Home » Public Forums » GMCnet » [GMCnet] Brake Booster Peculiarities
| [GMCnet] Brake Booster Peculiarities [message #178672] |
Wed, 01 August 2012 17:31  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Admittedly, I've never given a great deal of though nor study, and no
tear-down/analysis to vacuum brake boosters. But I did think I understood
how they work: Engine (or other aux. source) vacuum is stored "behind" two
diaphragms until foot pressure opens a valve to atmosphere. Then,
atmospheric pressure acting against the unsupported diaphragms provides the
force to actuate the master cylinder pistons.
That conception said to me that the booster and the master cylinder are two
cooperating, but stand-alone, systems. Today's events have me wondering:
A friend is in the process of installing a vacuum reservoir and a pump. As
a retired Delta Airlines pneumatics technician, he's knowledgeable and
cautious, so he tested each component before assembling the system. When
he got to the booster, he connected a vacuum pump and a gauge, intending to
draw the vacuum down and monitor the booster's leak-down rate. He was
surprised to find that he could only pull 5" in-Hg of vacuum!
After scratching his head a while, he called to ruin my day too. Baffled,
I volunteered to set up a similar test on the workbench using the booster I
removed last year. I thought that booster was OK, but I bought a
sensitized one from Leigh Harrison -- which doesn't feel very "sensitized"
to me.
My setup is vacuum pump, tee to gauge, then to a check valve at the
booster. All connections are good -- it will hold a vacuum up to the check
valve for a long time.
Now the surprise: My re-purposed icemaker compressor will easily pull an
idicated 29" in-Hg vacuum, and pretty quickly. But connected to the "good"
booster, it would only draw 2" in-Hg, and even I could hear air flowing
into the MC side of the booster. Hmmmm... I had a large soft plastic pipe
cap which just fit the recess on the MC side of the booster, so I plugged
that hole. The sound went away, and the vacuum immediately rose to 29
in-Hg.
On the pedal side of the booster, the pedal push rod passes through a ~1"
OD black plastic "sleeve". When I depress the pedal push rod, the rod, AND
the sleeve, move into the booster; the vacuum drops on the MC side, and, I
presume, the MC push rod moves toward the MC.
Questions for those who really do understand the booster:
(1) Should the MC be sealed to the booster in order to seal the vacuum, as
my plastic pipe plug does? Would that not expose the MC's hydraulic seals
to unwanted stress?
or
(2) Should the booster have an internal seal for that vacuum?
(3) Is the booster I tested (and my friend's mounted one) bad, or just
missing something?
(4) Was the boosted action I saw due to only one of the diaphragms, with
the other leaking?
(4) Has anyone tried DIY repair?
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake Booster Peculiarities [message #178681 is a reply to message #178672] |
Wed, 01 August 2012 19:29  |
Dave Mumert
Messages: 272
Registered: February 2004
Location: Olds, AB, Canada
Karma: 0
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Hi Ken
I did some quick research about boosters. It appears some are sealed and
some rely on the MC as a seal.
I doubt the less than 15PSI vacuum would have much effect on the hundreds of
pounds of brake fluid pressure.
It sounds like you need to further your brake experimentation by opening up
a booster, take lots of pictures.
Dave Mumert
> -----Original Message-----
> Subject: [GMCnet] Brake Booster Peculiarities
>
> Admittedly, I've never given a great deal of though nor study, and no
tear-
> down/analysis to vacuum brake boosters. But I did think I understood how
> they work: Engine (or other aux. source) vacuum is stored "behind" two
> diaphragms until foot pressure opens a valve to atmosphere. Then,
> atmospheric pressure acting against the unsupported diaphragms provides
> the force to actuate the master cylinder pistons.
>
> That conception said to me that the booster and the master cylinder are
two
> cooperating, but stand-alone, systems. Today's events have me wondering:
>
> A friend is in the process of installing a vacuum reservoir and a pump.
As a
> retired Delta Airlines pneumatics technician, he's knowledgeable and
> cautious, so he tested each component before assembling the system.
> When he got to the booster, he connected a vacuum pump and a gauge,
> intending to draw the vacuum down and monitor the booster's leak-down
> rate. He was surprised to find that he could only pull 5" in-Hg of
vacuum!
