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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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 Posted: Wed Feb 21, 2018 8:57 am Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| aeromech wrote: |
Ray,
I’m pretty sure I have a crusty one somewhere if I can find it. Do you need me to look? |
Yes....that would be great. Its not for me.....I dont drive a bus.....so by default....I "technically" don't care!  ......but in reality I do care because if I can easily help you guys solve your problem.....thats a good thing.
The thing about brake pressure regulators/proportioning valves...especially from that era.....and from the diagram the bus regulator is no different in these respects....aside from rust issues.....its about the piston cups, the body seals and any plastic parts that are used....(if any...but I am betting the small valve to the left of the ball is either nylon or brass) in the poppit valve section.
The bus unit is nice in several respects. It looks like it uses an o-ring seal between the two unit halves. This means that you can replace the seal between the two halves without changing the adjustment. Its not hard getting EPDM o-rings or o-ring cord stock.
Also if that posted diagram is correct...notice that the pistons have rounded or beveled areas outboard of the seal cups. This means they are MUCH easier to install. Which means you can use CNC machined EPDM o-rings which are slightly harder than molded ones.
There should also be a flat seal....part #8....that is also EPDM or it may just be a bevelled area if that valve...#9....is made of nylon or brass.
The thing that kills these things is hard, crispy, cracked seals....and rust. If the piston bores are pitted....its the same problem as a master cylinder. You need to hone until the pits are less than .003" in depth.....and at that point.....if the bore is now greater than .005" larger than the pistons.....the cylinder is shot.
But.....the way these are renovated.....is FIRST .....open one up....just generally clean it out.....and measure the two piston heads....then add .002"-.003" max.....and you now know the correct cylinder diameter.
You can acid wash the cast iron body parts to get rid of all rust.....then give it a run through with a proper sized 600-800 grit flex hone....the sizes for bores these small are cheap.
Really....if yours cleans up and you had no real pits.....and the bore is not oversized....just use it as is.
I can find you several places that can cut the cup seals for you CNC. Yeah.....each seal size will probably run you $150-$175.....for about 25-30 of each seal....but that works out to about $7 a seal.
The ability to do a quick and accurate refurb of one of these for $30-ish is a bargain.
The 914 and 411/412 brake proportioning valve is currently rebuilt only by PMB performance. Though ours is a little less complex than the bus in certain ways....its more complex in others.
They have a nice write up on their site.
From experience.....do not sit on your spares wityout opening them and cleaning them up and lubing with brake paste.....because they ROT and RUST while sitting still on the shelf. And.....the seal cups WILL harden up to the point that they do not work. These are no different than the seal cups in master cylinders....and are why NOS master cylinders past about 7 years age....are unreliable junk.
If you have NOS ones.....you would be better served to remove the pistons from the bore so they are not restrained as they harden up from age....and they absolutely do.....and keep the bores lubed with brake paste....and assemble tbem when you need to install them.
If you guys are interested in getting new seals made I can help you find the shops to do that. Post the seal ID on the pistons....the seal thickness and the piston head diameter....and some pictures.
Ray |
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SGKent 
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Joined: October 30, 2007
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Wed Feb 21, 2018 9:53 am Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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there is a big round ball that rolls around based on braking and shuts down the rear ports in a hard brake. No pistons on the late ones at least.
| SGKent wrote: |
Mike (DBM) has posted this a couple of times if it helps
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Wed Feb 21, 2018 10:57 am Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| SGKent wrote: |
there is a big round ball that rolls around based on braking and shuts down the rear ports in a hard brake. No pistons on the late ones at least.
| SGKent wrote: |
Mike (DBM) has posted this a couple of times if it helps
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Thats interesting!
So...the late ones are just the inclined/rolling ball....and the earlier ones like that diagram on the previous page are pistons AND the ball?
In the diagram that Kreemoweet posted...the primary piston...part #1 ...is functionally identical to what and how the type 4/914 regulator works and almost the same pistin shape....and betting same bore size.
In the type 4/914...that primary piston works by staying loaded against a spring that does not allow it to move until brake pressure from the MC reaches a pre-set level.
It then stops the fluid pressure from increasing and just maintains that pre-set max level. Its kind of an early anti-lock/anti-skid feature. This spring pressure is externally adjustable on the type 4/914 unit.
The gist on the type 4/914 model is that forward inertial "dive" is fairly predictable so you can pre-set the pressure and it should prevent rear wheel lockup in most cases.
