[GMCnet] Problem with brass body proportioning valve

[Matt Colie]

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
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[John R. Lebetski]

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

[Matt Colie]

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

[John R. Lebetski]

It’s under instructiin sheets and then miscellaneous .

--
John Lebetski
Woodstock, IL
77 Eleganza II

[Burl Vibert]

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

[John R. Lebetski]

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

--
John Lebetski
Woodstock, IL
77 Eleganza II

[Shawn Harris]

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

[Eelko Byker]

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

[mtb...@gmail.com]

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

[Thomas Pryor]

Well yet again Dave Lenxi hits a home run with his issue 154 (article) To
further support his findings if you look up the distribution valve in the
parts book it calls out ; "VALVE ASSY-metering balance and distribution
switch (SOA)(repl1236005)" It DOES NOT describe any rear brake pressure
limiting feature. DO NOT use the word PROPORTIONING when describing the
GMC MH distribution or combination valve. It is not supposed to limit
pressure in any way to the rear brake channel. The real problem that
should concern us all is, the available replacements for the GMC METERING
BALANCE AND DISTRIBUTION SWITCH valve assy are generically called PV2 or
PV4. These all have pressure limiting features to the rear wheels.
Without a direct replacement of the Cast iron Metering balance /
distribution valve we can follow the alteration/modification instructions
shown in:
https://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf


Again Dave uncovers a well hidden piece of knowledge, a tool that is
supposed to be employed when bleeding the brakes. You are supposed to
remove the electrical switch from the valve body and insert a tool in its
place. The tool then restricts the shuttle effect that actuates the switch
for the dash brake light. Holding that "shuttle" allows for more effective
rear brake Bleed. See pages 5-14 and 5-15 of the maintenance manual shows
the use of the J-23709 tool. That piece of information has been in our
Archives for 50yrs, who knew? That tool continues to be used on today's
available combination/proportioning valve. SEE:
https://techtalk.mpbrakes.com/proportioning-valve-bleeding-tool

The end result of this discussion is:
1. If you have a Cast iron distribution valve,......... care for it by
Flushing your brake system now and often. Moisture kills the Cast iron
sealing surfaces.

2. If you have a brass distribution(combination) valve fitted on your
coach,.... it is not as original equipment functionality and reduces rear
brake pressures significantly. In other applications the PV-2/PV4 valves
are appropriately modified as shown here:
https://www.classicperform.com/Instructions/PDF/Prop_Valve_Mod_Instructions.pdf
If you want cost effective braking improvement, just do it!

3 For those who have had issues with Brake bleeding get the bleeding tool

I am sure that many will comment that I have used Brass valves for the last
twenty years and have had good brakes and have been able to bleed them. "I
have always had good brakes." MY REPLY MUST NOW BE AS COMPARED TO
WHAT........SHOW ME THE DATA!


--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

1977 23'B named "CASPER", HARDLY ORIGINAL, (455 EFI) (Pwr. Drive)
(tailgate) (rear bunk beds)
(Webasto petrol boiler) (MB Elect fan clutch) (Brake reaction arms) BUT
STILL A WORK IN PROGRESS!

ReplyForward

[Greg Crawford]

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

[tomk...@comcast.net]

Great thread!

I just removed the piston from my new combination valve while mounted. All went very well with the exception that the shuttle came out with the
piston. It actually made it easier to remove the piston while out I simply removed the piston and pushed the shuttle back in the combination valve. I
hope this didn't damage the switch? If no damage, all went extremely well.
--
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D.

[tomk...@comcast.net]

I have the original combination valve, 8,000 mile and stored indoor for over 25 years. Should I use the old valve or the new corrected valve?

Thanks,
Tom K.

--
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D.

[Larry]

Greg C. wrote on Sat, 10 July 2021 19:05

> 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/

A definite maybe....Personally, I would not trust that it is correct until I took it apart and made sure that rear assembly was NOT pressure limiting.
Read SLIDE #7 of Dave Lenzi's "Brass Proportioning Valves" article in the Winter 2021 issue 154 on P.28 of GMC Vintage RVing. Or see the 154 issue at
this link. https://www.gmcmi.com/gmc-vintage-rving-2/

--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Matt Colie]

Tom Katzenberger wrote on Sat, 10 July 2021 20:40

> I have the original combination valve, 8,000 mile and stored indoor for over 25 years. Should I use the old valve or the new corrected valve?
>
> Thanks,
> Tom K.