>
> After scratching his head a while, he called to ruin my day too. Baffled,
I
> volunteered to set up a similar test on the workbench using the booster I
> removed last year. I thought that booster was OK, but I bought a
sensitized
> one from Leigh Harrison -- which doesn't feel very "sensitized"
> to me.
>
> My setup is vacuum pump, tee to gauge, then to a check valve at the
> booster. All connections are good -- it will hold a vacuum up to the
check
> valve for a long time.
>
> Now the surprise: My re-purposed icemaker compressor will easily pull an
> idicated 29" in-Hg vacuum, and pretty quickly. But connected to the
"good"
> booster, it would only draw 2" in-Hg, and even I could hear air flowing
into
> the MC side of the booster. Hmmmm... I had a large soft plastic pipe cap
> which just fit the recess on the MC side of the booster, so I plugged that
> hole. The sound went away, and the vacuum immediately rose to 29 in-Hg.
>
> On the pedal side of the booster, the pedal push rod passes through a ~1"
> OD black plastic "sleeve". When I depress the pedal push rod, the rod,
AND
> the sleeve, move into the booster; the vacuum drops on the MC side, and, I
> presume, the MC push rod moves toward the MC.
>
> Questions for those who really do understand the booster:
>
> (1) Should the MC be sealed to the booster in order to seal the vacuum,
as
> my plastic pipe plug does? Would that not expose the MC's hydraulic seals
to
> unwanted stress?
> or
> (2) Should the booster have an internal seal for that vacuum?
>
> (3) Is the booster I tested (and my friend's mounted one) bad, or just
> missing something?
>
> (4) Was the boosted action I saw due to only one of the diaphragms, with
> the other leaking?
>
> (4) Has anyone tried DIY repair?
>
> Ken H.
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| Re: [GMCnet] Brake Booster Peculiarities [message #178694 is a reply to message #178681] |
Wed, 01 August 2012 21:04 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Dave,
I agree that with modern O-ring MC piston seals, vacuum shouldn't be enough
to cause a problem. But older MC's with cup seals would seem to have a
potential problem -- maybe the booster designs changed with the MC's.
Sure hope someone already knows "all about boosters" -- I'm having enough
trouble just trying to understand the manual! :-)
Ken H.
On Wed, Aug 1, 2012 at 8:29 PM, Dave Mumert <gmcnet@mumert.com> wrote:
> Hi Ken
>
> I did some quick research about boosters. It appears some are sealed and
> some rely on the MC as a seal.
>
> I doubt the less than 15PSI vacuum would have much effect on the hundreds
> of
> pounds of brake fluid pressure.
>
> It sounds like you need to further your brake experimentation by opening up
> a booster, take lots of pictures.
>
> Dave Mumert
>
>
> > -----Original Message-----
> > Subject: [GMCnet] Brake Booster Peculiarities
> >
> > Admittedly, I've never given a great deal of though nor study, and no
> tear-
> > down/analysis to vacuum brake boosters. But I did think I understood how
> > they work: Engine (or other aux. source) vacuum is stored "behind" two
> > diaphragms until foot pressure opens a valve to atmosphere. Then,
> > atmospheric pressure acting against the unsupported diaphragms provides
> > the force to actuate the master cylinder pistons.
> >
> > That conception said to me that the booster and the master cylinder are
> two
> > cooperating, but stand-alone, systems. Today's events have me wondering:
> >
> > A friend is in the process of installing a vacuum reservoir and a pump.
> As a
> > retired Delta Airlines pneumatics technician, he's knowledgeable and
> > cautious, so he tested each component before assembling the system.
> > When he got to the booster, he connected a vacuum pump and a gauge,
> > intending to draw the vacuum down and monitor the booster's leak-down
> > rate. He was surprised to find that he could only pull 5" in-Hg of
> vacuum!
> >
> > After scratching his head a while, he called to ruin my day too.
> Baffled,
> I
> > volunteered to set up a similar test on the workbench using the booster I
> > removed last year. I thought that booster was OK, but I bought a
> sensitized
> > one from Leigh Harrison -- which doesn't feel very "sensitized"
> > to me.