A bus is not so predictable. You could have six passengers of 2000 lbs of stuff inside of the bus.
The really ingenious thing that I see from the posted diagram....is that instead of a fixed spring pressure operating on the primary piston valve.....you have a secondary piston...that varies the spring pressure...according to the bypass bleed from the inertia ball down below.
So..as inertial dive increases due to weight or loading of the bus....the secondary piston varies the spring pressure that controls when the primary piston vents or does not vent.
Very nice design. Ray |
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SGKent
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Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Wed Feb 21, 2018 1:39 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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I took my old one apart years ago and I do not recall a secondary system in it. I do recall this large ball that blocked the rear ports as it rolled. The design and shape of the early vs late regulators is somewhat different. Also the attachment point for the brake lines changes too.
early 1971 - 1972
late 1973 on
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kreemoweet
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Location: Seattle, WA
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Wed Feb 21, 2018 3:40 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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Thanks - photos below thanks to Kreemoweet & TCash
| Tcash wrote: |
To link to this post copy and paste
| Code: |
| [url=https://www.thesamba.com/vw/forum/viewtopic.php?p=8115511#8115511]Brake Pressure Regulator t2 211 612 501[/url] |
Brake Pressure Regulator t2 211 612 501
211 612 501 Brake Pressure Regulator Early t2. Note bleeder valve on top of valve.
211 612 501 A Brake Pressure Regulator Late t2. Note brake lines attach to the top. No bleeder valve.
Located on the frame rail.
GD
Tcash
| Welt wrote: |
Brake pressure regulator got the ultrasonic treatment too. Soaked the whole part in ethanol before disassembly.
Cleaned the mating surfaces with wet P800 paper.
Valve seal was fine. And all the piston bores looked ok. Piston seals were also in good condition.
Made my own gasket to replace the old crusty one.
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Wed Feb 21, 2018 4:06 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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So.....the late one does have a rubber valve seal and a piston seal. Its interesting how they simplified the late unit.
The seal on the late model is also a standard cup type seal and can be machined from EPDM stock. Ray |
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aeromech
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Joined: January 24, 2006
Posts: 16971
Location: San Diego, California
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| Posted: Wed Feb 21, 2018 6:02 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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Sorry Ray, I couldn't find the one I thought I had
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mlesniak
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Joined: April 08, 2015
Posts: 350
Location: Wisconsin
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| Posted: Wed Apr 29, 2020 2:43 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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My brake pressure regulator seems to be leaking. Im planning on taking it apart soon. Just curious what kind of gasket material will work with brake fluid? EPDM rubber? I've been having trouble find anything in store that's brake fluid compatible...
Also is it possible to replace the VW style brake pressure regulator with one thats more of a modern design / more readily available?
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kreemoweet
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Joined: March 13, 2008
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Location: Seattle, WA
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| Posted: Wed Apr 29, 2020 3:14 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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It was engineered specifically for the characteristics of the VW bus braking system, so I doubt you would find
anything remotely similar in a generic item. The gasket that usually leaks is "paper". There's an o-ring internal
to that with a rectangular cross-section. Someone posted within the last week or so on this forum their measurements
of all the seals in the pressure regulator.
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mlesniak
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Location: Wisconsin
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| Posted: Wed Apr 29, 2020 4:19 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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I still plan on taking my original one apart and rebuilding it...
Is Fel-Pro 3046 Karropak gasket material considered "Paper"?
...I did stumble upon this Wilwood brake proportioning valve. It'd be great if something like this was useable in the bus.
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Last edited by mlesniak on Wed Apr 29, 2020 5:28 pm; edited 1 time in total |
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raygreenwood
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Posts: 21520
Location: Oklahoma City
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| Posted: Wed Apr 29, 2020 5:28 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| kreemoweet wrote: |
It was engineered specifically for the characteristics of the VW bus braking system, so I doubt you would find
anything remotely similar in a generic item. The gasket that usually leaks is "paper". There's an o-ring internal
to that with a rectangular cross-section. Someone posted within the last week or so on this forum their measurements
of all the seals in the pressure regulator. |
Really finding an adjustable one that works for regulating the pressure...is not a problem. Summit alone has at least 400 part numbers and variations.
The difference....is that the bus unit ....uses the inertial forward shift of the bus to tell it WHEN to start regulating. What it regulates to....is not variable. Virtually none of them are.
