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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