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CorvettesRemoving
the proportioning valve.

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Removing the
proportioning valve.

4:46
AM 6/18/2002

A few years ago I ran into problems bleeding
the back brakes on my mustang.
I talked to my friend who
owns the local repair shop and I trust him. He
said he
often has trouble bleed the rear brakes on cars and it is
the
proportioning valve. I have also experienced problems
removing the
driveshaft on another mustang. The brakes
regardless of how hard pressed
would not stop the
driveshaft from turning. I also have a CanCar friend
who
has raced forever. They all said get rid of the
proportioning valve. If the
front is responsible for 70% or
the brakeing and the back 30% what if both
ends got 100%. I
removed the valve from both the vet and mustang and
the
increase in braking power was very noticable. The
problem bleeding the rear
brakes on the mustang was gone
and peddle feel or firmness is much improved.
If I wanted a
quick improvement in braking I would remove this
brass
proportioning valve. Plumb the front lines to the
front of the master
cylinder directly and another line from
the back of the master to the rear
brakes. If you loose one
end due to a failure the other end is totally
unaffected.
Try this with the proportioning valve installed. Open a
bleeder
and try hitting the brakes . The pedal goes to the
floor. Now with the
proportioning valve removed do the same
thing and the brake pedal will feel
almost normal. The line
pressure to the good end goes up and the brakes will
work
fine.
I am a big fan of the hydraboost but without it
removal of the proportioning
valve is the next best step
for improved brake feel.
I run sticky rear tires so why
shouldn't they do their share of the braking? I also never run
in the rain or snow. This could cause a problem with rear
lockup but for a fairweather car like mine it is a big
improvement.

_______

Norval

groovyjay
Senior
Member

1063 posts [100%]
Helsinki/London

Re: Removing the
proportioning valve. (norvalwilhelm)

7:57
AM 6/18/2002

Great info Norval, I wonder why I never thought
of that .

I bet there is lot of guys very thankful to you after they
see this. Great tip, thanks for sharing!
_______

1979,
454
LS-6,
Edelbrock EFI,
Edelbrock Aluminum Heads,

Crane Roller cam, Push Rods, Rockers, Stud Girdlers,

March billet serpentine conversion,
Chromed late-model
PS pump with polished Billet reservoir,
Polished Billed
aluminum over flow tank,
Stahl side pipe
headers,
Richmond 5-Speed Road Race Transmission,
Center
Force Dual Friction,
Hays Billet Steel
Flywheel,
Lakewood Bellhousing,
Steeroids Rack &
Pinion kit,
Speed Direct Clutch linkage,
Vintage Air
Compac Gen2 A/C,
Autometer Gauges,
20" American Racing
TT IIs,
Pirelli rubber all around,
Hi-Rise Hood,

Engine dynoed at Flywheel
541.5hp@6000rpm and
551.4 lbs/tq@3702rpm

and plenty of other goodies still to come...

Barry's70LT1
Senior
Member

461 posts [100%]
Halifax, Nova Scotia,
Canada

Re: Removing the
proportioning valve. (norvalwilhelm)

8:18
AM 6/18/2002

Hi Norval,
Great information.
A question,
is the proportioning valve on a Corvette really a
proportioning valve, or just a spring loaded piston, that when
seeing an imbalance in front/rear pressure will turn on the
"brake" light on the dash ?

Barry
_______

1970 Unrestored: 350/370, M21,
3:70, F41, PB, PW, TT, TI
Original Owner, Original Paint,
13.02 @ 110.30

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve

8:21
AM 6/18/2002

norval
in 1990 my 67 ford - pedal went to
floor, no brakes. 1 leaking wheel cyl.
What good is a dual
braking system????
so i threw away that valve
Proportioning should be with wheel
cyl/piston size.
What are those car engineers smoking?

_______

ASE Certified 1984 in
ENGINE PERFORMANCE, Engine Repair, and Electrical Systems...

