Ok, so Ive been lookin around today at bias bars, and havnt really seen anything that I was too impressed with as far as price, but I did see a
proportioning valve that looked interesting:
I was wondering, I know the rear should have less pressure than the front, but if I limit the pressure with the proportioning valve to the rear
should it cause me to have a very hard pedal feel? Because I will mount bothmaster cylinders dead even, they should put out the same pressure, wont it
cause one to get hard and since the 2 cylinders are together I wont be able to brake as well.
Am I delusional in my thinking or am I right?
Sounds right to me , but i'm no expert, i think you just explained it well !!, If you restrict one of the 'flows' the pedal would
become harder to press tooooo early.
Jason
Depending on the engine Locosts have roughly 49-51% front rear weight distribution this means about 66% of the braking is done by the front and 33%
by the rear in a 1 g stop.
With a straight limiting valve the rear line pressure after the valve won't increase beyond the set point --- but as this is the point just
before the brakes lock it won't make any difference anyway.
britishtrident, what you said made no sence to me at all, please explain as Homer Simpson would so I could grasp the concept, all I understood was thatit will stop flow after a certain point.
I was lead to believe that type of valve was for when you only had 1 cylinder.
Hi
I wouldn't connect the 2 masters to the brake pedal without a spherical bearing, if one firms up it wont allow the effort to go to the other
As for price on balance bar Rally design do one you weld in to your own pedals, £21.50 + VAT
Adrian
[Edited on 18/5/04 by ady8077]
They restrict the absolute amount of pressure that can go into a line. At lighter pressures, you can be doing a lot of braking with the rear
wheels.
In a single or tandem cylinder system, the excess pressure bypasses to the front wheels. One way to use in a twin cylinder system would be to have
two in diagonal circuits.
I wonder if in a rear brake circuit it could be plumbed in a loop, with the excess pressure going back into the input line.
That's a nice looking pedal mount derf! I'm guessing you're going to put a pivot on your proper pedals, even if you skip the
adjustable balance bar, right? Puhn has a shot in his book that shows adjustments made by changing pivot plates with different hole locations - not as
convenient but it works just as well.
If you do that, you don't really need the proportioning valve, though it's a handy for getting the brake force curve closer to ideal under
lighter braking.
The proporting valve isn't a limit valve at all - it does just what it's called. It does nothing till it hits the adjustable pressure
setting (100-1000psi). Pressure in is the same as pressure out. Then a valve closes and the output pressure is proportional to the input pressure -
in the wilwood case, the output pressure is 57% of the input pressure.
Are you using drums or discs on the rear?
drums in the rear.
Ive been reading this, kinda lost on what everyone is talking about, I think I need to read it a few more times and get smart.
But, can someone just give me a definitive yes, I use this and it works, or a no I tried it it dont work.
So far everything seems more like a no answer.
Found this nice pic at www.ecihotrodbrakes.com:
It's a good thing that the disc/drum issue came up. Automakers put a metering valve in-line to the front brakes, which holds back pressure from
the frontbrakes until a certain amount (I saw 30 psi one place, 140 psi another) is built up in the system. This gives the rear shoes time to react
before the more responsive front discs.
I was pleased to see the proportional valve in line to the rear brakes, not bypassing anywhere. I *think* this means you can install a proportioning
valve in your rear circuit as an alternative to a bias bar.
The residual pressure valves may be useful in your setup if the master cylinders will be below the calipers and/or the wheel cylinders. These
maintain pressure in the lines, keeping the brake fluid from siphoning away from the brakes. Drums need 10 psi and discs need 2 psi, according to
this site.
A fast Google showed that a lot of Detroit iron has used metering valves, so a junkyard might be the place to find one. Wilwood makes residual
pressure valves, less than $15 apiece.
I can't think of any reason a system like this could not work with your two master cylinders, but then again I don't know jack sh*t about
this topic, so am looking forward to input from others.
Playing straight man for MikeP here 
Pete
I have been reading about this residual pressure valve on the wilwood site to.
I'm using the ST pedalbox with master cilinders with internal reservoir ( different size front and rear).
Is it really neccesary to use these valves ??
Who is also using the ST
I am using an ST pedal box (it was cheap enough for me not to warrant making my own, as I have in the past!!)
The residual pressure valve is really useful with drum brakes, keeps the pedal nice and short, with discs I wouldn't bother unless it is a forest
rally car!! (even then I haven't used them and if you are going the get pad knockoff anywhere it's there!!)
as an aside, I am pretty sure quite a few Vauxhalls/Opels came with residual pressure valves as standard on the rear circuits, I think they are the hex shaped valves on the side of the master cylinder.
