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Problem with brass body proportioning valve

MC
Matt Colie
Fri, Jul 9, 2021 12:59 PM

If you have the replacement brake differential indicator and hold-off valve (it is not supposed to be a proportioning valve) and you have not read the
wonderful and very complete article post by Dave Lenzi, you should do that today and plan to complete the suggested mod as soon as it is possible (not
just practical).

Executive Summary:
The Brass replacement parts are not correct for TZE at all.  While they do the "hold-off", they also reduce the pressure delivered to the rear brakes.
This is not something we need or want.  The modification required to correct this looks simple enough.  It can probably be completed with the valve
in place, but I won't know that for a fact for a few days.

I will read the article again (probably several times) before I do the mod and mark the valve as done.

This annoys me because somehow I did not see the two issue of VR come into the house and so never read them.  I am hoping it is just a silly mistake.

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

If you have the replacement brake differential indicator and hold-off valve (it is not supposed to be a proportioning valve) and you have not read the wonderful and very complete article post by Dave Lenzi, you should do that today and plan to complete the suggested mod as soon as it is possible (not just practical). Executive Summary: The Brass replacement parts are not correct for TZE at all. While they do the "hold-off", they also reduce the pressure delivered to the rear brakes. This is not something we need or want. The modification required to correct this looks simple enough. It can probably be completed with the valve in place, but I won't know that for a fact for a few days. I will read the article again (probably several times) before I do the mod and mark the valve as done. This annoys me because somehow I did not see the two issue of VR come into the house and so never read them. I am hoping it is just a silly mistake. Matt -- Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms SE Michigan - Near DTW - Twixt A2 and Detroit
JR
John R. Lebetski
Fri, Jul 9, 2021 2:22 PM

First, we should call it a combination valve as proper terminology. The currently off shore produced MBM Brake PV2 disc drum combination valve that
Cinnabar and others install (with proportioning!) has been found to have a very high multiple mode fail rate. They have visibly smaller fluid ports as
well. The NOS GM brass valve number was sourced by Bob Stone and has had zero known defects over more that 10 years.  The rear section rubber can
easily be removed by end user and the “proportioning” function defeated, while retaining the hold off, safety shuttle valve and light switching
(grounding) functions.  I would talk to Bob or if you go on line to CPP (classicperform.com) there is a diagram with notes on removing the ‘rubber
piston’. There is a “drought” of good options out there as GM Restoration does not license brake related parts, so no incentive to get them made
by quality shops as reproductions.  Also remember GM phased out steel valves (like our original) due to corrosion. Some 80’s GM cars were still
delivered with steel combination valves, but by say 1990 all service parts were brass.  Most GM valves are now depleted.

John Lebetski
Woodstock, IL
77 Eleganza II

First, we should call it a combination valve as proper terminology. The currently off shore produced MBM Brake PV2 disc drum combination valve that Cinnabar and others install (with proportioning!) has been found to have a very high multiple mode fail rate. They have visibly smaller fluid ports as well. The NOS GM brass valve number was sourced by Bob Stone and has had zero known defects over more that 10 years. The rear section rubber can easily be removed by end user and the “proportioning” function defeated, while retaining the hold off, safety shuttle valve and light switching (grounding) functions. I would talk to Bob or if you go on line to CPP (classicperform.com) there is a diagram with notes on removing the ‘rubber piston’. There is a “drought” of good options out there as GM Restoration does not license brake related parts, so no incentive to get them made by quality shops as reproductions. Also remember GM phased out steel valves (like our original) due to corrosion. Some 80’s GM cars were still delivered with steel combination valves, but by say 1990 all service parts were brass. Most GM valves are now depleted. -- John Lebetski Woodstock, IL 77 Eleganza II
MC
Matt Colie
Fri, Jul 9, 2021 4:07 PM

JohnL455 wrote on Fri, 09 July 2021 10:22

First, we should call it a combination valve as proper terminology. The currently off shore produced MBM Brake PV2 disc drum combination valve
that Cinnabar and others install (with proportioning!) has been found to have a very high multiple mode fail rate. They have visibly smaller fluid
ports as well. The NOS GM brass valve number was sourced by Bob Stone and has had zero known defects over more that 10 years.  The rear section
rubber can easily be removed by end user and the “proportioning” function defeated, while retaining the hold off, safety shuttle valve and light
switching (grounding) functions.  I would talk to Bob or if you go on line to CPP (classicperform.com) there is a diagram with notes on removing the
‘rubber piston’. There is a “drought” of good options out there as GM Restoration does not license brake related parts, so no incentive to
get them made by quality shops as reproductions.  Also remember GM phased out steel valves (like our original) due to corrosion. Some 80’s GM cars
were still delivered with steel combination valves, but by say 1990 all service parts were brass.  Most GM valves are now depleted.

