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6 discs change to 4 disc 2 drums [message #268378]

Sat, 27 December 2014 18:53

cadelec

Messages: 303
Registered: September 2011
Location: Brisbane Australia

Karma: 1

Senior Member

I am trying to get a working park brake as i need to get this done for registration.
i have swapped my rear set of cadillac discs for a set of original drums

i assume the previous owner Bobby Moore would have modified the proportioning valve when he installed his 6 wheel disc set up.

as i am now removing a set of rear discs and replacing with drums
what proportioning valve do people use when installing discs to only the 2 front rear wheels.

Trevor Brisbane Australia Siesta Koala 76 Edgemont (old Bobby Moores) 71 Cadillac Eldo Convert 58 Cadillac Eldorado Brougham Project

[Updated on: Sat, 27 December 2014 18:55]

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Re: [GMCnet] 6 discs change to 4 disc 2 drums [message #268380 is a reply to message #268378]

Sat, 27 December 2014 19:29

Emery Stora

Messages: 959
Registered: January 2011

Karma: 4

Senior Member

Don't worry about the proportioning valve. Many of us with 6 wheel disks have never changed it. It won't make a difference in getting your registration. Don't just assume that Bobbie did it either. I have had 6 when disc brakes for probably 15 or more years and no problems with the original valve

Emery Stora

> On Dec 27, 2014, at 5:53 PM, Trevor Pordage wrote:
>
> I am trying to get a working park brake as i need to get this done for registration.
> i have swapped my rear set of cadillac discs for a set of original drums
>
> i assume the previous owner Bobby Moore would have modified the proportioning valve for the new 6 wheel disc set up.
>
> what proportioning valve do people use when installing discs to only the 2 front rear wheels.
>
>
> --
> Trevor
> Brisbane Australia
> Siesta Koala 76 Edgemont (old Bobby Moores)
> 71 Cadillac Eldo Convert
> 58 Cadillac Eldorado Brougham Project
>
> _______________________________________________
> GMCnet mailing list
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Re: [GMCnet] 6 discs change to 4 disc 2 drums [message #268383 is a reply to message #268380]

Sat, 27 December 2014 19:46

Jerry Wheeler

Messages: 246
Registered: January 2013

Karma: 2

Senior Member

Like Emery, I, too, have been running 6 disks with the proportioning valve
for 14 years; haven't had any problem stopping other than boiling the
brakes on some very long and steep grades; thankfully, I was able to pump
the brake pedal to get brakes and then find a spot to sit for several hours
to let everything cool. Since gas prices are low, thinking about driving
the coach from NC to the Oregon coast and back next summer. Maybe even
have an SOOR if I don't have too much work to do on our Oregon home or my
vehicles stored there.
JR Wheeler 78 Royale NC/OR

On Sat, Dec 27, 2014 at 8:29 PM, Emery Stora wrote:

> Don't worry about the proportioning valve. Many of us with 6 wheel disks
> have never changed it. It won't make a difference in getting your
> registration. Don't just assume that Bobbie did it either. I have had 6
> when disc brakes for probably 15 or more years and no problems with the
> original valve
>
> Emery Stora
>
>> On Dec 27, 2014, at 5:53 PM, Trevor Pordage
> wrote:
>>
>> I am trying to get a working park brake as i need to get this done for
> registration.
>> i have swapped my rear set of cadillac discs for a set of original drums
>>
>> i assume the previous owner Bobby Moore would have modified the
> proportioning valve for the new 6 wheel disc set up.
>>
>> what proportioning valve do people use when installing discs to only the
> 2 front rear wheels.
>>
>>
>> --
>> Trevor
>> Brisbane Australia
>> Siesta Koala 76 Edgemont (old Bobby Moores)
>> 71 Cadillac Eldo Convert
>> 58 Cadillac Eldorado Brougham Project
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Re: [GMCnet] 6 discs change to 4 disc 2 drums [message #268390 is a reply to message #268378]

Sat, 27 December 2014 20:42

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Trevor,

When I bought Double Trouble it had 6 wheel disks like your coach and the COMBINATION valve had been removed so the master cylinder
fed all six disks at the same time as per:

http://gmcgreatlakers.org/GMCGreatLakers/Technical/CadDisk-Brakes/GMC%20Disk%20Brake%20Conver..htm

I needed to have an "emergency brake" to get it registered in New Jersey so Ken Frey replaced the rear disks with drums and he did
not install a COMBINATION valve. It stopped fine.

