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Prop valve question

Reply #15
I think this is the valve that you are talking about off the sn95. Couldn't I just use this valve and no aftermarket rear proportioning valve since it came off a disc/disc car?



Prop valve question

Reply #16
Guys, let me offer an opinion.
It seems a lot of us are swappping around brake stuff, converting to bigger, better brakes. Obviously some using OEM parts, some with aftermarket. Some a combination of the two.
There is a certain percent of difference built into the braking system of any car; front to rear. Fronts can have up to 100% of the braking force. Ever see a sportbike up on it's front wheel under braking? That is 100% weight transfer with ALL the braking being done by the front.
It is easy to get the designed ratio off when swapping components. It can be anything from annoying to dangerous.
Drum brakes are "self-energizing" meaning the rotation of the drum helps "pull" the brake shoes into the drum, increasing braking force. This is why there is a delay built into the system with the rear drums.
Getting this "ratio" right when swapping discs is made much easier by simply "teeing" the front lines and adding an aftermarket proportioning valve in the rear line so you can adjust the amount of rear brake force used. You ALWAYS want the fronts to lock up first.
I think Gumby showed, in a recent post, the best and easiest way to plumb a modified braking system.
Just my $.02
Dave

Prop valve question

Reply #17
resurrecting this one....  I currently have:

Cobra 2 port M/C.  1 line feeding prop valve 'front' and one line feeding prop valve 'rear'.  The prop valve is gutted and the 'front' line, which should now flow straight through the gutted valve (making is just a union) splits with a T after the stock valve and goes to both front brakes.  The 'rear' line comes off the stock valve to a wilwood prop valve before going to the rear and splitting.

I want to eliminate the stock prop valve but a few ppl on various fox car forums say NO.  But in all reality, it's completely pointless on my setup....  am I missing something?
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Prop valve question

Reply #18
well, idk..  I'm gonna give it a shot.  I dont know why it'd be necessary...
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Re: Prop valve question

Reply #19
Resurrecting this, as this seems to be the closest thread to my needs...If I am doing the same sn95 master cylinder upgrade as O/P, in an attempt to reduce mushy pedal after my 11" brake upgrade, AND I am converting to rear discs, could I use an SN95 2 in, 3 out prop valve?  My only other options being modifying a turbo coupe prop valve, as OP may have done, or just getting a wilwood 2 in, 3 out prop valve.  I'm not opposed to a wilwood prop valve, i just thought it may be a very easy solution to swap out my stock valve for an SN-95 and mount it in the same place, not have to remake any lines, potentially.
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 3.8 V6 - Rescue
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 5.0 V8 - Survivor

Re: Prop valve question

Reply #20

1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 3.8 V6 - Rescue
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 5.0 V8 - Survivor

Re: Prop valve question

Reply #21
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I have an NOS prop valve from 87-88 T/C  available for sale if interested.
Rick
[SIGPIC][/SIGPIC]
1988 T/C body with a 5.0 transplant. Motor has a Vortech V-2 supercharger, Edlebrock Performer RPM II intake, heads, FRPP F-303 cam, Comp Cams roller rockers, Power Pipe, LMAF, full Mac exhaust, lowered, Koni's, 5 lug conversion, Cobra wheels, 13" Cobra brakes, etc.
SOLD September 2020. Will miss this car after 19 years of building/driving/showing it off. Time for a new chapter in my life.
Dynoed 446 horse/409 torque at the wheels.
2003 Tenth Anniversary Cobra Convertible. 1 of 369 Torch Red made.
2021 Chevrolet 3500 dually, crew cab Duramax.

Re: Prop valve question

Reply #22
is it 2 in, 3 out??
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 3.8 V6 - Rescue
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 5.0 V8 - Survivor

Re: Prop valve question

Reply #23
It has 2 ports top and 2 on the bottom.
[SIGPIC][/SIGPIC]
1988 T/C body with a 5.0 transplant. Motor has a Vortech V-2 supercharger, Edlebrock Performer RPM II intake, heads, FRPP F-303 cam, Comp Cams roller rockers, Power Pipe, LMAF, full Mac exhaust, lowered, Koni's, 5 lug conversion, Cobra wheels, 13" Cobra brakes, etc.
SOLD September 2020. Will miss this car after 19 years of building/driving/showing it off. Time for a new chapter in my life.
Dynoed 446 horse/409 torque at the wheels.
2003 Tenth Anniversary Cobra Convertible. 1 of 369 Torch Red made.
2021 Chevrolet 3500 dually, crew cab Duramax.

