brake question
#3229289
04/26/24 09:11 AM
04/26/24 09:11 AM
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Joined: Mar 2005
Posts: 1,596
Michigan
Kiddart
OP
pro stock
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OP
pro stock
Joined: Mar 2005
Posts: 1,596
Michigan
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I have a question; it might be controversial but i still have it. I was reading i think on here and can't find the thread. If you have a modern master cylinder from a mid 80s pickup in an older car do you need to run a proportioning valve? If i recall, there were a few guys saying with 4-wheel disc setup and new master cylinder the prop valve renders its self-useless?? I did a 4-wheel disc setup on my demon and just wondering as I will be doing a line lock and if i can get rid of the prop valve I will.
True or false? and any comments or experience is welcome.
I know I ask a lot of questions i should know the answers to.
Thank you
Kiddart
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Re: brake question
[Re: Kiddart]
#3229359
04/26/24 05:36 PM
04/26/24 05:36 PM
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Joined: Dec 2014
Posts: 6,713
ohio
ruderunner
master
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master
Joined: Dec 2014
Posts: 6,713
ohio
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I have a question; it might be controversial but i still have it. I was reading i think on here and can't find the thread. If you have a modern master cylinder from a mid 80s pickup in an older car do you need to run a proportioning valve? If i recall, there were a few guys saying with 4-wheel disc setup and new master cylinder the prop valve renders its self-useless?? I did a 4-wheel disc setup on my demon and just wondering as I will be doing a line lock and if i can get rid of the prop valve I will.
True or false? and any comments or experience is welcome.
I know I ask a lot of questions i should know the answers to. A proportioning valve is needed for disc drum systems. It's not required for drum drum or disc disc. It would be beneficial in those cases for fine tuning though. BTW, that 80s truck MC has 2 problems with disc disc systems. 1 it may have a residual pressure valve, no bueno for disc brakes. 2 the reservoir for the rear brakes is much smaller than typically found on disc brakes, if you keep an eye on fluid levels this isn't a problem.
Angry white pureblood male
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Re: brake question
[Re: Andrewh]
#3229360
04/26/24 05:38 PM
04/26/24 05:38 PM
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Joined: Nov 2006
Posts: 6,001
Star Idaho
67vertman
master
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master
Joined: Nov 2006
Posts: 6,001
Star Idaho
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I have four wheel disc brakes on my 70 E Body, I installed a disc brake master cylinder and I am still running the proportioning valves. No issues after 12 years. I think you can do without it though.
My Monster are real!
Living within your means makes life pretty easy.
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Re: brake question
[Re: 67vertman]
#3229377
04/26/24 07:52 PM
04/26/24 07:52 PM
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Joined: Dec 2005
Posts: 12,954
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 12,954
Fulton County, PA
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Just throwing a mix of parts together and the answer is "maybe". I always considered them a bandaid. Sometime a necessary one, but still a bandaid.
Figuring out pedal ratios, bore sizes of the MC and the calipers along with the number of pistons to get total area of the bores, tire sizes (big tire drag car vs all tires relatively the same size), getting it all right, and putting it all together and it should not be needed,
If the results don't match the theory, change the theory.
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Re: brake question
[Re: Kiddart]
#3229385
04/26/24 09:34 PM
04/26/24 09:34 PM
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Joined: Jan 2003
Posts: 16,277
Omaha Ne
TJP
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,277
Omaha Ne
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You won't know for sure what you need until you install and test it. There are a ton a variables involved that cannot be assumed or guessed at. pedal ratio, piston sizes, drum and disc sizes, vehicle weight, brake lining friction coefficient, tires sizes, their compounds and the list goes on. You will likely need the residual pressure valves as previously mentioned You can install an adjustable if your replumbing the rears or roll the dice and see if you need one  
Last edited by TJP; 04/26/24 09:36 PM.
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Re: brake question
[Re: CMcAllister]
#3229409
04/27/24 05:25 AM
04/27/24 05:25 AM
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Joined: Dec 2014
Posts: 6,713
ohio
ruderunner
master
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master
Joined: Dec 2014
Posts: 6,713
ohio
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Just throwing a mix of parts together and the answer is "maybe". I always considered them a bandaid. Sometime a necessary one, but still a bandaid.
Figuring out pedal ratios, bore sizes of the MC and the calipers along with the number of pistons to get total area of the bores, tire sizes (big tire drag car vs all tires relatively the same size), getting it all right, and putting it all together and it should not be needed, This is all true. Starting completely from scratch and designing and specifying every aspect means you can do it without any proportioning valve. Think OEM research and development. But, we're limited to what's available and it's going to be less than ideal. I recommend installing an adjustable valve from the start. Due to the differences in operating pressures, a disc drum system needs one no matter how much math and research you do.