Early VWs came with residual pressure valves attached to the master cylinder.
just another source if you're wondering the scrapyard.
All the best Dan.
brakes are not something I really want to go with used items of unknown condition, I think I'll be going with all new stuff on this one. I
already plan to replace everything except the calipers already, so why not a $15 item, and spend an extra $30. I was actually trying to save money
over buying a balance bar, ($60), but with the brake adjuster, plus the pressure valves, it is about the same.
The big plus of the adjuster is the in the seat ability to change the brake bias, I love easy adjustability, plus since the system has been used for a
while it seems like more of a sure thing.
Never mind my last post, as I read more into the site about residual pressure vales, still wont hurt to use them:
Residual Pressure Valves are used in a both front and rear brake system as follows:
2 PSI Valves - These valves are used in a disc brake system only and are required when the master cylinder is at, or below, the height of the
calipers. It's purpose is to act as an anti-siphon valve preventing the brake fluid from siphoning back into the master cylinder when the brake
pedal is released. Even if the master cylinder is even or slightly above the calipers, put one in anyway. If you don't and you park on a hill,
fluid will siphon! These valves are cheap insurance - put them in!
NOTE: You will know if you need one of these valves if you had to pump the pedal twice to get a good pedal. See illustration for more.
10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake
pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system
which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some
disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can
tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if
you are not sure whether you have one or not, put one in. They are not cumulative and it won't hurt anything if you have two. Don't worry
about brake drag, it takes roughly 75 PSI to overcome the return springs.
Double post
[Edited on 19/5/04 by derf]
hehehe Pete .
I agree Derf, you should use a residual pressure valve in the rear lines and don't bother on the fronts as Nat says. It looks like you're
using the tilton style single line masters, they won't have a residual pressure valve built in.
My advice would be to use a pivoting balance bar of some kind rather than the proportioning valve. The proportioning valve will only work if
you've got more force to the rears than you need. I don't know how to calculate braking force on drums - the servo action messes me up - so
I don't know how to tell without testing. The balance bar lets you move the brake bias in whichever direction is needed. The other alternative
is to swap in different size masters till you get the right balance, but that can get expensive too.
You can usually get a cockpit adjustment for the balance bars. There's not really much point in either IMO unless you're racing and
you're good enough to feel what's needed. For the street, I'd set up the balance by testing on a dry road and leave it there.
I'd be worried about using the bent RHS for the brake pedal, just a guess, maybe someone has better advice. I noticed that your donor pedals have
been cut off and welded right across, so I wouldn't use those either. I know the tilton style pedals are pretty pricey. Maybe you could cut a
new one the size and shape that you need out of some thick plate?
the pedal unit is tilton, master cylinders are all 3/4" wilwood, single output, as shown 2 are remote resevoir. I dont see a problem with the
bent rhs tube, I can reinforce it as I need to, I was planning on weldng a 1" sectiion of tube on the bottom at 75 deg angle, and adding the
actual pedal on the end of that. I dont really see the pedal bending back to it's original shape.
For $30 US the tilton piece was definatly a good bargain, but now I have to redesign my steering colum, as it will sit where the column is now.
[Edited on 19/5/04 by derf]
MikeP is quite right on the balance bar, if you are concerned about adjustment from the seat, just put a remote adjustment cable on it and you can
move it from a know on the dash etc.
He is also quite right in that once set, you really don't need to fiddle, it is fine apart from track use, and probably still fine then!!
quote:
Originally posted by derf
For $30 US the tilton piece was definatly a good bargain
Going back to the metering valve, it still seems like a good idea for the front. This site wants $85 for one, which is a bit high. Could probably
use anything that fits your lines.
Though Derf won't be using a proportioning valve, I'm glad for the discussion as one would work well for me, I think. The stock RX-7 setup
is a tandem M/C with a non-adjustable valve. I'm going to see if I can use the stock M/C, an adjustable valve, omit the servo, and get the pedal
effort right with pedal ratio.
Here's an inspiration for our UK friends who might like to use a proportioning valve but are concerned about passing SVA. It's a
'stealth' valve that can be hidden in cars that are not allowed to use them! From www.speedwaymotors.com. Anarchists!!
Edit: was friggin' incoherent
[Edited on 19/5/04 by pbura]
How much is the valve pictured, somewhere I have a load of those, (from the scrap bin at my old job) they are standard high pressure hydraulic variable restrictor valves!!
quote:
Originally posted by NS Dev
How much is the valve pictured, somewhere I have a load of those, (from the scrap bin at my old job) they are standard high pressure hydraulic variable restrictor valves!!