72&61: 355's Jetted w/oxygen sensors. 650DP, crank
scraper, anti-hot soak system, 87 octane 9.65:1, 1 3/4
headers... 61:AFR 190, CC 270 4spd 4.11, anti-wheelhop clamps.
72:self-ported SRT's,xe262 1.6,TH400 recalibrated to shift at
5700 in D WOT. 3.08

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve. (Barry's70LT1)

8:26
AM 6/18/2002

Barry
i think you are right. it just
triggersthe red light

Wrencher
Senior
Member

1301 posts [100%]
CA

Re: Removing the
proportioning valve. (norvalwilhelm)

8:29
AM 6/18/2002

I am considering this as well with the main
difference being the addition of a cockpit adjustable manual
proportioning valve. That way I can adjust the rear wheel
braking myself, depending on the conditions.

Hans
_______

The Larry Shinoda Collection: '69
L-68, '70 BOSS 302, '65 Corvair Monza... http://www.corvetteforum.net/c3/wrencher/

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Removing the
proportioning valve. (Barry's70LT1)

8:36
AM 6/18/2002

Barry. I agree it is a switch to turn the dash
light on but fluid still has trouble going through it. If you
loose one end like I said open a bleeder and push the pedal,
it will go to the floor. Without this little light switch it
will not. The pedal will still feel firm. Why? Because the
system's are isolated from each other and if one fails the
other doesn't know it so it continues to act normal. The pedal
will still activate one end fully.
If you only get 30%
braking on the rear what happens to the rest of the
pressure?
I ran big stickly MT ET streets on the rear and
they did little braking. After removing the proportioning?
valve they felt like someone grabbed the back bumper and was
hanging on. I could get them to lock if I tried after the
valve was gone. The important thing was they were giving 100%
in trying to stop the car not just riding along. The mustang
is the same , it had power brakes but the back was very
difficult to bleed and with the bleeder open the fluid did not
come squirting out, just trickle.
I believe my system is
safer then stock. I lost a brake line on my ford truck and I
almost went through the light. I had to work at stopping,
slowly pump the brake to get alittle pressure and downshift.
The master cylinder has a very shallow dividing wall that
allows nearly all fluid to drain out the leak. Our vets have
full internal walls seperating the front and rear, so no
pressure loss in the remaining working side.
If you ever
had a brake failure you know what I am talking about. Remove
the light proportioning valve and have this happen and you
will hardly feel the difference in the pedal. Try it . You
might find out I am
right.
_______

Norval

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Removing the
proportioning valve (drives61)

8:41
AM 6/18/2002

drives61. Barry is right it triggers the light
but it also reduces or totally destroys the pressure to the
rear brakes. I have experience this 3 different times with
different vihicles. Like I told Barry my ford truck lost a
line and it was almost totally without brakes. I bet anyone
without a valve, 2 seperate systems running from the master
cylinder you can open the bleeder on one end and still go out
and lock the other end without the peddle going to the floor.
Try this with a light switch connected in the
system.
_______

Norval

StingrayRacing
Senior Member

884 posts [100%]
NYC NY

Re: Removing the
proportioning valve. (norvalwilhelm)

9:26
AM 6/18/2002

Norval,

Just curious if you have braked hard while in a turn and it
was ok?

I have a willwood adjustable valve somewhere around here
that I haven't put in yet.
_______

Rich P
72
Stingray 383 DFI 6 Speed 438rwhp/414rwtq
AFR210's, Solid
Roller, Wheels: 17 x 8 w/255's & 17 x 9.5 w/285's
VB
Front Transverse & Rear Glass Springs

Best 2000 Times:
11.54 @ 120.47 60'1.72 On Hoosiers( 1
5/8 Headers)
11.60 @ 120.26 60'1.68 On Nittos (with 1 3/4
headers)

Best 2002 Times:
???
Stingray
Racing

JSB69
Senior
Member

341
posts [100%]
West Chester PA

Re: Removing the
proportioning valve. (norvalwilhelm)

9:50
AM 6/18/2002

Page 9-2 of the Haynes Corvette Manual #24040
says the valve will prevent loss of pressure in one side if
the other fails. On the other hand, your statement about
opening a bleeder is correct. I wonder if anyone can explain
how this works.

