Anyone else doing brake proportioning valves? (Page 4/4)
SP1200 MAY 01, 10:30 PM
yea never got an answer to my question ether. I hate how that keeps happening.
wftb MAY 02, 12:51 PM
Here is some good reading on the subject of the prop valve. It helped me a lot to understand how it works, how to mod it and disable it. We are a smallish group of people on here and most of us are not here every day. Sometimes questions just don't get answered, and a lot of threads just die without any resolution. The nature of the beast nowadays.
http://www.fiero.nl/forum/Forum2/HTML/109173.html

If you look at the drawing on pge one, second drawing down you will see the plug and spring and if you look carefully you will see a rubber ring 'flapper' style valve drawn in blue. Removing that rubber valve and putting the prop valve back together turns the prop valve in to a fluid junction and you should get a 50/50 brake distribution front to rear. I did this on my setup and the right front locked up same as before. That told me that I needed to send more than 50% pressure to the rear brakes. Since aftermarket prop valves are primarily designed to reduce pressure, then putting one on the rear brake circuit would increase braking to the front circuit.The best I could get would be a 50/50 split and I proved that was not good enough for my set up. So I put my Wilwood valve on the front circuit and now I have the brakes I have always wanted. It is a mistake to call these aftermarket valves combination proportional valves because even if you run all circuits in and out of the valve, there is no interaction between the front and rear circuits. If you look at a pic of my setup (last pge of above thread I think) you will see 2 empty holes on the valve body.

[This message has been edited by wftb (edited 05-03-2018).]

ag9123 MAY 04, 12:29 PM
So it looks like there are 3 different proportioning valves on the Fiero per Ogre:
I'm just grabbing some info from some previous posts...

Kudo's to Fierobsessed for putting a lot of info out there.
http://www.fiero.nl/forum/Forum2/HTML/109173.html

"Prop valve part numbers:
84 exc Y82 10026021 (not sure on spool diameter/color)
84 w/ Y82 10036563 (RPO Y82 is Merchandised Pkg, Fiero = Fiero Indy) 0.286" spool (gold)
85-87 10036563 0.286" spool (gold)
88 10071501 1/4" diameter spool (red)"

The 84-87 brake caliper pistons:
49mm FT
47.75mm RR

The 88 brake caliper pistons:
47.75 FT
47.75mm RR

Ignoring the proportioning valve for a moment, it would appear that the 88 has a slight FT bias (based solely on caliper piston area alone)
Per Fierobsessed:
Based on spool diameter:
0.20" 84% above 477 PSI
0.25" 75% above 306 PSI (My 88GT Fiero) RED
0.286 67% above 233 PSI (My 84 Indy Fiero) GOLD
0.30" 64% above 212 PSI
0.35" 51% above 155 PSI

"So if you wanted more rear brake bias, you would need a narrower spool, and vice versa. The spring's cracking pressure also changes greatly with the different spool sizes, so I listed them as well, assuming the spring delivers about 15 lbs of force."

The 88 appears to be using the .25 prop valve spool to increase rear brake bias at higher brake pressures vs the .286 spool in the Indy/85-86

In keeping with Pontiac's design theory, I would think an 88 prop valve on a GA FT/RR setup would restore braking bias to stock (88) specs..

Does this sound about right?

Stock for stock, do the 88 brakes actually perform better than the 84-87 brakes (shorter stopping distance) ,vented rotors aside?

------------------
1984 Indy Fiero

[This message has been edited by ag9123 (edited 05-04-2018).]

wftb MAY 04, 08:26 PM
According to every test and almost everything that has been posted on here the 88 brakes stop shorter and are more fade resistant than 84-87 brakes.
cvxjet MAY 04, 09:17 PM
I have recently finished swapping my 85 Fiero to 88 brakes (Rear subframe/suspension/brake swap, and front 88 calipers with Sluppy brackets/hubs and 12" vette discs) I grabbed several prop' valves from the JY...I would swear that an 87 had a red spool but a different spring from the 88 I grabbed....I ended up with a red spool and the softest spring so that the prop' valve starts working earlier......Before, stock 85 gold spool, very front-biased, with red spool but strong spring somewhat front-biased....Now, I seem to have come very close to proper balance.....

(By the way, the 88 brakes have better fade resistance simply because they are...Ventilated discs!)
fieroguru MAY 04, 09:30 PM

quote
Originally posted by ag9123:
Stock for stock, do the 88 brakes actually perform better than the 84-87 brakes (shorter stopping distance) ,vented rotors aside?



The two largest differences are:
88's have a larger rotor diameter (10.43 vs. 9.69), so their calipers have more leverage to stop the car.
88's are vented so they are more fade resistant.
ag9123 MAY 05, 10:46 PM
Ah, I didn’t know the 88 had larger rotors...