So I want to ditch the factory brake prop valve on the van. It was designed from the factory to tie the FR RL together and the FL RR together, so if you lost pressure on one side, you wouldn't lose the entire axle. I want to ditch this system and go to a more traditional F/R setup.
I also need an adjustable valve since the braking system is a mix of parts. The original specs were 10.5 in rotors with 60mm calipers up front and 220mm drums in the rear. Now it is 11" vented rotors in the front ('93 caravan) and 11" solid rotors in the rear ('01 caravan).
I'm looking at this: http://www.summitracing.com/parts/wil-260-11179/overview/
It seems like it only splits the front, so it's basically a T, and then has the knob built in to adjust the pressure to the rear. I'm assuming that will achieve my goals.
But, I also see this: http://www.summitracing.com/parts/sum-g3905/overview/
It seems I could use a T for the front and then just run the rear in to this and then T the lines at the rear.
Is there any reason to spring for the first one? This isn't exactly a challenge build, but I'm not trying to break the bank either. That being said if it is safer to run the first one I'll pony up the dough.
I was just gonna recommend that first thing:
http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-11179
The advantage of the first one over the second is that it gives you full control over brake bias, the second only lets you decrease whatever the pressure going to the rear happens to be.
GameboyRMH wrote:
I was just gonna recommend that first thing:
http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-11179
The advantage of the first one over the second is that it gives you full control over brake bias, the second only lets you decrease whatever the pressure going to the rear happens to be.
I don't think it controls front pressure at all.
Wilwood link said:
The combination block maintains full isolation between front and rear fluid circuits and can be used in conjunction with any tandem outlet or dual mount master cylinder assemblies
It doesn't, but it takes the pressure from the MC (presumably 50/50 pressure balance) and then lets you dial down the rear pressure, allowing you a full range of settings that might be useful on anything less radical than the DeltaWing.
The other valve takes the pressure going to the rear which has already been proportioned by a stock valve and lets you decrease it - so basically it's only useful if you want less rear bias than stock.
GameboyRMH wrote:
The other valve takes the pressure going to the rear which has already been proportioned by a stock valve...
Two lines out of the master cylinder. One to a stand-alone 'T' junction for the front circuit. One through the aftermarket single inlet/outlet proportioning valve to a stand-alone 'T' junction for the rear circuit. Where is the requirement for a stock valve in the rear circuit? It seems the only additional feature of the combination valve is that it integrates the front 'T' junction into the block itself.
Guess you could do that and it would be the same as using the combination proportioning valve, but a lot of stock cars use a proportioning valve between the MC and brakes or proportion the pressures at the MC.
In reply to Driven5:
I assumed the same thing.
The factory MC had to have equal pressure output from each port, since each port runs one front wheel and one rear wheel. I'd be running full MC pressure to the front brakes and would need a valve to turn down the pressure to the rear. Either way should do the same thing.
I wasn't sure if I was overlooking something or not.
Of course I may buy the first one anyway just to keep things tidy, I also might be able to use the warning light sensor on it to keep the factory brake idiot light functional.
In reply to moparman76_69:
it's a brake system and must be considered as such. For example, consider how much larger one front caliper is versus one rear (caliper or wheel cylinder, whichever is applicable to your van). your master is sized to supply the original circuits, which as you noted are arranged diagonally, so the primary and secondary MC volumes are identical (aka 50/50). Now, put two fronts together on one circuit and two rears together on the other, and you're asking your 50/50 master to supply a (roughly) 75/25 volume demand. is your OE 50/50 master going to bottom out the front circuit at something less than wheel-lock pressure, leaving you underbraked in a high-mu panic situation? maybe.
also, consider the total amount of braking available in the event of a leak somewhere. could be a bad piston seal in the MC, could be a hole in a line somewhere, could be a leaking caliper or wheel cylinder, doesn't really matter. the reason for diagonal splits is to maintain 50% braking capability in the event of such a leak. consider again the sizing of your brakes, front to rear. the fronts are significantly larger because they do a lot more work, probably something like 75%. now, let's have a front circuit failure when you hit the brakes to make a stop at about 35% of max. guess what: you can't do 35% max decel with rears only, because there's no weight back there!
so, on a FWD (yeah, i know, in your case AWD but it's a FWD platform) vehicle that has probably 60% front static weight -- and even more than that when actually braking -- a F/R split is not a great idea.
if you insist on going down this path, at least choose a F/R master cylinder so you're not under-braking the fronts at high decel.
oh, and re. the two parts you linked above, the only reason they run both MC lines into the combo valve is so they can sense a pressure difference between the two (ie a leak on one circuit), which would trip the switch to light the red brake light in the dash.