> >
> > My setup is vacuum pump, tee to gauge, then to a check valve at the
> > booster. All connections are good -- it will hold a vacuum up to the
> check
> > valve for a long time.
> >
> > Now the surprise: My re-purposed icemaker compressor will easily pull an
> > idicated 29" in-Hg vacuum, and pretty quickly. But connected to the
> "good"
> > booster, it would only draw 2" in-Hg, and even I could hear air flowing
> into
> > the MC side of the booster. Hmmmm... I had a large soft plastic pipe
> cap
> > which just fit the recess on the MC side of the booster, so I plugged
> that
> > hole. The sound went away, and the vacuum immediately rose to 29 in-Hg.
> >
> > On the pedal side of the booster, the pedal push rod passes through a ~1"
> > OD black plastic "sleeve". When I depress the pedal push rod, the rod,
> AND
> > the sleeve, move into the booster; the vacuum drops on the MC side, and,
> I
> > presume, the MC push rod moves toward the MC.
> >
> > Questions for those who really do understand the booster:
> >
> > (1) Should the MC be sealed to the booster in order to seal the vacuum,
> as
> > my plastic pipe plug does? Would that not expose the MC's hydraulic
> seals
> to
> > unwanted stress?
> > or
> > (2) Should the booster have an internal seal for that vacuum?
> >
> > (3) Is the booster I tested (and my friend's mounted one) bad, or just
> > missing something?
> >
> > (4) Was the boosted action I saw due to only one of the diaphragms, with
> > the other leaking?
> >
> > (4) Has anyone tried DIY repair?
> >
> > Ken H.
>
> _______________________________________________
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake Booster Peculiarities [message #178696 is a reply to message #178672] |
Wed, 01 August 2012 21:47 |
GMC Cruse
Messages: 606
Registered: June 2009
Location: SE Michigan
Karma: 3
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Senior Member |
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I recently did work on a '95 Sable. A rubber seal went over the end of the end of the master cylinder that bolted to the booster. When putting it together I didn't realize that the seal fell off. The car stopped like they do when the booster is bad. I then saw the seal on the fllor and put it where it belonged and the car stopped normally. So yes the master cylinder should be sealed to the booster.
Mike K.
'75 PB
Southeast Michigan
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| Re: [GMCnet] Brake Booster Peculiarities [message #179024 is a reply to message #178696] |
Sat, 04 August 2012 21:45 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Some off line discussions indicate that there SHOULD be a seal between the
MC and the booster. I've just uploaded the IPB here:
http://www.gmcmhphotos.com/photos/uploads/40/Brake_Booster_Parts.pdf
or
http://goo.gl/SUiW5
My coach does not have, and has not had during my 14 years' ownership, IPB
#9. I'm now suspecting that is at least a contributor to the poor
performance of my original and my sensitized booster. It may also explain
the reports we've heard of boosters leaking while the pedal is depressed.
That's about all I know at this point; does anyone else know more?
Especially, has anyone replaced that seal and/or know a source for it?
Does anyone have access to a booster rebuilder who may help us clarify this
and perhaps supply seals?
Or am I completely out in left field?
Ken H.
On Wed, Aug 1, 2012 at 10:47 PM, Mike wrote:
>
>
> I recently did work on a '95 Sable. A rubber seal went over the end of
> the end of the master cylinder that bolted to the booster. When putting it
> together I didn't realize that the seal fell off. The car stopped like
> they do when the booster is bad. I then saw the seal on the fllor and put
> it where it belonged and the car stopped normally. So yes the master
> cylinder should be sealed to the booster.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake Booster Peculiarities [message #179076 is a reply to message #179070] |
Sun, 05 August 2012 11:32 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Actually I believe it was meant to be a dirt or dust seal.
Emery Stora
On Aug 5, 2012, at 10:18 AM, gene Fisher <mr.erfisher@gmail.com> wrote:
>>
>> That's about all I know at this point; does anyone else know more?
>> Especially, has anyone replaced that seal and/or know a source for it?
>> Does anyone have access to a booster rebuilder who may help us clarify this
>> and perhaps supply seals?
>>
>
> will be interesting,
> it does not look like a pressure seal
> more like a liquid seal.
