It's a fine line between the right amount of slip and lockup.
If you're not on the edge of locking the tires, then you're leaving lots of deceleration on the table (not enough slip). If that's the case, then you can forget about stopping in as short a distance as your 2014 Focus.
Stopping quickly without ABS is all about driver skill; you need to adjust the brake pedal force to find the optimum tire slip. If you don't want to do this, well that's what ABS does...
I am more than capable of modulating the brakes .This car is going to be used for track days and setting a car up for a road course means minimizing required driver inputs so you can concentrate on keeping the car on line and improve every lap .You dont want a car that you are constantly worried about locking up the brakes .As far as my skill level goes I used to race street stockers on the local paved oval and I won more than my share of races . In a 1968 Javelin that I set up myself .A friend of mine built the car .That was a long time ago , early 80's .Anyway, I am happy to report that the valve I installed works . I backed the pressure way off and I managed to get the rears to lock up .Then I put more to the front and I got to a point where all 4 tires locked up at the end of a panic style stop.I do not want the rears to lock up so I put more to the front and now it is close to where I want to be .It is only 46*F out so it is impossible to set up for the tires I have on the car right now (fairly old Kumho Ecsta SPT's) .As you can see in the pictures , there is nothing going to the holes that you would normally plumb the front brakes to .The brake switch that will never be used anyway is only activated by the front brake circuit .So , I may just cut that part of it off since it is just wasting space . The tube that goes to the stock prop valve from the MC has 2 different sized fittings on it .One of which I could not find .Hence the ugly stack of fittings . I did not want to cut up the original tube and fittings in case this did not work . It is a fine line from full rear lock /no front lock to full front lock/no rear lock .About 3 turns of the knob , once you find the spot where all this starts to happen .And with this set up , you still have a working brake warning switch . In the spring , I am going to get slightly bigger tires that should have a lot more grip .Fronts are going to be 215/55/16 and rears 255/50/16 .In a BFG sport comp 2 high performance summer tire .I like the lighter steering I get with the 205/245 combo I have now but for good braking the 205' are just too small .
[This message has been edited by wftb (edited 10-24-2016).]
So in summary you 1 disabled your factory proportioning valve to keep stock pressure 50/50 front and rear 2 then only utilized the rear circuit of the Wilwood combo prop valve attached to the front input circuit of the fiero combo/prop valve 3 reduced the pressure of your front brakes given your upgraded brake scenario.
So a standard wilwood proportioning valve would have worked just as well attached to the front fiero input circuit
That is correct .I bought this Wilwood valve thinking I was going to get rid of the stock prop valve altogether .When I realized how easy it was to disable the stock prop valve , I put the adjustable part of the Wilwood on the front brakes only .I could have saved some money there . I am now thinking of buying 2 of the cheaper valves and putting one on each circuit . Right now I am trying to control both ends with one adjustment .It seems to me if I had an adjuster for each axle , it would be easy to get it just right .
I feel your pain.. I'm adapting a 2001 Z06 setup to an 88. So I'm dealing with dual piston front calipers with single piston rears.. similar setup to yours...
Was looking into putting stronger and stronger springs into combo block prop valve or have aaron88's adjuster remanufactered but might very well take a path similar to yours.
That is correct .I bought this Wilwood valve thinking I was going to get rid of the stock prop valve altogether .When I realized how easy it was to disable the stock prop valve , I put the adjustable part of the Wilwood on the front brakes only .I could have saved some money there . I am now thinking of buying 2 of the cheaper valves and putting one on each circuit . Right now I am trying to control both ends with one adjustment .It seems to me if I had an adjuster for each axle , it would be easy to get it just right .
Since it's a ratio between the two you only need to be able to adjust one.
I have the HD C4 calipers on both ends and an adjustable prop valve on the rear line. I race it so am only interested in how it performs at the limit.
Since it's a ratio between the two you only need to be able to adjust one.
