Opel Corsa B 1993–2000 Service and Repair Manual: Hydraulic system - bleeding

Note: Hydraulic fluid is poisonous; wash off immediately and thoroughly in the case of skin contact and seek immediate medical advice if any fluid is swallowed or gets into the eyes.

Certain types of hydraulic fluid are inflammable and may ignite when allowed into contact with hot components; when servicing any hydraulic system it is safest to assume that the fluid is inflammable and to take precautions against the risk of fire as though it is petrol that is being handled. Hydraulic fluid is also an effective paint stripper and will attack plastics; if any is spilt, it should be washed off immediately using large quantities of fresh water. Finally, as it is hygroscopic (it absorbs moisture from the air) - old fluid may be contaminated and unfit for further use. When topping-up or renewing the fluid, always use the recommended type and ensure that it comes from a freshly opened sealed container.

General

1. The correct operation of any hydraulic system is only possible after removing all air from the components and circuit; this is achieved by bleeding the system.

2. During the bleeding procedure, add only clean, unused hydraulic fluid of the recommended type; never re-use fluid that has already been bled from the system.

Ensure that sufficient fluid is available before starting work.

3. If there is any possibility of incorrect fluid being already in the system, the brake components and circuit must be flushed completely with uncontaminated, correct fluid and new seals should be fitted to the various components.

4. If hydraulic fluid has been lost from the system, or air has entered, because of a leak ensure that the fault is cured before proceeding further.

5. Park the vehicle on level ground, switch off the engine and select first or reverse gear, then chock the wheels and release the handbrake.

6. Check that all pipes and hoses are secure, unions tight and bleed screws closed. Clean any dirt from around the bleed screws.

7. Unscrew the master cylinder reservoir cap and top the master cylinder reservoir up to the `MAX' level line; refit the cap loosely and remember to maintain the fluid level at least above the `MIN' level line throughout the procedure or there is a risk of further air entering the system.

8. There are a number of one-man, do-it-yourself brake bleeding kits currently available from motor accessory shops. It is recommended that one of these kits is used whenever possible as they greatly simplify the bleeding operation and also reduce the risk of expelled air and fluid being drawn back into the system. If such a kit is not available the basic (two-man) method must be used which is described in detail below.

9. If a kit is to be used, prepare the vehicle as described previously and follow the kit manufacturer's instructions as the procedure may vary slightly according to the type being used; generally they are as outlined below in the relevant sub-section.

10. Whichever method is used, the same sequence must be followed (paragraphs 11 and 12) to ensure that the removal of all air from the system.

Bleeding sequence

11. If the system has been only partially disconnected and suitable precautions were taken to minimise fluid loss, it should be necessary only to bleed that part of the system (ie. the primary or secondary circuit).

12. If the complete system is to be bled, then it should be done in the following sequence.

Non ABS models

1. Left-hand rear brake.
2. Right-hand front brake.
3. Right-hand rear brake.
4. Left-hand front brake.

Models equipped with ABS

1. Left-hand front brake.
2. Right-hand front brake.
3. Left-hand rear brake.
4. Right-hand rear brake.

Bleeding - basic (two-man) method

13. Collect a clean glass jar, a suitable length of plastic or rubber tubing which is a tight fit over the bleed screw and a ring spanner to fit the screw. The help of an assistant will also be required.

14. Remove the dust cap from the first screw in the sequence. Fit the spanner and tube to the screw, place the other end of the tube in the jar and pour in sufficient fluid to cover the end of the tube.

15. Ensure that the master cylinder reservoir fluid level is maintained at least above the `MIN' level line throughout the procedure.

16. Have the assistant fully depress the brake pedal several times to build up pressure, then maintain it on the final stroke.

17. While pedal pressure is maintained, unscrew the bleed screw (approximately one turn) and allow the compressed fluid and air to flow into the jar. The assistant should maintain pedal pressure, following it down to the floor if necessary and should not release it until instructed to do so. When the flow stops, tighten the bleed screw again, release the pedal slowly and recheck the reservoir fluid level.

18. Repeat the steps given in paragraphs 16 and 17 until the fluid emerging from the bleed screw is free from air bubbles. If the master cylinder has been drained and refilled and air is being bled from the first screw in the sequence, allow approximately five seconds between cycles for the master cylinder passages to refill.

19. When no more air bubbles appear, tighten the bleed screw securely, remove the tube and spanner and refit the dust cap. Do not overtighten the bleed screw.

20. Repeat the procedure on the remaining screws in the sequence until all air is removed from the system and the brake pedal feels firm again.

Bleeding - using a one-way valve kit

21. As their name implies, these kits consist of a length of tubing with a one-way valve fitted to prevent expelled air and fluid being drawn back into the system; some kits include a translucent container which can be positioned so that the air bubbles can be more easily seen flowing from the end of the tube.

22. The kit is connected to the bleed screw, which is then opened. The user returns to the driver's seat and depresses the brake pedal with a smooth, steady stroke and slowly releases it; this is repeated until the expelled fluid is clear of air bubbles.

23. Note that these kits simplify work so much that it is easy to forget the master cylinder reservoir fluid level; ensure that this is maintained at least above the `MIN' level line at all times.

Bleeding - using a pressure bleeding kit

24. These kits are usually operated by the reservoir of pressurised air contained in the spare tyre, although note that it will probably be necessary to reduce the pressure to a lower limit than normal; refer to the instructions supplied with the kit.

25. By connecting a pressurised, fluid-filled container to the master cylinder reservoir, bleeding can be carried out simply by opening each screw in turn (in the specified sequence) and allowing the fluid to flow out until no more air bubbles can be seen in the expelled fluid.

26. This method has the advantage that the large reservoir of fluid provides an additional safeguard against air being drawn into the system during bleeding.

27. Pressure bleeding is particularly effective when bleeding `difficult' systems or when bleeding the complete system at the time of routine fluid renewal.

All methods

28. On completion, when firm pedal feel is restored, wash off any spilt fluid, tighten the bleed screws securely and refit the dust caps.

29. Check the hydraulic fluid level and top-up if necessary.

30. Discard any hydraulic fluid that has been bled from the system; it will not be fit for re-use.

31. Check the feel of the brake pedal. If it feels at all spongy, air must still be present in the system and further bleeding is required.

Failure to bleed satisfactorily after a reasonable repetition of the bleeding procedure may be due to worn master cylinder seals.