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  #1  
Old 08-24-2009, 12:41 AM
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XKE brake booster applying brakes all the time

My friend has a 1967 XKE convertible. We bled the brakes and got a nice firm pedal. Couldn't go anywhere because when we started the engine, the vacuum booster caused the brakes to apply. Disconnect the vacuum connection at the intake manifold and the brakes release. Apply the vacuum and the brakes go on.

Is there some adjustment to address this issue? The shop manual is no help.

Our frustration with the incredibly complicated brake system notwithstanding, I totally love my friend's Jag. I think it is the prettiest car I've seen. Mechanically and structurally, it is so much wilder than 99% of the cars on the road.
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Old 08-24-2009, 06:26 AM
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No experience with Jags, but I know with Fords there is an adjustment. There is even a gauge in the Service manual to be copied and used that shows the correct setting for the shaft that goes from the booster to the Master cylinder. I'd remove the booster, and see if these shaft on either side ( pedal to booster, and booster to MC) is adjustable, and go from there.

Was the MC, or booster recently changed? If so, are the old parts available for inspection and comparison?
If the there has been no recent work then what caused the change? Could the booster have failed from just sitting?
There has to be a Jag forum somewhere--it probably won't be a nice of a community as we have here, but maybe they'd help.
We agree on the look of the Jag.
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  #3  
Old 08-24-2009, 08:43 AM
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Quote:
Originally Posted by MS Fowler View Post
...Was the MC, or booster recently changed? If so, are the old parts available for inspection and comparison?
If the there has been no recent work then what caused the change? Could the booster have failed from just sitting?...
Before we bled the brakes, he had a soft pedal. We pumped out some air and a bunch of really nasty brake fluid. The pedal got firm, but when vacuum is applied to the booster the brakes come on.

I've looked at a few Jag sites, but having found anything on point yet.
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  #4  
Old 08-24-2009, 08:55 AM
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Check the brake pedal free play. Someone may have lengthened the pushrod in an attempt to compensate for the low pedal. Or the M/C may have leaked brake fluid into the booster, causing damage.
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  #5  
Old 08-24-2009, 08:59 AM
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Kerry,
I found this:


TROUBLESHOOTING THE XKE
April 1, 2005

1. Brake problems. Common brake problems on the 4.2 and V12 cars concern the brakes sticking on. One of the common problems is the hoses getting old and collapsing internally while looking normal on the outside. Using hose that is not designed to hold a vacuum can also be a problem. The master cylinder has a vacuum valve on the end that has both chambers equalized when the brakes are off. This way the booster is not activated and the brakes not applied even if the vacuum is low. If both sides of the booster are not equal, the brakes can be applied. A collapsed hose can cause this along with the master cylinder sticking on. The master cylinder has an adjustment for pedal free play on the 4.2 liter cars, the V12 are self adjusting.. Not having any free play will keep the master cylinder from turning off and allowing the fluid to return to the reservoir. This adjustment his needs to be checked anytime the master cylinder is replaced. Lack of brake boost is most likely caused by a collapsed vacuum line on the supply side coming from vacuum reservoir. There is a one way valve in the system and it could be faulty but this is very rare.
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Old 08-24-2009, 09:19 AM
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Originally Posted by MS Fowler View Post
Kerry,...
Who?
Quote:
...The master cylinder has a vacuum valve on the end that has both chambers equalized when the brakes are off...
That sounds promising. I need to go get educated on that vacuum valve.

Thank you.
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  #7  
Old 08-24-2009, 10:12 AM
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Originally Posted by dculkin View Post
Who?That sounds promising. I need to go get educated on that vacuum valve.

Thank you.
I am having a bad time. First I give Representative Frank a compliment, and call him Senator, and then I change your name.

And to think I have my finger on the nuk-ler trigger....
Oh my
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Old 08-24-2009, 03:40 PM
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If MS Fowler's info turns out not to be it, try jaguarforums.com
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Old 08-24-2009, 05:50 PM
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Are vacuum hoses special made to hold vacuum?
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Old 08-24-2009, 10:47 PM
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I think british cars, and Jags in particular, tend to do things like this occasionally just to remind the owner that they were made in England.
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  #11  
Old 08-24-2009, 10:54 PM
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Originally Posted by MaydayMike View Post
I think british cars, and Jags in particular, tend to do things like this occasionally just to remind the owner that they were made in England.
All right, ya ruckur.
Just what is that supposed to mean?


- Darby
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  #12  
Old 08-25-2009, 05:48 AM
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Originally Posted by MaydayMike View Post
I think british cars, and Jags in particular, tend to do things like this occasionally just to remind the owner that they were made in England.
I'm sure many people on this forum have nicknamed their Mercedes Benzes "Hitler's Revenge," I know I sure have
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Old 08-25-2009, 08:20 AM
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Originally Posted by WVOtoGO View Post
All right, ya ruckur.
Just what is that supposed to mean?


- Darby
Beautiful to the eye, sublime in design with just a bit of madness thrown in to add character and maintain interest...
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Old 08-25-2009, 08:34 PM
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"Madness" is such a delightful, typically British term.
I like "madness"
the madness of multiple SU carburetors
The madness of those British overdrives
To say "the madness of Lucas electrics" is too easy, so I won't
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Old 08-25-2009, 10:03 PM
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Originally Posted by KarTek View Post
Beautiful to the eye, sublime in design with just a bit of madness thrown in to add character and maintain interest...
I agree with MS Fowler. That's a perfect description.
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