Angry white pureblood male
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Re: brake question
[Re: 67vertman]
#3229410
04/27/24 05:29 AM
04/27/24 05:29 AM
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Joined: Dec 2014
Posts: 6,713
ohio
ruderunner
master
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master
Joined: Dec 2014
Posts: 6,713
ohio
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I have four wheel disc brakes on my 70 E Body, I installed a disc brake master cylinder and I am still running the proportioning valves. No issues after 12 years. I think you can do without it though. Originally a 4 wheel drum or disc drum? If Originally a disc drum setup, you're leaving alot of rear braking power unused. If drum drum, you're good.
Angry white pureblood male
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Re: brake question
[Re: ruderunner]
#3229537
04/27/24 02:47 PM
04/27/24 02:47 PM
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Joined: Jan 2003
Posts: 27,359
Rio Linda, CA
John_Kunkel
The Erection Connection
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The Erection Connection
Joined: Jan 2003
Posts: 27,359
Rio Linda, CA
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A proportioning valve is needed for disc drum systems. It's not required for drum drum or disc disc.
And, yet, the factory often uses them in disc/disc installations. IMO, the only way to know is actual testing...slam on the brakes at speed and see what happens.
The INTERNET, the MISinformation superhighway
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Re: brake question
[Re: John_Kunkel]
#3229598
04/27/24 09:12 PM
04/27/24 09:12 PM
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Joined: Jan 2003
Posts: 16,277
Omaha Ne
TJP
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,277
Omaha Ne
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A proportioning valve is needed for disc drum systems. It's not required for drum drum or disc disc.
And, yet, the factory often uses them in disc/disc installations. IMO, the only way to know is actual testing...slam on the brakes at speed and see what happens.  100%
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Re: brake question
[Re: TJP]
#3229622
04/27/24 10:53 PM
04/27/24 10:53 PM
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Joined: Dec 2005
Posts: 12,954
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 12,954
Fulton County, PA
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A proportioning valve is needed for disc drum systems. It's not required for drum drum or disc disc.
And, yet, the factory often uses them in disc/disc installations. IMO, the only way to know is actual testing...slam on the brakes at speed and see what happens. 100% All true. However, I would drive it first and see what is needed, or not...and where.
If the results don't match the theory, change the theory.
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Re: brake question
[Re: John_Kunkel]
#3229641
04/28/24 06:56 AM
04/28/24 06:56 AM
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Joined: Dec 2014
Posts: 6,713
ohio
ruderunner
master
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master
Joined: Dec 2014
Posts: 6,713
ohio
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A proportioning valve is needed for disc drum systems. It's not required for drum drum or disc disc.
And, yet, the factory often uses them in disc/disc installations. IMO, the only way to know is actual testing...slam on the brakes at speed and see what happens. Why not include the entire statement. I did say it's good to have for fine tuning.
Angry white pureblood male
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Re: brake question
[Re: Stanton]
#3229687
04/28/24 09:44 AM
04/28/24 09:44 AM
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Joined: May 2019
Posts: 6,688
nowhere
Sniper
master
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master
Joined: May 2019
Posts: 6,688
nowhere
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And the tune will change between a full tank and an empty tank. Unfortunately there is no “automatic” prop valve.
Yes there is. My turbo minivan had one. Will it work on our stuff? Dunno. ![[Linked Image]](https://www.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/03/c8/f7/medium/0900c1528003c8f7.gif)
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Re: brake question
[Re: Sniper]
#3229700
04/28/24 10:39 AM
04/28/24 10:39 AM
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Joined: Sep 2003
Posts: 20,742
north of coder
moparx
Buying your homeless and unwanted bolt on battery terminals
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Buying your homeless and unwanted bolt on battery terminals
Joined: Sep 2003
Posts: 20,742
north of coder
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And the tune will change between a full tank and an empty tank. Unfortunately there is no “automatic” prop valve.
Yes there is. My turbo minivan had one. Will it work on our stuff? Dunno. i was just going to mention that as well, but you treed me............  all the minivans i have owned or junked over the years has had one of those things. also wondered if adding one would work in other applications.
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Re: brake question
[Re: moparx]
#3229740
04/28/24 01:05 PM
04/28/24 01:05 PM
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Joined: Dec 2014
Posts: 6,713
ohio
ruderunner
master
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master
Joined: Dec 2014
Posts: 6,713
ohio
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Those have been used on lots of different vehicles over the years. Problem is they're typically designed for a specific vehicle and the odds that they will be close for our stuff are slim.
Plus, they're all old. Pretty much disappeared when ABS became common.
Angry white pureblood male
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Re: brake question
[Re: Sniper]
#3229954
04/29/24 11:26 AM
04/29/24 11:26 AM
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Joined: Jan 2003
Posts: 75,418
A gulag near you.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,418
A gulag near you.
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And the tune will change between a full tank and an empty tank. Unfortunately there is no “automatic” prop valve.
Yes there is. My turbo minivan had one. Will it work on our stuff? Dunno. Also used on various 80's/90's pickups with rear wheel only ABS .
Mainstream Media is the new Pravda
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