hose Porsche 993 Diagram
1471-47

Note

When replacing the hydraulic unit on vehicles with ABD (Automatic Brake Differential) or if the hydraulic unit has been removed, the ABD circuit (in the hydraulic unit) must be bled as well (refer to p. 47 - 7).

Bleeding the ABD Circuit

Preparatory operations: Bleed brakes in conventional manner (page 47 - 5/6)

Leave the bleeding device connected (switched on) to bleed the ABD circuit. Bleeding pressure approx. 1.5...2.0 bar. Overflow hose (for venting) on expansion tank is clamped off with a hose.

Connect System Tester 9288 to the diagnostic socket. Switch on ignition. Select "Bleed" menu.

Close right-hand rear bleeder valve. Then immediately actuate Stop button taste on System Tester.

Switch off ignition and disconnect System Tester.

Correct brake fluid level if required.

Open right-hand rear bleeder valve (use recipient bottle).

Press Start button on System Tester. This causes certain functions in the hydraulic unit to be started (return feed pump, ASV valve and USV valve are triggered).

Bleed until the escaping brake fluid is free from air bubbles.

Additionally and during the whole bleeding process, depress brake pedal (at least 10 times) across the full pedal stroke (to the pedal stop) (pumping). Warning: On high-mileage or older vehicles, double the pump cycles and use only half the brake master cylinder stroke (to avoid damage to the master brake cylinder/primary cup).

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Responses

  • ulrike
    How to bleed brakes vacuum booster on older cars?
    6 years ago
  • Athanaric
    How to bleed 993 brake booster pump motor?
    3 years ago

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