I have the HD C4 calipers on both ends and an adjustable prop valve on the rear line. I race it so am only interested in how it performs at the limit.
do you have any pics of your setup ? How much piston area do you have front / rear ? Just curious , I wont be doing any more tinkering till I get my new tires next May or so .
Originally posted by msweldon: So in summary you 1 disabled your factory proportioning valve to keep stock pressure 50/50 front and rear 2 then only utilized the rear circuit of the Wilwood combo prop valve attached to the front input circuit of the fiero combo/prop valve 3 reduced the pressure of your front brakes given your upgraded brake scenario.
So a standard wilwood proportioning valve would have worked just as well attached to the front fiero input circuit
Yes he did and PV to limit front brakes is Not a good plan. Big problem is PV are known to fail and w/o warning. If they fail to lowest pressure then the car will take a long time to stop and likely have a wreck.
Again... Front brakes do 70% to 90+% of work to stop because of weight shift to stop. Faster you go, the more weight will shift trying to stop. This is a Dynamic Weight when the car is moving and the same reason why big tires on back will help to accelerate from a stop. G force for turning is measuring same Dynamic Weight.
Worse, by killing rear PV the car can spin out very easy because the weight shift removes traction to the rear axle while stopping.
As setup as above, the spool may move and trip the warning light on when you hit the pedal.
[This message has been edited by theogre (edited 10-24-2016).]
do you have any pics of your setup ? How much piston area do you have front / rear ? Just curious , I wont be doing any more tinkering till I get my new tires next May or so .
No pictures at the moment. The HD C4s have twin 1.5" pistons and I use the same calipers on both ends. I also use Acura RDX rotors on the front (12" x 1.1") and Jetta rotors on the back (11.75" x 1.1").
I was going to say, isn't putting a prop valve on the front brake circuit bad juju?
Yes. It basically goes against the reasons a car would be fitted with such a valve in the first place, which was well explained on the previous page by Fierobsessed:
quote
Originally posted by Fierobsessed:
Thats simple, the proportioning's sections cracking point becomes zero, so no matter what the pressure is on the front brakes, the rear brakes will be exactly 75% or 67% of that pressure, depending on which spool you have. The springs purpose is to disable the PV untill a certain pressure is obtained. This helps the brakes to work much more evenly, rather then running the fronts really hard all the time. Think about it, if you are in stop and go traffic you do a lot of light braking. There is no weight transfer and traction issues to speak of, so the brakes are much better off working evenly.
Then, in the braking and deceleration ranges where the weight transfer and rear traction become an issue, the pressures start to diverge offering more braking force where there is the most traction, at the front.
So a proportioning valve on the front would (qualitatively) work as follows: Low pedal pressure -> more front biased -> When trying to threshold brake in low-traction conditions, the fronts will lock prematurely before the rear brakes can pull their weight Heavy pedal pressure -> more rear biased -> When trying to threshold brake in high-traction conditions, the rear of the car will get unstable under braking
That is not the way it works .When I disabled the stock valve , I drove the car and the fronts still locked up at the same time or close to it with a theoretical 50/50 split front/rear .Since I need more power to the rear brakes than a 50/50 split will give me , I needed to put the Wilwood on the front .It is definitely bad juju to have another prop valve in place if the stock valve is still working .That is asking for trouble . I have a stock fiero MC and a stock vacuum booster .And no matter what braking system I have had , I have never had a problem with a low pedal or high effort .And I do not have that problem now .Racing cars , where it is allowed by the rules , will have a pressure reduction valve on each brake line .The knobs then usually are in the interiour so the driver can fine tune while he is racing .Of course more modern cars will just use ABS and then all this becomes obsolete .The pedal pressure where lock up occurs has not changed .With full power to the front wheels , lock up is premature at about 20 MPH when I push hard on the pedal .Pretty much the same as with the stock prop valve .Back way off on the valve and you get rear lock up at about the same speed and pedal pressure .Slowly increasing pressure to the fronts will stop the rears from locking up and I got to the point where the fronts lock up at about 10 MPH and that is the best I can do with the tires that I have now .But this is a big improvement and diving deep in to a corner and braking late is much easier now .Do I recommend this mod to any one else ? No .I really think the answer is a smaller diameter brake disc based system .The Fiero is just not heavy enough to warrant the big discs we are putting on them .My Focus has 10" discs in the front and weighs about 400 lbs more than a Fiero GT .I see all these people here putting 13" discs on but I never hear how they actually work . One of my favourite threads all time on Pennocks is by DonP about his teams Lemons /Chump car 88 Fiero .And you know what they did to the 88 Fiero brakes ? Nothing .They put better pads on but the brakes stayed stock .If I could just adapt brakes from an 88 Fiero on to my car I would .
