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411-412 rear brake pressure regulator
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raygreenwood
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PostPosted: Sat Oct 01, 2016 5:07 pm    Post subject: 411-412 rear brake pressure regulator Reply with quote

Ok…the 411-412 rear brake pressure regulator. First…as usual…some back-story/history.

I have never in my life even during the internet years seen a NEW/NOS, complete brake pressure regulator available. These went on…as far as I know….VW 411/412, Porsche 914 and from what I have just recently figured out….some BMW of the era like some of the 2002, the 2.8 CS, 3.0 csi and E9 and E21 series. I have read anecdotal info that also suggests some Mercedes etc. It was an adjustable ATE brake product so I could see it being on anything from Audi to Saab to Volvo etc.

It makes no difference. If you find one of these intact and NOS……its ancient, worthless as anything but a core and it and will have the EXACT same failings as an ancient NOS master cylinder because it has an EPDM pressure cup…and more likely might even have an EPR rubber cup if its pre-1970.

Add to that…since the BMW and Porsche crowd routinely glean the market for these parts….the going rate of the few that I have seen…all used…. and supposedly “Fun-k-shun-ull”…range in the $200-$300 range. I cannot imagine what an NOS part with a 40 year dead seal would cost.

When I got my first 411 in 1978, and on into my first 412 in the early 80’s…and onward…the brake pressure regulator was one of the normal frequently failing parts. At that time the dealer listed…about circa 1980…prices that ranged from about $350 (far above what my sacking groceries and being a lifeguard/water safety instructor paycheck could afford)….and later the microfiche changed and the price was listed at $999 at the dealer.

The dealer informed me that price listings of $999 were unofficial “code” to let them know that there were no longer any parts on this continent and all had been shipped back to Germany for either storage, destruction or who knows what. They were not YET listed as NLA…because technically they were still available but only if you had the money, connections and drive to demand and import the parts.

The EFI system harness, Windshield gasket set and a few other parts were also listed as $999 price. Very telling.

So what does this thing do?

I will keep this simple. There are two basic ways (not looking at newer more modern cars) that brake pressure regulators are employed.

1. Brake pressure PROPORTIONING UNIT: On some cars the regulator has twin circuits inside. The front fluid input side from the master cylinders for the front brakes…goes straight into the regulator and straight out to the front calipers. The regulator does nothing to change the front pressure. It just measures or senses that pressure.

While it’s going through the regulator…the fluid presses on a piston or a diaphragm. Call that the sensor segment. That sensor segment moves or changes an orifice.
That orifice …controls the rear brake circuit pressure.
So the rear brake output line from the master cylinder goes into a separate port on the regulator….and the outlet orifice which is controlled by the pressure in the front circuit….REDUCES the rear circuit outlet pressure to the rear wheel brakes ….in a manner that is Proportional to the rise in pressure on the front circuit. It may either have a linear ratio or may have a rising rate ratio.

Image may have been reduced in size. Click image to view fullscreen.


An example of a nice aftermarket proportioning unit from Wilwood. Note that it has inlet/outlet for both front and rear, twin outlets for left and right front and a single metered outlet for rear, an adjuster knob and a brake light connection. Nice part for $100 or less

2. Rear brake pressure REGULATOR (simple): These are simpler. The regulator only has one fluid inlet from the rear brake circuit of the master cylinder. It may have two outlets…one to the left and right rear wheel brakes…or it may have a single outlet that goes to a tee to feed both sides. This unit lets master cylinder pressure go straight through 1:1 to the rear brakes….until….the input pressure from the Master cylinder reaches a pre-set/pre-determined level. Then….the regulator prevents it from rising any higher than the pre-set pressure.

It still maintains pressure so you don’t stop braking in the rear. Many of these also may not prevent the pressure from rising higher…but they greatly slow the rate of rise.

Image may have been reduced in size. Click image to view fullscreen.


Other than our stock configuration, this is one of the most common. It has a single inlet and outlet and is for the rear brake circuit (or front depending on what you need). Not bad for $40

Do I need a rear brake pressure regulator?