that switch on the Wilwood integrated prop valve is there to activate the rear brake lights on a street rod or something like that... it won't work to trigger the "BRAKE" light in the dash in the event of a catastrophic loss of pressure to either the front or rear brakes- but it has been my experience in the past that the light in the dash only comes on AFTER the pedal goes to the floor after a brake line bursts in a panic stop situation, anyways, so you aren't really losing anything important and might be getting rid of a potential distraction in the form of a red light that pops on in your dash when you need to be figuring out how to properly downshift/swerve/pull the emergency brake in the space of .5 seconds..
so i'd still use the integrated one, if only to make for a couple less potential leakage points in the system.. i've been thinking about getting that one for my Camaro when i get around to converting that to manual brakes..
novaderrik wrote:
that switch on the Wilwood integrated prop valve is there to activate the rear brake lights on a street rod or something like that... it won't work to trigger the "BRAKE" light in the dash in the event of a catastrophic loss of pressure to either the front or rear brakes
hmmm, i hadn't thought of it as a trigger for the brake lights on the rear of the car. seems like they over-complicated the valve assembly if that's the only purpose, as they could've triggered off the rear circuit and not included all the casting and machining of running the front circuit through the valve.
You could also remove the sensor that comes with it and install an analog pressure sensor for a data logger.
To trigger the dash indicator you should stick with a float in the MC reservoir. Anything else you could hook up to indicate a brake system leak would be telling a decent driver something they already know.
GameboyRMH wrote:
You could also remove the sensor that comes with it and install an analog pressure sensor for a data logger.
To trigger the dash indicator you should stick with a float in the MC reservoir. Anything else you could hook up to indicate a brake system leak would be telling a decent driver something they already know.
but a decent driver would never let their fluid level get low. 
The light will come on with just a slight drop in the fluid level, that could notify you of slight leaks that you can't feel from the pedal.
GameboyRMH wrote:
The light will come on with just a slight drop in the fluid level, that could notify you of slight leaks that you can't feel from the pedal.
no, it takes a significant drop in fluid level, otherwise it would come on under hard acceleration / deceleration / cornering (depending on float location). systems are designed such that the light comes on when the fluid level is at or slightly below the MIN line when the vehicle is stationary on level ground.
Oh on my 'rolla and sammy the trigger level is less than 1cm below the max. level mark (edit: which is the recommended min. level, but below that there's a reserve of about 8x as much fluid). And if the level drops a little it will come on under hard accel/decel/cornering (right turns on the 'rolla).
In reply to AngryCorvair:
The issue I have, is none of the brakes I'm running are original to this van. The fronts are 11" vented off a 93 van that are the same brakes used on the spirit and daytona r/ts, the rears are 11" solid rotors off an '01 awd van. The original brakes are 10.5 vented fronts and 220mm drum rear. The bias on the factory 89 prop valve will probably be insufficient for my current setup. I think there will be too much rear pressure and cause the rears to lock early. I could run adjustable valves after the factory valve, but I'd need two and have to figure out how to set them identical to one another. Also, I'm re-plumbing the entire system, so I figured I would just set it up for a f/r split and save myself another headache.
EDIT: also, there is a sensor on the factory valve that looks identical to the one on the wilwood part, I assumed it was for a brake idiot light.
In reply to moparman76_69:
I think you'll find just the opposite, because (within a given wheel package) an OE drum brake will generate more torque for a given pressure than an OE disc brake. So switching from rear drum to rear disc and keeping the OE prop valve, you will be UNDER-braked at the rear.
i don't know the specifics of mopar minivan prop valves, but i'd start going through the parts catalogs looking for a prop that was used on a rear disc vehicle. it will certainly be closer to correct than the rear-drum valve you've got. i'd also use the master cylinder from the rear-disc vehicle. are there applicable parts from the '01 AWD van?
the switch on factory valve is almost certainly a "differential pressure switch" which lights the idiot light in case of a big pressure delta between circuits, indicating a leak somewhere.
GameboyRMH wrote:
AngryCorvair wrote:
In reply to moparman76_69:
I think you'll find just the opposite, because (within a given wheel package) an OE drum brake will generate more torque for a given pressure than an OE disc brake. So switching from rear drum to rear disc and keeping the OE prop valve, you will be UNDER-braked at the rear.
Really? I always thought stock prop valves meant for drum brakes send more pressure to the rear than ones meant for all-round-disc setups. I thought drums need more pressure than discs.
fixed quote format.
nope, what i stated is correct. you may be thinking of converting an all-drum vehicle to front disc, in which case the rear pressure has to be dialed down, but again that's because of the higher specific torque of a drum brake -- changing fronts from drum to disc reduces front brake torque, which requires lowering rear pressure to avoid rear bias.
Just found this in my Escort shop Manual.
testing the brake pressure differential valve without ABS.
Pressure gauges are needed.
Front brake pressure -284psi
Rear pressure- 284 psi +-28 psi
Then, press the pedal until 427 psi front.
rear pressure- 384 psi +-
Front pressure - 853 psi
rear pressure-498-611 psi
