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We were looking at the Duff car last month and while it goes through front brakes with some regularity (2-3 days of track driving), the rear brakes are in their 4th year and still almost new. We wanted to try an adjustable proportioning valve to send some more pressure to the rear, but it doesn't look like the stock system is really set up for adding the valve. It has a dual proportioning valve that uses an "X" pattern and can't see a way to add the adjustable valve unless I either add 2 valves and try to match them (not my first choice) or get rid of the stock proportioning valve. If I get rid of the stock valve, then I lose the redundancy of a dual master cylinder, but this is a track car and I can live with that.

I wanted to check and see if I'm looking at this wrong, so I made a diagram of the stock system and what I'm thinking that it should look like after I am done. This would cost me about $65 in fittings/lines and probably take a couple of hours of work:

https://docs.google.com/drawings/d/1oif ... sp=sharing

Please let me know if there is another way of doing this that I should be looking at.

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"Every ship is a minesweeper, once."

Thinking about it further, I could just take the outputs of my two front brake ports on the stock proportioning valve and send one to the rear brakes through the aftermarket valve and the other to the front through an open T, while capping the rear outlets. That would let me bias them while retaining the redundancy of the dual master cylinder, just in a front-back pattern instead of an X.

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"Every ship is a minesweeper, once."

Using the stock calipers, my guess is the proportioning is setup correctly from the factory. Changing the bias more to the rear will likely induce rear lock-up and make it a real handful under hard braking.

If you want to test the effect of more rear brake bais, why not simply bump up the aggressiveness of the rear pads?

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Vincent Keene
'06 Ford Mustang GT (track rat)
'15 Dodge Charger R/T (yeah, it's got a HEMI!)
'07 Ford Fusion SE (205,000 miles and counting)
'98 Chevy Z-24 (retired)
'93 Acura Integra (Team SWB 24HOL Car)

We got the car after it had already been through multiple engine and suspension swaps, and the calipers (and control arms and knuckles) are ones that I got off of an Integra, while I'm not sure where the proportioning valve that is on it came from. It definitely has an Integra master cylinder, but some of the brake lines are hand-bent, not sure if that's because they got replaced because they were bad or because the master cylinder is different. I believe this model was a DX when new, which would have had tiny disks up front and drums on the rear, as well as the non-VTEC engine. It had the VTEC engine at the time of the collision that took it off the road, but that got sold before we got it, and it had tiny disks in the front, but big disks in the rear, indicating that someone was mashing crap from different cars into it. Also, all of the big bolts that hold the front subframe assembly to the unibody were very loose (the car rattled and shook violently when we first started driving it), so at some point it may have gotten a different front clip. I may try an Integra proportioning valve and see if that's better.

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"Every ship is a minesweeper, once."

My experience with a proportioning valve is Miata only with a single master. Miata's are heavily front biased. What I did on my car is very much like what you have drawn in the 2nd diagram (lower). I replaced the factory bias valve with the adjustable prop valve and connected the front brake lines where they connected to the bias valve with a union. The idea is to have full, uninterrupted pressure to the front brakes and use the prop valve to tune the rears. I can brake harder now than before and use trail braking into a turn without the car pushing as much.

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92 Miata 1.9L naturally aspirated. SSM 21

The 1.8L Miatas are more rearward biased; however, I think Roger isn't going to get what he's looking for with a valve (imho, more pistons in the caliper but uh... good luck with tech inspection).

When you get on the brakes do the rears or fronts lock up first?

The fronts lock up, but the rears never do.

Kraig was saying that it pushed under trail braking at VIR last month. I haven't noticed it doing that when I drive it, but this is the only car that I have ever trail braked, so I have nothing to compare it to, where Kraig has his Miata (and maybe others, not sure how many cars Kraig has). That (and the complete lack of wear on the rear brakes) was what initially prompted me to look into this.

I'll set it up like Jordan said, using the two high pressure ports of the stock dual prop valve to run the front and rear and putting the Wilwood valve in series with the rear brakes. That should let me keep the redundancy of the dual master cylinder while letting me adjust the bias so my rear brakes can do some more work.

We'll be at CMP next weekend, so we'll get to try it on track and see what it does.

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"Every ship is a minesweeper, once."

Yeah, in that case I'd definitely look to send more pressure to the rears.

This is what I keep telling him. Every time he's changed Honda's engineering, he's regretted it.

I'm the one who locks the breaks. And now he's screwing with the balance... I wouldn't want to be my instructor this weekend. I've looked; what has been done can be undone in the span of a classroom session.

(Maybe I should put more effort into sorting out the bug. It's not holding boost.)

I made it so that I can uninstall the whole thing in a few minutes if we don't like it. I drove it around for a while today, and it works as expected. With the valve wide open, the rears now lock up much sooner than the fronts. After a few turns of the valve, they are locking up at about the same time, although the right side seems to lock up before the left side. There's not a lot that I can do on public streets with it, but the brakes are working and it seems close, so we'll play with the valve at CMP this weekend to dial it in. It does feel better under hard braking, and while it's not at the level of my E36 M3, it no longer feels like I'm standing the car on it's nose.

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"Every ship is a minesweeper, once."

It worked; we now use the rear brakes. They have visible wear after a weekend of driving. I was braking much later and ran under 2:00 at CMP in the Duff car for the first time.

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"Every ship is a minesweeper, once."

Indeed. It's a little weird to not have it plow in nose first under heavy braking. At first, I couldn't tell how hard I was on 'em. Given I was getting in the car hot all day Saturday, I didn't get to experience the full potential until my out lap last session, post head gasket replacement I hit the brakes at my normal-for-the-day point (the timing line) for T1 -- "let's see what she does with cold tires" followed shortly by "holy crap!" -- I could've made the right to east course!