Tom,

I can't think of a good reason to replace the existing and functioning part. The reason I did was that one of the supply lines from the master
cylinder did not re-seat right the second time I had to have the front frame out.

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

[tomk...@comcast.net]

Thanks Matt,

I saved the old one. I will keep it in a zip lock bag. If I have and issue with the new one I will promptly switch it back. I very much appreciate
your and everyone's advice, tips and tricks.

Take care,

Tom K.
--
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D.

[John R. Lebetski]

The GM unit sold by Highway Stars is the best current solution today. Mr.Stone has been using this part number for over a decade ‘as is’ with
proportioning and zero failures. The MBM PV2 have had what I would very kindly call a high fail rate. At times the 2nd replacement still either
leaking or not passing pressure. Bob can elaborate on this. The end user can modify the GM brass valve per the CPP link and defeat the proportioning
so valve retains hold off, safety shuttle and light switch. Again, this is to be done by end user in a simple pre install procedure. Stock, the GM
brass unit when above threshold, reduces rear pressure as a PROPORTION of front pressure as drum brakes are self energizing and in most cases
untethered this leads to rear drum lockup before front disc lockup. Remember that Cinnabar installs MBM PV2s with proportioning as common practice.
The MBM PV2 has visually smaller fluid ports which may add milliseconds to wheel cyl fill time by acting as a fluid orifice. Scientific testing needs
to be done to time this. Bob has done pressure gauge testing on GM valve stock and with CPP mod completed and confirmed the modification does
eliminate proportioning.
The MBM PV2 is so prevalent because there is really no competition in the aftermarket. GM does not license reproduction brake parts due to liability.
So having a company build the OE TZE valve but in brass would have no endorsement possible by GM. The best bet I see is to do the CPP mod on the GM
old stock brass valve.
I would not trust an OE steel valve shuttle to function in a one sided fluid loss scenario. GM vehicles had steel combination valves from factory into
the 80s. However by 1990 GMSPO had replaced the steel with brass. I believe there were TSBs or recalls due to steel corrosion when DOT 3 became wet
saturated.

--
John Lebetski
Woodstock, IL
77 Eleganza II

[Greg Crawford]

John, thanks for addressing my question. Just so I am clear, in reading your reply it looks like my combination valve does have a proportioning
component, but it provides the pressure applied to the rear brakes as a predetermined fraction of pressure applied to the front discs, in order to
prevent premature rear wheel lock up.

Do I have this right?

If this is the case, it doesn't sound like the proportioning component is a bad thing.

Or am I wrong? Do I need to disassemble and modify mine?

After replacing every component in my brake system, changing to 80mm front calipers and 1-1/16" mid axle wheel cylinders, and bleeding with a Hupy
style pressure bleeder, I am still not impressed with braking performance

Thank you.

--
Greg Crawford
KM4ZCR
Knoxville, TN

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

[Bill Van Vlack]

Greg C. wrote on Sun, 11 July 2021 19:29

> John, thanks for addressing my question. Just so I am clear, in reading your reply it looks like my combination valve does have a proportioning
> component, but it provides the pressure applied to the rear brakes as a predetermined fraction of pressure applied to the front discs, in order to
> prevent premature rear wheel lock up.
>
> Do I have this right?
>
> If this is the case, it doesn't sound like the proportioning component is a bad thing.
>
> Or am I wrong? Do I need to disassemble and modify mine?
>
> After replacing every component in my brake system, changing to 80mm front calipers and 1-1/16" mid axle wheel cylinders, and bleeding with a Hupy
> style pressure bleeder, I am still not impressed with braking performance
>
> Thank you.

