George,
M/C's and boosters are a matter of taste. The main parameters of the M/C are
the bore, stroke, and split. A larger bore will get you a more firm pedal, but
is
going to require you to push harder on the pedal to stop. Conversely, a smaller
bore is going to give you more pedal travel, but less force required. The split
determines how much of the total M/C volume is used for the primary (front) and
secondary (rear) circuits.
Boosters have three main parameters also. I'm a little rusty on the technical
names
(it's been awhile since I've had to talk boosters) but they are: jump in force,
booster
ratio, and here's where my mind goes blank, the point where the boost runs out.
The
jump in force is the amount of pedal force required to get the booster to start
operating.
The ratio is how much helping force the booster is doing, and the point where
the boost
runs out is just what it sounds like; the system pressure at which the boost
ratio drops
to 1:1.
Playing around with these can have signifcant effects on how the vehicle
responds to how
you apply the brake pedal. If you can get the rear wheels to lock with the
adjustable prop
valve wide open, then I probably wouldn't change these. If you are going to
change these,
from my personal driving preferences, I'd say the M/C bore and stroke are
probably pretty
good, but the boost ratio and runout pressure are probably a bit low.
Seth
#1544
*********** REPLY SEPARATOR ***********
On 4/8/2004 at 12:40 AM George Schiro wrote:
>I had planned on installing an adjustable valve. All the brake lines are
>being replaced with stainless steel tubing. I did plan to keep the M/C and
>Booster. If I wanted to install a larger capacity M/C, what would you
>recommend?
>
>-----Original Message-----
>From: owner-bricklin@autox.team.net [mailto:owner-bricklin@autox.team.net]
>On Behalf Of Seth
>Sent: Wednesday, April 07, 2004 11:01 PM
>To: bricklin@autox.team.net
>Subject: RE: AMC parts; proportioning valve, etc.
>
>George,
>
>That's the kicker, I couldn't spec a prop for that combination if I wanted
>to. I'd need to know the caliper sizes, rotor effective radii, brake lining
>friction for the front and rear, CG height, weight distribution (llvw and
>gvw), and tire rolling radius just to get an estimate. The next best thing
>is to get an adjustable prop and spend a day (and probably a set of tires)
>at the track doing dry asphalt stop after dry asphalt stop (straight line
>and during turning) until you're satisfied with the stopping power of the
>vehicle and the stability of the vehicle.
>
>If you do go with an adjustable, you need to remove the original prop. Yuo
>don't want to be proportioning on top of proportioning. Aftermarket shops
>also make plugs so you can pull the guts out of your current prop and just
>add the adjustable one further on down the line.
>
>I went surfing and found a site that explains it decently (for a fox
>mustang). The one thing I didn't like about the site though is he mentions
>using teflon tape. You never ever want to use any thread sealant on a brake
>system. Brake systems are very sensitive to contaminents, causing potential
>seal failure or clogging of ports (more of an issue with ABS equipped
>vehicles, but still...)
>
>http://www.binaryweb.com/fordtech/manual_prop/index.shtml
>
>on a final note, your master cylinder is possibly now undersized for your
>rear brakes. The secondary circuit of your M/C was onyl designed for a
>volume load of two wheel cylinders (wheel cylinder diameters are much
>smaller than disc brake pistons). This is only an issue if it is severly
>undersized as you may stroke the M/C before you get full pressure on the
>rears.
>
>Seth
>#1544
>
>
>
>*********** REPLY SEPARATOR ***********
>
>On 4/7/2004 at 10:04 PM George Schiro wrote:
>
>>Seth,
>>
>>I'm putting Cadillac disk brakes in the rear and keeping the Kelsey brakes
>>in front. What kind of proportioning valve would you recommend?
>>
>>George
>>
>>
>>-----Original Message-----
>>From: owner-bricklin@autox.team.net [mailto:owner-bricklin@autox.team.net]
>>On Behalf Of Seth
>>Sent: Wednesday, April 07, 2004 7:09 PM
>>To: bricklin@autox.team.net
>>Subject: Re: AMC parts; proportioning valve, etc.
>>
>>You need to be careful changing prop/combo valves. Since the brick has
>>disc/drum, you need a combo valve (prop and meter). The metering slows
>down
>>the inital apply rate of the disc brakes since inherently disc brakes
>apply
>>faster than drums do to the engagement distance drums require. Getting the
>>metering right is important, but not as critical as getting the
>>proportioning right. The prop valve has two distinct parameters when
>sizing
>>them, the slope and knee point. The knee point is the point at which the
>>ratio goes from 1:1 to the slope ratio. The brake configuration (caliper
>>size, rotor effective diameter, lining material, etc) and vehicle weight
>>distribution will determine your Z critical (the vehicle deceleration at
>>which your vehicle goes from front biased to rear biased). Typically, a
>>brake system is designed to be inherently rear biased (for parking brake
>>effectiveness and failed systems and such) so a prop valve is used to move
>>the bias to as close to neutral as poss!
>>ible for all loadings while remaining slightly front biased. So, trying to
>>cut to the chase, changing your prop to an aftermarket can cause you to be
>>rear biased which caused worse brake performance and can cause the vehicle
>>to oversteer since the rear wheels will lock before the front ones. An
>>aftermarket prop can also cause you to be front biased which is safer
>>because it doesn't induce oversteer, but it still decreases overall
>>potential braking. That's why the prop for the Brick is unique. As a side
>>note, most new vehicles don't have a prop valve because they have ABS. ABS
>>can electronically control the rear pressure and does a better job, giving
>>a
>>neutral bias for all loading conditions.
>>
>>Seth
>>ABS/TC/Stability Control Vehicle Development Engineer
>>#1544
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