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| Brake Mystery [message #132716] |
Thu, 30 June 2011 02:10  |
bhayes
Messages: 263
Registered: March 2010
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I have a bit of a mystery on my hands. Last summer after I purchased my coach, I noticed that the brakes were a little spongy. I had them power bled, and they worked great for about a month until they started getting slightly spongy again. That was September.
I parked it for the winter and started up the engine and generator once or twice a month. But now, the brake pedal travels all the way to the floor, and there's very little braking power. The master cylinder still has brake fluid in it.
The brakes were rebuilt by the PO, and has newer stainless steel brake lines, proportion valve, master cylinder, 80mm front calipers, new wheel cylinders on the rears, and a vacuum pump.
So what would cause the brakes to do this, even though it wasn't driven during the winter?
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
[Updated on: Thu, 30 June 2011 02:10] Report message to a moderator |
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| Re: [GMCnet] Brake Mystery [message #132717 is a reply to message #132716] |
Thu, 30 June 2011 04:02  |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Probably internal lekage in the MC.
Emery Stora
On Jun 30, 2011, at 1:10 AM, Bryan Hayes <hayesnet1@gmail.com> wrote:
>
>
> I have a bit of a mystery on my hands. Last summer after I
> purchased my coach, I noticed that the brakes were a little spongy.
> I had them power bled, and they worked great for about a month until
> they started getting slightly spongy again. That was September.
>
> I parked it for the winter and started up the engine and generator
> once or twice a month. But now, the brake pedal travels all the way
> to the floor, and there's very little braking power. The master
> cylinder still has brake fluid in it.
>
> The brakes were rebuilt by the PO, and has newer stainless steel
> brake lines, proportion valve, master cylinder, 80mm front calipers,
> new wheel cylinders on the rears, and a vacuum pump.
>
> So what would cause the brakes to do this, even though it wasn't
> driven during the winter?
>
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
> --
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Brake Mystery [message #132724 is a reply to message #132717] |
Thu, 30 June 2011 06:04 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Bryan, you in all likelyhood have a failed primary piston in the Master
Cylinder. The most effective cure is to replace with a known quality
replacement master cylinder. Be sure to follow the bench bleeding
proceedures before installing it, and power bleed the entire system. Brakes
are nothing to do half way. Lives depend on them working correctly.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Thu, Jun 30, 2011 at 2:02 AM, Emery Stora <emerystora@mac.com> wrote:
> Probably internal lekage in the MC.
>
>
>
> Emery Stora
>
> On Jun 30, 2011, at 1:10 AM, Bryan Hayes <hayesnet1@gmail.com> wrote:
>
> >
> >
> > I have a bit of a mystery on my hands. Last summer after I
> > purchased my coach, I noticed that the brakes were a little spongy.
> > I had them power bled, and they worked great for about a month until
> > they started getting slightly spongy again. That was September.
> >
> > I parked it for the winter and started up the engine and generator
> > once or twice a month. But now, the brake pedal travels all the way
> > to the floor, and there's very little braking power. The master
> > cylinder still has brake fluid in it.
> >
> > The brakes were rebuilt by the PO, and has newer stainless steel
> > brake lines, proportion valve, master cylinder, 80mm front calipers,
> > new wheel cylinders on the rears, and a vacuum pump.
> >
> > So what would cause the brakes to do this, even though it wasn't
> > driven during the winter?
> >
> > Bryan Hayes
> > '76 Eleganza II
> > Salt Lake City, Utah
> > --
> > Bryan Hayes
> > '76 Eleganza II
> > Salt Lake City, Utah
> > _______________________________________________
> > 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:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Brake Mystery [message #132740 is a reply to message #132716] |
Thu, 30 June 2011 08:25 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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i had done the same total rebuild of my brakes in '04 and this summer i suddenly had the same problem. replaced the MC and fixed it.
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: [GMCnet] Brake Mystery [message #132754 is a reply to message #132716] |
Thu, 30 June 2011 09:57 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Bryan,
Sitting on the other side of the world I'd guess it was your master
cylinder.
BTW you might want to re-consider starting the engine and Onan during
storage and not driving the GMC I think you'll find that it's not really a
good idea.
Anybody else want to chime in on that?
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Bryan Hayes
Sent: Thursday, 30 June 2011 5:10 PM
To: gmclist@temp.gmcnet.org
Subject: [GMCnet] Brake Mystery
I have a bit of a mystery on my hands. Last summer after I purchased my
coach, I noticed that the brakes were a little spongy. I had them power
bled, and they worked great for about a month until they started getting
slightly spongy again. That was September.