>
> will like to see the results of this
> gene
>
>
>>
>> Or am I completely out in left field?
>>
>> Ken H.
>>
>>
>> On Wed, Aug 1, 2012 at 10:47 PM, Mike wrote:
>>
>>>
>>>
>>> I recently did work on a '95 Sable. A rubber seal went over the end of
>>> the end of the master cylinder that bolted to the booster. When putting
>> it
>>> together I didn't realize that the seal fell off. The car stopped like
>>> they do when the booster is bad. I then saw the seal on the fllor and
>> put
>>> it where it belonged and the car stopped normally. So yes the master
>>> cylinder should be sealed to the booster.
>>> --
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>
>
>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Brake Booster Peculiarities [message #179079 is a reply to message #179076] |
Sun, 05 August 2012 12:23 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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yup
not a pressure seal
would not stop a pressure leak
gene
On Sun, Aug 5, 2012 at 9:32 AM, Emery Stora <emerystora@mac.com> wrote:
> Actually I believe it was meant to be a dirt or dust seal.
>
>
>
> Emery Stora
>
> On Aug 5, 2012, at 10:18 AM, gene Fisher <mr.erfisher@gmail.com> wrote:
>
> >>
> >> That's about all I know at this point; does anyone else know more?
> >> Especially, has anyone replaced that seal and/or know a source for it?
> >> Does anyone have access to a booster rebuilder who may help us clarify
> this
> >> and perhaps supply seals?
> >>
> >
> > will be interesting,
> > it does not look like a pressure seal
> > more like a liquid seal.
> >
> > will like to see the results of this
> > gene
> >
> >
> >>
> >> Or am I completely out in left field?
> >>
> >> Ken H.
> >>
> >>
> >> On Wed, Aug 1, 2012 at 10:47 PM, Mike wrote:
> >>
> >>>
> >>>
> >>> I recently did work on a '95 Sable. A rubber seal went over the end of
> >>> the end of the master cylinder that bolted to the booster. When
> putting
> >> it
> >>> together I didn't realize that the seal fell off. The car stopped like
> >>> they do when the booster is bad. I then saw the seal on the fllor and
> >> put
> >>> it where it belonged and the car stopped normally. So yes the master
> >>> cylinder should be sealed to the booster.
> >>> --
> >>>
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >>
> >
> >
> >
> > --
> > Gene Fisher -- 74-23,77PB/ore/ca
> > “Give a man a fish; you have fed him for today --- give him a URL and
> > -------
> > http://gmcmotorhome.info/
> > Alternator Protection Cable
> > http://gmcmotorhome.info/APC.html
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] Brake Booster Peculiarities [message #179120 is a reply to message #179024] |
Sun, 05 August 2012 19:48 |
Kosier
Messages: 834
Registered: February 2008
Karma: 1
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Senior Member |
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Ken,
That part, #5460935, was used on a bunch of Moraine boosters back in the
day.
Cadillac, 69 to 75
Buick, 67 to 74
Olds, 70 to 72 (some)
Chevy, 67 to 74 (most)
Corvette, 67 only
It is listed as a separate part or part of a rebuild kit.
Haven't checked on availability(Sunday)
Gary Kosier
-----Original Message-----
From: Ken Henderson
Sent: Saturday, August 04, 2012 10:45 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Brake Booster Peculiarities
Some off line discussions indicate that there SHOULD be a seal between the
MC and the booster. I've just uploaded the IPB here:
http://www.gmcmhphotos.com/photos/uploads/40/Brake_Booster_Parts.pdf
or
http://goo.gl/SUiW5
My coach does not have, and has not had during my 14 years' ownership, IPB
#9. I'm now suspecting that is at least a contributor to the poor
performance of my original and my sensitized booster. It may also explain
the reports we've heard of boosters leaking while the pedal is depressed.
That's about all I know at this point; does anyone else know more?
Especially, has anyone replaced that seal and/or know a source for it?
Does anyone have access to a booster rebuilder who may help us clarify this
and perhaps supply seals?
Or am I completely out in left field?
Ken H.