The way I see it, the GM Engineers decided that they wanted full pressure to the rear brakes for some reason; perhaps because unlike passenger cars
and pickup trucks, there is close to half of the weight of the vehicle over the rear wheels. It makes sense to me to have a combination valve that
does not have a proportioning section that limits pressure to the rear brakes.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

[James Hupy]

The disc brakes require more hydraulic pressure to operate than the drum
brakes do. That is why the engineers limited the pressure to the drum
brakes. When you have all discs on a coach, there needs to be the same
amount of pressure to front and rear, and no delay to the front brakes like
there is with a combination disc/drum system. Not too complex, really.
Jim Hupy
Salem, Oregon

On Sun, Jul 11, 2021, 9:24 PM Bill Van Vlack <bill.va...@gmail.com>
wrote:

[Bill Van Vlack]

James Hupy wrote on Sun, 11 July 2021 23:33

> The disc brakes require more hydraulic pressure to operate than the drum
> brakes do. That is why the engineers limited the pressure to the drum
> brakes. When you have all discs on a coach, there needs to be the same
> amount of pressure to front and rear, and no delay to the front brakes like
> there is with a combination disc/drum system. Not too complex, really.
> Jim Hupy
> Salem, Oregon

That makes sense, but it gets more complex when trying to understand why the GMC Motorhome engineers did not do it that way. If I understand Dave
Lenzi's article correctly, the GMCMH disk/drum coach came with a steel combination valve that provided the same amount of pressure to the front and
rear brakes (after the front brake delay).

[James Hupy]

Because they could not "just pick some part off of another GM brand" to do
that exact job, they went with what was available at the time. Just my best
guess, anyway.
They engineered some weird stuff in the 70's. Ask me about Converted
gasoline engines to diesel, set crosswise on top of the transaxle in the
front end of Olds "C" bodies. You had to remove the motor mount fasteners
to get at the glow plugs and injectors. WHAT A PITA that was.
Jim Hupy
Salem, Oregon

On Mon, Jul 12, 2021, 8:34 AM Bill Van Vlack <bill.va...@gmail.com>
wrote:

[Wally Anderson]

Matt Colie wrote on Fri, 09 July 2021 07:59

> 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

Rather than taking the valve out and apart to inspect what is really inside it you can test brake pressure at a bleeder port on the front and rear and
see if they are substantially equal.
--
Wally Anderson
Omaha NE
75 Glenbrook
Megasquirt III injection
Bob Stone hydroBOOOOST
Manny reaction arm system
Branscombe Kelsey Hayes park brake
http://wallyandsue.blogspot.com/

[Mark Sawyer]

There's a company in detroit that offers both a disc/drum and disc/disc replacement valve...

I don't know much about it other than seeing it on their site.... Few years ago I bought their dual power steering pulley and it was nicely built,
fwtw.....

Disc/disc:

https://www.inlinetube.com/products/pr101

Disc/drum:

https://www.inlinetube.com/products/pr100
--
Mark S. '73 Painted Desert,
Manny 1 Ton Front End,
Howell Injection,
Leigh Harrison 4bag and Rear Brakes,
Fort Worth, TX

[Bill Van Vlack]

TR 1 wrote on Mon, 12 July 2021 12:44

> There's a company in detroit that offers both a disc/drum and disc/disc replacement valve...
>
> I don't know much about it other than seeing it on their site.... Few years ago I bought their dual power steering pulley and it was nicely
> built, fwtw.....
>
> Disc/disc:
>
> https://www.inlinetube.com/products/pr101
>
> Disc/drum:
>
> https://www.inlinetube.com/products/pr100

Since they call them 'Proportioning Valves', I'd guess they have a proportioning function which we don't want. Also, Dave Lenzi tested several brass
valves and all of them had a proportioning function. John L. says the 'HighwayStars' valve is superior to all other brass valves, so if I wanted a new
brass valve that duplicated the function of the OEM steel combination valve, I'd buy one of those and disable the proportioning function per the CPP
datasheet.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

[Mark Sawyer]

Bill Van Vlack wrote on Mon, 12 July 2021 13:31

> Since they call them 'Proportioning Valves', I'd guess they have a proportioning function which we don't want. Also, Dave Lenzi tested several
> brass valves and all of them had a proportioning function. John L. says the 'HighwayStars' valve is superior to all other brass valves, so if I
> wanted a new brass valve that duplicated the function of the OEM steel combination valve, I'd buy one of those and disable the proportioning
> function per the CPP datasheet.

Again, I'm not running one of these valves, nor do I know anything about them... However, they have an online chat feature on the Inlinetube website,
and I initaited a chat with someone at the company, and they confirmed the disc/disc" proportioning valve is a 50/50 split front to rear...

The valve is also made in the USA, if that matters to you. So this may be an alternative to buying a valve and modifying it... But again, I don't
have or run one... Just throwing this out there as an option someone might like to consider...

