You asked for it. You got it. PMB Pressure regulator service!

Link to "Member Vendor Thread":

http://www.914world.com/bbs2/index.php?showtopic=261407

Repeat after me, "Pressure Regulator" -- "Pressure Regulator"

That's right, this little beast is a pressure regulator, "NOT" a proportioning valve. It proportions "NADA". It is the first anti-lock brake device ever to be installed on a Porsche. Here's the story:

The 914 is a mid-engine automobile. As such, it has amazing handling characteristics... to a point. Once that point is reached, it can bite you like a rabid dog. It's a physics principle called "Polar Moment Inertia". We're all familiar with the childs play toy the "top". Here it is straight out of Mr. Elford's mouth: http://www.amazon.com/Porsche-High-Perform...d/dp/0760327548

Porsche knew the issues with rear and mid-engined automobiles so, they installed this pressure regulator in the system to prevent the rear wheels from ever locking up. You see, if you lock your rear wheels in a rear or mid-engine car and your front wheels are anything but straight, you can be that "top" we were talking about and, that's not a fun toy at that time. This pressure regulator senses a panic stop (which it is set and locked at 525psi). Once it sees that pressure on the system, the valve body slides over and activates a micro-switch check valve which shuts off pressure to the rear wheels. This is a panic stop mind you, this device flows fluid like a "T" fitting until you need it. That's why we insist that it proportions "Nothing". Once the pressure equalizes in the chamber, it brings the rear calipers back into the circuit. This is "split second" stuff gang, not a leisurely event.

So, yeah, the internet guru's steered you in the wrong direction. You "never" want to replace this regulator with a "T" fitting in a street car and, you want to make sure it's operating properly otherwise, your rear calipers aren't even working and, that's 30% of your braking power.

Here's what we do; We will completely disassemble the regulator. We will zinc plate the spring housing and the valve housing. We will clean and reseal the valve body using new EPDM seals throughout. We will repaint the freshly plated spring housing and the valve housing. We will zinc plate the mount and the fasteners. We will then reassemble the regulator and reset the pressure switch to 525psi. We will then epoxy the lock nut just like the factory and send you back a perfectly operating pressure regulator that not only makes sure you and your passengers are safe but, it give you back your full braking potential so your 914 stops as good as it did when it was new (and that's still damn good my friends).

$169.95 plus $15.00 shipping in the Continental United States (we ship worldwide)

Early Cars (you'll have a brass "T" fitting at the top):
http://www.pmbperformance.com/914-brakes/E..._Regulator.html

Late Cars (you'll have a different right line that exits the valve in the rear):
http://www.pmbperformance.com/914-brakes/L..._Regulator.html

Spot on factory two-tone finish:

Of course.... I already sent Scott a message to ship mine to you Eric. Thanks for taking care of our brakes and keeping our cars safe.

Repair Kits are available now as well!

http://www.914world.com/bbs2/index.php?showtopic=261415

how do we know if ours needs servicing?

Zach - don't worry. You have no chance of spinning out in your car.

How much are repair kits. I can't find them on the site.

ha!

nice

Eric, I just ordered four newly rebuilt calipers, rotors, and brake lines from you (thanks!). How do I know if I need this proportioning valve (oops) I mean pressure regulator?

Since I am replacing all of my brake components, this is a no brainer.

I was waiting on this as well. After 40 years of use I can't see how it would be a mistake to get this done. It's a pain if the car won't go, it's frightening if it won't stop.

I believe they regulate proportionally.

http://www.pmbperformance.com/diy-caliper-...ulator_Kit.html

Sit in your lonely garage tonight and tromp on the pedal. If you hear a "click-click" from behind your drivers seat it should be working. Emulate a panic stop.

If you've properly set your venting clearance and your rear calipers are still not working, you may have a problem. Look for less material being taken off the rotor. We've had customers that have rust on their rear rotors. That's a good indicator.

Do I need this or want this with my 930 calipers? Right now I just have a T fitting.

Can you post a video of this valve clicking?

If it's a street car, yes.

A microswitch is an electronic device. Where, pray tell, are the wires that go to the switch? Please point them out to me.