On Wed, Aug 1, 2012 at 10:47 PM, Mike wrote:
>
>
> I recently did work on a '95 Sable. A rubber seal went over the end of
> the end of the master cylinder that bolted to the booster. When putting
> it
> together I didn't realize that the seal fell off. The car stopped like
> they do when the booster is bad. I then saw the seal on the fllor and put
> it where it belonged and the car stopped normally. So yes the master
> cylinder should be sealed to the booster.
> --
>
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| Re: [GMCnet] Brake Booster Peculiarities [message #179124 is a reply to message #179082] |
Sun, 05 August 2012 20:24 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Rob,
My old booster does not have the segmented black "seal" around the 3/4" OD
cylinder into which the MC pushrod fits.
Finding that missing, I decided to try another experiment: Finding a new
MC in my spares stock, I made a rubber seal to fit between it and the
booster, then bolted them together into what should be an, at least nearly
vacuum-tight, assembly. With the same vacuum pump setup I used earlier, I
drew the maximum possible vacuum: 5 in-Hg. :-(
That says to me that the obvious vacuum leak is internal and that the
absence of a seal at the MC output of the booster is not significant.
BUT, that conclusion is in conflict with the results when I seal that same
port with the plastic cup; that arrangement allows full vacuum in the
booster.
================
So, back to the shop (immediately after typing above): When I removed the
MC and examined it more closely, I found a sort-of concealed MC leak drain
hole at the bottom of the MC flange adjacent to the "nose". Sealing the MC
flange to the booster still left that port open to atmosphere and the
secondary diaphragm.
Let's try something else: I used hole saws to make a 3/8" thick rubber
"faucet washer" to seal the "nose" of the MC to the bottom of the recess in
the booster, leaving the push rod carrier free to move. With the MC bolted
to the booster, the bore of the MC provides the only access from the
"outside world" to the secondary diaphragm. Now, the vacuum rapidly rises
to 28+ in-Hg! A firm index finger push on the input clevis rod is all
that's required to cause full booster & MC travel!!! Hooray!
Jerry Holloway, telling me about his MC told me something I never knew:
That MC-side 3/4" OD plastic cylinder into which the push rod is inserted
is itself removable from the booster -- just pull it straight out. It has
a step at the inner end which fits snugly into a socket in something -- the
"hub" of the secondary diaphragm, I assume. That inner end is sealed and
is the axial bearing surface for the metal pushrod. Which brings us to
another neat fact I discovered as I measured things: Even if one leaves
the metal push rod out between the booster and the MC, there should be
little effect on braking action! The reason? That plastic carrier has
only about 0.030"-0.040" clearance from the MC piston -- it can press on
the flat surface around the dimple into which the push rod seats. The
design allows for simple adjustment of the push rod to MC clearance, by
changing the metal rod, while providing a sure-fire backup in case of
production line or repair screw-up. Certainly there may be a little extra
pedal travel, and a slight reduction in maximum fluid displacement, but
most of the basic design parameters should be met. Of course, when we
tinker with things, such as by adding a P-30 MC, which requires moving the
top bracket to between the MC and the booster, we upset that -- now we've
introduced another 0.110" or so which the push rod carrier doesn't "know
about". :-( Be sure you adjust the length of that metal push rod! Which
by the way, calculates from measurements to be almost exactly the length I
determined empirically with modelling clay.
OK, on with the story: After finding that the MC really must seal the
booster, I went to my GMC and removed the MC (without opening the hydraulic
lines, thanks to large anti-vibration loops in them). Sure 'nuff, there
sat the segmented rubber seal shown in Rob's photo. I grabbed the MC push
rod and its plastic carrier and pulled until they and that seal came out.
Carrying them to the work bench, I inserted them into my old MC (not
completely 'cause its recess is slightly smaller) and lit the vacuum pump.
The seal sucked into position as the vacuum rose to almost 28 in-Hg (I
still had some leakage)!
SO, my conclusion is that the segmented rubber seal IS an active vacuum
seal, highly essential to the correct operation of the booster. If you
examine it closely, you'll find that its OD and ID are feathered so that
vacuum tends to seat them more securely against their mating surfaces.
There should be no movement of the seal in the booster housing, but the
plastic push rod carrier must move to & fro slightly -- the segmentation is
intended to reduce any sliding motion between the seal and carrier; I'll
lubricate that interface when I reassemble it.
