Home » Public Forums » GMCnet » Combination Valve/Metering Valve leak (Any reason for it now?)
| Combination Valve/Metering Valve leak [message #262175] |
Wed, 17 September 2014 20:03  |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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I recently replaced the entire brake system on my coach. Master all the way to the wheel cylinders and everything in between.
It has been probably a month or more since that was all done. No leaks anywhere, Good brakes, etc.
Today I notice a small puddle of brake fluid under the driver front wheel. Tracing it back its coming from the metering valve of the combination valve. Not any of the lines, but the metering valve that has the black rubber cap on it. The combination valve was ALSO replaced with the correct part from a supporting vendor.
Any ideas as to why it would start leaking now? The only real difference is I have driven the coach a few times, maybe 20 miles or so. No issue with the brakes, checked the fluid afterward and no issues. It has sat where it is now since Saturday.
I was able to tighten that metering valve just a bit, not too much at all, but it still has fluid seeping from the threads.
What would you all suggest to remedy this? And thank you very much.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: Combination Valve/Metering Valve leak [message #262178 is a reply to message #262175] |
Wed, 17 September 2014 20:40  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I had same thing happen. I snugged up that front nut, and it quit leaking Been over a year now.
I thought it was top lone, but ended up being that valve nut.
Cant tell you how tight, because it could strip out. But that was my fix.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] Combination Valve/Metering Valve leak [message #262186 is a reply to message #262175] |
Wed, 17 September 2014 21:41 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Wayne,
I don't know whether it will be of any help, but this photo of the OEM
valve shows an O-ring on that end cap; perhaps yours is the same and the
O-ring's defective:
http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5317.html
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Wed, Sep 17, 2014 at 9:03 PM, Wayne Rogewski wrote:
> I recently replaced the entire brake system on my coach. Master all the
> way to the wheel cylinders and everything in between.
>
> It has been probably a month or more since that was all done. No leaks
> anywhere, Good brakes, etc.
>
> Today I notice a small puddle of brake fluid under the driver front
> wheel. Tracing it back its coming from the metering valve of the
> combination
> valve. Not any of the lines, but the metering valve that has the black
> rubber cap on it. The combination valve was ALSO replaced with the correct
> part from a supporting vendor.
>
> Any ideas as to why it would start leaking now? The only real difference
> is I have driven the coach a few times, maybe 20 miles or so. No issue
> with the brakes, checked the fluid afterward and no issues. It has sat
> where it is now since Saturday.
>
> I was able to tighten that metering valve just a bit, not too much at all,
> but it still has fluid seeping from the threads.
>
> What would you all suggest to remedy this? And thank you very much.
>
>
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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: Combination Valve/Metering Valve leak [message #262206 is a reply to message #262175] |
Thu, 18 September 2014 07:49 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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Thank you both, I will check it again this morning and see if there is any additional fluid.
Im wondering if a few wraps of teflon tape would help? or if anyone would highly recommend against it?
I can pull the valve to see if the Oring is there or pinched possibly. Just dont want to make a bigger mess.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: [GMCnet] Combination Valve/Metering Valve leak [message #262217 is a reply to message #262206] |
Thu, 18 September 2014 09:59 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Wayne,
Teflon tape is meant to be used on tapered pipe threads NOT straight machined threads. Wrapping Teflon tape around the threads on
the end of the combination valve is not a good idea at all.
As Ken noted there is an O-ring(s) that seal the combination valve; the correct way to fix it is to remove, disassemble, inspect,
and replace the defective parts.
Here's a cutaway photo of a brass combination valve so you can see where the O-rings are:
http://www.gmcmhphotos.com/photos/aa-miscellaneous-photos/p37696-combination-valve-cros.html
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Wayne Rogewski
Thank you both, I will check it again this morning and see if there is any additional fluid.
Im wondering if a few wraps of teflon tape would help? or if anyone would highly recommend against it?
I can pull the valve to see if the Oring is there or pinched possibly. Just dont want to make a bigger mess.
--
77 Royale
Mid Michigan
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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: Combination Valve/Metering Valve leak [message #262218 is a reply to message #262175] |
Thu, 18 September 2014 10:15 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Got it and glad I asked, Hope its not defective as its only got 2 months and 20 miles on it.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: [GMCnet] Combination Valve/Metering Valve leak [message #262228 is a reply to message #262218] |
Thu, 18 September 2014 11:08 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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If it is the brass valve made for an all disc system, or a combination
valve made for a Disc/Drum system, they are made off shore, and quality
control on the thread forms as well as the seats for the tubing flares can
be poorly machined. I have had a couple of them leak. When retightening
them does not stop the leak, replace them. Such is the state of the
replacement part stream today. Not good.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Thu, Sep 18, 2014 at 8:15 AM, Wayne Rogewski wrote:
> Got it and glad I asked, Hope its not defective as its only got 2 months
> and 20 miles on it.
>
>
> --
> 77 Royale
> Mid Michigan
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| Re: [GMCnet] Combination Valve/Metering Valve leak [message #262230 is a reply to message #262229] |
Thu, 18 September 2014 11:34 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Been my experience with most but not all GMC vendors that a replacement
will be coming to him with just a phone call. My experience at least.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Thu, Sep 18, 2014 at 9:31 AM, A. wrote:
> James Hupy wrote on Thu, 18 September 2014 11:08
>> If it is the brass valve made for an all disc system, or a combination
> valve made for a Disc/Drum system, they are made off shore, and quality
>> control on the thread forms as well as the seats for the tubing flares
> can be poorly machined. I have had a couple of them leak. When retightening
>> them does not stop the leak, replace them. Such is the state of the
> replacement part stream today. Not good.
>> Jim Hupy
>> Salem, OR
>> 78 GMC Royale 403
> He bought it from one a GMC vendor. I am sure if he calls the vendor, he
> can exchange it for a replacement and might not even have to pay shipping.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> Perpetually annoyed that "political correctness" and Secular Humanism
> control every aspect of American life
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| Re: Combination Valve/Metering Valve leak [message #262232 is a reply to message #262175] |
Thu, 18 September 2014 12:27 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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I checked it out and I think it has stopped. I have a paper towel on it now, and will check in an hour or so to see if there are any drops.
Im dreading unhooking all the lines and re bleeding everything if its a bad valve.
Just scratching my head as to why it would start leaking now, and not when I put it on, or after the first couple of test runs.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: Combination Valve/Metering Valve leak [message #262710 is a reply to message #262175] |
Wed, 24 September 2014 07:47 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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Just an update, I unscrewed the metering valve, Inspected everything and it looked fine, no debris, tears or markings of any kind on the rubber parts.
Wiped it off, put it back in and snugged it down. This appears to have resolved the issue. There is no more mass fluid dripping out of it.
Thanks for the information as usual. Hopefully this may help someone down the road before the pull the whole thing off.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: Combination Valve/Metering Valve leak [message #262944 is a reply to message #262710] |
Sun, 28 September 2014 16:15 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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Senior Member |
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I just finished trying to bleed my brakes after going through everything and replacing the combo valve in the process. We couldn't get the backs to clear of air and when we moved to the front we found fluid dribling off the new valve. Closer inspection revealed it's coming out of the threads around the front cap, not from any line fitting. Will be calling the vendor in the AM for a resolution. Disappointing 
1978 Eleganza II
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