[Saloon-lovers] 65 Mark X Brake Booster Problem

When you step on the brake, the first time you apply it, the pedal
is normal. Brakes stay engaged for up to a minute before
releasing. The 2nd time you step on it in succession, the pedal
goes further down, but still has pressure. The 3rd time you step on
it, it flops around loosely until the brakes release. My brake
booster retracts slowly. After applying the brakes, it can take a
much as a minute for the brakes to release. With the booster out of
the car, if you press the pedal side, it still returns very slowly
and pushing on the master cylinder actuator rod doesn’t make it
retract any faster. I have disassembled the booster twice, cleaned
it and reassembled it. All rubber seals and diaphrams are soft &
supple and have no tears. Does anyone have any ideas why it would
be retracting so slowly and have any fixes for such problem? I
appreciate any help or ideas you might have. Thanks!–
charkdavis
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In reply to a message from charkdavis sent Sun 27 Apr 2008:

Have you taken a good look at your vac. supply? Tank–lines–check
valve? If you have done as you said it sounds like you have a
problem in this area!–
The original message included these comments:

supple and have no tears. Does anyone have any ideas why it would
be retracting so slowly and have any fixes for such problem? I


George Camp
Columbia SC, United States
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How are you brakes hoses?? Sometime a “flap” developes internally in the
hose and it can cause problems.

When you step on the brake, the first time you apply it, the pedal
is normal. Brakes stay engaged for up to a minute before
releasing. The 2nd time you step on it in succession, the pedal
goes further down, but still has pressure. The 3rd time you step on
it, it flops around loosely until the brakes release. My brake
booster retracts slowly. After applying the brakes, it can take a
much as a minute for the brakes to release. With the booster out of
the car, if you press the pedal side, it still returns very slowly
and pushing on the master cylinder actuator rod doesn’t make it
retract any faster. I have disassembled the booster twice, cleaned
it and reassembled it. All rubber seals and diaphrams are soft &
supple and have no tears. Does anyone have any ideas why it would
be retracting so slowly and have any fixes for such problem? I
appreciate any help or ideas you might have. Thanks!

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In reply to a message from charkdavis sent Sun 27 Apr 2008:

I had a similar problem with my Dad’s 65 and never could figure out
why other than possibly a bind in the sleeve durring the 1st
rebuild. My cure is actually in progress. I have a shop making me
an adapter plate that will allow the use of a Series III XJ booster
unit in the Mk10. The master cylinder bolts right up and with the
longer shaft of the XJ push rod it will allow for a spacer/plate
(the holes for the two booster units are not the same). The real
nice thing is the MK10 Girling unit is NLA or to rebuild the unit
is now over $400 while a used XJ unit can be had for $50 or less!!–
The original message included these comments:

retract any faster. I have disassembled the booster twice, cleaned
it and reassembled it. All rubber seals and diaphrams are soft &
supple and have no tears. Does anyone have any ideas why it would
be retracting so slowly and have any fixes for such problem? I
appreciate any help or ideas you might have. Thanks!


Bill Fleming
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In reply to a message from charkdavis sent Sun 27 Apr 2008:

Hello Chark,

The first thing I would do is disconnect and plug the vacuum line
to the booster and see if the problem goes away. If your brake
hoses are new and the problem occurs only with the booster
connected, I would try adjusting the operating rod clearance to the
larger figure in the repair manual. We have seen heat related
brake drag and lockup due to insufficient operating rod clearance.
There should be a few posts about it in the archives. Once that is
out of the equation, I would suspect a weak spring or a leak in the
reaction valve.

Paul–
The original message included these comments:

When you step on the brake, the first time you apply it, the pedal
is normal. Brakes stay engaged for up to a minute before
releasing. The 2nd time you step on it in succession, the pedal
goes further down, but still has pressure. The 3rd time you step on
it, it flops around loosely until the brakes release. My brake
booster retracts slowly. After applying the brakes, it can take a
much as a minute for the brakes to release. With the booster out of


PS
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