Now my question is where to find a replacement seal for my old booster,
which is apparently in good shape except for the seal which has apparently
been missing for 14+ years, leaving me driving 80,000 miles or so with a
single-diaphragm booster. :-( One could use it with the 3/8" thick "faucet
washer" in place, but that exposes the MC to vacuum, which is probably not
a good idea.
If anyone has better ideas, let's hear 'em.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Sun, Aug 5, 2012 at 1:48 PM, Rob Mueller wrote:
> Ken,
>
> Here's a photo of the modified OEM bracket for the P-30 on the front of
> the booster:
>
>
> http://www.gmcmhphotos.com/photos/member-galleries/p28378-master-cylinder-bracke.html
>
> IIRC there is an o-ring on the part of the M/C goes into the booster as
> there is no way that the M/C would seal to the booster due
>
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake Booster Peculiarities [message #179129 is a reply to message #179120] |
Sun, 05 August 2012 20:39 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Thanks, Gary,
That answers the question of what to do about the (now spare) old MC which
I just discovered, within the past hour, how to repair. :-)
Ken H.
On Sun, Aug 5, 2012 at 8:48 PM, Kosier wrote:
> Ken,
>
> That part, #5460935, was used on a bunch of Moraine boosters back in the
> day.
> Cadillac, 69 to 75
> Buick, 67 to 74
> Olds, 70 to 72 (some)
> Chevy, 67 to 74 (most)
> Corvette, 67 only
> It is listed as a separate part or part of a rebuild kit.
> Haven't checked on availability(Sunday)
>
> Gary Kosier
>
> -----Original Message-----
> From: Ken Henderson
> Sent: Saturday, August 04, 2012 10:45 PM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Brake Booster Peculiarities
>
> Some off line discussions indicate that there SHOULD be a seal between the
> MC and the booster. I've just uploaded the IPB here:
>
> http://www.gmcmhphotos.com/photos/uploads/40/Brake_Booster_Parts.pdf
> or
> http://goo.gl/SUiW5
>
> My coach does not have, and has not had during my 14 years' ownership, IPB
> #9. I'm now suspecting that is at least a contributor to the poor
> performance of my original and my sensitized booster. It may also explain
> the reports we've heard of boosters leaking while the pedal is depressed.
>
> That's about all I know at this point; does anyone else know more?
> Especially, has anyone replaced that seal and/or know a source for it?
> Does anyone have access to a booster rebuilder who may help us clarify this
> and perhaps supply seals?
>
> Or am I completely out in left field?
>
> Ken H.
>
>
> On Wed, Aug 1, 2012 at 10:47 PM, Mike wrote:
>
> >
> >
> > I recently did work on a '95 Sable. A rubber seal went over the end of
> > the end of the master cylinder that bolted to the booster. When putting
> > it
> > together I didn't realize that the seal fell off. The car stopped like
> > they do when the booster is bad. I then saw the seal on the fllor and
> put
> > it where it belonged and the car stopped normally. So yes the master
> > cylinder should be sealed to the booster.
> > --
> >
> _______________________________________________
> GMCnet mailing list
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake Booster Peculiarities [message #179130 is a reply to message #179127] |
Sun, 05 August 2012 20:41 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Yes, that IS #9. My new booster from Harrison did come with it. I don't
know what happened to the one on my old MC -- I don't THINK I ever saw one
there all these years, but it's certainly possible that I lost it somewhere
along the way during one of my experiments.
Ken H.
On Sun, Aug 5, 2012 at 9:32 PM, gene Fisher wrote:
> so this is not part #9?
> or it is?
>
> and did the new boosters come with it ?
>
>
> gene
>
>
>
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Ken Henderson
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Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Brake Booster Peculiarities [message #179134 is a reply to message #179130] |
Sun, 05 August 2012 20:50 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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maybe this is why my "rebuilt" sensitized MS leaked, and KenB swearers his
OEM never leaked...
now to find a source
gene
On Sun, Aug 5, 2012 at 6:41 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> Yes, that IS #9. My new booster from Harrison did come with it. I don't
> know what happened to the one on my old MC -- I don't THINK I ever saw one
> there all these years, but it's certainly possible that I lost it somewhere
> along the way during one of my experiments.
