[xj] Series I Brake & Vacume Question

Hello Fellow Listers,

I have question about the amount of vacuum my Series I produces. At idle,
it produces only about 10 lbs. Upon acceleration it goes up to about 20lbs.
Another issue that may be related is the audible hiss from the vacuum
booster and decrease in rpm (at idle) when I step on the brakes. The brakes
in general feel dead with a lot of travel.

My questions are, what can cause low vacuum and is the hiss from the booster
normal? Just as important, are these two things related?

Thanks,
Dan Whitney
1970 XJ===================================================
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Dan, could well be that the booster is leaking vacuum internally and needs
replacing. Plug up the hose to it and see if the idle is now right. You can
also try sucking on a hose to the booster’s spigot and see if it’s very leaky.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Dan Whitney wrote:

Hello Fellow Listers,

I have question about the amount of vacuum my Series I produces. At idle,
it produces only about 10 lbs. Upon acceleration it goes up to about 20lbs.
Another issue that may be related is the audible hiss from the vacuum
booster and decrease in rpm (at idle) when I step on the brakes. The brakes
in general feel dead with a lot of travel.

My questions are, what can cause low vacuum and is the hiss from the booster
normal? Just as important, are these two things related?

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

To remove yourself from this list, go to http://www.jag-lovers.org/cgi-bin/majordomo.

// please trim quoted text to context only

In reply to a message from Dan Whitney sent Tue 29 Jun 2004:

Dan
In answer to your question
Most engines run aproximatly 19.5 to 21.5 lbs vacuum
This can be varied with changes in ignition timing.
To test your booster turn off the engine & pump tme brake pedal
sevral times then place your foot on the pedal & start the engine
the pedal should sink aproximatly 1 inch if this does not happen
then your booster is in need of a rebuild
It should not leak air through the rear of the booster
check it out & let us know.
BAJ–
The original message included these comments:

I have question about the amount of vacuum my Series I produces. At idle,
it produces only about 10 lbs. Upon acceleration it goes up to about 20lbs.
Another issue that may be related is the audible hiss from the vacuum
booster and decrease in rpm (at idle) when I step on the brakes. The brakes
in general feel dead with a lot of travel.
My questions are, what can cause low vacuum and is the hiss from the booster
normal? Just as important, are these two things related?


Bruce Beleura Hill Mtrs MK11,XJC,MG Twin Cam
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

To remove yourself from this list, go to http://www.jag-lovers.org/cgi-bin/majordomo.

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Dan:

My recollection is that 20 lbs… at idle is the norm.

It sound like there’s a vacuum leak around or in the brake booster.

Remove the hose from the booster inlet and plug it so the hole is closed.
Any hiss now? If so, the hose may be cracked. If not, check the booster.

Take piece of clean, new hose connect it to the booster. Use a brake
bleeder pump, other vacuum source, or if you don’t have one, just suck
mightily on the hose. Can you suck air easily? If so, the diaphragm inside
the booster is split.

Regards
Lou
71 XJ6----- Original Message -----
From: “Dan Whitney” dwhitney@landmarketing.com
To: “Xj Lovers” xj@jag-lovers.org
Sent: Tuesday, June 29, 2004 8:33 AM
Subject: [xj] Series I Brake & Vacume Question

Hello Fellow Listers,

I have question about the amount of vacuum my Series I produces. At idle,
it produces only about 10 lbs. Another issue that may be related is the
audible hiss from the vacuum

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

To remove yourself from this list, go to http://www.jag-lovers.org/cgi-bin/majordomo.

// please trim quoted text to context only