--
Mark S. '73 Painted Desert,
Manny 1 Ton Front End,
Howell Injection,
Leigh Harrison 4bag and Rear Brakes,
Fort Worth, TX

[Greg Crawford]

Since my coach had terrible brakes when I bought it, I can only compare its current braking capability with what it was like at purchase.

I absolutely believe what Mr. Lenzi has to say about it. I have no reservations about his qualifications after speaking with him and purchasing a
front hub assembly from him.

That being said, does anyone on the forum have the experience of driving a coach with an aftermarket proportioning valve installed, then modifying it,
to provide a before and after comparison?

Or an experienced coach owner who has driven another coach with the unmodified valve?

--
Greg Crawford
KM4ZCR
Knoxville, TN

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

[John R. Lebetski]

Greg, consensus is that there was no proportioning from the factory. At this point in time the best bet is to do the simple mod on the GM brass valve
to have it basically same as factory but in brass. As reported here and in the article and on the instruction sheet .pdf it’s s simple mod.
Here is a simple analogy to the self energizing effect of drum brakes, and why proportioning is almost always needed with disc/drum (but not on TZE
due to weight, length, heavy Onan, propane, water weight aft of rear ‘axle’ ) Imagine walking down a gravel road and holding a shovel handle at
your side allowing the shovel to drag behind you at 45 deg. . It creates very little friction. Now do the same but have the shovel at 45 deg in front
of you. Yes it digs in much like the forward shoe is pulled against the rotating drum on drum brakes. This is actually a free benefit that discs do
not have.

--
John Lebetski
Woodstock, IL
77 Eleganza II

[Greg Crawford]

Good enough.

I guess I will put this on my to do list, which keeps getting longer. Right now, the remains of my factory dash are in the trash can and I am
fabricating a complete new dash, driver to passenger, along with redesigning the A/C ducting and converting to a Jeep A/C control panel.


Thank you for the quick reply.

--
Greg Crawford
KM4ZCR
Knoxville, TN

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

[Matt Colie]

wally wrote on Mon, 12 July 2021 12:55

> Rather than taking the valve out and apart to inspect what is really inside it you can test brake pressure at a bleeder port on the front and rear
> and see if they are substantially equal.

Wally,

The idea has merit, but I know from the brake tests that I had to do in the 4th of July traffic that my brakes are not as good as they were before I
changed that valve out.

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

[Bill Van Vlack]

TR 1 wrote on Mon, 12 July 2021 14:34

> Again, I'm not running one of these valves, nor do I know anything about them... However, they have an online chat feature on the Inlinetube
> website, and I initaited a chat with someone at the company, and they confirmed the disc/disc" proportioning valve is a 50/50 split front to
> rear...
>
> The valve is also made in the USA, if that matters to you. So this may be an alternative to buying a valve and modifying it... But again, I
> don't have or run one... Just throwing this out there as an option someone might like to consider...

Here is my chat with Inlinetube yesterday - the PR101 is their 4 wheel disc brake valve ....
Quote:
> Does your PR101 Proportion Valve have a proportioning section?
> Jul 12 1:38 PM
>
> Yes it provides a small amount of proportioning.
> Michael C · Jul 12 1:41 PM · Appreciate
>
> What does it proportion? (Meaning that the common definition of a proportioning valve is that it sends less pressure to the rear brakes than
> to the front brakes.)
> Jul 12 1:42 PM
>
> Yes, there is a slight bias between the front and the rear.
> Michael C · 6:20 AM ·

While I don't understand what '50/50 split front to rear' means (volume?, pressure?), I'm pretty sure that they said that their PR101 reduces pressure
to the rear brakes - for what it's worth.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

[John R. Lebetski]

Greg the best bet is to do the simple mod to the genuine GM brass part. To answer your question, proportioning does not begin until a certain pressure
is reached, then it is a percentage reduction to counteract the self energizing forward shoe characteristics. But per Dave’s article it was not
utilized in the steel assembly line part. GM service parts switched to brass because they knew about the rust issues. But by then GM no longer
supported TZE as all that had already been bought out by Cinnabar. Personally knowing of the corrosion issues, I would only want brass and made in USA

--
John Lebetski
Woodstock, IL
77 Eleganza II

[tomk...@comcast.net]

Tom,

I purchased the valve from Jim K. and completed the modification. Is this valve and modification not acceptable? I have an original steel valve with
8,000 mile, but it has been in storage for 40 years. Is the steel valve worthy. I have converted to 6 wheel disc system which is sold by Jim at
Applied. I am simply trying to make a safer brake system.