Bluntly put: these units are needed when the way a cars suspension or weight distribution is designed…..causes the nose to dive far enough and fast enough….in relation to forward motion and enertia….to cause significant enough forward weight transfer and lifting in the rear of the car (which removes tractive weight from the tires)….to allow the rear brakes to lock up prematurely and skid with the increase in brake fluid pressure….which is largely the same as what the front wheels are receiving at the same time.

With bone stock struts, springs and stock tire sidewall heights…..and the fact that they do not have self-adjusting rear drums so that at any given time the braking efficiency on the rear may not be perfect….the 411 and 412 sedans MOST ASSUREDLY need this regulator.

Why does the 411/412 wagon/Variant not have a regulator?: I had to look at my notes from over the years and what I found out a long time back….but the most stand out reasons are this:

1. The wagons came from the factory with gas shocks in the rear. They had a lot more control over both rebound and compression. If you look at the springs on the variant as well…the rear coil springs are fatter in the load control area. In short…..the wagons do not have as much forward dive or weight transfer/rear lifting as the sedans. This does not mean they handle better…they just don’t have as much inertia dive on hard braking.

The regulator on the 411/412 really only comes into play during panic braking….meaning slamming on the brakes at speed. This causes severe forward inertia shift and lifting. 99% of the rest of the time…even normal hard braking will not cause the regulator to kick in.

But…..in the handful of times I have actually needed it….. and I knew mine was not working properly…. it was clear that it does work…when it’s working.

The few times that a poorly operating rear brake pressure regulator reared its ugly head…were almost always either when my tires were almost bald (low traction), I was on very rough uneven pavement (variable traction)…or on wet pavement (no traction).
The symptom is a sharp poke on the brakes…causes a sharp dive to the front end….and the rear wheels instantly lock up…and the rear end starts to come around and try to pass the front end. Scary.

It can also be readily seen….that having very bad compression control on worn out front struts…will also add HEAVILY to this problem.


IMPORTANT: For the last 40K miles of my car driving…when it last drove….it has no brake pressure regulator. I could not get parts. So….I put in a tee and rear lines from a wagon and ran the fluid straight through.

And…I had no issues at all. This is most probably because the front suspension is much more controlled because I have the Audi 4000 strut mod…and I am using KYB rear shocks. This controls the level and inertia dive of the car greatly.
There is about a 90+% chance that with these modifications the rear regulator is no longer required. I am also using 205/60-15 tires which have much more tractive effort as well….so that probably plays into the equation. I also have the dual rear sway bar mod. That should help as well.

Regulator failure points/symptoms:

It’s a pretty good design over all. Its main suffering is from materials as many other items from that era.

1. The plastic bypass pintle is Nylon 6. It absorbs moisture and crumbles to dust. In cars where the owners have not flushed the brakes on a regular enough basis…..the moisture in the system is absorbed into the nylon and it rots away.

So…the unit can either not function when needed and/or in many cases the crumbled nylon eventually blocks fluid flow and you start getting normal braking issues in the rear because fluid will not pass.

2. This same moisture issue can rust the inside of the bore causing fluid to bypass the cup (usually this is known when fluid fills the spring cavity and starts leaking from the seals and adjusting screw and the unit does not function right)….and this same rusted bore even before damaging the seal cup…causes drag on the piston movement which throws off the calibration.

3. The seal material…on the early ones and the repair kits…was obviously EPR instead of EPDM in some cases as the seal cups and O-ring would break down with some of the newer fluids.

4. The O-ring inside….it took me a long time to understand its function….is an important seal. It is designed to keep the fluid flowing from the inlet orifice of the piston, through the outlet valve end and into the brake lines…instead of letting fluid bypass from the outlet valve end of the piston and back towards the inlet side effectively causing a loop and poor metering. This is the only weak part of the design. When this fails…you can get oscillations of the rear brakes…on again off again locking in rapid succession on hard braking.

