| brake pedal to floor [message #86039] |
Tue, 25 May 2010 14:55  |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
Karma: 0
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About one month ago, Rear brake hoses were replaced and brakes were bled. At that time the shop told me the fluid drained was pretty 'nasty looking'. Now the pedal sinks to the floor and I am basically unable/unwilling to drive/stop the coach.
When I tried to press the little button on the combo valve, it did not seem to move at all (which makes me wonder how well the brakes were bled).
A few days of Googling and I now suspect the master cylinder may be at fault (I believe it is the original)..but possibly the combo valve.
I have ordered both a master cylinder and combo valve from one of our GMC suppliers. Any advice on how to determine the root cause...or do I just replace them both??
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: brake pedal to floor [message #86042 is a reply to message #86039] |
Tue, 25 May 2010 15:01  |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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If they're both original, replace them both, flush and bleed brakes, and check rear wheel cylinders for leaks!
With something this crucial, why take chances?
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: brake pedal to floor [message #86044 is a reply to message #86042] |
Tue, 25 May 2010 16:08 |
pzerkel
Messages: 212
Registered: September 2007
Location: Salisbury, IL
Karma: 0
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I should add that when the shop replaced rear hoses, they did also check the condition of the shoes and wheel cylinders and Reported no leaks. I have been monitoring the brake fluid level and it is staying up.
After 32 years replacing both the mc and the combo valve does seem prudent.
Paul Zerkel
'78 Eleganza II
Salisbury IL (near Springfield)
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| Re: brake pedal to floor [message #86053 is a reply to message #86039] |
Tue, 25 May 2010 17:22 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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what happens is that when you bleed the brakes the MC piston goes into an area that it has not been in for a long time. the seals get scraped and start to leak past. this is very common; i've experienced it too.
the combo valve pin should push out forward when you push the brake pedal (won't happen right now).
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: [GMCnet] brake pedal to floor [message #86092 is a reply to message #86088] |
Tue, 25 May 2010 21:44 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Mac,
The new combination valve is made of brass block.
we sell few every week.
On Tue, May 25, 2010 at 7:08 PM, D C *Mac* Macdonald <k2gkk@hotmail.com> wrote:
>
> Hmmmmmmmmmm!
>
> Very interesting, Rob.
>
> That may be part of my problem where my pedal was going
> virtually to the floor and the brake warning light coming
> on. Â I have bench bled and installed a new master cylinder,
> but have not progressed farther.
>
> I suspect I would save myself much grief to just buy a new
> combination valve. Â Jim K or where?
>
> I don't really understand what the special tool is that is
> used to disable the combination valve to bleed the front
> disks after the rear drums have been bled.
>
> I have "favorited" the link to the rebuild for future
> reference.
>
> Mac "only slightly less noobie than a few" Macdonald
>
> * Mac Macdonald *
> * USAF, Retired *
> * Oklahoma City *
> ** "Money Pit" **
> * '76 ex - P.B. *
>
>
>
>
> From: robmueller@iinet.net.au
> To: gmclist@temp.gmcnet.org
> Date: Wed, 26 May 2010 09:29:09 +1000
> Subject: Re: [GMCnet] brake pedal to floor
>
> Paul,
>
> I reckon it's the master cylinder.
>
> As far as the combination valve goes Ken Henderson has
> posted pictures of how to disassemble and clean it:
>
> http://www.gmcmhphotos.com/photos/showgallery.php?cat=3510
>
> If you are not interested in so I would be.
>
> I would be happy to reimburse you for the valve and the
> cost to ship it to:
>
> Rob Mueller
> c/o John Sharpe
> 19706 Caroling Oaks Court
> Houston, TX 77346
>
> Regards,
>
> Rob Mueller
> Sydney, Australia
> AUS '75 Avion-The Blue Streak TZE365V100428
> USA '75 Avion-Double Trouble TZE365V100426
>
>
>
>
> -----Original Message-----
> From: Paul Zerkel
>
> I have ordered both a master cylinder and combo valve from one of our GMC
> suppliers. Any advice on how to determine the root cause...or do I just
> replace them both??
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] brake pedal to floor [message #86098 is a reply to message #86094] |
Tue, 25 May 2010 22:58 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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You never want to run w/o a combination valve.
We carry 2 types; Disc / Disc and a Disc / Drum.
Both will tell you when there is pressure differential of the front vs rear.
Your fooling yourself if you feel it is not needed. Warning light can
tell you that half of the brakes are working.
On Tue, May 25, 2010 at 7:45 PM, Rob Mueller <robmueller@iinet.net.au> wrote:
> Mac,
>
> As I understand it the combination valve houses a "shuttle" that grounds the
> brake light circuit if there is a problem in the system. Since yours does
> that means it is working.
>
> The tool, J23709 (ref MM X-7525 page 5-14 Figure 3) is nothing but an "L"
> shaped piece of metal. The horizontal part of the "L" contacts the little
> tit on the combination valve. The vertical part of the "L" has a slot in it
> that allows you to slide it to bring the horizontal part of the "L" into
> contact with the little tit and depress it. Once the tit is depressed you
> tighten the retaining nut on the side of the combination valve to keep the
> tool in place. It would be simple to make one.
>
> Double Trouble did not have a combination valve installed as it had been
> converted to all disk brakes. When I rebuilt the system using a stainless
> steel brake line kit it needed to be re-installed. I was at the COOP so I
> and Jim B got it for me.
>
> Regards,
> Rob Mueller
> Sydney, Australia
> AUS '75 Avion-The Blue Streak TZE365V100428
> USA '75 Avion-Double Trouble TZE365V100426
>
> -----Original Message-----
> From: D C *Mac* Macdonald
>
> That may be part of my problem where my pedal was going
> virtually to the floor and the brake warning light coming
> on. Â I have bench bled and installed a new master cylinder,
> but have not progressed farther.
>
> I suspect I would save myself much grief to just buy a new
> combination valve. Â Jim K or where?
>
> I don't really understand what the special tool is that is
> used to disable the combination valve to bleed the front
> disks after the rear drums have been bled.
>
> Mac
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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