Subject: [Healeys] Brake Servo Operation

From: mitch <[email-masked]>
Date: Fri, 18 Mar 2016 06:57:36 -0400

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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=E2=80=A6.idling ,foot on brake=
=E2=80=A6=E2=80=A6the idle increases by about 300-500 rpm=E2=80=A6 is this =
normal?  Also noticed the brake peddle is a little lower when applied.  =20
The car appears to stop =E2=80=A6OK
What tests can I do ?
Can I put a new check valve in vacuum line =E2=80=A6=E2=80=A6without removi=
ng the valve on the servo?  Or would that cause a problem?
And yes I looked in the archives=E2=80=A6=E2=80=A6.little confusing
Any help would be appreciated

Cheers
Mitch

Sent from Mail for Windows 10

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ss=3DWordSection1><p class=3DMsoNormal>Hello,</p><p class=3DMsoNormal><o:p>=
&nbsp;</o:p></p><p class=3DMsoNormal>I have the original servo on my 1966 B=
J8=C2=A0 (Girling MK2A) it was rebuilt by PO at some time</p><p class=3DMso=
Normal>I recently noticed=C2=A0 when stopped at a light=E2=80=A6.idling ,fo=
ot on brake=E2=80=A6=E2=80=A6the idle increases by about 300-500 rpm=E2=80=
=A6 is this normal?=C2=A0 Also noticed the brake peddle is a little lower w=
hen applied.=C2=A0=C2=A0 </p><p class=3DMsoNormal>The car appears to stop =
=E2=80=A6OK</p><p class=3DMsoNormal>What tests can I do ?</p><p class=3DMso=
Normal>Can I put a new check valve in vacuum line =E2=80=A6=E2=80=A6without=
 removing the valve on the servo?=C2=A0 Or would that cause a problem?</p><=
p class=3DMsoNormal>And yes I looked in the archives=E2=80=A6=E2=80=A6.litt=
le confusing</p><p class=3DMsoNormal>Any help would be appreciated</p><p cl=
ass=3DMsoNormal><o:p>&nbsp;</o:p></p><p class=3DMsoNormal>Cheers</p><p clas=
s=3DMsoNormal>Mitch<o:p></o:p></p><p class=3DMsoNormal><o:p>&nbsp;</o:p></p=
><p class=3DMsoNormal>Sent from <a href=3D"https://go.microsoft.com/fwlink/=
?LinkId=3D550986">Mail</a> for Windows 10</p><p class=3DMsoNormal><span sty=
le=3D'font-size:12.0pt;font-family:"Times New Roman",serif'><o:p>&nbsp;</o:=
p></span></p></div></body></html>=

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Archive: http://www.team.net/archive

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From: Bob Spidell <[email-masked]>
Date: Fri, 18 Mar 2016 14:14:51 +0000 (UTC)

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re: ' ... when stopped at a light=E2=80=A6.idling ,foot on brake=E2=80=A6=
=E2=80=A6the idle increases by about 300-500 rpm=E2=80=A6 is this normal?'=
=20

Nope. When you step on the brake pedal, a slave cylinder in the servo moves=
 a 'T' valve which vents atmospheric pressure air into the large 'vacuum' c=
anister, pressing on a large piston which works against below-atmospheric p=
ressure--i.e. vacuum--on the other side (in normal running, vacuum is appli=
ed to both sides of the piston). If your idle increases when you apply brak=
es that means you have an air leak somewhere in the system. I can only spec=
ulate where the leak(s) might be originating, but my first guess would be t=
he around the seal on the vacuum/air piston in the canister. Since the seal=
 is a leather strip bolstered by a large rubber O-ring--both of which are k=
nown to dry out and crack or even disintegrate--atmospheric air could get p=
ast the seal into the vacuum half of the piston, which vents directly to th=
e intake manifold (through the check valve). The check valve--which, I beli=
eve, is there to permit one final application of boosted brakes should the =
engine quit--would, in theory, prevent that from happening, but they can fa=
il as well. An alternate cause might be the seals on the T-valve, which sho=
uld close vacuum input when the brakes are applied, but if those seals have=
 failed it might allow atmospheric air into the system.=20

A failed check valve--it's a flimsy reed-type valve--would not cause this p=
roblem, but a working valve might mitigate the high idle. At any rate, you =
need to fix the cause(s) of the problem (see above), and if your check valv=
e has failed you need to replace it as well. Unfortunately, I don't know of=
 any source for new replacements, but I was able to get a good used one fro=
m BCS many years ago. My original valve had apparently failed in the past, =
and a PO had installed a plastic replacement on the side of the wheel well,=
 which worked fine but looked wrong.=20

Servo rebuilds seem to be hit-or-miss; I rebuilt mine many years ago and it=
's worked perfectly since. There is a dry lubricant coating on the inside o=
f the vacuum canister which prevents the leather/rubber seal from sticking;=
 I spent quite a few bucks to get a proper coating--I think it's molybdenum=
-based--and applied several coats. I wouldn't be surprised if the PO skippe=
d this step, possibly causing premature wear on the leather/rubber seal.=20

Bob=20

----- Original Message -----

Hello,=20

I have the original servo on my 1966 BJ8 (Girling MK2A) it was rebuilt by P=
O at some time=20