The parts:

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This is the book showing the Tee on the variant with no regulator

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This is the book for the two and four door sedan showing the regulator, part #15

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The part # for the regulator is 411 611 955

The internal parts:

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This book (Haynes) has a typo in it. The part labeled #10 on the left hand side is actually #14

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This is the unit taken apart. The piston assembly as you can see has the tail broken off the right end and is missing the pressure cup.



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The piston and valve is an integral unit. The poppet valve assembly is the brass part with the nylon button. The groove in the middle is where the separating O-ring goes. You can see from the lower holes where the fluid enters…that the piston is hollow so that fluid flows through it.

Image may have been reduced in size. Click image to view fullscreen.


…and when the piston is pushed up against the outer cap…the nylon button is pushed a fluid flows freely through the two orifices in the brass valve body to the rear brakes in a 1:1 ratio.

Image may have been reduced in size. Click image to view fullscreen.


This is what’s inside. So…..the fluid inters the semi sealed chamber on the right side of that O-ring groove and enters the hollow piston through those two holes in the aluminum piston.

The small brass hex nut at the right hand base of the spring is not a nut. It’s a hex shaped block…yes…with a screwdriver slot…

Image may have been reduced in size. Click image to view fullscreen.


Here it is standing up to see the slot on the right in this picture.

.....but that slot is sitting on top of a precision orifice inside and is there to allow fluid past the flat bottom of that piece of brass.

At the top of the spring on the left side is a nylon valve that plugs an opening in the brass hex nut on the right. The hex nut has openings to let fluid out. This is carefully engineered….as the nylon flare/seat of the valve cannot
TOTALLY fully stop fluid flow…but it greatly limits it in a precision manner.

Image may have been reduced in size. Click image to view fullscreen.


It’s hard to see in this picture…but the third step down from the top on the inside view of the piston is a stainless “cup” pressed in. The bras hex shaped spring seat fits in this. There is a precision drilled orifice hole in the bottom.

Parts break down of the piston/valve assembly:

Image may have been reduced in size. Click image to view fullscreen.


Ok….look at this first. The cylinder and spring is not on it in this view. This piston is shown as it would look during normal driving and braking with the nylon button up against the steel outer cap from main spring pressure, allowing full fluid flow to the rear brakes

How the 411/412 regulator works:


Image may have been reduced in size. Click image to view fullscreen.


Sorry for the crude drawing…but this is normal flow…..meaning it has not started regulation yet and the nylon button is up against the steel outer cap…which is what actuates it. You can see the main spring to the right.

So fluid flows in….and does push against and inflate the piston cup to the right, but does not have enough pressure until it reaches 530 psi…to move the piston to the right and pull the nylon button away from the steel outer cap…to close the valve inside…and start the pressure regulation.

So if you follow the red arrows, they enter the orifices in the aluminum piston in the middle, flow through the center orifice, around the spring, around the flared nylon poppet valve, into the brass valve head and out of the two fluid orifices into the chamber surrounding and out to the rear brake lines.

Image may have been reduced in size. Click image to view fullscreen.


If you look closely…it’s not the same sketch. The piston has moved slightly to the right because it now has over 529 psi of inlet pressure. The nylon poppet valve button is now extended as the piston moves away from the steel cap.

This causes the nylon valve to plug (at least for the most part) the opening that lets fluid out of the brass valve body. Notice also that the red flow arrows have gotten smaller.

So….a simple Wilwood or similar unit installed either at the rear or better yet under the dash next to the master cylinder should be able to fully replace the stock unit. You can slightly stretch the stock lines and connect a standard brass brake Tee in the rear…or pull pre-bent lines from a wagon along with the Tee or get about 3 feet of new steel line for each side of the car and bend some lines to connect between the tee and the flexible brake lines on the trailing arms.
Ray
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titan3c
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PostPosted: Mon Oct 03, 2016 4:49 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Thank you Ray for this detailed lesson on the brake regulator. It gives me the understanding and information I need. Now I can proceed with my brake problems with more intelligence than I had. My car has the sway bar, and the KYB shocks. Someday I hope to get to the front Audi suspension, however the front suspension on my car seems to be very solid and works fine. But I'm not an expert on that.