Thanks,

Tom K.
--
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D.

[Matt Colie]

Tom Katzenberger wrote on Thu, 29 July 2021 21:53

> Tom,
>
> I purchased the valve from Jim K. and completed the modification. Is this valve and modification not acceptable? I have an original steel valve
> with 8,000 mile, but it has been in storage for 40 years. Is the steel valve worthy. I have converted to 6 wheel disc system which is sold by Jim at
> Applied. I am simply trying to make a safer brake system.
>
> Thanks,
> Tom K.

Tom,

Look at the bottom of the brass valve. If it is a PV2, you don't want it. If it is a PV4 it might work with all wheel disk. You really want the
PVMH.

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

[Larry]

I changed my Combination/Proportioning valve back in 2005 when I did the whole braking system. At that time that "valve" was the old steel one and was
quite rusty, so got one from, IIRC, Applied GMC. It was Brass, so I felt I had to check it for the proportioning rubber plug. I did it while installed
on the coach. First thing I did was make sure the master cylinder was full and then put the proportioning valve bleed tool for holding to the
differential spool valve in place. Then remove the brake line going to the rear wheels, and capped the line off with a inverted flare cap. With fluid
trickling out of the combination valve, using a mirror and a flashlight, looked up the valve for the rubber plug and spring. NOT THERE!! So I put it
back together and bled the line. Apparently some of the brass ones sold back in the early 2000's did not have that proportioning spring and plug in
them. So it is possible that some of you may have the correct brass "combination valve". IMO it is best to check it anyway.

--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Bill Van Vlack]

Jp Benson wrote on Sat, 31 July 2021 21:19
> Should I check mine that was purchased from a vendor several years ago? I'm not inclined to open up the hydraulic brake lines.
>
> JP

I did and it did; I don't think anyone's found a brass valve on the market that didn't have the proportioning section. I'm hoping Tom Pryor's efforts
change that. I put the steel valve back in.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

[Matt Colie]

Larry wrote on Sun, 01 August 2021 14:03

> I changed my Combination/Proportioning valve back in 2005 when I did the whole braking system. At that time that "valve" was the old steel one and
> was quite rusty, so got one from, IIRC, Applied GMC. It was Brass, so I felt I had to check it for the proportioning rubber plug. I did it while
> installed on the coach. First thing I did was make sure the master cylinder was full and then put the proportioning valve bleed tool for holding to
> the differential spool valve in place. Then remove the brake line going to the rear wheels, and capped the line off with a inverted flare cap. With
> fluid trickling out of the combination valve, using a mirror and a flashlight, looked up the valve for the rubber plug and spring. NOT THERE!! So I
> put it back together and bled the line. Apparently some of the brass ones sold back in the early 2000's did not have that proportioning spring and
> plug in them. So it is possible that some of you may have the correct brass "combination valve". IMO it is best to check it anyway.

Tom Pryor found out that the design for the PVMH has existed a long time and they believe some were made. You may have gotten one.

Look underneath and see if it is stamped PVMH or PV2/4.

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

[Larry]

Matt Colie wrote on Sun, 01 August 2021 14:37

> Larry wrote on Sun, 01 August 2021 14:03
> > I changed my Combination/Proportioning valve back in 2005 when I did the whole braking system. At that time that "valve" was the old steel one
> > and was quite rusty, so got one from, IIRC, Applied GMC. It was Brass, so I felt I had to check it for the proportioning rubber plug. I did it
> > while installed on the coach. First thing I did was make sure the master cylinder was full and then put the proportioning valve bleed tool for
> > holding to the differential spool valve in place. Then remove the brake line going to the rear wheels, and capped the line off with a inverted
> > flare cap. With fluid trickling out of the combination valve, using a mirror and a flashlight, looked up the valve for the rubber plug and spring.
> > NOT THERE!! So I put it back together and bled the line. Apparently some of the brass ones sold back in the early 2000's did not have that
> > proportioning spring and plug in them. So it is possible that some of you may have the correct brass "combination valve". IMO it is best to check
> > it anyway.
>
> Tom Pryor found out that the design for the PVMH has existed a long time and they believe some were made. You may have gotten one.
>
> Look underneath and see if it is stamped PVMH or PV2/4.
>
> Matt

Awwww Geese...do I have to? :( Maybe next time I have the front end up and the drivers side wheel and wheel well off.....