[This message has been edited by wftb (edited 10-24-2016).]
what fierobsessed was explaining in the quote above was what happens when you remove the spring from the stock prop valve .I have turned my prop valve in to a fluid junction .It no longer does anything except become a convenient place to add valves .
Heck... thank you for this wonderful thread. It's allowing a lot of us here to do vicariously what we're not able to do with our Fieros (for a variety of reasons) in real life. I look very forward to all your updates.
It was kind of a shame that Don and the team decided to change course and go with the truck. I understand why they did it... but nevertheless it was disappointing to see their Fiero adventure come to an end.
There is a wrecking yard near me that has 3 fieros in it . It has been about 4 years since I looked at any of them .I decided to pick up a stock prop valve while I could still get one .The owner helped me find one of them ( the place is getting seriously overgrown with tall grass and shrubs and trees) This was a black 85 .It now has a shrub growing inside it .Got the valve and all the fittings for 15.00 .Now if I ever need to I can put this valve on the car .Allways good to have a backup plan .The yard is going to close and all the cars there are going to be crushed .The owners want to retire .
Thought I would update this thread as I am now driving my car again. I have not changed anything from the way the car was when I parked it last year. The only thing I did after I got the Wilwood PV set where I wanted it was give the system a good bleed. I was going to change the Wilwood to the rear circuit but I do not see the need. I could not be happier with my brakes now (unless I figured out how to adapt an ABS system). I have put another 750 KM on the car so far and I think the pads getting bedded in has made a big improvement. All the pads were brand new when I started experimenting with all this. So everything is staying just the way it is for now.
I had the car out for a track session at Grand Bend Motorplex Road course on thursday and the brakes worked way better than expected. I can stomp on them without any lockup and they dragged me down from 90 and 100 mph in short order. The only improvement I think could be made is some pads that would stand the heat a bit better. Not much fade happening, but you could smell them pretty good. It was a hot evening (for around here) of over 80 F.
[This message has been edited by wftb (edited 10-13-2017).]
Just wanted to add that the track day was with my old tires still on. I finally got new tires, still the same size because of space limitations but they are BFG comp2 AS and they are awesome. I have not had to adjust the prop valve and I could not be happier with my brakes. No more track days till next year unfortunately.
I just wanted to chime in here...I have an 85 SE V6 with 88 rear subframe and 88 brakes all around....I used the stock rear discs(10.5") and 12" Vette discs up front....At first, with the stock P-Valve, it would lock up the front and basically never touch the rear...So I went to the JY and picked up an 87 and 88 P-Valve plunger(Red) and springs.......Swapped the plunger in but used the small/short spring...Still locked up the front but at least the rear was doing something.....So then I swapped in the stronger spring, and now it seems to be very close to perfect....I Got it up to the limit in a cloverleaf and then jumped on them and the rear just came out a little while the car stopped quickly.
To reiterate; 88 calipers all around, 10.5" 88 discs rear, 12" Vette discs up front (Using Sluppy123's aluminum hubs and brake adapter brackets) and then the original 85 Proportioning valve BODY with an 87/88 Red plunger and the strong spring....I'm afraid I don't remember which car the strong spring came out of........(87 vs 88)
One more detail that should be obvious but I'll present it clearly; Even tho the P-valve screw-in plug looks completely different from year-to-year, the valve bodies will accept the plugs from different years- Use the plug that fits the plunger spring (Different diameter springs)...