It's interesting to know that the regulator only performs in a panic situation, and has no purpose for normal everyday driving(without a panic stop). Also the rainy slick surface situation could be a scary event without a regulator. So that's a decision making situation----to have or not to have a regulator.

The Wildwood regulator is the one I had picked(not the one next to the MC). Since it is a simple installation, and simple to adjust, why not have one. You can't ever tell when that emergency panic situation will happen.

Your illustrations, descriptions and comments are very professional, and I commend you for that. Thank you, Bob
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PostPosted: Mon Oct 03, 2016 8:04 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Thamnks again Ray for sharing your knowledge, this regulator really needed a detailed explanation!

/Lars S
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PostPosted: Mon Oct 03, 2016 9:38 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Thank you Lars!...and thank you for your link to the 914 regulator in the PM. Awesome information! Very Happy

. If you don't mind..I am going to add that in here as well as my musings/answer....just to keep this all in one place.

Lars note to me:

Quote:

Hallo Ray!

Thanks again for sharing the info!

I happen to have a description for this regulator written for the 914 in the Porsche workshop manual, maybe you already have it - if not you can find it in the link below. Guess the regulated pressure curve is not exactely the same for the Type4.

Thanks again!

/Lars S

http://www.lsmteknik.se/914/914brakereg.pdf

Thank you Lars!....this technical note does confirm something for me. That is that the operation of this regulator ...yes....has a regulation start point (I have read both 525 and 530 psi).....but...as the brake pressure from the MC continues to increase.....the brake pressure for the rear wheels also continues to increase through back and forth operation of the piston....but in a PROPORTIONAL rising manner.

I was not sure if it just reached 525 or 530 psi...and kept that pressure from rising or not.

For example:

When brake pressure hits 525 psi...because of the design of the front and rear circuit pistons in the MC (which have identical stroke length and diameter)...even though there are other small issues at play in the piston design...one "could" infer that brake pressures in the front and rear circuit are identical up until the 525 psi regulation point.

The rear circuit is regulated at a ratio (whatever that ratio is) that is proportional to the front.

So....at 0-525 psi pressure:
Front: 525 psi
Rear: 525 psi

Lets say that the rear is regulated to a rate of 25% less than the front...may be more or less I have no idea

As the pressure in both circuits goes higher past the 525 psi regulating point:
the pressure increase causes this:

Front: 600 psi (100 psi =an increase of 12.5%)
Rear: 574.5 psi (49.2 psi= an increase of 12.5%...minus 25% which = 9.375%).

By piston diameter , cup area and spring force design...I can see how ...as your article noted....the piston would keep oscillating back and forth allowing the fluid pressure to rise...but at a lower designed in proportional ratio.

Thank you! If you don't mind I will cross post your link and answer. Ray


Yes...as per your point about the 914 using a different calibration level....I have also seen in the other link I posted from titan3c's thread...that the BMW used the same regulator but also used a different calibration level.

http://www.e9coupe.com/forum/threads/brake-pressure-regulator-2800cs.14304/

Scroll down to the middle of this thread.

In general..we should be able to use the the simple $40 Wilwood regulator with some testing and adjusting.

Ray
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PostPosted: Mon Oct 03, 2016 9:52 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

raygreenwood wrote:


Yes...as per your point about the 914 using a different calibration level....

Ray


Intresting to see that they made the effort to make another calibration curve also for the 914/6 (6 cylinder model) ....which should be to compensate for its extra rear weight I suppose.


//Lars S
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PostPosted: Mon Oct 03, 2016 10:53 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Yes...probably a combination of things on the 914-6.....heavier weight, stiffer springs and shocks and wider tires/more traction. Ray
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PostPosted: Mon Oct 03, 2016 11:08 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

raygreenwood wrote:
Yes...probably a combination of things on the 914-6.....heavier weight, stiffer springs and shocks and wider tires/more traction. Ray


I noted in the diagram that the 914/6 had a lower rear brake pressure than the 914/4...I would have guessed the opposite since it would be harder to lock up the rear in a 914/6 thanks to heavier in rear and better traction...but again the rear discs and brake pistons for a 914/6 are larger than on the 914/4.