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Removing the
proportioning valve. (StingrayRacing)

9:54
AM 6/18/2002

I have never had to brake hard in a turn. I
have never while driving the vet had to do a panic stop. I
have in fun done repeated 100 mph panic stops and locked up
the brakes at lower speeds just for fun. But no I have never
had an emergency stop in the vet. I know all 4 wheels would
lock up solid. Do you ever watch the Grand national stock cars
come into the pits and just stop, no front end dive, just
stop. My car feels like that. It feels like the rear is doing
alot of the stopping, nice feeling, feeling the rear end
pulling back while the front is doing it's thing. Once again I
am a fair weather driver so in a real emergency I would
probably panic and lock everything up but in just shear
brakiing power from 100 mph I will stop as well as anyone. The
cockpit does get a little smokey.
_______

Norval

inqbus383
Senior
Member

97 posts [100%]
Seattle WA

Re: Removing the
proportioning valve. (norvalwilhelm)

10:23
AM 6/18/2002

Just be carefull without the proportioning
valve, it may cause the rear brakes lock up before the front
wheels. You'll be spinning around quick if this
happens.
_______

High Performance small block 405 and 4+3
transmission =
More pics and info at http://students.washington.edu/aro/index.html

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve. (inqbus383)

10:38
AM 6/18/2002

the rear pistons are smaller.
the valve is
just a warning light, that tells you the brakes won't work
beacuse it wasted them

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve (norvalwilhelm)

10:53
AM 6/18/2002

from my 1972 Chilton:
PRESSURE DIFFERENTIAL
WARNING VALVE..."the signal consists of warning light
activated by a differential pressure switch located below the
master cyl.....warns the driver that a failure has occurred"

_______

ASE Certified 1984 in
ENGINE PERFORMANCE, Engine Repair, and Electrical Systems...

72&61: 355's Jetted w/oxygen sensors. 650DP, crank
scraper, anti-hot soak system, 87 octane 9.65:1, 1 3/4
headers... 61:AFR 190, CC 270 4spd 4.11, anti-wheelhop clamps.
72:self-ported SRT's,xe262 1.6,TH400 recalibrated to shift at
5700 in D WOT. 3.08

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve (drives61)

12:19
PM 6/18/2002

Oh i get it
This is how it works.
With a direct
connection as norval suggests, you could drive around for
years not knowing there was a partial failure.
The
government mandated safety switch causes the car to lose all
brakes, so you have to get it fixed right away.

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Removing the
proportioning valve (drives61)

12:22
PM 6/18/2002

Oh i get it
This is how it works.
With a
direct connection as norval suggests, you could drive around
for years not knowing there was a partial failure.
The
government mandated safety switch causes the car to lose all
brakes, so you have to get it fixed right away.

Good analyises
drives61
_______

Norval

mrvette
Senior
Member

1802
posts [100%]
Orange Park Florida

Re: Removing the
proportioning valve (norvalwilhelm)

1:18
PM 6/18/2002

OK, guys, from personal experience, I guess I
will have to speak up here....
some years ago I bought a
drum brake version of a Pontiac Lemans...4 drum brakes, damn
thing barely stopped, had no proportioning valve, as all the
brakes were sized and of the same type for even enough
stopping...
drum brakes are self-actuating to a
degree...hold that thought now....
so I go convert the
front to more modern disc brakes off a 70's firebird...no
sweat..just do the obvious...but no proportioning valve....I
say screw it and set it up...go for a drive...well obviously I
needed something,...junkyard was bare at the moment...so I put
in a Chrysler adjustable pressure valve in the rear brake
line...acts like a proportioning valve sort of....
well
that evened out the braking just fine....worked like a
charm...
but in a 4 wheel disc setup I agree with Norval
there...can't see the need, and may at some point just change
my system over to just two brass distributiion blocks and have
over with it....frankly never had any trouble in MY car
traceable to the proportioning valve....but seen a few other
cars that did...
and think it's better to get rid of it,
trouble is...on their cars there is a liability issue...on MY
car....well I gotta remember how to drive....

