Stock S14 Proportioning Valve Info

[AceInHole]

I'm working on increasing rear brake pressure, and the first step is either bypassing or modifying the stock proportioning valve. Luckily, the S14 has an external proportioning valve, so tonight I took apart a spare (body comes apart with a couple 22mm wrenches):

http://i114.photobucket.com/albums/n247/AceInHole/PirateS14/Brakes/DSC_8266.jpg

The black phallic looking thing (second to the right) is the piston and flow control. The spring next to it controls the split point, where rear brake pressure is cut off at a set maximum (just above 400psi for the S14).

http://i114.photobucket.com/albums/n247/AceInHole/PirateS14/Brakes/DSC_8267.jpg

As pressure below the spring builds, it moves up and blocks flow.

Two options are to shim the spring to raise the split point, or remove the entire assembly and run an adjustable prop valve on the rear brake line. For now, since I'm not expecting my adjustable valve to come in till next week, I might do some experimenting shimming the valve to see how much rear pressure rises.

[shoes59]

Luckily, the S14 has an external proportioning valve
It does? Where is it located?

[mmdb]

Two options are to shim the spring to raise the split point, or remove the entire assembly and run an adjustable prop valve on the rear brake line.

I did the latter using Tilton's knob style proportioning valve. By totally removing the proportioning valve and adding the tilton unit adds more brake pressure to the rear, but I have yet to find a combination to effectively control the front/rear brake pressure with the knob. It's either the pads rears are too aggressive, or the fronts are. Ultimately, I stuck with the same pads all around with a tad more break pressure up front.

[eye-5]

I'm very interested in this. I did the Q45 rotors & calipers up front but kept the rear stock. Brake modulation and pure stopping is a night and day difference but I still seem to lock the fronts first.

[AceInHole]

It does? Where is it located?

It screws into the master cylinder on the bottom at an angle, and the rear brake hard line goes into it from there.

I did the latter using Tilton's knob style proportioning valve. By totally removing the proportioning valve and adding the tilton unit adds more brake pressure to the rear, but I have yet to find a combination to effectively control the front/rear brake pressure with the knob.

I'm probably going to experiment with shimming the valve until I'm close, and then add the aftermarket valve in-line after that. The Tilton manual (http://www.tiltonracing.com/pdfs/98-1261_Prop_valves.pdf) indicates that it's only adjusting where pressure reduction begins, whereas the S14 prop valve is completely cutting off pressure at a set amount. What I'm shooting for is using the adjustable valve to adjust the pressure curve, and modify the stock valve for majority of bias.

Anyways, I did some simple measurements:

- The piston is roughly 0.25" in diameter, with an area of 0.049 sqin.
- The FSM lists the pressure split at 427psi, which means the spring must be preloaded 20.96 lbs.
- With roughly 0.125 lbs of preload, the spring constant should then be 167.68 lbs/ in.

If I'm looking for a 10% increment in rear brakes, I'll need a 0.0125" spacer. For anyone looking to attempt the same thing, McMaster part number 99040A512 should work (0.012" thick, pack of 25). For more adjustability, there's other shims in varying thicknesses all the way down to 0.001", but I'd have to wonder if the stock valve is consistent enough to notice small changes. I'm also fairly certain my rough estimates using a scale (ruler) aren't accurate enough :P If I get the chance I'll head down to the inspection department at work and measure it up with some real tools.

[eye-5]

here is a wilwood proportioning valve. Probably simmilar to the Tilton's. Would you remove the stock one and replace it with this or would you put it in line? Interested to see how Ace's setup works.

http://silverminemotors.com/product.sc?categoryId=11&productId=37

[2Fass240us]

It screws into the master cylinder on the bottom at an angle, and the rear brake hard line goes into it from there.I was wondering what that retarted-looking thing was. :) Need an extra one? :)

[AceInHole]

I've already got a spare, although I ended up shimming the crap out of the stock prop valve since all I had in the garage were some small washers. I have the adjustable valve in-line with it, and will remove the stock limiter if needed later, which I'm doubting since I have about a 1/16" shim in there.

[mmdb]

It'd be quicker to tweak the tilton unit, or similar, on the fly; rather than adjusting the valve with washer and getting air into the brake system. Ultimately, you'll accomplish the same thing with a knob as with the washer, but the knob style will allow dynamic adjustment while on the track, rather than when you're car is in the pit. My opinion anyway.

[AceInHole]

Eventually I'll run the prop valve into the cabin, since I already have the adjustable unit. For now I'm just looking for an incremental adjustment to see if something like shimming the stock prop valve will work.

There's also the difference in limiting as well, as the stock prop valve seems to do a full cutoff at a certain point. This gives you a second method of controlling bias and setting up a 2nd split point, for 3 stages of bias. I'm assuming brake pressure isn't exactly linearly proportional to weight transfer on braking, so this may help tailor the bias curve a bit more.

[eye-5]

I saw one that was a lever type that clicks specifically for adjusting in cockpit. Sounds like F1 stuff adjusting brake bias during the race.

[AceInHole]

I'm sure adjusting bias would be useful in some forms of racing, especially when tire wear or changing temps play a big role, like enduros and such. For autocrossers, you're pretty much never going to make a change while driving.

[eye-5]

I hear ya. I am an autocrosser myself. I don't even like to look at a gauge during a run let alone adjust anything. Too busy looking ahead. I end up doing my work assignment in the morning (technology setting up the computers timing etc.) so I rarely get more than one course walk.