When I replaced all the steel brake lines with stainless steel lines I installed a brass COMBINATION valve which JimB supplied.
AFAIK it was a direct replacement for the OEM COMBINATION valve.

As of today Double Trouble has:

a) 80mm calipers with carbon metallic pads on the front wheels
b) 80mm calipers with carbon metallic pads on the middle wheels (no parking brake)
c) OEM drums on the rear wheels with carbon metallic shoes (with parking brake)
d) P-3 master cylinder (I can't remember the bore size)
e) brass COMBINATION valve
f) braided stainless steel flex lines
g) sensitized booster
h) backup vacuum assist pump

Double Trouble stops on a dime and gives 8 cents change! ;-)

I've got the set of rear disk brakes packed in a crate that will be sailing for Australia shortly to install on the middle wheels of
The Blue Streak. Those calipers have the parking brake and I bought all the parts necessary to rebuild them.

Yes I KNOW those calipers can be a PITA but I believe that if the Acme screws that adjust the pistons for the parking brake mode are
lubricated with copper anti-seize grease regularly and the parking brake is used regularly and consistently they will work just
fine.

Everybody keeps calling the COMBINATION valve a proportioning valve which it is not as I understand how a proportioning valve works
(I may be wrong). Here is what the maintenance manual says:

METERING VALVE FUNCTION (Spring and poppet on left side of Combination Valve)
The metering section of the combination valve operates to 'hold off' hydraulic flow (pressure) until about 130 psi has been built up
in the system before applying the front brakes. The pressure then blends to a full line pressure at approximately 400-600 psi line
pressure. There is no flow restriction when the brakes are released.

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426

-----Original Message-----
From: Trevor Pordage

I am trying to get a working park brake as i need to get this done for registration.
i have swapped my rear set of cadillac discs for a set of original drums

i assume the previous owner Bobby Moore would have modified the proportioning valve for the new 6 wheel disc set up.

what proportioning valve do people use when installing discs to only the 2 front rear wheels.

Trevor

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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: [GMCnet] 6 discs change to 4 disc 2 drums [message #268393 is a reply to message #268390]

Sat, 27 December 2014 21:27

cadelec

Messages: 303
Registered: September 2011
Location: Brisbane Australia

Karma: 1

Senior Member

thanks for the answers
rob i think i will have a very similar system to yours
i will leave the valve as is and then investigate further if i have problems

Trevor Brisbane Australia Siesta Koala 76 Edgemont (old Bobby Moores) 71 Cadillac Eldo Convert 58 Cadillac Eldorado Brougham Project

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Re: 6 discs change to 4 disc 2 drums [message #268406 is a reply to message #268378]

Sat, 27 December 2014 23:29

GeorgeRud

Messages: 1380
Registered: February 2007
Location: Chicago, IL

Karma: 0

Senior Member

Wildwood makes a clamp type, mechanically actuated parking brake. I wonder if it could be made to work with the all disc setup?

George Rudawsky
Chicago, IL
75 Palm Beach

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Re: 6 discs change to 4 disc 2 drums [message #268412 is a reply to message #268406]

Sun, 28 December 2014 03:01

cadelec

Messages: 303
Registered: September 2011
Location: Brisbane Australia

Karma: 1

Senior Member

i had a look at these but the rear discs i had were 1 1/4 inches thick so this was a problem.
i could have gone and bought caddilac rear calipers but that was another expense .

also i am in australia not easy to find caddy rear calipers
i swapped a set of discs for a set of drums with someone in australia so this was a no cost option .
and a win win situation

Trevor Brisbane Australia Siesta Koala 76 Edgemont (old Bobby Moores) 71 Cadillac Eldo Convert 58 Cadillac Eldorado Brougham Project

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Re: [GMCnet] 6 discs change to 4 disc 2 drums [message #268414 is a reply to message #268412]

Sun, 28 December 2014 07:18

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Trevor,

If you get documentation from the Queensland Department of Transportation and Main Roads that approves your mod please let me know.