I parked it for the winter and started up the engine and generator once or
twice a month. But now, the brake pedal travels all the way to the floor,
and there's very little braking power. The master cylinder still has brake
fluid in it.
The brakes were rebuilt by the PO, and has newer stainless steel brake
lines, proportion valve, master cylinder, 80mm front calipers, new wheel
cylinders on the rears, and a vacuum pump.
So what would cause the brakes to do this, even though it wasn't driven
during the winter?
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
_______________________________________________
GMCnet mailing list
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Brake Mystery [message #132760 is a reply to message #132754] |
Thu, 30 June 2011 10:30 |
Jim Galbavy
Messages: 1443
Registered: August 2007
Karma: 7
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Senior Member |
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Rob,
I'll chime in with you. Just starting and running the engine and generator while in storage w/o driving around for about a half hour or running the generator under load for the same about of time you are wasting gas and causing moisture problems in the engine and and exhaust system 'cause you aren't getting them up to operating temperature and keeping them there. Speaking of getting rid of built up moisture. ....how often do you purge the moisture from your air tank? Just another thought....
jim galbavy
'73 x-CL // ANNIE
Lake Mary Fl
[Updated on: Thu, 30 June 2011 10:32] Report message to a moderator |
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| Re: [GMCnet] Brake Mystery [message #132763 is a reply to message #132760] |
Thu, 30 June 2011 10:38 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jim,
Exactly!
I installed a little air filter / water separator on the air tank where the
pump feeds in. It captures a fair bit of water; however, I still get some
when I open the drain valve in the tank.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Jim Galbavy
Sent: Friday, 1 July 2011 1:30 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Brake Mystery
Rob,
I'll chime in with you. Just starting and running the engine and generator
while in storage w/o driving around for about a half hour or running the
generator under load for the same about of time you are wasting gas and
causing moisture problems in the engine and and exhaust system 'cause you
aren't getting them up to operating temperature and keeping them there.
Speaking getting rid of built up moisture. ....how often do you purge the
moisture from your air tank? Just another thought....
jim galbavy
'73 x-CL // ANNIE
Lake Mary Fl
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Brake Mystery [message #132801 is a reply to message #132716] |
Thu, 30 June 2011 12:45 |
John Wright
Messages: 118
Registered: September 2008
Karma: 0
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Senior Member |
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I agree that the master cylinder is probably leaking internally. This could have been caused by improper bleeding of the master cylinder. Care must be taken to not depress the piston too far any time during the process of installing or bleeding the brakes. If bleeding the brakes with the engine running it is wise to put a piece of 2 X 4 under the brake pedal to prevent the piston from bottoming out and damaging the O-ring.
J.R. Wright
GMC GreatLaker
TZE Zone Restorations
78 Buskirk Stretch
1975 Avion (Under Reconstruction)
In Vancouver on the way home from Alaska
On Jun 30, 2011, at 3:10 AM, Bryan Hayes wrote:
>
>
> I have a bit of a mystery on my hands. Last summer after I purchased my coach, I noticed that the brakes were a little spongy. I had them power bled, and they worked great for about a month until they started getting slightly spongy again. That was September.
>
> I parked it for the winter and started up the engine and generator once or twice a month. But now, the brake pedal travels all the way to the floor, and there's very little braking power. The master cylinder still has brake fluid in it.
>
> The brakes were rebuilt by the PO, and has newer stainless steel brake lines, proportion valve, master cylinder, 80mm front calipers, new wheel cylinders on the rears, and a vacuum pump.
>
> So what would cause the brakes to do this, even though it wasn't driven during the winter?
>
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
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| Re: [GMCnet] Brake Mystery [message #132802 is a reply to message #132716] |
Thu, 30 June 2011 12:47 |
John Wright
Messages: 118
Registered: September 2008
Karma: 0
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Senior Member |
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I agree that the master cylinder is probably leaking internally. This could have been caused by improper bleeding of the master cylinder. Care must be taken to not depress the piston too far any time during the process of installing or bleeding the brakes. If bleeding the brakes with the engine running it is wise to put a piece of 2 X 4 under the brake pedal to prevent the piston from bottoming out and damaging the O-ring.