GENE
_______

http://home.att.net/~ncmpics/mrvette.htm

Gordonm
Senior
Member

2389 posts [100%]
Marlton NJ

Re: Removing the
proportioning valve (mrvette)

1:25
PM 6/18/2002

My brakes are OK right now but it looks like
this winter I will put in a hydro boost system and remove the
prop. valve. My rotors are at the limit also so I will rework
the whole system this winter. Providing I don't break anything
else that ties up money for the Vette.
_______

72
Red LT1 Convertible. AFR 190 heads, Hooker Headers Jet Hot
Coated, custom 2 1/2 exhaust with 50 Series Delta Flow
Flowmasters, Comp Cams 294S, Crane HI6 Ignition, 750 DP
Holley, Vette Brakes Suspension, 3.70 gears Best time 12.70 at
110 Marlton NJ

Homepage http://corvetteforum.net/c3/gordon72/

A78Corvette
Senior
Member

757
posts [100%]
Southpittsburg TN

Re: Removing the
proportioning valve. (norvalwilhelm)

1:39
PM 6/18/2002

First of all i am not a mechanic. I just bought
a new preportioning valve from GM when i had trouble with
mine. Second I have a friend who installed an adjustable
preportioning valve on his 454 heavily modified Vett. His
valvle has an adjustment knob to put the braking power where
you want it front or rear. I don't know the brand of valve he
used. Hope this helps.

FroDaddy
Senior
Member

733 posts [100%]
Green Cove Springs
FL

Re: Removing the
proportioning valve. (norvalwilhelm)

1:45
PM 6/18/2002

For C5 vettes, I believe Doug Rippie
Motorsports used to sell a similar setup but it adjusts the
front/rear to be more agressive. I just went over their
website but couldn't find the valve by itself anymore; it
looks like they are selling it in a package to make more $$. I
think the newer vettes have larger brakes in the front than in
the rear, so maybe that's why they are selling them in a
package now?

Wow, this is a must-do mod for a C3!! This and the
hydraboost is definitely on my list of to-do mods.
_______

'81 Vette:
The 61st born at Bowling Green : 383 Stroker :
Coming Soon -- 17" wheels and Tremec TKO 5sp

jyounane
Senior
Member

34
posts [100%]
Melbourne VIC

Re: Removing the
proportioning valve (norvalwilhelm)

5:24
PM 6/18/2002

Assuming it is a pressure differential switch,
and not a proportioning valve, the switch should keep the
front and rear fluid systems completely separate. Under
failure conditions, the pressure differential switch ought to
make no difference to the braking system, other than activate
the light.

For the pedal to go to the floor, are you suggesting that
the differential switch can operate or fail in such a way as
to kill the good half of the braking system in the event that
the other half fails?

Perhaps folks familiar with the inner workings of this
switch might be able to comment on this. Personally, I'd be
amazed if GM could get away with such an unsafe design without
being sued to eternity!

In any case, I'll have to have a closer look at this
question, just for peace of mind.

Regards,
Joe

yellow 72
Senior
Member

873 posts [100%]
cincinnati ohio

Re: Removing the
proportioning valve (jyounane)

6:42
PM 6/18/2002

I have mine off right now and it is no way a
proportioning valve, not in any way I can see. It has two
seperate chambers one connecting the front half of the master
cylinder with the front hydraulics and the other connecting
the rear of the master with the rear. Between the two is a
normally open switch that is grounded when the pressure is
unbalanced and pushes a piston of sorts one way or the other
and grounds the switch and lights the dash light.
OK, we
all knew how it worked but I wanted to say it anyway
As far as I can tell the two sides of
the system are completely isolated inside the valve. Seperated
by the piston which moves back and forth but passes no
fluid.
So how does it allow total brake failure when one
side is open
_______

73ragtop
Senior
Member

26
posts [100%]
Denton Texas

Re: Removing the
proportioning valve (jyounane)

7:32
PM 6/18/2002

quote:

Assuming it is a pressure differential switch, and not a
proportioning valve, the switch should keep the front and
rear fluid systems completely separate. Under failure
conditions, the pressure differential switch ought to make
no difference to the braking system, other than activate the
light.