[Solo_S14]

I really hope nobody hates me bumping threads from the summer. If you do, or if it's a forum rule, let me know and I'll try pm'ing the users.

But what was the outcome of your shimming experiments? Did it work well at all, or did you end up giving up on this and using the proportioning valve?

This could potentially help with my braking issues, so I'm very interested to hear what came of this. Thanks.

[AceInHole]

Sorry for the late reply.

The shimming seemed to help a lot. I'm still going to be taking out the stock prop valve entirely, since we're still locking up fronts due to the staggered tire size creating a leverage disadvantage for the rear brakes.

Considering the cost (time, brake fluid, and a small set of washers), I'd just keep shimming the stock prop valve till it worked better if I didn't want to run an adjustable prop valve.

[2Fass240us]

PJ: What is your front:rear stagger? Can you go any larger in the front?

I always think it's funny that S-chassis guys stagger as much as they do, even given the fitment difficulty in the front. My goal is to have the same size rubber on all 4 corners.

[SM240]

Thats not a hard goal unless

a- you want 315s all around
b-you have an s13 :)

[2Fass240us]

Good thing neither of those conditions applies. I am shooting for 285's or 295's.

And Bumnah always wonders why I like S14's better. :)

[Solo_S14]

Luckily, the S14 has an external proportioning valve,


I've got a few questions about the Z32 17/16" BMC.
I don't think it has an external proportioning valve like the S14 BMC.
I assume I can't take advantage of this then?

2nd (and more outside the box) question.
I have 2 front outputs and one rear.
Previously, only one of the fronts was used, plumed into the ABS block.
What if the rear was plugged, and one of the fronts used for the rear?
Then I would assume that both lines would get equal pressure, and you could run a prop valve for the rear?
Any reason this would be unsafe?

[AceInHole]

PJ: What is your front:rear stagger? Can you go any larger in the front?

I always think it's funny that S-chassis guys stagger as much as they do, even given the fitment difficulty in the front. My goal is to have the same size rubber on all 4 corners.

Fronts - 24.9" rolling diameter
Rear - 25.6" diameter + 0.9" tread width

I'd go bigger up front but it's already a tight fit, and SCCA Solo SM rules won't let me tub the front to run any bigger without jacking up the front (and I'm trying to get the car even lower). Meanwhile, I need as much rubber as I can get in back to keep the torque in check, and to keep the AWD guys from killing off the lights at ProSolos.

[AceInHole]

I've got a few questions about the Z32 17/16" BMC.
I don't think it has an external proportioning valve like the S14 BMC.
I assume I can't take advantage of this then?
My 17/16" BMC has what looks to be an adjustable prop valve in it (either that or it's just a set screw that I was turning for no reason?). I'll try and snag a pic of it next time I'm at the garage.

[Solo_S14]

When I bought my car I got a CD with some pics of previous progress.
One of the folders had a bunch of pics looking like a BMC swap.
Feel free to browse this album and see if you can pick out the set screw you were talking about. I think one of them may just hold the inners in, but I really know little about BMC's, as I've never taken one apart.

http://picasaweb.google.com/puddincole/BMC?authkey=Gv1sRgCKPj0fX8qsb0cA#


Also, this pic is interesting.
Is this a "bmc bleed" or something?

http://lh6.ggpht.com/_bPcbild_wyQ/S9eKCo2Q6nI/AAAAAAAACjU/r7FnXK4LX7Q/_MG_9739.JPG

[e1_griego]

Yeah, that's how you bench bleed the master.

[Solo_S14]

So if I've got brand new brake lines, unbled.
And my bmc has been sitting on a shelf for months.

Should I just bleed through all calipers as normal instead of doing this?
Everything is installed dry right now, I can do either, but normal bleeding would be easier.

Also Ace, is this the set screw you're talking about?

http://lh4.ggpht.com/_bPcbild_wyQ/S9eKBB04NAI/AAAAAAAACjE/9FHg__dhzSw/_MG_9671.JPG

[AceInHole]

Thats what I assumed to be the prop valve, although its not listed as being adjustable in the z32 FSM I have...

[Solo_S14]

Yeah mine actually has some "metallic tape" over that end. I assume it's so that people don't pick at it.

Is there an assembly pic in the FSM?
It might just be there to hold everything in?

[Solo_S14]

Something I hadn't even checked on my bmc.
Apparently some have this and some do not have this.
It's the flare for the 3rd hole in the Z32 bmc (the 2nd front hole).

If I don't have this, any idea where I can find one very quickly?
Dealer part maybe???

http://importnut.net/240pics/brake_upgrade/mcswap/MCswap15.JPG

[Solo_S14]

Turns out you can use a bubble flair on that fitting instead of the inner flair part.

And I found out how to make a bubble flair with a double flair tool.
http://www.youtube.com/watch?v=HVbHk0kkX8k

[cdlong]

generally, it's suggested to cut one out of your old MC. mine was already set up and i have an old s14 MC if you're desperate. it's been in a box for 4 years, i don't think i need it. i highly highly doubt the prop valve is adjustable, probably just to hold everything in as mentioned.

[Solo_S14]

Do you guys not approve of the bubble flare?
My "deadline" for the car was supposed to be this weekend, and I don't want to get held up on this.

Any reason I can't just re-flare the line?