Can you also explain the pressure graph in the factory workshop manual, that shows the pressure coming out of the valve rising with the pressure going in, and then the slope of the curve changing at one pre-defined point, even though it continues to rise?

There is no microswitch. The thing on the firewall behind the driver is a spring-loaded valve. Actually, a couple of spring-loaded valves that work together.

I realize you know brakes like very few of us do, but you are utterly wrong on at least some of the specifics of this part. I will continue to call it a proportioning valve, because that is now popular parlance for it, even though the factory manuals call it a "pressure regulator".

For those of you following this at home, please check the factory manuals, pages 0.1-4/1 and 0.1-4/2.

--DD

Its a "small-switch" Dave...

Calling it a "Proportioning Valve" is "Utterly Wrong" Dave. Two wrongs don't make a right.

Friends... there is a "very small switch" in the valve body (is it a switch Dave?) that shuts the flow of fluid to the rear calipers until the pressure equalizes in the chamber. So small it could be considered "micro" kinda like Dave's point.

I'll refrain from "Micro-Switch" and call it a "Check Valve".

Here's the factory manual.

Click to view attachment

It's not a switch. Switches are electrical. It's a valve--it's even two valves in one body, I think.

I wish you'd attached the next page in the manual, which shows the graph of the pressure in versus the pressure out. It does NOT stop abruptly at 525 PSI. The outlet pressure continues up, proportionally to the inlet pressure, but at a lesser rate.

--DD

I agree with dave

Hi Eric. I think the -6 has different curves from the -4. Do you rebuild for the -6?

Yikes !
Calm down boys.
Seems a good time to ask...... " 6 " brake regulators are different right ? or are they just the same as early cars and operate at the same pressures ?

The "knee" in the curve is in a different location.

If I am doing it correctly, the graph should be on the second page of the attachment to this post. The first page is the same one that Eric posted.

--DD

Explain to me what, "when" and how it proportions then gents.

Everything I've read in the factory manual says exactly what I've parroted herein (I think) so, perhaps there are different ways to interpret the data?

To me, that "regulator" only regulates once you get to 525psi. Help me understand otherwise. And Chris, you've been down this road before... The thread where you pulled all your comments after you found out how the device worked? What are you seeing now, again, that I'm not?

All current kits in-house sold BTW. Thanks gang. Still taking restoration orders on pressure regulators if you'd like your to work the way it was designed.

Dave, that was the only PDF I had in my computer. You make it sound like I purposely omitted it, which I did not because it actually proves the point. The graph is totally linear as you apply pressure to the system. Once the "CHECK VALVE" releases you get your "abrupt" knee which is where the fluid is shut off to the rears until pressure equalizes in the chamber.

Take one apart. Then post "how" it can magically do what you're telling everyone it does. Specifically, explain how the single "check valve" will do as suggested.

Proportional is linear, the graph in the factor manual is not linear.

http://www.stoptech.com/technical-support/...rtioning-valves

Read down a bit to "Combining Strategies - The Misnamed Proportioning Valve"

Hi Eric, So do you rebuild 914-6 regulators (with the different "knee point")?

As far as I can remember I haven't ever removed comments regarding the rear brake regulator.

My empirical tests and experience tell me the factory description of the regulator operation is inaccurate.
The device does in fact displace fluid to a proportional degree, above the preset starting point. That displacement is linear as the pressure increases, thereby reducing the rate at which the rear brake pressure increases as compared to the front brake pressure.

All this petty bickering over nomenclature...

Eric, I don't have one at all. Is there a core charge if I want to buy one?

As it sits, my 930 brakes work really well. I cannot lock up the rears even if I stand on the pedal. I can lock up the fronts given the same force. I'm long due for a fluid change and would want to install this prior to new fluid.

I have a "T" fitting on mine and have had for the last 10 years. I do not have one of those regulating, proportioning, knee point valve, pressure switch, flow interrupter, check valve thingies. I know the largest tire that can be installed on my car, I don't use WD40 on my paint, I don't use chop sticks to check TDC and I politely explain to people where the motor is.

How about "Rear Brake Pressure Limiting Valve"????


