Problem with brass body proportioning valve

> 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).
--
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.
 
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
wrote:

> > 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).
> --
> 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.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
> 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/
 
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
 
> 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.
 
> 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
 
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
 
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
 
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
 
> 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
 
> 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.
 
Well again Thanks to Dave Lenzi, he created the need for more knowledge on
what happened with the replacement Brass combination valve for our
coaches.

In a previous life I worked for Kelsey Hayes ABS group as quality "Grunt"
Foundation brakes knowledge was available to me. So I decided to swim
upstream and found out that a brass replacement valve for our coaches WAS
DEVELOPED and put on an engineering drawing. The Code name was PVMH, who
knew!
That engineering drawing resurfaced in China and Jim Kanamota has been
provided with the manufacturer name /contact info. He is negotiating a MOQ
(Minimum Order Quantity) . I have been assured that all valves will be
function tested before shipment from the China factory.

MY FINAL THOUGHTS;
1. You can modify the PV2 valve to eliminate the pressure limiting to the
rear brakes. Your option, your risk!
2. If you have the original KH86702 Cast Iron Valve.( no rear pressure
reduction) Flush the brake fluid per the GMC maintenance manual, It may
look ugly on the outside and perform all required tasks admirably.
3. If you ever have to replace the Combination valve make sure it is a
PVMH.

If you want to follow my investigative /archival information please see:
http://www.gmcmhphotos.com/photos/combination-valves/p68277-gm-valve-autopsy.html

--
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
 
Thanks for this news, Tom. I'm so glad that there people constantly
working in the background for our safety.
Jim is to be commended for always having our backs. I hope to be one of
the first adopters in support of his business.

bdub

> Well again Thanks to Dave Lenzi, he created the need for more knowledge on
> what happened with the replacement Brass combination valve for our
> coaches.
>
> In a previous life I worked for Kelsey Hayes ABS group as quality "Grunt"
> Foundation brakes knowledge was available to me. So I decided to swim
> upstream and found out that a brass replacement valve for our coaches WAS
> DEVELOPED and put on an engineering drawing. The Code name was PVMH, who
> knew!
> That engineering drawing resurfaced in China and Jim Kanamota has been
> provided with the manufacturer name /contact info. He is negotiating a MOQ
> (Minimum Order Quantity) . I have been assured that all valves will be
> function tested before shipment from the China factory.
>
> MY FINAL THOUGHTS;
> 1. You can modify the PV2 valve to eliminate the pressure limiting to the
> rear brakes. Your option, your risk!
> 2. If you have the original KH86702 Cast Iron Valve.( no rear pressure
> reduction) Flush the brake fluid per the GMC maintenance manual, It may
> look ugly on the outside and perform all required tasks admirably.
> 3. If you ever have to replace the Combination valve make sure it is a
> PVMH.
>
> If you want to follow my investigative /archival information please see:
>
> http://www.gmcmhphotos.com/photos/combination-valves/p68277-gm-valve-autopsy.html
>
> --
> 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
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
If you have a PV2 valve and after reading Dave's article in Vintage Motorhome, you thing just gutting the back part of the valve sounds like a good
idea, sit down. Have another drink and think again. This would not be all that tough on the bench, in a vice and with the right tools and good
light...

I strongly suggest that you not consider doing it in place. All I did was pull out the rubber plug. That broke the pick tool I tried to use first.
I did have to bleed the brake system. I have not test driven the coach yet. Tests in place look real good.

When I have more data, I will broadcast it here.

The coach is back on the ground, but I have a serious amount of cleanup to do after the recent power outage.

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
 
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
 
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.
 
> 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
 
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.
 
> 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.
 
> 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
 
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