For the pedal to go to the floor, are you suggesting that
the differential switch can operate or fail in such a way as
to kill the good half of the braking system in the event
that the other half fails?

Perhaps folks familiar with the inner workings of this
switch might be able to comment on this. Personally, I'd be
amazed if GM could get away with such an unsafe design
without being sued to eternity!

Regards,
Joe

People get confused about C3 brakes because we assume since
they all have 4 piston calipers, they are all alike; one of
the chief differences is whether or not your car has a
combination valve or a proportioning valve. Here is a quote
from the Haynes manual:

"Two basic variations of this valve have been used. On 1968
through 1974 models, the valve includes a pressure failure
warning switch which illuminates a warning light if hydraulic
pressure drops in either the front or rear brake circuit. On
1975 and later models, the valve also includes a porportioning
function. Under heavy braking, the proportioning section
reduces hydraulic pressure to the rear brakes to prevent early
rear wheel lock-up. The valve is also designed to assure full
pressure to one brake system should the other system fail. The
design of the switch and valve are such that the switch will
stay in the 'warning' position once a failure has occurred.
The only way to turn the light off is to repair the cause of
the failure and apply very high brake pedal pressure."

Also, I know it is conventional wisdom on this forum that
brakes should be bled from the caliper farthest from the
master cylinder to the nearest. This is usually postulated in
threads where all the participants bemoan the difficulty of
getting all the air out of the lines, or of achieving the much
desired "firm pedal." This is a quote from an original 1973
Chevrolet Service Manual, copyright 1972 General Motors
Corporation. Section 5-18 in the Brakes chapter.

"It is advisable to bleed one valve at a time to avoid
allowing fluid level in reservoir to become dangerously low.
The correct sequence is to bleed the valve, either front or
rear system, nearest master cylinder first. This sequence
expels air from lines and calipers or wheel cylinders nearest
to the master cylinder first and eliminates the possibility
that air in a line close to the master cylinder may enter a
line farther away after it has been bled."

Now that is mere common sense. When you press the brake
pedal to bleed the brakes, the fluid obviously moves toward
the wheels, not toward the master cylinder. It also makes no
difference whether you bleed the back or front wheels first.
Note the two reservoirs of fluid in the master cylinder; they
are separate and do not exchange fluid or air so long as the
master cylinder is functioning properly.

Now, here's the kicker I don't know the answer to, since my
1973 Corvette has a combination, not a proportioning, valve.
Many of you guys who have 1975 and later cars WITH
proportioning valves should check into whether it needs to be
mechanically held open during brake bleeding. During 1973,
some other Chevy cars, not the Corvette, used proportioning
valves. If you used pressure bleeding, the following paragraph
applied to those cars:

"NOTE: On disc brake cars a combination metering,
proportioning and failure warning switch is in the hydraulic
system and mounted either on the frame rail or under the
master cylinder. This valve must be held in the open position
while bleeding. This can be accomplished by installing Tool
J-23709 with the open slot undr the mounting bolt and pushing
in on the pin in the end of the valve (fig. 38). Be sure to
re-torque the mounting bolt after removing ToolJ-23709."

I don't know if later Corvettes used the same type of valve
as mentioned above, but if you have trouble bleeding your
brakes, I would check the manual.

After messing with these cars for a long time, I've found
that Chiltons and Haynes manuals are too generic to be of
great value. It is worth the money to buy and utilize the
Service Manuals for your year Vette. I trust the people who
built the car to know how it needs to be fixed; the service
manual for your specific year car is the first place you
should look.

Best regards,
Eddie

jyounane
Senior
Member

34
posts [100%]
Melbourne VIC

Re: Removing the
proportioning valve (73ragtop)

8:15
PM 6/18/2002

Thanks Eddie,

That was a very useful post. There is a lot of mythology in
Vette brakes.