>
> Ken H.
>
>
> On Sun, Aug 5, 2012 at 9:32 PM, gene Fisher wrote:
>
> > so this is not part #9?
> > or it is?
> >
> > and did the new boosters come with it ?
> >
> >
> > gene
> >
> >
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] Brake Booster Peculiarities [message #179147 is a reply to message #179124] |
Sun, 05 August 2012 22:40 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Ken,
Did you shoot some pictures to show the assembly of the MC/washer/
Booster?
JR WRIGHT
On Aug 5, 2012, at 9:24 PM, Ken Henderson wrote:
> Rob,
>
> My old booster does not have the segmented black "seal" around the
> 3/4" OD
> cylinder into which the MC pushrod fits.
>
> Finding that missing, I decided to try another experiment: Finding
> a new
> MC in my spares stock, I made a rubber seal to fit between it and the
> booster, then bolted them together into what should be an, at least
> nearly
> vacuum-tight, assembly. With the same vacuum pump setup I used
> earlier, I
> drew the maximum possible vacuum: 5 in-Hg. :-(
>
> That says to me that the obvious vacuum leak is internal and that the
> absence of a seal at the MC output of the booster is not significant.
> BUT, that conclusion is in conflict with the results when I seal
> that same
> port with the plastic cup; that arrangement allows full vacuum in the
> booster.
> ================
> So, back to the shop (immediately after typing above): When I
> removed the
> MC and examined it more closely, I found a sort-of concealed MC leak
> drain
> hole at the bottom of the MC flange adjacent to the "nose". Sealing
> the MC
> flange to the booster still left that port open to atmosphere and the
> secondary diaphragm.
>
> Let's try something else: I used hole saws to make a 3/8" thick
> rubber
> "faucet washer" to seal the "nose" of the MC to the bottom of the
> recess in
> the booster, leaving the push rod carrier free to move. With the MC
> bolted
> to the booster, the bore of the MC provides the only access from the
> "outside world" to the secondary diaphragm. Now, the vacuum rapidly
> rises
> to 28+ in-Hg! A firm index finger push on the input clevis rod is all
> that's required to cause full booster & MC travel!!! Hooray!
>
> Jerry Holloway, telling me about his MC told me something I never
> knew:
> That MC-side 3/4" OD plastic cylinder into which the push rod is
> inserted
> is itself removable from the booster -- just pull it straight out.
> It has
> a step at the inner end which fits snugly into a socket in something
> -- the
> "hub" of the secondary diaphragm, I assume. That inner end is
> sealed and
> is the axial bearing surface for the metal pushrod. Which brings us
> to
> another neat fact I discovered as I measured things: Even if one
> leaves
> the metal push rod out between the booster and the MC, there should be
> little effect on braking action! The reason? That plastic carrier
> has
> only about 0.030"-0.040" clearance from the MC piston -- it can
> press on
> the flat surface around the dimple into which the push rod seats. The
> design allows for simple adjustment of the push rod to MC clearance,
> by
> changing the metal rod, while providing a sure-fire backup in case of
> production line or repair screw-up. Certainly there may be a little
> extra
> pedal travel, and a slight reduction in maximum fluid displacement,
> but
> most of the basic design parameters should be met. Of course, when we
> tinker with things, such as by adding a P-30 MC, which requires
> moving the
> top bracket to between the MC and the booster, we upset that -- now
> we've
> introduced another 0.110" or so which the push rod carrier doesn't
> "know
> about". :-( Be sure you adjust the length of that metal push
> rod! Which
> by the way, calculates from measurements to be almost exactly the
> length I
> determined empirically with modelling clay.
>
> OK, on with the story: After finding that the MC really must seal the
> booster, I went to my GMC and removed the MC (without opening the
> hydraulic
> lines, thanks to large anti-vibration loops in them). Sure 'nuff,
> there
> sat the segmented rubber seal shown in Rob's photo. I grabbed the
> MC push
> rod and its plastic carrier and pulled until they and that seal came
> out.
> Carrying them to the work bench, I inserted them into my old MC (not
> completely 'cause its recess is slightly smaller) and lit the vacuum
> pump.