J.R. Wright
GMC GreatLaker
TZE Zone Restorations
78 Buskirk Stretch
1975 Avion (Under Reconstruction)
In Vancouver on the way home from Alaska
On Jun 30, 2011, at 3:10 AM, Bryan Hayes wrote:
>
>
> I have a bit of a mystery on my hands. Last summer after I purchased my coach, I noticed that the brakes were a little spongy. I had them power bled, and they worked great for about a month until they started getting slightly spongy again. That was September.
>
> I parked it for the winter and started up the engine and generator once or twice a month. But now, the brake pedal travels all the way to the floor, and there's very little braking power. The master cylinder still has brake fluid in it.
>
> The brakes were rebuilt by the PO, and has newer stainless steel brake lines, proportion valve, master cylinder, 80mm front calipers, new wheel cylinders on the rears, and a vacuum pump.
>
> So what would cause the brakes to do this, even though it wasn't driven during the winter?
>
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
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| Re: [GMCnet] Brake Mystery [message #132813 is a reply to message #132801] |
Thu, 30 June 2011 13:29 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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In "olden times", master cylinders, like drum brake cylinders, used
cup seals which could indeed be damaged by over compression of the MC.
I'm not sure that's a concern with modern O-ring sealed cylinders.
Here are the innards of a P-30 MC.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=4538&cat=3457
http://goo.gl/MKZNk
Hard to see how they, sliding in a smooth-walled cylinder can be
damaged. Now if it's a used MC with rough deposits or erosion of the
wall, moving the piston into an unused area could certainly damage the
O-rings.
JWIT,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Thu, Jun 30, 2011 at 1:45 PM, John Wright <powwerjon@gmail.com> wrote:
> I agree that the master cylinder is probably leaking internally. This could have been caused by improper bleeding of the master cylinder. Care must be taken to not depress the piston too far any time during the process of installing or bleeding the brakes. If bleeding the brakes with the engine running it is wise to put a piece of 2 X 4 under the brake pedal to prevent the piston from bottoming out and damaging the O-ring.
>
> J.R. Wright
> GMC GreatLaker
> TZE Zone Restorations
> 78 Buskirk Stretch
> 1975 Avion (Under Reconstruction)
> In Vancouver on the way home from Alaska
>
> On Jun 30, 2011, at 3:10 AM, Bryan Hayes wrote:
>
>>
>>
>> I have a bit of a mystery on my hands. Last summer after I purchased my coach, I noticed that the brakes were a little spongy. I had them power bled, and they worked great for about a month until they started getting slightly spongy again. That was September.
>>
>> I parked it for the winter and started up the engine and generator once or twice a month. But now, the brake pedal travels all the way to the floor, and there's very little braking power. The master cylinder still has brake fluid in it.
>>
>> The brakes were rebuilt by the PO, and has newer stainless steel brake lines, proportion valve, master cylinder, 80mm front calipers, new wheel cylinders on the rears, and a vacuum pump.
>>
>> So what would cause the brakes to do this, even though it wasn't driven during the winter?
>>
>> Bryan Hayes
>> '76 Eleganza II
>> Salt Lake City, Utah
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
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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 Mystery [message #132896 is a reply to message #132882] |
Thu, 30 June 2011 20:11 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Bryan,
While you're at it you might consider:
1) Using ATE Dot 4 brake fluid:
ATE Super Blue Racing: Dry boiling point: 536°F Wet boiling point: 388°F
http://www.tirerack.com/brakes/accessoryDetail.jsp?ID=21
ATE TYPE 200: Dry boiling point: 536°F Wet boiling point: 388°F
http://www.tirerack.com/brakes/accessoryDetail.jsp?ID=22
The blurb notes: "The formula offers a minimal drop in boiling point due to
outstanding water binding properties resulting in a long-lasting fluid that
may not need to be changed for up to 3 years under normal highway driving
conditions" and "The identical specifications of the fluid and color
difference make it easy to know when the old fluid is completely flushed out
of the system."
2) Get a pressure bleeder from Jim Hupy; I GAR-RON-TEE it will make your
life a lot simpler when it comes to bleeding / flushing the brake system!
You probably can find cheaper ones on eBay but trust me they are CRAP!
http://bdub.net/jhupy/
3) Install a sensitized booster (I'm not going to say where as I don't want
to create a problem for myself!)
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Bryan Hayes
Sent: Friday, 1 July 2011 10:18 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Brake Mystery
Thanks for the advice, everyone. I foresee a new master cylinder in my
future.
--
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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