I was unaware of the differences between early C3's and
later. Mine is a 69 and only has the pressure differential
switch. I agree completely with the comments on bleeding
sequences and have had no real problems bleeding brakes (one
of the lucky ones!). It seems "Yellow 72" has a similar
system.

My reason for posting here at all, is that I couldn't
believe that in a (properly maintained) dual circuit braking
system, a single failure in one half could lead to failure of
the remaining half.

Thanks for your advice,
Joe

69 427L36 M21 3.08 White Coupe

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve (jyounane)

3:33
AM 6/19/2002

possible reasons for the failure:
1. that
little piston leaks bad when it slides over to work the
switch, connecting the good side to the bad side.
2. the
piston moves enough that it creates a cavity big enough to
cause the good side to lose pressure
3. poor engineering
allowing 1,2; not checked in the real
world

[Modified by drives61, 7:01 AM
6/19/2002]

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Removing the
proportioning valve. (norvalwilhelm)

4:41
AM 6/19/2002

This is very easy to prove or disprove. Any
time you have a wheel off bleed whatever wheel is off. Open
the bleeder valve while someone pushes the pedal and if it
goes to the floor you have lost your brakes. If the pedal goes
1/2 way the other system is still getting pressure. All you
loose is a little brake fluid and you know if loosing a line
will destroy the brakes.
Anyone who has bled their system
knows what happens to the peddle while
bleeding.
_______

Norval

yellow 72
Senior
Member

873 posts [100%]
cincinnati ohio

Re: Removing the
proportioning valve. (norvalwilhelm)

5:27
AM 6/19/2002

That is what happens when I open one
side...no brakes. So the valve is either defective or a bad
design.
I can't recall this on any other brakes I've bled

73ragtop
Senior
Member

26
posts [100%]
Denton Texas

Re: Removing the
proportioning valve. (norvalwilhelm)

12:05
PM 6/19/2002

quote:

This is very easy to prove or disprove. Any time you have a
wheel off bleed whatever wheel is off. Open the bleeder
valve while someone pushes the pedal and if it goes to the
floor you have lost your brakes. If the pedal goes 1/2 way
the other system is still getting pressure. All you loose is
a little brake fluid and you know if loosing a line will
destroy the brakes.
Anyone who has bled their system
knows what happens to the peddle while bleeding.

Well, no, not exactly. If you have the pre 1975 brake
distribution switch (non proportional), I'd say you had
problems. But if you have the proportioning valve, the test
you propose is like buckling one of the inertia reel seat
belts and moving the shoulder belt back and forth and
determining that it is defective because it slips. So
obviously, it wouldn't work in a crash? The two errors people
are making by saying the valve must be faulty if you crack a
bleeder screw and the pedal goes to the floor are (1) the car
is at rest, unless you are agile enough to crack a bleeder at
speed, and (2) you assume the proportioning valve operates at
normal brake pedal pressures. Neither is true. The
proportioning valve improves "front-to-rear brake balance at
high deceleration. During high deceleration stops, a
percentage of the rear weight is transferred to the front
wheels."

But, more importantly, "The proportioner does not operate
during normal brake stops. Fluid normally flows into the
proportioner, through the space between the piston center hole
and valve stem, through the stop plate and out to the rear
brakes. The spring loads the piston so that it rests against
the stop plate for normal brake pressures."

The above quoted material is from the 1973 Chevrolet
Service Manual, copyright 1972 General Motors Corporation.
Anyway, with the symptoms some of you have mentioned, I'd
check the mounting bolts for the master cylinder and / or an
incorrect master cylinder push rod adjustment, or just a
garden variety defective or non-bench bled master cylinder.

Most important of all, before we remove or modify an
integral part of the most important safety system of our
precious cars, we should ask ourselves, as Richard Newton did
in much of his writing, "Am I really smarter than Zora
Duntov?"

On top of that, I can't believe this thread was started
about a Mustang.