> The seal sucked into position as the vacuum rose to almost 28 in-Hg (I
> still had some leakage)!
>
> SO, my conclusion is that the segmented rubber seal IS an active
> vacuum
> seal, highly essential to the correct operation of the booster. If
> you
> examine it closely, you'll find that its OD and ID are feathered so
> that
> vacuum tends to seat them more securely against their mating surfaces.
> There should be no movement of the seal in the booster housing, but
> the
> plastic push rod carrier must move to & fro slightly -- the
> segmentation is
> intended to reduce any sliding motion between the seal and carrier;
> I'll
> lubricate that interface when I reassemble it.
>
> Now my question is where to find a replacement seal for my old
> booster,
> which is apparently in good shape except for the seal which has
> apparently
> been missing for 14+ years, leaving me driving 80,000 miles or so
> with a
> single-diaphragm booster. :-( One could use it with the 3/8" thick
> "faucet
> washer" in place, but that exposes the MC to vacuum, which is
> probably not
> a good idea.
>
> If anyone has better ideas, let's hear 'em.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> www.gmcwipersetc.com
>
>
>
> On Sun, Aug 5, 2012 at 1:48 PM, Rob Mueller wrote:
>
>> Ken,
>>
>> Here's a photo of the modified OEM bracket for the P-30 on the
>> front of
>> the booster:
>>
>>
>> http://www.gmcmhphotos.com/photos/member-galleries/p28378-master-cylinder-bracke.html
>>
>> IIRC there is an o-ring on the part of the M/C goes into the
>> booster as
>> there is no way that the M/C would seal to the booster due
>>
> _______________________________________________
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Brake Booster Peculiarities [message #179148 is a reply to message #179024] |
Sun, 05 August 2012 22:46 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
|
Senior Member |
|
|
here it was
gene
On Sat, Aug 4, 2012 at 7:45 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> Some off line discussions indicate that there SHOULD be a seal between the
> MC and the booster. I've just uploaded the IPB here:
>
> http://www.gmcmhphotos.com/photos/uploads/40/Brake_Booster_Parts.pdf
> or
> http://goo.gl/SUiW5
>
> My coach does not have, and has not had during my 14 years' ownership, IPB
> #9. I'm now suspecting that is at least a contributor to the poor
> performance of my original and my sensitized booster. It may also explain
> the reports we've heard of boosters leaking while the pedal is depressed.
>
> That's about all I know at this point; does anyone else know more?
> Especially, has anyone replaced that seal and/or know a source for it?
> Does anyone have access to a booster rebuilder who may help us clarify this
> and perhaps supply seals?
>
> Or am I completely out in left field?
>
> Ken H.
>
>
> On Wed, Aug 1, 2012 at 10:47 PM, Mike wrote:
>
> >
> >
> > I recently did work on a '95 Sable. A rubber seal went over the end of
> > the end of the master cylinder that bolted to the booster. When putting
> it
> > together I didn't realize that the seal fell off. The car stopped like
> > they do when the booster is bad. I then saw the seal on the fllor and
> put
> > it where it belonged and the car stopped normally. So yes the master
> > cylinder should be sealed to the booster.
> > --
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
_______________________________________________
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| Re: [GMCnet] Brake Booster Peculiarities [message #179151 is a reply to message #179120] |
Sun, 05 August 2012 23:20 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
Surely there's a better source than this:
http://shop.docrebuild.com/1963corvettepbfrontshellsealoriginalgm5460935.aspx
Then there's this from www.v8buick.com:
-------------------------------------
The part number your looking for is #5452549.......
in 5/77 changed to a #5460935......
in 2/85 changed to a #18005270.......
discontinued 10/94..............
-------------------------------------
Ken H.
On Sun, Aug 5, 2012 at 8:48 PM, Kosier wrote:
> Ken,
>
> That part, #5460935, was used on a bunch of Moraine boosters back in the
> day.
> Cadillac, 69 to 75
> Buick, 67 to 74
> Olds, 70 to 72 (some)
> Chevy, 67 to 74 (most)
> Corvette, 67 only
> It is listed as a separate part or part of a rebuild kit.
> Haven't checked on availability(Sunday)
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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