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PostPosted: Mon Oct 03, 2016 6:49 pm    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Lars S wrote:
raygreenwood wrote:
Yes...probably a combination of things on the 914-6.....heavier weight, stiffer springs and shocks and wider tires/more traction. Ray


I noted in the diagram that the 914/6 had a lower rear brake pressure than the 914/4...I would have guessed the opposite since it would be harder to lock up the rear in a 914/6 thanks to heavier in rear and better traction...but again the rear discs and brake pistons for a 914/6 are larger than on the 914/4.


Lars S


Just keep in mind.....that the inertial shift....meaning the heavt weight in the rear causing rear lifting....is because that heavy weight (engine and drivetrain).....cannot slide forward. The back half of the car is literally pivoting around the front axle......so heavier weight means faster lift with more energy. Ray
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PostPosted: Mon Oct 03, 2016 9:50 pm    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

raygreenwood wrote:
Lars S wrote:


I noted in the diagram that the 914/6 had a lower rear brake pressure than the 914/4...I would have guessed the opposite since it would be harder to lock up the rear in a 914/6 thanks to heavier in rear and better traction...but again the rear discs and brake pistons for a 914/6 are larger than on the 914/4.


Lars S


Just keep in mind.....that the inertial shift....meaning the heavt weight in the rear causing rear lifting....is because that heavy weight (engine and drivetrain).....cannot slide forward. The back half of the car is literally pivoting around the front axle......so heavier weight means faster lift with more energy. Ray


Wery true Ray all parameters has to be considered...with that in mind have you found out why the Variant should not have the brake regulator?

/Lars S
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PostPosted: Mon Oct 03, 2016 10:30 pm    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Lars S wrote:
raygreenwood wrote:
Lars S wrote:


I noted in the diagram that the 914/6 had a lower rear brake pressure than the 914/4...I would have guessed the opposite since it would be harder to lock up the rear in a 914/6 thanks to heavier in rear and better traction...but again the rear discs and brake pistons for a 914/6 are larger than on the 914/4.


Lars S


Just keep in mind.....that the inertial shift....meaning the heavt weight in the rear causing rear lifting....is because that heavy weight (engine and drivetrain).....cannot slide forward. The back half of the car is literally pivoting around the front axle......so heavier weight means faster lift with more energy. Ray


Wery true Ray all parameters has to be considered...with that in mind have you found out why the Variant should not have the brake regulator?

/Lars S


I am speculating here.....I am pretty sure it has to do with the rear shocks and springs on the wagon. The wagon came with gas shocks and very wide cross section springs.....and it was slightly heavier but it was spread out.
Weights:
2-door: 2381 lbs.....rear axle gross weight: 1918 lbs.
4-door: 2425 lbs.....rear axle gross weight: 1918 lbs.
Wagon: 2469 lbs.....rear axle gross weight: 2227 lbs.

Front axle gross weight: 1500 lbs. For all.

The springs on the front changed a little over the years.....but the rear coil springs looked like this:

Effective coils: sedans- 7. Wagons- 7.5
Mean coil diameter: sedans-135mm. Wagons- 135 to 139
Wire thickness: sedans- 15.1mm. Wagons- 16.6mm

I also suspect that since the shock extension and compression rod length are the travel stop....the gas shocks on the variants were probably shorter.
Knowing how stiff the oil shocks on the sedans were....and they were VERY stiff......and looking at the load capacity of the variant......the valving on the gas shocks must have been hugely stiff. That would control forward inertial shift a lot. Ray
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PostPosted: Tue Oct 04, 2016 8:32 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Just philosphizing...in a Variant with heavy load in the rear does it matter to the rear lock up question if the load is tied down to the floor or not?
(This is similar to " jumping in a falling elevator" question I know Very Happy )


