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CorvetteforumC3
CorvettesRemoving
the proportioning valve.

yellow 72
Senior
Member

873 posts [100%]
cincinnati ohio

Re: Removing the
proportioning valve. (73ragtop)

4:27
PM 6/19/2002

"Parking brake " .....Iget it
_______

Chris O'
Senior
Member

496
posts [100%]
Brisbane, Australia 1977 Coupe

Re: Removing the
proportioning valve. (73ragtop)

4:28
PM 6/19/2002

The more I read this thread, the more confused
I get! Take it off, leave it on, on, off......

I'm just afraid of replacing/changing one more thing that
makes no difference to my spongy brakes!

Barry's70LT1
Senior
Member

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

Re: Removing the
proportioning valve. (norvalwilhelm)

7:53
PM 6/19/2002

I will make an assumption here.

Yes, when the bleeder is opened the peddle will go down,
perhaps to the floor.

Now, in the real world, if a line blows, the peddle will
also go down and the differential in pressure between front
and rear will transfer the "insides" of the proportioning
valve to what ever end has lost the pressure.

Now, on the second pump, you "should" have a relatively
firm peddle, since the valve has now already did it's thing.

When bleeding, typically no one ever gives a second pump
with the bleeder open, so we don't know what happens on a real
failure.

drives61
Senior
Member

1699
posts [100%]
Central FL

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

12:07
AM 6/20/2002

barry
i used to give 6 to 8 pumps before
closing the bleeder, depending on the capacity of the MC. they
never "pump up"

of course now i use gravity on my
72.

ZD75blue
Senior
Member

3579 posts [100%]
NC,USA

Re: Removing the
proportioning valve. (norvalwilhelm)

5:40
AM 6/20/2002

Pretty cool information guys...

I wonder if ya could run the lines in the shape of an x...
so left front is pared with right rear, right front to left
rear.... so if ya lose one, it moves the load to the oposite
corner

A friend of mine was talking about this, maybe it was on an
86 Celbrity? might have been the abs system or something...

Tom454
Senior
Member

2035 posts [100%]
Raleigh North
Carolina

Re: Removing the
proportioning valve. (norvalwilhelm)

6:12
AM 6/20/2002

I have the original master cylinder for my 70
in a box. I recently used it for testing another forum members
brake system.... although it has a few pits in it, it still
works good.

This master cylinder has the bleeders in the side of it.

If I were to install & bleed this M/C (and the rest of
the system), then remove one of the master cylinder output
lines and one bleeder, and connect a properly constructed
steel tube to allow fluid to flow from the output port
directly back into the master cylinder through the bleeder
port (simulating a leak/failure).... and then drove the
car....would this be a good test of all the ideas we are
kicking around (assuming my combo switch is in perfect working
order) ??

What would y'all predict?

I am willing to perform this test if you guys think it
would serve a purpose.

Don't worry about the driving part being "naughty" or
"dangerous".... I never had apron strings tied to my butt, and
never will.

MikeC
Senior
Member

1098 posts [100%]
St. Thomas
Ontario

Re: Removing the
proportioning valve. (Tom454)

6:24
AM 6/20/2002

quote:

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

I'll be the first one to call on that one. I have had failures on both
systems and when that happens, I had virtually no brakes
during either incident! my brake pedal went to the
floor.
_______

1978 L-82 4 spd
Mods: Hooker sidepipes, Crane
cam, Centerforce clutch, hurst
shifter

yellow 72
Senior
Member

873 posts [100%]
cincinnati ohio

Re: Removing the
proportioning valve. (Tom454)

6:24
AM 6/20/2002

Great idea, that should settle some of the
debate. I predict the other side of the system will take over
braking duties

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Removing the
proportioning valve. (Tom454)

6:37
AM 6/20/2002

If you just jacked your car up and removed one
wheel regardless of which and opened the bleeder screw and
then jumped in the car and hit the brakes really hard a few
times would your peddle go to the floor, would you feel safe
driving the car?
While bleeding my rear brakes with my son
doing the honors of opening and closing the bleeder screws I
felt the peddle was still firm with the screw open and the
fluid poring out the screw. I would not have worried at all
taking the car out on the road with just the front brakes
working.
My wife came home twice with a older Bonneville
with blown rear wheel cylinders and both times she make it
home OK but the peddle was almost to the carpet before it
would stop. Very scary.
Forget the safety issue and just
concentrate on the increased braking power from a performance
point of view. I definitely noticed a big improvement in rear
brake performance after removing this proportioning/light
brass block. I would definitely do it agian to any fair
weather vehicle I get in the future. The before and after
testing convinced me this is a step towards better more
aggressive braking.
It is very nice of you to offer to do
the testing but is it worth all the effort?
You bleed lots
of brakes in the past and in the future. Remember how the
peddle felt when someone openned the bleeder screw? I pressure
bleed now so the memory is fading.
Have a nice
day.
_______

Norval

Tom454
Senior
Member

2035 posts [100%]
Raleigh North
Carolina

Re: Removing the
proportioning valve. (norvalwilhelm)

6:49
AM 6/20/2002

"It is very nice of you to offer to do the
testing but is it worth all the effort?"