Eddie

Fevre
Senior
Member

1467
posts [100%]
Ann Arbor MI

Re: Removing the
proportioning valve. (73ragtop)

12:16
PM 6/19/2002

quote:

"Am I really smarter than Zora Duntov?"

Depends on the subject.

quote:

On top of that, I can't believe this thread was started
about a Mustang.

Pretty much uncalled for.
_______

73 ragtop,
temporary 350, 4 spd, MSD 6A, ProBillet Dist, Holley 4150 600
with vac sec, Aluminum Trick Flow 23 dgr heads (waiting in the
wings), Weiand Stealth intake, 3.70 rear, Two Boxers (1 male
& 1 female) and no money

drives61
Senior
Member

1699
posts [100%]
Central FL

Re: Removing the
proportioning valve.

1:01
PM 6/19/2002

someone should call/write NHTSA and find out
exactly how the mandated dual brake system should
function.
my experience is with older cars, but i never saw
one that had decent brakes with, say, a cut rubber brake hose.
Seems the dual system is, at least in old cars, a total
failure.

deftones1407
Senior
Member

41
posts [100%]
boxford MA

Re: Removing the
proportioning valve.

1:12
PM 6/19/2002

AHHHHHHHHH HE SAID MUSTANG!!!

_______

1981
All matching
Numbers... 50 K miles... not bad for 19 years old!

Wrencher
Senior
Member

1301 posts [100%]
CA

Re: Removing the
proportioning valve. (deftones1407)

1:55
PM 6/19/2002

Mustang! Mustang! Mustang! Aaah Haa Haa Haa,
watch 'em squirm....

Hans
_______

The Larry Shinoda Collection: '69
L-68, '70 BOSS 302, '65 Corvair Monza... http://www.corvetteforum.net/c3/wrencher/

jyounane
Senior
Member

34
posts [100%]
Melbourne VIC

Re: Removing the
proportioning valve. (yellow 72)

3:39
PM 6/19/2002

Norval is correct, the pedal does drop much
further if you open one of the bleeder screws and we have all
experienced that.

So, let's assume that the differential pressure switch does
keep the front and rear circuits separate. Now if we apply the
brakes and open a bleeeder screw the pedal drops. See http://www.howstuffworks.com/master-brake1.htm

for an animation of what happens. You can click on the red
arrow to see why the pedal drops.

However, the system is designed to reach full pressure on
the remaining circuit. This SHOULD happen before the master
cylinder bottoms out or the pedal reaches the floor, even
though the pedal travels much further.

I guess if it doesn't, that means there are other problems
with air in the system or master cylinder problems.

Check that link out and let me know what you think.

Thanks
Joe

69 427L36 M21 3.08 White Coupe

The Dude
Senior
Member

4917 posts [100%]
Your Town

Re: Removing the
proportioning valve. (norvalwilhelm)

4:00
PM 6/19/2002

Great thread.

Although I am surprised nobody's chimed in to say that
removing the proportioning valve will increase global warming,
kill all the whales and turn innocent children into porn
stars.

_______

Looking for a new pic.
(Without the sandals )

73ragtop
Senior
Member

26
posts [100%]
Denton Texas

Re: Removing the
proportioning valve. (jyounane)

4:13
PM 6/19/2002

quote:

However, the system is designed to reach full pressure on
the remaining circuit. This SHOULD happen before the master
cylinder bottoms out or the pedal reaches the floor, even
though the pedal travels much further.

I guess if it doesn't, that means there are other
problems with air in the system or master cylinder problems.

Check that link out and let me know what you think.

Thanks
Joe

69 427L36 M21 3.08 White Coupe

Neat site. I think the system shown, with the electrical
fluid level sensor, is a little more modern than our antiques,
but the principle is the same. Perhaps if a failure happens
during some of our more, shall we say "spirited" driving, 50%
brakes feel like no brakes as we approach the rear of a parked
police car at double the speed limit. At least we've got that
wonderful parking brake right there to haul us down on a dime.
<--- I don't usually like to use these
little animated thingies, but for the accountants among us who
don't understand sarcasm, I guess I must.

Eddie

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