Re: Prop valve question

Reply #24
wont work, i need 2 in, 3 out
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 3.8 V6 - Rescue
1988 Cougar LS - Cinnabar/Rose Quartz Metallic two tone - 5.0 V8 - Survivor

Re: Prop valve question

Reply #25
https://www.summitracing.com/parts/wil-260-11179       This worked for me.  Bolted in directly and the lines still connected. I did the 11" on the front and I kept my rear drums with Porterfield shoes and oversized wheel cylinders.
84 COUGAR/90 HO, 1.7RRs, performer RPM,700DP, equal length shorties, stainless EXH ,T-5,Hurst pro-billet, KC clutch, 8.8/ 4.10s, line-lok, bla ,bla, bla.
71 COMET/289,351w heads, 12.5 TRWs, 750DP, Liberty TL, 9"/6.00s, 11.9x @112 , bla,bla,bla.

Never shoot your mouth off, unless your brain is loaded! ....I may get older, but I'll never grow up!....If you're not laughing, you're not living!  :laughing:

Re: Prop valve question

Reply #26
So any MC you use that has two port you have two choices.  First, the combination valve (that is what you have in your picture) a proportioning valve and also has a shuttle valve in it.  The shuttle will move to block the front or rear port if you develop a leak in that circuit or at least that is what it is supposed to do by design and then trip the brake light on your dash if the combination valve is so equipped with a switch.  The proportioning valve is what decreases the pressure to the rear brakes under heavy braking.  Diagram is here with my notes from when I did this on my Mustang and my Bird:



The majority of factory front disc and rear drum Fox cars that I have seen converted to rear disc have had the proportioning valve removed from the front of the combination valve and the front plug replaced with a solid one as the stocker will leak with the proportioning valve removed.  This is done to keep the factory shuttle and dash brake light functioning.  Replacement end plug is here:

https://www.maximummotorsports.com/Brake-Proportioning-Valve-Plug-1979-2004-P1411.aspx

If you plan on deleting the proportioning valve on the factory combination valve then it allows you to leave the factory brake lines from the combination valve to the front and rear brakes alone as they are a bitch to break loose.  Typically most folks option for the 1993 Mustang Cobra MC as it has a 1" bore but it is a two port MC like all SN95 MC's.  This only poses a problem on I believe the 87 and up Birds and Cougars as they switched to a three port MC in 87 and used it through the 93 year in the Mustangs with the exception of the Cobra.  If you have a three port MC then you will need a 3 to 2 conversion kit like this one:

https://www.maximummotorsports.com/Master-Cylinder-Installation-Kit-1993-Cobra1994-95-GT-mc-in-1987-93-Mustang-P673.aspx

Description says 93 Cobra or 94/95 GT MC's but the V6 cars had the vacuum boosted brakes through 98 so those MC's will work as well.  Realize the94/95 GT and 94-98 V6 MC's have a 1-1/16" bore so they push more fluid at a lower pressure and can give you a very stiff pedal compared to an MC with a smaller bore. Do a search on this as there are a several posts on this.

So now you have your MC plumbed in and the proportioning valve deleted you still need a manual proportioning valve between the rear brakes and the feed line to them.  On the Mustangs they had a really convenient union on the upper right hand side of the firewall and that is where most put their proportioning valve.  Bird and Cougars do not have this so use your imagination.  I built a bracket and put it right in front of the combination valve for easy adjustment but once you set it you will not move it unless you start messing with brake compounds.

Now you have solved installing a 2 port MC into a factory 3 port MC car with the 3 to 2 kit and a 2 port MC as well as factored in the necessary braking bias change of swapping to rear disc brakes by removing the stock proportioning valve from the combination valve and installing the manual proportioning valve,   All this to keep from replumbing brake lines, flaring lines, keeping the stock shuttle valve in the combination valve and keeping the brake warning light in your dash function like factory.

If you don't give a rats ass about the shuttle valve or dash brake light then punt the combination valve, replumb by splitting the front brake port on the MC to the two front calipers, connect the rear brake supply line to the rear port on the MC, and install a manual proportioning valve in the rear brake supply line at a choice of yours.  This will require multiple flares and so good knowledge on how to do this as well as bend brake lines so they don't look like ass, secured properly, and in general don't look like ass.

83 351W TKO'd T-Bird on the bottle


93 331 Mustang Coupe - 368 rwhp

Re: Prop valve question

Reply #27
One last note, the '93 Cobra MC or the 94/95 Mustang GT MC or the 94-98 Mustang V6 MC will all work with the following brake set ups:
Stock 11" 87-88 TC front brakes and 87-88 style TC rear brakes or SN95 rear brakes
Stock SN95 V6 or GT brakes all the way around
Stock SN95 Cobra front brakes and stock SN95 GT or V6 brakes in the rear
Stock SN95 Cobra brakes all the way around

Couple of things:
I can verify this as I have installed and or helped install all those combinations and they all worked just fine.
The 93 Mustang Cobra unit has SAE threads and the SN95 units are metric so keep that in mind.
All of the SN95 (94-98) rear calipers are identical.  The only thing that differentiates the Cobra from the GT/V6 is the caliper bracket.  Again, we have gone into detail on this a couple of times on here.

83 351W TKO'd T-Bird on the bottle


93 331 Mustang Coupe - 368 rwhp