There are two different kinds of rear brake pressure regulating that are important....not just on a bus but on any car:
1. Long moderate to hard braking (think like downhill at 60 mph) where pressure is increasing...shoes/pads are getting hotter...and therefore brake efficiency will keep increasing (to the point where they get too hot and fade).
The inertial shift is not a big issue with this one but you CAN get rear skidding. At some point when pressure gets high enough....most rear brake pressure regulators....LOCK....the pressure at that point....but sustain it. This prevents wheel skid.
2. Panic braking....sharp, hard jab at the brakes....which causes the rear of th vehicle to lift and the nose to dive. You may not have yet even reached peak "regulating" brake pressure at the rear....but when the weight lifts off the wheels....it takes less force to cause them to lock up.
This is where the inertial (the rolling incline ball) feature comes in handy. It should lock or sustain pressure so it cannot rise any further.
From the cross section diagram posted earlier....I 'think"....the bus regulator does both jobs.
While the layout is different than the 914/411/412 unit.....the parts shape, size and function based on their fluid ducting are the same. That type of unit has a pre-set pressure (based on the spring between the primary and secondary piston).
So even with non-panic braking....when you increase pressure to the pre-set point....it cuts off the feed but maintains the braking pressure on the line. You let off...it instantly bleeds down just like the front brakes at the same time.
The ball keeps the poppit valve closed...until inertia pulls it away...and that just bleeds pressure off....but then when that back chamber floods with this pressure it should equalize across the primary piston...and "may" also modulate the pressure and not just bleed it off. But that last part is speculation.
That inertia effect is pretty important on the bus....for panic braking.
However....if you just needed the normal brake pressure modulation I described earlier....yes....you can find a whole rage of adjustable rear pressure regulators....but you need to choose carefully. It has to have the right range of adjustment and should maintain pressure at the stop point...not just bleed it off.
The 914 model does this. It has no inertia feature like the bus. It has a sensitive set up that is designed to stop increasing brake pressure at 530 lbs.
I have a little bit about aftermarket pressure regulators in this thread
https://www.thesamba.com/vw/forum/viewtopic.php?t=664753
But...with the height and weight of the bus...you really need teh inertia feature....unless you do something that prevents a good portion of it (i.e...less weight in the back, some lowering and suspension stroke limiters).
Ray |
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mlesniak
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Joined: April 08, 2015
Posts: 350
Location: Wisconsin
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| Posted: Wed Apr 29, 2020 5:42 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| raygreenwood wrote: |
| kreemoweet wrote: |
It was engineered specifically for the characteristics of the VW bus braking system, so I doubt you would find
anything remotely similar in a generic item. The gasket that usually leaks is "paper". There's an o-ring internal
to that with a rectangular cross-section. Someone posted within the last week or so on this forum their measurements
of all the seals in the pressure regulator. |
Really finding an adjustable one that works for regulating the pressure...is not a problem. Summit alone has at least 400 part numbers and variations.
The difference....is that the bus unit ....uses the inertial forward shift of the bus to tell it WHEN to start regulating. What it regulates to....is not variable. Virtually none of them are.
There are two different kinds of rear brake pressure regulating that are important....not just on a bus but on any car:
1. Long moderate to hard braking (think like downhill at 60 mph) where pressure is increasing...shoes/pads are getting hotter...and therefore brake efficiency will keep increasing (to the point where they get too hot and fade).
The inertial shift is not a big issue with this one but you CAN get rear skidding. At some point when pressure gets high enough....most rear brake pressure regulators....LOCK....the pressure at that point....but sustain it. This prevents wheel skid.
2. Panic braking....sharp, hard jab at the brakes....which causes the rear of th vehicle to lift and the nose to dive. You may not have yet even reached peak "regulating" brake pressure at the rear....but when the weight lifts off the wheels....it takes less force to cause them to lock up.
This is where the inertial (the rolling incline ball) feature comes in handy. It should lock or sustain pressure so it cannot rise any further.
From the cross section diagram posted earlier....I 'think"....the bus regulator does both jobs.
While the layout is different than the 914/411/412 unit.....the parts shape, size and function based on their fluid ducting are the same. That type of unit has a pre-set pressure (based on the spring between the primary and secondary piston).
So even with non-panic braking....when you increase pressure to the pre-set point....it cuts off the feed but maintains the braking pressure on the line. You let off...it instantly bleeds down just like the front brakes at the same time.
The ball keeps the poppit valve closed...until inertia pulls it away...and that just bleeds pressure off....but then when that back chamber floods with this pressure it should equalize across the primary piston...and "may" also modulate the pressure and not just bleed it off. But that last part is speculation.
