Opel Corsa B 1993–2000 Service and Repair Manual: Master cylinder - removal and refitting

Note: Before starting work, refer to the warning at the beginning of Section 2 concerning the dangers of hydraulic fluid.

Removal

1. Remove the master cylinder reservoir cap and syphon the hydraulic fluid from the reservoir.

Note: Do not syphon the fluid by mouth, as it is poisonous; use a syringe or an old poultry baster.

Alternatively, open any convenient bleed screw in the system and gently pump the brake pedal to expel the fluid through a plastic tube connected to the screw.

2. Release the cable retainer from around the master cylinder body (where applicable).

3. Wipe clean the area around the brake pipe unions on the side of the master cylinder and place absorbent rags beneath the pipe unions to catch any surplus fluid. Make a note of the correct fitted positions of the unions then unscrew the union nuts and carefully withdraw the pipes (see illustration). Plug or tape over the pipe ends and master cylinder orifices to minimise the loss of brake fluid and to prevent the entry of dirt into the system.

Wash off any spilt fluid immediately with cold water.

Slackening the brake pipe union from the pressure regulating valve

4. Where necessary, unscrew the pressure regulating valve(s) from the master cylinder.

5. Unbolt the master cylinder from the brake vacuum servo unit (booster) (see illustration).

Removing the master cylinder

Overhaul

Note: On models equipped with ABS, the master cylinder is a sealed unit and cannot be overhauled. If the cylinder is faulty it must be renewed.

ATE type cylinder

6. With the master cylinder removed, clean away all external dirt.

7. Prise the fluid reservoir from the cylinder body (see illustration).

Exploded view of ATE master cylinder

3. Reservoir cap/low level switch
4. Float guide sleeve
5. Reservoir
6. Cylinder body
7. O-ring
8. Seals
9. Stop screw
10. Repair kit in assembly tube
11. Pressure regulating valve

8. Depress the primary (rear) piston slightly and remove its retaining circlip.

9. Withdraw the primary piston. Make sure that the stop washers do not catch in the circlip groove.

10. Depress the secondary (front) piston with a suitable rod and remove the stop screw from the cylinder body.

11. Shake or tap out the secondary piston.

12. Clean all the parts in brake fluid or methylated spirit. Examine the pistons and the cylinder bore for scoring, rust, or evidence of metal-to-metal contact; if found, renew the cylinder complete. Strip the seals from the primary piston if it is to be re-used noting which way round they are fitted.

13. The makers do not supply a seal kit alone, but provide a repair kit consisting of a complete secondary piston and the other necessary seals springs, washers etc in a special assembly tube. Should a proprietary seal kit be available, fit new seals using the fingers only, and make sure that the new seals are fitted the same way round as the old ones.

The remainder of this Section describes the fitting of the maker's repair kit.

14. Lubricate the cylinder bore with brake fluid or brake rubber grease.

15. Clamp the cylinder in a soft-jawed vice with the bore more or less horizontal. Screw in the stop screw a little way, but not so far that it protrudes into the bore.

16. Remove the large plug from the assembly tube. Remove all the components from the short part of the tube and push the short part into the long part until they are flush.

17. Insert the assembly tube into the cylinder bore as far as the collar on the short sleeve.

Use a blunt rod to push the secondary piston into the bore until it contacts the end of the cylinder. Nip up the stop screw, withdraw the rod and sleeve and tighten the stop screw fully.

18. Reposition the master cylinder in the vice with the bore opening facing upwards.

19. Smear the primary piston skirt and seal grooves with the special grease provided in the repair kit. Fit the stop washer to the piston.

20. Adjust the assembly tube so that the end of the long part is flush with the inner shoulder of the short part.

21. Fit the front seal to the primary piston with the open end of the seal facing the front of the master cylinder. Place the assembly tube over the cylinder to compress the seal, insert the piston and tube part way into the bore and withdraw the tube.

22. Place the intermediate ring on the primary piston, then fit the other seal using the assembly tube in a similar manner.

23. Place the end washer on the primary piston, then depress the piston slightly and fit the circlip. Make sure that the circlip is properly seated and that the piston is free to move.

24. Fit new sealing rings and press the fluid reservoir into position.

25. Prime the cylinder by pouring clean brake fluid into the reservoir and working the pistons with a rod until fluid is ejected from all orifices.

GMF type cylinder

26. With the master cylinder removed, clean off all external dirt (see illustration).

Exploded view of GMF master cylinder

1. Body
2. Seals
3. Circlips
4. Reservoir
5. Reservoir cap/low level switch

7. Spring
8. Spring retainer
9. Secondary seals
10. Shims
11. Secondary piston
12. Primary seals
13. Circlip
14. Spring sleeve
15. Spring
16. Spring retainer
17. Primary piston
18. Circlip

27. Remove the fluid reservoir by carefully pulling it away from the master cylinder, at the same time releasing the circlips with a screwdriver.

28. Clamp the cylinder in a soft-jawed vice, rear end uppermost, and prise out the pushrod seal.

29. Use a blunt rod to depress the primary (rear) piston by 10 mm or so until it can be retained in the depressed position by inserting a smooth rod (eg a knitting needle) onto the primary inlet hole.

30. Carefully extract the circlip from the end of the cylinder by prising it out with a screwdriver.

31. Knock, shake or blow the pistons out of the cylinder.

32. Clean all parts with brake fluid or methylated spirit. Examine the pistons and the cylinder bore for scoring, rust or evidence of metal-to-metal contact; if found, renew the cylinder complete.

33. The makers do not supply a kit of seals alone, but provide a repair kit consisting of both pistons in a special assembly tube.

Should a proprietary seal kit be obtained, note the direction of fitting of the seals before removing them from the pistons.

34. Lubricate the cylinder bore with brake fluid or brake rubber grease. Clamp the cylinder with the bore horizontal.

35. Remove the plug from the assembly tube and insert the short part of the tube into the cylinder bore as far as the shoulder on the tube. Use a blunt rod to push the piston out of the tube and into the bore; retain the pistons in the bore with the smooth rod or needle used when dismantling. Withdraw the rod and the tube.

36. Fit a new circlip to the end of the cylinder.

Depress the primary piston and withdraw the retaining rod or needle. Make sure that the circlip is properly seated and that the pistons are free to move.

37. Fit new sealing rings to the master cylinder and new circlips to the reservoir.

Press the reservoir into position until the circlips click into place.

38. Prime the cylinder by pouring clean brake fluid into the reservoir and working the pistons with a rod until fluid is ejected from all orifices.

Refitting

39. Refitting is a reversal of removal, use new reservoir rubber seals and tighten all nuts and bolts to the specified torque settings (where given). On completion bleed the complete hydraulic system.