BTW TSM sells ALL the different GM calipers; some new some rebuilt:

http://www.tsmmfg.com/calipers.html

Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426

-----Original Message-----
From: Trevor Pordage

i had a look at these but the rear discs i had were 1 1/4 inches thick so this was a problem.
i could have gone and bought caddilac rear calipers but that was another expense .

also i am in australia not easy to find caddy rear calipers
i swapped a set of discs for a set of drums with someone in australia so this was a no cost option .
and a win win situation
--
Trevor

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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: 6 discs change to 4 disc 2 drums [message #268465 is a reply to message #268378]

Mon, 29 December 2014 02:10

John Heslinga

Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada

Karma: 4

Senior Member

Re :

Quote:

Remove PROPORTIONING VALVE, off frame and splice lines
Front to Front.
Rear to Rear.

WOOOOOHHHHH!!!! STOP!!!! DO NOT DO THIS!!!!

Yes I'm Yelling!!! (Crying out really)

If any of you have this done to your coach this way you are playing with your life and the life of others and you are playing with a "Short Deck". (Highly Risky and You will Lose) Personally I cannot believe that anyone would condone, endorse, or otherwise suggest this to be done to a coach. I (Or any vehicle for that matter.) I feel this photo pretty well describes what I'm hearing.
http://www.gmcmhphotos.com/photos/discussion-photos/p56761-i-27ve-never-had-a-problem-and-it-worked-for-me.html

The Brake Valve that is being referred to here is a "Combination Valve" It does a few things and by not including it or disabling it, you are disabling the safety features inherent in this unit.

There have been a number of discussions on this forum on this valve and this is the poorest set of suggestions I've ever heard. I would certainly like to see the people suggesting this to show some engineering support for removing this valve and making this change. It is not my intent to fully describe how the system works but here are a few things to think about.

The Brake system in our coaches is a split system with two independent systems. This ensures that you have some brakes, even if a major leak in one of the systems disables it. While they are independent they are still somewhat interconnected through the master cylinder and the combination valve. (a hydraulic lock between the front and rear sections of the master cylinder actuates the rear brake system. A finger on the front system pushes the rear system if this hydraulic lock is compromised through a leak. (a low pedal will result) if the other system leaks, you will not feel a problem.

Even though the rear brakes are isolated from the front brakes the combination valve manages the two systems. While that valve does not do any proportioning, it ensures that both systems have similar final pressures and warns the driver if the system pressures are different, This Valve Highlights the problem by shining a warning light on the dash.

The valve is also designed to isolate and balance two different types of brake designs. (Disc and Drum) The valve stops, or blocks fluid flow to the front disks until the shoes of the drum brakes are in contact with the drums. (The disk pads are always ready to touch the disks) This way both brake systems will apply at the same time. Brakes that do not apply at the same time start skids and loss of control. Our drum Brakes are also "Servo action designs" which mean that they actually use wheel movement to self apply or pressure the secondary shoes into the drum. Up here in the north these issues become much more of a problem because we seem to be constantly driving on ice and snow and slippery roads. Once a wheel loses traction it takes a long time to gain that traction back. The Combination Valve helps to solve some of these problems.

Brake proportioning (or front rear brake balance is done by system design.) Shoe design, cylinder sizes, Pad design, etc. Of course if these things are changed then balance is changed.

Those that tell you they have not had a problem by not using parts of the system as they are designed: (not using the front valve when using disk / drum combinations)::

http://www.gmcmhphotos.com/photos/discussion-photos/p56762-ive-never-had-a-problem-and-it-worked-for-me.html

They will not have a problem until the road get slippery. A dry ideal road with no emergency braking, is not where you will find brake problems. A slippery, gravely, sandy, icy, snowy road is where the problems show up. (in other words the hard hat I'm showing in the picture will certainly be "No problem" until something falls on this guys head.)

John and Cathie Heslinga 1974 Canyonlands 260 455, Manny tranny and 1 ton, 3:70 LS, Red Seal Journeyman, DTE, BEd. MEd. Edmonton, Alberta

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