Re: Brake Pressure Question
[Re: justinp61]
#2468790
03/19/18 09:47 PM
03/19/18 09:47 PM
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Joined: Sep 2014
Posts: 4,457 Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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That sounds low to me.
I like 1200.
But I would verify that. I sold my race car a decade ago.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Brake Pressure Question
[Re: justinp61]
#2468846
03/19/18 11:42 PM
03/19/18 11:42 PM
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Joined: Dec 2005
Posts: 11,706 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,706
Fulton County, PA
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It sounds like the master is plumbed backwards or something is mis-matched. On the Strange Mopar style unit, the port nearest the pushrod supplies the highest volume of fluid. Typically on a drag car with big tires and larger brakes on the rear, that is where the rears are plumbed to. I would look at the Wilwood calipers and compare the bore size to the Strange units. I've had certain Wilwood calipers with small pistons relative to what Strange and others use. I've had to go to a 7/8 master to make the brakes work with those. I stopped using them, but still have to deal with them sometimes. I also have not needed or used a prop valve in years, once the system is set up correctly.
Last edited by CMcAllister; 03/19/18 11:45 PM.
If the results don't match the theory, change the theory.
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Re: Brake Pressure Question
[Re: justinp61]
#2468907
03/20/18 02:34 AM
03/20/18 02:34 AM
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Joined: Feb 2011
Posts: 1,454 Glendora Ca.
Just-a-dart
pro stock
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pro stock
Joined: Feb 2011
Posts: 1,454
Glendora Ca.
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My old adjustable prop valve would still reduce pressure even at the "least" setting. I would take it out and put a coupling there to start.
"Just a Bracket car dressed up like a streetcar"
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Re: Brake Pressure Question
[Re: SportF]
#2469029
03/20/18 11:56 AM
03/20/18 11:56 AM
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Joined: Oct 2003
Posts: 11,686 W. Kentucky
justinp61
OP
I Live Here
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OP
I Live Here
Joined: Oct 2003
Posts: 11,686
W. Kentucky
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If the proportioning valve is doing nothing, and the shuttle valve is doing nothing, then all pressure front and back would have to be equal.
Because all of the oil is coming from a common same size bore I don't know how you would get those different pressure readings.
As such, one of those valves must be doing something. The rear brakes don't go through it.
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Re: Brake Pressure Question
[Re: justinp61]
#2469032
03/20/18 12:00 PM
03/20/18 12:00 PM
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Joined: Dec 2005
Posts: 1,495 Shelby mi.
JAKE68
pro stock
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pro stock
Joined: Dec 2005
Posts: 1,495
Shelby mi.
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I thought the wildwood prop valve produce more pressure when turned in. Just the opposite you would think. Try that
JAKES AUTOMOTIVE
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Re: Brake Pressure Question
[Re: JAKE68]
#2469054
03/20/18 12:26 PM
03/20/18 12:26 PM
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Joined: Oct 2003
Posts: 11,686 W. Kentucky
justinp61
OP
I Live Here
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OP
I Live Here
Joined: Oct 2003
Posts: 11,686
W. Kentucky
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I thought the wildwood prop valve produce more pressure when turned in. Just the opposite you would think. Try that It's not a Wilwood valve but I did adjust it and check to make sure it was wide open. I just got off the phone with Wilwood, they said it's not far off on the rear pressure but the front is low. The tech suggested I start at the mc checking pressures and work my way through the system. I'm going to remove the adjustable proportioning first and check the pressure. If that doesn't improve it I'll fab up lines and go through the system. Thanks guys, Justin.
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Re: Brake Pressure Question
[Re: justinp61]
#2469158
03/20/18 03:01 PM
03/20/18 03:01 PM
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Joined: Jan 2003
Posts: 25,988 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,988
Rio Linda, CA
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Do the math; with a 1 1/32" MC, 6-1 pedal ratio and 100 lbs. leg pressure your line pressure should be 716 psi. http://www.wallaceracing.com/brake-master-cyl-calc1.phpIn your case, the unknown factors are pedal ratio and leg pressure. "Surprise stop" leg pressure will vary with the individual, bathroom scales between your foot and the pedal will give you a number to compute from.
The INTERNET, the MISinformation superhighway
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Re: Brake Pressure Question
[Re: justinp61]
#2469164
03/20/18 03:09 PM
03/20/18 03:09 PM
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Joined: Dec 2005
Posts: 11,706 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,706
Fulton County, PA
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The Wilwoods are 1.38" and the Strange have 1.625 and 1.750" pistons.
Thanks There you go. Do the math to figure the difference in piston area x eight pistons. The bigger the piston, the more pressure is applied to the pads. Put a decent caliper on it, plumb the rears to the MC port closest to the pushrod if the rear tires are larger than the front, throw the prop valve out. Expect to need the MC bore to be bigger with appropriate calipers on there.
If the results don't match the theory, change the theory.
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Re: Brake Pressure Question
[Re: CMcAllister]
#2469321
03/20/18 07:29 PM
03/20/18 07:29 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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On your A-body the line pressure should be in the 1700 to 2000 psi on MAX breaking.. it does sound like the lines are backwards
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Re: Brake Pressure Question
[Re: justinp61]
#2469799
03/21/18 04:50 PM
03/21/18 04:50 PM
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Joined: Dec 2005
Posts: 11,706 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,706
Fulton County, PA
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Consider 500psi of fluid pressure at one 4-piston caliper.
With 1.38 pistons, the force exerted on the pads is 2960lb. total. With 1.75 pistons, the force exerted on the pads is 4800lb. total.
Or another way to look at it - I can get just about the same amount of force on the pads with 4 1.75 pistons @ 300psi as I can with 4 1.38 pistons @ 500psi.
The calipers are not correct for a skinny front tire-big rear tire application. The front brakes are being forced to do all the work. Knowing the fluid pressure is useless without taking caliper piston bore size into consideration. If you have the same caliper on all 4 corners of the car, then you can compare front and rear pressures and get an idea of what's going on.
A lot of Stockers and Super Stockers have gone to four 4-piston calipers on the rear with either two 2-piston or two 4-piston calipers on the front. All with the bigger pistons. Then matching MC size to the total fluid requirements of the system.
Last edited by CMcAllister; 03/21/18 05:02 PM.
If the results don't match the theory, change the theory.
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