lavamadness

I was considering installing an adjustable proportioning valve in the near future and had a few questions:

1) If I follow the tech article on this site for the installing the wilwood prop valve, not only will i lose the brake warning light (not TOO big a deal I guess), but will I also lose the redundancy whereby if either the fronts or rears fail, the other set will get full line pressure?

2) On summit, I noticed this adj prop valve: TIL-90-1003. If I got that instead of the wilwood one, I wouldn't need any adapters for the fittings would I?

18inchboyds

i have a question , is his 1st question true or what , and does it matter if i put the adj prop valve by the rear end for ease of install. or does it have to go in the front ?

18inchboyds

goddammit will someone answer, im needing to know this.

rsn932

i dont know about the first question.

if you do the "bolt mod" to your stock proportioning valve (basically giving the rears full pressure), then you could put the adj valve near the rear.

it isnt that hard to install it up front. i put mine up front. i had 2 leaks on my first try, but you just cut and reflare.

rsn932

also to the original poster, that other prop valve that you have linked, im just about positive you would still need some adapter fittings. i highly recommend just getting the wilwood one (its cheaper!) and just follow the tech article on how to install it. it tells you all the fittings you need and everything. good luck.

lavamadness

Thanks rsn932. I'll probably get the wilwood one anyway. At twice the price the other one hardly seems worth it.

As for modding the stock prop valve, I was under the impression that the mod was if you were going from drum to disk, and it wasn't recommended if you had the 4WD stock. I'll reresearch again though. I was also under the impression that it was a bad idea to put an adj prop valve in along with the stock valve. I guess this isn't so much an issue if the stock valve is modified to send full line pressure to the rears to begin with.

I'd still like to know about the whole safety thing though. Certainly with a adj prop valve, you lose that, whether the mod the stock valve or remove it completely. But I'd like to know if the stock prop valve itself does do that or not. It would be nice to know if I'm losing a safety feature, of if it didn't exist in the first place.

RTFC

Here's a great article that will explain to everybody WHY the factory brake valv is called a "COMBO" valve and not a "prop" valve. The basic reason is it has a combination of functions that it is peforming.
http://auto.howstuffworks.com/master-brake2.htm

You can now see after reading the article the importance and benefits of leaving the factory combo valve in place and the further installing the aftermarket adj prop valve behind it in the line leading to the rear brakes. the pressure you have back there generally always is too much and has to be turned down in every case I have seen so far when dealing with 3rd gens and retro fitting new brake systems that are working properly without used parts.
Note the part that talks about an example where a 70% combo valve will have the rear proportion pressure lower than the front. This means that the fronts take 100% and the rears take 70% of the full pressure. Most people comfuse that too be the fronts take 70% and the rears take 30%-not true.

Now by installing an adjustable prop valve in the rear line BEHIND the factory Combination vavle, you can further reduce that exampled 70% pressure down by 57%max (in other words 75% 0f 70 = 30.1%) so the range of rear pressure adjustment would be from 70% - 30.1% with the inclusion of an inline adj valve. This while retaining the rear pressure "buildup" before the fronts come on that the factory combo valve metering section performs for the rubber effect explained in the link.

RTFC

Comparison-

remove fatory prop valve:
No pressure safety switch
No metering section
100% front pressure
Adj prop valve in rear lines yeild a pressure adjustment range of 100%-43%

Retain factory combo valve and add adj prop valve to rears:
Safety switch
Metering section
100% front pressure
Adjustable valve in rear lines after factory combo valve yeilds an adjustable pressure range of 70% - 30 %

Factory combo valve WITHOUT an adjustable aftermarket valve:
Safety switch
metering section
100% front pressure
70% rear pressure

18inchboyds

so rtfc are you saying to not do anything with the stock one and just put a prop valve in the back and then use it from there. I mean that sounds like an awesome and easier idea to me . Since i wanna add linelock too it will be easier and less plumbing to just put it in the back .I should have to do any mods to it like rsn932 said do it . THe back will get x % and with the valve in the back i can further reduce it ?

lavamadness

1) RTFC, you're saying that when everything is working aokay stock, that you need to REDUCE the pressure going to the rear brakes? Why is this?

2) From the article, it seems that it's the master cylinder that allows one set of brakes to get the pressure if the other set fails. Not the combo valve?

3) The article said the metering section was needed for front discs/rear drums, which I'd also read in a couple other places. Does the combo valve for the stock disc/disc cars do any metering as well?

RTFC

Lava,
1)A complete stock setup really does not need an adj prop valve. At least the 4-wheel disc 10.5" setups with the same exact rotor,caliper piston, and pad sizes front and rear. This was with a 1le combo valve designed for the factory 1LE 4-wheel disc cars with the larger performance package brakes. I had slightly more rear pressure on the rears than maybe ultimate stopping power, but it was so damn close it wasn't funny- not worth the bother of an adj prop valve to turn down maybe only from 70%-68%.

Now that same valve on the setup it was designed for- the performance package brakes- which consists of:
Fronts 11.65" rotors, Alum dual piston calipers and larger pads
Rears 11.65" rotors, Alum single piston calipers with smaller pads.
That same 1LE combo valve is in fact designed for this setup and this setup has more front brake power than the first 10.5" 4-wheel setup. So this setup has slightly more front power hence the rear pressure bias being more suited perfect.


Here's where the adition of an adjustable prop valve comes into play- When you start messing with something like LS1 brakes or C4 and C5 brake combos, etc. Different combinations front to rear that did not come factory on our cars will tend to possibly through off the brake bias because of the different size rotors, different size calipers, etc.

Take mine for instance. I have Wilwood setups front and rear.
6 pistons fronts on 12.9" rotors, 4 piston rears on 12.2" rotors with that same 1LE combo valve. Believe it or not, my rear pressure is much too high and I definately have to get an adj prop valve in the rear line to further reduce the rear pressure. I can lock the rears so quickly right now and flatspot tires if I am not careful. I am actually really showing massive wear on my rear tires because they are taking a greater pecentage of the braking force than they should be. My plate has been so full lately that the adition of an adj prop valve is just on a back burner. By summer I will fit one in-line on the hardline leading towards the rear just about gear selector area so it can be dialed on-the-fly in cockpit.

RTFC

2) the master cylinder is the redundant factor for brake failure. It separates the front and rear brake systems so only one fails and the other hopefully still works. What the safety switch does in the combo valve is simply warn you of a pressure drop in either the fronts or the rears due to an imbalance. Its a warning device that is required on all vehicles driven on US highways by law. Its a major safety factor with a bright red light on your dash board telling you something is not kosher with your brake system.

3)The disc, disc 1LE combo valve meters also. It allows for rear pressure to still set the pads against the rotor so they are snug against and working as the fronts are applied. Hence why the rears will generally have more pressure "bias" than the fronts when the system componants are altered from factory parts. That combo valve whether it be the J50 or the J65 (disc/disc, or disc drum) is set up with a metering section designed for its counterparts. Drum brakes will generally require 10psi Residual pressure to retain pad contact where disc will require only 2 psi metering. All in all the rears need to make contat first so the car remains stable under hard initial braking (aka- the rudder effect)

lavamadness

Thanks for clearing things up.

bsw

Could you mod the prop valve (removing needle and spring) and then install the adj prop valve in between the main rear line and the stock prop valve?