That inertia effect is pretty important on the bus....for panic braking.
However....if you just needed the normal brake pressure modulation I described earlier....yes....you can find a whole rage of adjustable rear pressure regulators....but you need to choose carefully. It has to have the right range of adjustment and should maintain pressure at the stop point...not just bleed it off.
The 914 model does this. It has no inertia feature like the bus. It has a sensitive set up that is designed to stop increasing brake pressure at 530 lbs.
I have a little bit about aftermarket pressure regulators in this thread
https://www.thesamba.com/vw/forum/viewtopic.php?t=664753
But...with the height and weight of the bus...you really need teh inertia feature....unless you do something that prevents a good portion of it (i.e...less weight in the back, some lowering and suspension stroke limiters).
Ray |
I actually started reading your thread! Thats where I got the idea for the Wilwood regulator. I'll have to look more into it. Thanks! Sounds like I should stick with rebuilding the original for now. I'll do more research on the aftermarket ones.
I edited in a question about Karropak gasket material on my other post. Any idea if this would be a suitable replacement for the paper gasket in the original VW brake pressure regulator?
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kreemoweet
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SGKent
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Wed Apr 29, 2020 6:44 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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many of the folks here ask basic questions like how to adjust timing, find a fuel leak or find a fuse. Does anyone really think folks are going to find a reliable skid pad, and know how to tune an "adjustable" proportioning valve? Whats next, multiple masters with biasing rods? Give me a break. Someone has been sitting at home too long munching on wheaties.
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mlesniak
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Posts: 350
Location: Wisconsin
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| Posted: Wed Apr 29, 2020 8:00 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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Thanks I'll definitely send a PM. Ive also messaged some other samba members that have rebuilt theirs.
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kreemoweet
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Joined: March 13, 2008
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Location: Seattle, WA
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| Posted: Wed Apr 29, 2020 8:56 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| SGKent wrote: |
| many of the folks here ask basic questions like how to adjust timing, find a fuel leak or find a fuse. Does anyone really think folks are going to find a reliable skid pad, and know how to tune an "adjustable" proportioning valve? Whats next, multiple masters with biasing rods? Give me a break. Someone has been sitting at home too long munching on wheaties. |
If NASkeet hasn't done it yet, it's only a matter of time ...
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Wed Apr 29, 2020 10:04 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| SGKent wrote: |
| many of the folks here ask basic questions like how to adjust timing, find a fuel leak or find a fuse. Does anyone really think folks are going to find a reliable skid pad, and know how to tune an "adjustable" proportioning valve? Whats next, multiple masters with biasing rods? Give me a break. Someone has been sitting at home too long munching on wheaties. |
Why not?
I have done it many times.
People do it all the time.
Thats why they sell THOUSANDS of aftermarket adjustable brake regulators.
Its just not that hard. You don't need some "scientific".......... reliable ........skid pad. Its not like you need a perfect surface . You are not going to get to drive on one.
Relatively smooth.....about 1/4 mile...max....flat...and no one around except a buddy to help. Typically large parking lots work just fine. Or find a local track and work there. Its just not that hard.
Try it hot...try it cold. You do not have to be any particular speed. It just requires hard braking and good adjustment of your parts.
You don't need to get this up to highway speed....at all. About 35-45 mph....and jam on the brakes. You are simulating panic stop. Just jab hard and let them off.
You are not waiting around for the rear end to swing around....you want to see if they lock. It takes 1 second. Then adjust up or down.
It just not that hard. Ray |
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SGKent
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Wed Apr 29, 2020 10:08 pm Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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Ray, get help. You've gone over the edge. These are 40 to 50 year old antiques where people point to something in a photo and say, what's this? Then someone says that is what is left of an old beach sandal that melted.
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mlesniak
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Posts: 350
Location: Wisconsin
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| Posted: Thu Apr 30, 2020 5:02 am Post subject: Re: Brake Pressure Regulator/Proportioning Valve |
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| SGKent wrote: |
| Ray, get help. You've gone over the edge. These are 40 to 50 year old antiques where people point to something in a photo and say, what's this? Then someone says that is what is left of an old beach sandal that melted. |
Let's stick to the subject. I asked if the VW brake pressure regulator is replaceable with an aftermarket one and Kreemoweet and RayGreenwood did a great job answering my question. Thanks! I'll be rebuilding my original one for now, but one of these days I'd like to try an aftermarket one. Thanks again!
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