I was actually surprised that it the plug and spring were not there. I was under the impression from all of the talk about it, that ALL brass combo
valves had it....but...noooooo!!

--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Burl Vibert]

I just stuck my phone in and took a photo of the underside of the valve, looks like I have a shiny new PV2 courtesy of the previous owner's brother.
He did tell me he never got the rear brakes bled right either.
With the wheel and well liner out it doesn't look horrible to work on in place, I might try that first and see if there is indeed a rubber piston in
it, as I suspect there is.
--
Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model but we call her Roxie

[Thomas Pryor]

Be Advised that Applied is receiving a MOQ (minimum order quantity) of the tested and confirmed combination brake BRASS replacement valve for our
fleet!

Look for this image in the Brake section of the Applied website, http://www.gmcmhphotos.com/photos/combination-valves/p68350-appled-pvmh.html

With the availability of these tested valves there should be no need to modify or take responsibility for modifying a PV2 Valve. Just Say'n.

[Larry]

Before you go and replace the BRASS proportioning valve, check the one you have first. I got mine back in 2005 from one of the vendors, and not
knowing if it was correct or not, I pulled the line going to the rear brakes off and using a mirror, looked inside ready to pull the proportioning
portion out only to find that my brass valve did not have the proportioning portion in it. Check first. JWID

--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Burl Vibert]

Thomas Pryor wrote on Fri, 17 September 2021 12:38

> Be Advised that Applied is receiving a MOQ (minimum order quantity) of the tested and confirmed combination brake BRASS replacement valve for our
> fleet!
>
> Look for this image in the Brake section of the Applied website,
> http://www.gmcmhphotos.com/photos/combination-valves/p68350-appled-pvmh.html
>
> With the availability of these tested valves there should be no need to modify or take responsibility for modifying a PV2 Valve. Just Say'n.

I'm looking at the Applied GMC site and can only find the old valves, not the PVMH??
Gotta put in an order soon.

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

[Russell Keith]

So, is this the wrong combination valve?, Which I installed a few years ago. I see the PV2 / 12M86 part number. If I do the modification, am I more
likely to flat-spot the rears before the fronts lock up? The brakes "appear" to be fine now, but perhaps I don't know any better. :roll:

http://www.gmcmhphotos.com/photos/data/7010/medium/Combination_Valve2.jpg


--
Russell Keith,
1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
Onan, Dunedin, Florida

[Emery Stora via Gmclist]

That looks like the valve that I put on years back. I checked mine out some time back and it didn’t need a modification.
I don’t think that you could lock up the fronts before the rears if you had the modification or not.
If I were you I would not do anything to it. If your brakes are working now I would not mess with the valve.

By the way it really isn’t a proportioning valve. It should be properly called a combination valve. It puts a small amount of pressure on the front brakes before it puts the full pressure to both the front and read. It does not proportion any pressure to either the front or rears.
It also has a shuttle inside it which will turn on a light on the dash telling you if there is no pressure on either the front or rear. This is to tell you that you might have a leak in the system or low fluid on the front or rear.

Emery Stora
emery...@mac.com

[Ken Henderson]

Emory,

Either your age is showing, or mine's about to!: IIRC, the combination
valve PREVENTS pressure from reaching the front brakes until the rears
receive about 135 psi. The purpose being to take up the free play in the
rear drums before the fronts engage. After reaching that point, the front
and rear brakes soon receive the same pressure. With all disc brakes, that
delay function is not required and should not be in the "proportioning"
valve -- which really keeps only the distribution and system monitor
functions. This may help some to understand how it works:
http://www.gmcmhphotos.com/photos/g3510-deciphering-the-combination-valve.html

Ken H.

[Jim Kanomata]

The shipment from China that Tom P. has tested should arrive this week and
will be available and will have an Identifying mark.
I am as leary as anyone on a product made there, but who else will do few
hundred at affordable price?
I will soon find out.

