Defender 90 NAS. Manual — part 71
BRAKES
1
OVERHAUL
Key to master cylinder
1. Water ingress seal
2. Transfer housing
3. Vacuum seal
4. Guide ring
5. Retaining ring
6. ’O’ ring seal
7. Primary plunger assembly
8. ’L’ seal
9. Secondary plunger
10. Washer
11. Recuperating seal - primary cup
12. Seal retainer
13. Springs - 2 off
14. Swirl tube
15. Master cylinder body
16. Reservoir seals
17. Reservoir
18. Low fluid level switch and cap
70
BRAKES
2
OVERHAUL
MASTER CYLINDER
Service repair no - 70.30.09
Before starting overhaul procedure refer to general
brake service practice.
See Repair, General brake
service practice
Dismantling master cylinder
1. Disconnect battery and remove master cylinder
from servo
See Repair, Master cylinder
2. Before commencing overhaul procedure
thoroughly clean master cylinder and inspect
outer surfaces for damage and condition, renew
complete assembly if necessary.
3. The reservoir is a push fit in master cylinder and
secured by seals. Carefully ease reservoir from
master cylinder by rolling it from seals as
illustrated.
4. Using soft jaws, one either side of master
cylinder flange and clamp flange in a suitable
vice. Remove water ingress ’O’ ring seal from
master cylinder to servo flange and discard.
5. Hold outside of transfer housing with a suitable
pair of grips, carefully pull, while working pliers in
a backwards and forwards rocking motion to
ease housing off master cylinder, discard
housing and vacuum seal.
6. Withdraw 2 reservoir seals from master cylinder
inlet ports, seals are different and should be
noted for assembly. Discard both seals.
7. Remove retaining ring and ’O’ ring seal from
machined outer surface of master cylinder,
discard both seal and retaining ring.
BRAKES
3
OVERHAUL
8. Remove guide ring from mouth of master
cylinder which supports primary plunger
assembly and place to one side, this component
is not part of master cylinder service kit and is to
be refitted on assembly of unit.
9. Pull primary plunger assembly out of master
cylinder.
NOTE: The primary plunger assembly
cannot be broken down any further and is
serviced as a complete unit. Discard
assembly.
10. The secondary plunger assembly will remain at
bottom of master cylinder bore, plunger can be
easily expelled by tapping assembly on a piece
of timber until plunger appears at cylinder mouth,
carefully pull plunger out of master cylinder.
11. If swirl tube was not expelled at same time as
secondary plunger, repeat above operation to
expel it from bottom of master cylinder bore and
discard.
12. Clean all parts with Girling cleaning fluid or
unused brake fluid and place cleaned parts on to
a clean sheet of paper. Inspect cylinder bore and
plungers for signs of corrosion, ridges and score
marks. Provided working surfaces are in perfect
condition, new seals from a Girling Service
repair kit may be used.
Renewing secondary plunger seals
13. Remove following components from secondary
plunger and discard:
NOTE: A small screwdriver with end
rounded and polished is required to
remove ’L’ seal. DO NOT damage
secondary plunger. A. Springs B. Seal retainer C.
Recuperating seal (primary cup) D. Washer E. ’L’
seal
14. Coat new seals in unused brake fluid and firstly
fit ’L’ seal to plunger.
15. Fit washer followed by recuperating seal. Fit seal
retainer and springs, ensure springs are
correctly seated.
70
BRAKES
4
OVERHAUL
Assembling master cylinder
CAUTION: It is important that the following
instructions are carried out precisely,
otherwise damage could be caused to new
seals when inserting plungers into cylinder bore.
Generous amounts of new brake fluid should be
used to lubricate parts during assembly.
NOTE: Thoroughly check that no debris is
lodged in fluid passageways and drillings.
If debris is found, carefully remove,
re-clean cylinder and re-check.
16. Fit new swirl tube to bottom of cylinder bore.
17. Lubricate secondary plunger and cylinder bore.
Offer plunger assembly to cylinder until
recuperation seal is resting centrally in mouth of
bore. Gently introduce plunger with a circular
rocking motion, as illustrated. Ensuring that seal
does not become trapped, ease seal into bore
and slowly push plunger down bore in one
continuous movement.
18. Fit primary plunger assembly using same
method as for secondary plunger, push plunger
down bore.
19. Fit original guide ring to support primary plunger.
20. Coat a new ’O’ ring with brake fluid and fit to its
respective groove on outer location surface of
master cylinder.
CAUTION: ’O’ ring should not be rolled
down outer location surface of master
cylinder but should be slightly stretched
and eased down cylinder and into its groove. Do
not over stretch seal.
21. Fit a new retaining ring on outer surface of
master cylinder ensuring that serrations of ring
are facing mounting flange.
22. Fit two new reservoir seals in ir respective ports.
23. Fit a new vacuum seal to either primary plunger
or to bottom of transfer housing bore, open face
of seal towards primary plunger guide ring.
24. Lubricate vacuum seal with brake fluid, fit
transfer housing to master cylinder, push
housing fully up to cylinder mounting flange. Do
not adjust transfer housing after fitting.
25. Lubricate a new water ingress seal with brake
fluid, slightly stretch seal and ease it down
housing until seal is in correct position between
housing and flange.
26. Roll reservoir into top of master cylinder,
reversing procedure described in instruction 3.
27. Fit master cylinder to servo.
See Repair,
Master cylinder
28. Reconnect battery, and road test vehicle.
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