[Healeys] Brake Servo Operation

[Larry Wendland]

When you apply the brake a small gulp of air is momentarily introduced to the intake manifold from the brake booster in an effort to replenish the vacuum in the booster chamber through the large vacuum hose that is between the booster and the intake manifold .  The gulp of air momentarily leans the normally rich idle mixture out increasing the idle speed.  I am assuming the increase in idle returns to normal as long as you keep the pedal depressed and when you release the brakes.  Now if the idle stays elevated with the pedal depressed, there could be a vacuum leak.  I used to repeatedly depress the brake pedal when stopped at a stop light and watch the idle increase and stay increased until I stopped depressing the pedal repeatedly and hold the pedal down till it was time to continue my journey.  Why did I do that?  To prove to my self that air was being introduce to the intake manifold upon brake application.

Larry
'67 BJ8


-----Original Message-----
From: mitch <dayton21 at comcast.net>
To: Healeys <Healeys at autox.team.net>
Sent: Fri, Mar 18, 2016 6:57 am
Subject: [Healeys] Brake Servo Operation



Hello,
 
I have the original servo on my 1966 BJ8  (Girling MK2A) it was rebuilt by PO at some time
I recently noticed  when stopped at a light….idling ,foot on brake……the idle increases by about 300-500 rpm… is this normal?  Also noticed the brake peddle is a little lower when applied.   
The car appears to stop …OK
What tests can I do ?
Can I put a new check valve in vacuum line ……without removing the valve on the servo?  Or would that cause a problem?
And yes I looked in the archives…….little confusing
Any help would be appreciated
 
Cheers
Mitch
 
Sent from Mail for Windows 10
 

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