On Mon, Oct 11, 2021 at 1:56 PM Ken Henderson <hend...@bellsouth.net>
wrote:

--
Jim Kanomata ASE
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502

[Thomas Pryor]

I placed an image of a Combination Valve on the Photo site that shows the
three segments of the Combination valve.
http://www.gmcmhphotos.com/photos/combination-valves/p68350-appled-pvmh.html

THE CENTER section is a SWITCH that shuttles between front and rear brake
channels. If pressure is different in either channel the switch goes to
"on" and the Safety dash light is illuminated.
All cast iron TZE coach combination valves had this feature.


THE FRONT section is a Hold Off section (called metering) valve to delay
the engagement with the front brake channel. All cast iron TZE coach
combination valves had this feature.


THE REAR section of our cast iron TZE coach combination valve had NO
FUNCTION other than a place to thread together the rear brake line
channel. "Brake design intent" for our TZE coaches was focused on all the
rear wheels receiving all the pressure that could be produced by the
vacuum assisted master cylinder.



THE REST OF THE STORY:

AFTER THE END OF TZE PRODUCTION;
All cast iron combination valves were replaced with brass combination
valves that were designed for 4 wheel pass cars/light trucks with disc/drum
designs. Those designs added a 3rd function...........limit the pressure
to the rear brake channel. WHY? Much lighter passenger and light truck
vehicles could and did suffer from rear wheel lockup, skidding and loss of
control. Brake designs of that period required not only improved stopping
distances but also improved stop control. That is the fundamental reason
for rear pressure limiting combination valves. That also meant that no
brass valve could NOT achieve the exact and necessary requirements for our
coaches. REPLACEMENT VALVES available to the Tribe were limited to the PV2
version that limits the pressure to the rear wheels, but it plumbs right in!

In my previous life as a QC guy working at Kelsey Hayes and after the
transition from Cast iron to Brass Valves, I was able to find the technical
drawing of a brass valve that had no rear pressure limiting feature. I
found that drawing in China and also discovered it was never produced,
probably because of low demand!

If you have the OE standard TZE brake configuration on your coach use the
valve that Applied GMC offers. The PVMH is the only commercially available
brass brake combination valve that replaces the Cast Iron valve in form and
function. Jim has not yet posted the images and pricing on
his site. Patience!

--
Regards,

Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186

1977 23'B named "CASPER", HARDLY ORIGINAL, (455 EFI) (Pwr. Drive)
(tailgate) (rear bunk beds)
(Webasto petrol boiler) (MB Elect fan clutch) (Brake reaction arms) BUT
STILL A WORK IN PROGRESS!

ReplyForward

[Eelko Byker]

Dave Lensy in the aetical in vintage rv magazine showes 2 ways to modify the pv2 valve I removed the rear screw in part in place on the coach I
thought that it was easy to remove the small diameter extention as as I had it in my hand I left the rubber valve in place as you read in my earler
post I had great brakes however what I found out the hard way there was considerable pressure being held in the rear brakes In the next 12 hours of
use this summer I burned off all 4 rear brakes I have since replaced the rear shoes and springs there was enough pressure in the rear brakes that when
I lossened a brake line there was a big spurt of fluid way more than anyone would expect I have now removed th rubber valve as well All seems well on
the last trip Now on the recomenddation ov a local brake rebuild shop I had a 10 psi line pressure valve in my rear brake line [ sinse removed] I was
told that rear line pressure valve was part of the function of the combination valve but I do not see anything in the vlave or in the vareous
descriptions of a line pressure fuction [ old 4 wheel drum master cylinders had that fuction in the master cyl] where is that line pressure vlave now
or do we not need it and why not thanks Eelko Byker Port Colborne Ont Canada

[Burl Vibert]

I see that the valves are on the Applied GMC site, I just ordered one along with some other bits.
Thanks Jim




jimk wrote on Mon, 11 October 2021 20:17

> The shipment from China that Tom P. has tested should arrive this week and
> will be available and will have an Identifying mark.
> I am as leary as anyone on a product made there, but who else will do few
> hundred at affordable price?
> I will soon find out.
>
>
>

> --
> Jim Kanomata ASE
> Applied/GMC, Newark,CA
> ji...@appliedairfilters.com
> http://www.gmcrvparts.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:

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

[Jim Kanomata]

For those that want the correct one, we have 250each in stock.