I recently noticed when stopped at a light=E2=80=A6.idling ,foot on brake=
=E2=80=A6=E2=80=A6the idle increases by about 300-500 rpm=E2=80=A6 is this =
normal? Also noticed the brake peddle is a little lower when applied.=20

The car appears to stop =E2=80=A6OK=20

What tests can I do ?=20

Can I put a new check valve in vacuum line =E2=80=A6=E2=80=A6without removi=
ng the valve on the servo? Or would that cause a problem?=20

And yes I looked in the archives=E2=80=A6=E2=80=A6.little confusing=20

Any help would be appreciated=20

Cheers=20

Mitch=20

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<html><body><div style=3D"font-family: Arial; font-size: 12pt; color: #0000=
00"><div>re: ' ... when stopped at a light=E2=80=A6.idling ,foot on brake=
=E2=80=A6=E2=80=A6the idle increases by about 300-500 rpm=E2=80=A6 is this =
normal?'<br></div><div><br></div><div>Nope.&nbsp; When you step on the brak=
e pedal, a slave cylinder in the servo moves a 'T' valve which vents atmosp=
heric pressure air into the large 'vacuum' canister, pressing on a large pi=
ston which works against below-atmospheric pressure--i.e. vacuum--on the ot=
her side (in normal running, vacuum is applied to both sides of the piston)=
.&nbsp; If your idle increases when you apply brakes that means you have an=
 air leak somewhere in the system.&nbsp; I can only speculate where the lea=
k(s) might be originating, but my first guess would be the around the seal =
on the vacuum/air piston in the canister.&nbsp; Since the seal is a leather=
 strip bolstered by a large rubber O-ring--both of which are known to dry o=
ut and crack or even disintegrate--atmospheric air could get past the seal =
into the vacuum half of the piston, which vents directly to the intake mani=
fold (through the check valve).&nbsp; The check valve--which, I believe, is=
 there to permit one final application of boosted brakes should the engine =
quit--would, in theory, prevent that from happening, but they can fail as w=
ell.&nbsp; An alternate cause might be the seals on the T-valve, which shou=
ld close vacuum input when the brakes are applied, but if those seals have =
failed it might allow atmospheric air into the system.<br></div><div><br></=
div><div>A failed check valve--it's a flimsy reed-type valve--would not cau=
se this problem, but a working valve might mitigate the high idle.&nbsp; At=
 any rate, you need to fix the cause(s) of the problem (see above), and if =
your check valve has failed you need to replace it as well.&nbsp; Unfortuna=
tely, I don't know of any source for new replacements, but I was able to ge=
t a good used one from BCS many years ago.&nbsp; My original valve had appa=
rently failed in the past, and a PO had installed a plastic replacement on =
the side of the wheel well, which worked fine but looked wrong.<br></div><d=
iv><br></div><div>Servo rebuilds seem to be hit-or-miss; I rebuilt mine man=
y years ago and it's worked perfectly since.&nbsp; There is a dry lubricant=
 coating on the inside of the vacuum canister which prevents the leather/ru=
bber seal from sticking; I spent quite a few bucks to get a proper coating-=
-I think it's molybdenum-based--and applied several coats.&nbsp; I wouldn't=
 be surprised if the PO skipped this step, possibly causing premature wear =
on the leather/rubber seal.<br></div><div><br></div><div>Bob<br></div><div>=
<br></div><hr id=3D"zwchr"><div style=3D"color:#000;font-weight:normal;font=
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--></style><div class=3D"MsoNormal"><p class=3D"MsoNormal">Hello,</p><p cla=
ss=3D"MsoNormal">&nbsp;</p><p class=3D"MsoNormal">I have the original servo=
 on my 1966 BJ8&nbsp; (Girling MK2A) it was rebuilt by PO at some time</p><=
p class=3D"MsoNormal">I recently noticed&nbsp; when stopped at a light=E2=
=80=A6.idling ,foot on brake=E2=80=A6=E2=80=A6the idle increases by about 3=
00-500 rpm=E2=80=A6 is this normal?&nbsp; Also noticed the brake peddle is =
a little lower when applied.&nbsp;&nbsp; </p><p class=3D"MsoNormal">The car=
 appears to stop =E2=80=A6OK</p><p class=3D"MsoNormal">What tests can I do =
?</p><p class=3D"MsoNormal">Can I put a new check valve in vacuum line =E2=
=80=A6=E2=80=A6without removing the valve on the servo?&nbsp; Or would that=
 cause a problem?</p><p class=3D"MsoNormal">And yes I looked in the archive=
s=E2=80=A6=E2=80=A6.little confusing</p><p class=3D"MsoNormal">Any help wou=
ld be appreciated</p><p class=3D"MsoNormal">&nbsp;</p><p class=3D"MsoNormal=
">Cheers</p><p class=3D"MsoNormal">Mitch</p><p class=3D"MsoNormal">&nbsp;</=
p><br></div><div><br></div></div><div><br></div></div></body></html>
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[email-masked]

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From: Larry Wendland <[email-masked]>
Date: Fri, 18 Mar 2016 21:10:06 -0400

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 <[email-masked]>
To: Healeys <[email-masked]>
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

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