John,

I went to the link and I found two others that were about adding proportioning valves, but did not find anything that related to out issue.  It could
well be there and I just did not open the right article.  Can you hint please?

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

JohnL455 wrote on Fri, 09 July 2021 10:22 > First, we should call it a combination valve as proper terminology. The currently off shore produced MBM Brake PV2 disc drum combination valve > that Cinnabar and others install (with proportioning!) has been found to have a very high multiple mode fail rate. They have visibly smaller fluid > ports as well. The NOS GM brass valve number was sourced by Bob Stone and has had zero known defects over more that 10 years. The rear section > rubber can easily be removed by end user and the “proportioning” function defeated, while retaining the hold off, safety shuttle valve and light > switching (grounding) functions. I would talk to Bob or if you go on line to CPP (classicperform.com) there is a diagram with notes on removing the > ‘rubber piston’. There is a “drought” of good options out there as GM Restoration does not license brake related parts, so no incentive to > get them made by quality shops as reproductions. Also remember GM phased out steel valves (like our original) due to corrosion. Some 80’s GM cars > were still delivered with steel combination valves, but by say 1990 all service parts were brass. Most GM valves are now depleted. John, I went to the link and I found two others that were about adding proportioning valves, but did not find anything that related to out issue. It could well be there and I just did not open the right article. Can you hint please? Matt -- Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms SE Michigan - Near DTW - Twixt A2 and Detroit
JR
John R. Lebetski
Fri, Jul 9, 2021 7:07 PM

It’s under instructiin sheets and then miscellaneous  .

John Lebetski
Woodstock, IL
77 Eleganza II

It’s under instructiin sheets and then miscellaneous . -- John Lebetski Woodstock, IL 77 Eleganza II
BV
Burl Vibert
Fri, Jul 9, 2021 8:00 PM

https://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf

Is it this?

Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model but we call her Roxie

https://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf Is it this? -- Burl Vibert Kingston, Ontario 1976 GMC 26 foot, Sheridan reno, don't know original model but we call her Roxie
JR
John R. Lebetski
Fri, Jul 9, 2021 10:40 PM

Yes. That’s it.  Link is good.  To big to post as a screen shot. Thanks.

John Lebetski
Woodstock, IL
77 Eleganza II

Yes. That’s it. Link is good. To big to post as a screen shot. Thanks. -- John Lebetski Woodstock, IL 77 Eleganza II
SH
Shawn Harris
Sat, Jul 10, 2021 4:35 AM

Still fighting w/ my brakes and, once again, perfect timing for this post. Literally putting in my new valve tomorrow. Did the mod. Super easy.
Fingers crossed.

Shawn

Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403

Still fighting w/ my brakes and, once again, perfect timing for this post. Literally putting in my new valve tomorrow. Did the mod. Super easy. Fingers crossed. Shawn -- Shawn Harris North Vancouver, Canada 1977 Palm Beach 403
EB
Eelko Byker
Sat, Jul 10, 2021 12:43 PM

my rear brakes will lock up if I need them to after Dave Lensi mod Ps I have hydro boost

my rear brakes will lock up if I need them to after Dave Lensi mod Ps I have hydro boost
M
mtb8114@gmail.com
Sat, Jul 10, 2021 3:01 PM

So are you having to bleed the brakes after this mod?

M Beam
75’ Avion
TBI EBL , 3.70 LSD and other stuff
Zuki Sidekick,
Dozier Al

So are you having to bleed the brakes after this mod? -- M Beam 75’ Avion TBI EBL , 3.70 LSD and other stuff Zuki Sidekick, Dozier Al
GC
Greg Crawford
Sun, Jul 11, 2021 12:05 AM

So I was told that this valve is the only genuine and correct GMC brass combination valve that is New Old Stock and was the one to use.

Was I mislead?

https://www.highwaystars.net/brake-combination-valve-genuine-gm-1257177-for-gmc-motorhome-1974-sd-455-trans-am/

Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags

So I was told that this valve is the only genuine and correct GMC brass combination valve that is New Old Stock and was the one to use. Was I mislead? https://www.highwaystars.net/brake-combination-valve-genuine-gm-1257177-for-gmc-motorhome-1974-sd-455-trans-am/ -- Greg Crawford KM4ZCR Knoxville, TN "Ruby Sue" 1977 Royale Rear Bath 403 Engine American Eagle Wheels Early Version Alex Sirum Quad bags