Harvey

It wouldn't work right with those big calipers.

Well they work great now and I don't want to screw it up. Plus my car is not a street car. It's a race car with license plates...

Maybe I'll just keep the T fitting.

It was this thread... read my post #9. To "me" the factory manual never describes it as you stated:

"...the limiting valve does act the same as a racing prop valve, with the check valve opening and closing seamlessly as brake pressure increases."

http://www.914world.com/bbs2/index.php?sho...=191189&hl=

Again, to me, at 525psi this "Check Valve (Dave )" shuts fluid to the rears. This is the clicking that you hear when you tromp on your brake pedal. They go on to state that as the pressure in the line and the chamber rises, the force is sufficient to push the valve back to the left opening the valve again.



OK, I'll bite (again); how do the calipers affect the pressure coming from the master cylinder to this regulator? How do the calipers affect the way this safety device operates?

I will have one on every single street driven 914 I own. Race car = another story.



Bruce Stone called Friday mentioning that he has a few cores.

I feel left out, where's my video?

Sorry, I did not mean to imply that--just that I wished the next page had also been there.




It does not shut off flow. If it shut off the flow, the outlet pressure would be constant. Instead of going up at a shallower slope, the graph would go completely flat. Instead, the outlet pressure continues to rise, in proportion to how much the inlet pressure is over the "knee" pressure.

The first paragraph on the second page of the PDF I posted says "Pressure regulation is governed by the ratio of the surface differential between the annular surface in the chamber and the total piston surface in the chamber." That's how the pressure continues to go up, but at a slower rate than the pressure going in.

--DD

It does shut off flow, exactly as described in the factory manual. As pressure equalizes in the chamber, the valve slides to the left again and opens. Rinse and repeat. In a manner that will give you the exact curve shown.

Again, exactly as described and exactly what I'm attempting to say... "This is not a proportioning valve. It proportions "nada". It is basically one of the very first antilock brake devices, preventing your rear calipers, on your spin susceptible mid-engined 914, from locking.

Sorry, again, please explain how a simple/single check valve will do as you say. The spring and the pressure on the system cause an on/off effect that prevents the rears from locking, that's how. On/Off (it is simply the only way this check valve can possibly work). Aside from the check-valve/micro-switch thingy... you're saying?

Okay i'll bite.... I installed a "T" back in 86 when I installed my first six motor in my car. I was running 911S aluminum calipers in the front and 914-6 rear calipers. Never had a problem in all sorts of street and track driving. I am still running the "T", but now I am running stock Boxster brakes front and rear. Once again never had a problem on street or track. Since the six had a different "valve" setup than the four, is it possible to set one up for the various brake solutions such as my Boxster brakes?

I found this helpful. I hope you all do as well. Let Eric know if you have any questions. You can clearly see the brake proportioning valve in the middle diagram.

Eric ,
Thanks for providing such a service.
Regarding big brakes, I know someone that is running 993 Turbo front and rear brakes. ...includes rotors too.
The only thing that was changed regarding this topic was an adjustable brake balance in place of OEM unit
Yes , car sees track time too.

Dave,
Can you explain how the pressure is regulated by the ratio of the surface differential between the annular surface in the chamber and the total piston surface in the chamber? Is there a dynamic movement of the piston (?) that is causing an increase (or "pulsation") of pressure after the "knee"

Tommy

[/b]Can you explain how the pressure is regulated by the ratio of the surface differential between the annular surface in the chamber and the total piston surface in the chamber?

Pascal's Law of hydraulics.

Is there a dynamic movement of the piston (?)

Assuming you are referencing the wheel cylinder pistons as pulsating then, no. It don't work like the modern anti brake. The check valve merely limits the pressure on the rears as the advantage of that "annular surface" is decreased. The so called "knee" pressure. So there is more pressure to the front and thus more friction to the rotors in the front. Kind of ingenious back then.

Go back to Elliots "Pre Pascal" brake system. Pretty funny for a pilot to joke about!

Sounds like a semantic discussion me thinks.

Don't mean to answer for Dave...I believe we are all friends here? Maybe?