Lars S
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PostPosted: Tue Oct 04, 2016 9:25 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Lars S wrote:
Just philosphizing...in a Variant with heavy load in the rear does it matter to the rear lock up question if the load is tied down to the floor or not?
(This is similar to " jumping in a falling elevator" question I know Very Happy )


Lars S


Yes....having a heavy load strapped down in the car would probably also negate the some of the need for the regulator. A long time ago...thinking about this lack of regulator on the wagon issue.... I always figured that the VW engineers were going off of pure logic. If you bought a wagon...why would the back ever be empty? Very Happy

I mean...they use some of that same type logic when they designed the front suspension....creating what to me...is a moderate design error. The front load carrying ability is so large that without about 150-200 lbs in the trunk...the front end rides artificially high all the time.

Why would one have a huge trunk in the front end if they dont drive around with it full...therefore keeping the front end nicely level?...problem solved if you simply use the car as it was meant to be used! Laughing
Ray
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PostPosted: Fri Oct 07, 2016 7:39 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

I have one more question. Could a mal-function(of some sort) in the regulator cause a lock in the rear breaks that would release only after sitting idle for about ten minutes? I realize there are other conditions that would cause this, but I was wondering if the regulator could also be a possible cause. Bob
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PostPosted: Fri Oct 07, 2016 8:40 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Yes. Typically this is usually a gummed up or corroded compensation port or flap valve in the MC...and/or it can be swelled up rear rubber brake lines...common.....or it can be the rubber seal coming apart in the brake regulator and plugging the fluid ports.

It can also be pistons on wheel cylinders seizing and shoes not returning due to crusty backing plates and old or broken springs

Also...in the rare case...just had to add this....I have seen this issue when people put DOT 5 fluid in and the system is not squeaky clean. Ray
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PostPosted: Sat Feb 18, 2017 6:21 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Sometime back I replaced my right brake hose because the right rear brake was locking, and would release after sitting about ten minutes. This seemed to correct the problem, but now it has started again. So I'm back on the regulator possibly being the problem. Is it possible the seal Ray mentioned could have crumbled and debris cause a problem with the right brake side of the regulator, and not the left side? I haven't inspected the wheel cylinder situation yet, or the adjustment of the brake shoe clearance. It puzzles me because I ran for several months without a problem after installing the new brake hose. The car isn't driven much, but does get some action. I'm just about ready to remove the regulator, but probably should check the wheel cylinder first. But I keep thinking the problem is with the regulator. It is 46 years old, if that means anything. Bob
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raygreenwood
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PostPosted: Sat Feb 18, 2017 6:57 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

This is a common issue with either the regulator or the wheel cylinder.....if they are both old.

By the way....just this week I discovered that PMB performance has a service to rebuild and restore your brake pressure regulator. I cannot find the right page from my phone....but they also stock a few rebuilt ones.

They range from about $169....which is a fair price. Their paragraph about these is pretty spot on that they are a brake pressure regulator and not a proportioning valve. Really...they are an early anti-skid/anti-lock device.

Its worth it to pull and replace the wheel cylinders if they are old. Ray
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titan3c
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PostPosted: Sat Feb 18, 2017 7:20 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

The wheel cylinders were replaced 3 or 4 year ago, so they should be OK. Anyhow it's a good idea to check it out. That's good information about PMB, I'll check that out too. Question: would there rebuild be properly adjusted for a type 4 vw?
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titan3c
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PostPosted: Sat Feb 18, 2017 7:50 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

Just checked out PMB, and they have a repair kit for Porsche 914 for $59.00. Would that work?
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titan3c
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PostPosted: Sat Feb 18, 2017 9:27 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

As Ray mentioned PMB rebuilds these regulators. I just checked them out, and they do a complete rebuild for $169.00. So I'm planning to do that
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mr white
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PostPosted: Sat Feb 18, 2017 11:41 am    Post subject: Re: 411-412 rear brake pressure regulator Reply with quote

This is probably one of the best technical reads on the samba I have ever read! Great info!! Thanks for taking the time to post it.
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