S13/Z32 BMC - Disabling Prop Valve?

[Def]

So on an S13/Z32 brake master cylinder the front looks kinda like this (random pic):



The left "cylinder," closest to the motor on a LHD car, is covered by this sticker type thing that covers a plug that has an allen wrench drive on it. Take that out and it's got a spring that looks like it's pushing against some sort of o-ring/seal/maybe piston (I couldn't get it out in my 15/16" one).

So if one takes out this spring, does that disable the internal proportioning valve to the rear circuit? Or does anything else need to be taken out.

The other option on installing an adjustable rear prop. valve is to just tee off one of the front circuits and cap the rear circuit off.

[Tower240sx]

I noticed that and disassembled the M/C that came in my 180sx clip,

Didn't dig deep enough into it to really determine but it looks as if you could use shims or maybe just tighten to change the setting...would just take a couple 0-1500psi gauges to tell really

[Def]

I don't want to change the stock one, just want to get it putting full pressure on the rear line.

I'm going to run an adjustable proportioning valve to tweak the car. Seems cheap enough and a big enough benefit for trail braking and overall brake balance.

[Razi]

Def, a quick look at the FSM shows that there are no other proportioning valves in the system besides the one in the master cylinder.

[cdlong]

If you cap off the rear channel, it will continue to build pressure, but not go anywhere. All the fluid would come off the front channel. You'd have an abnormally stiff pedal with less power. I think your only option is to disable the stock one, and I think what you had in mind would do it. Though, you may need to remove more or hack some stuff off the plug so you're left with just a cap.

[AceInHole]

On the S14, I shimmed the prop valve spring to increase rear pressure:


Exploded view:


My next step is to either remove or bore out the floater, although other than locking up fronts on occasion the car already rotates under braking, so I'll probably see how it is with ABS first.

I'm guessing the S13 prop valve is just internal compared to the removeable S14 unit?

[Def]

Looks to be that way.

Where is that valve in relation to the MC/brake lines out of curiousity?

[AceInHole]

Looks to be that way.

Where is that valve in relation to the MC/brake lines out of curiousity?

Sticks right off the MC. The hard line to the rear comes directly off of it.

[CodyAce]

On the S14, I shimmed the prop valve spring to increase rear pressure:

My next step is to either remove or bore out the floater, although other than locking up fronts on occasion the car already rotates under braking, so I'll probably see how it is with ABS first.

Is that a Z31 or Z32 MC?

[hai1206vn]

Ace's mod is for s14 MC only.

[Ando]

I was just checking this out with the reman Z32(B30) master cylinder that I got. I took my original S13 non abs master cylinder Prop valve plug out and I could not remove the proportioning spring assembly inside. It was wedged in there good. Short of drilling it and tapping the hole and using a bolt to pull it out, it would not come out. I took the prop valve plug out of the reman B30 MC and there was NO spring assembly inside. I did a quick air flow check(blowing on the plug opening) and there was NO air flow internally between the front and rear cylinders. So I installed the B30 MC in my DefSport front and stock rear braked S13, bleed and went. I have an adjustable proportioning valve installed inline right at the outlet on the rear of the MC. With the stock S13 rears and the Prop valve all the way open I still lock the fronts first, but I am getting good action out of the rears, they heat up well and seem to be braking well.

Potential issues are;
Just blowing on the MC may not be a comprehensive determinant of internal flow.

With the B30 MC, rear S13 brakes could use more pressure, Z32s should be in the right range.

Is my reman MC missing the factory proportioning spring?

How can you comprehensively bleed these dumb Nissan master cylinders with so much internal capacity?

Something like this
Wilwood tandem master
would be an easy adaptation and get the brake lines on the right side of the car away from the exhaust.

But a true dual master cylinder set up with balance bar would be an easy install. just a piece of square tubing against the fire wall with the stock pedal assembly, two $70 single MCs with a $50 balance bar and you have a truly race grade assembly. Not to mention the space you would save with no brake booster.

Additionally, the MC that I got was the same part number for both ABS and non-ABS cars. So of course it has the plug in the second front outlet and NO flare in the plugged hole, so I could not just attach my lines. The flares from my old MC would not come out no matter what I tried. So I had to get a brass flared fitting, and grind it down until it fit inside.

Why the Dual MC is better then the Adjustable proportioning valve.
http://www.stoptech.com proportioning_valves