Ans- I think it is... might answer some of our questions.
Brake systems are a piece of cake for me.

"You bleed lots of brakes in the past and in the future. "

Ans- Affirmative on that.... I have been classified as a
"professional" mechanic for over 30 years. Not that it means
anything.... but I have done a LOT of brake jobs. Remember...
when you do brake jobs for other people... you are responsible
(and liable) for their lives.

"Remember how the peddle felt when someone openned the
bleeder screw? "
Ans- Yes... I bled Jennys brakes yesterday
just for fun.

I just want to know if you guys think it will be a valid
"test" BEFORE I go through the trouble. I wouldn't want to do
the work and then have some dude come on here and say the test
is dumb and invalid.

Sooo.... what do y'all think?

Fevre
Senior
Member

1467
posts [100%]
Ann Arbor MI

Re: Removing the
proportioning valve. (norvalwilhelm)

7:27
AM 6/20/2002

Also you would feel the difference when
breaking after one side of the system failed which would tell
you to deal with it immediately. If both sides failed you
would be screwed with or without the
block.
_______

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. (Tom454)

12:27
PM 6/20/2002

Tom
i think EVERYBODY should check this out
next time they bleed the brakes.
all anyone has to do is
push on some fish tank hose, route it away from the tire, tie
it up so it wont get tangeled. then open the bleeder 1 turn
and go down the driveway 10 mph and slam on the brakes. (make
sure there is plenty of room to coast to a stop and prepare to yank the hopeless e-brake
last chance to avoid collision: shift into
R

Barry's70LT1
Senior
Member

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

Re: Removing the
proportioning valve. (Tom454)

3:02
PM 6/20/2002

Tom, if you are willing to take the time to do
this test, I think the results may be very interesting.
For
myself, I would like to know the answer.
If the answer is
NO BRAKES, then Norval makes a great case to remove the block.
(For safety reasons if nothing else)
If you still have
brakes, but after the second pump, or something, it would be
nice to know.
In an emergency situation, if the knowledge
of how it reacts to a loss of fluid is in the back of your
mind, it may save your butt someday.

Tom454
Senior
Member

2035 posts [100%]
Raleigh North
Carolina

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

5:57
PM 6/20/2002

Okay...

I'll give it a shot.

Should be done before the end of next week.

I believe I have an assistant (witness?) lined up as
well.
Should be fun.

Flareside
Senior
Member

1698 posts [100%]
Roxbury NJ

Re: Removing the
proportioning valve. (Tom454)

6:26
PM 6/20/2002

Tom, doesn't the bleeder thread into the same
high pressure area that the output line connects to? I would
think that a line between both ports would act the same as if
you plugged both port.

Am I missing something? (again...)

-Joe
_______

'68 big block 427/390 convertible

-Fuel injected Merlin
540
-Richmond 5-speed
-F.A.S.T. Wideband O2
EFI
-Custom Victor EFI intake that fits under the stock big
block hood!
-SpeedDirect rack and pinion
steering
-Dart 335cc/400cfm CNC
heads

Tom454
Senior
Member

2035 posts [100%]
Raleigh North
Carolina

Re: Removing the
proportioning valve. (Flareside)

8:00
PM 6/20/2002

Yup Joe... I think you are correct. Brain Fart
on my part.

So instead, I'll take a junky old spare cover and drill
holes in it.

One way or the other... I'll test the valves function under
stress.
I'll take a closer look at the old clunker
tomorrow.

Thanks for the heads up Joe.

Flareside
Senior
Member

1698 posts [100%]
Roxbury NJ

Re: Removing the
proportioning valve. (Tom454)

4:23
AM 6/21/2002

quote:

Yup Joe... I think you are correct. Brain Fart on my part.

So instead, I'll take a junky old spare cover and drill
holes in it.

One way or the other... I'll test the valves function
under stress.
I'll take a closer look at the old clunker
tomorrow.

Thanks for the heads up Joe.

Hey, even a broken clock is right once a day Glad I could help.

-Joe

[Modified by Flareside, 7:24 AM
6/21/2002]

CF6873
Senior
Member

386
posts [100%]
Lancaster PA

Re: Removing the
proportioning valve. (Flareside)

7:22
PM 6/21/2002

Joe, Do you only have 12 hours in your day?
Craig

Ingar, Norway
Senior
Member

456
posts [100%]
Kristiansand

Re: Removing the
proportioning valve. (norvalwilhelm)

1:33
AM 6/22/2002

As pointed out by Joe, the master cylinder is
designed so than one circuit will maintain pressure if the
other developes a leak.
However, since it will take some
fluid to move the piston in the differential valve, the pedal
will drop on the first pump after you open one circuit.
May
this is what Norwal experienced?
_______

Tom454
Senior
Member

2035 posts [100%]
Raleigh North
Carolina

Re: Removing the
proportioning valve. (Ingar, Norway)

3:57
AM 6/22/2002

We'll all know in a few days.... when do the
"test".

The point has already beem made that when you are bleeding
the brakes on a C3 with a dual master cylinder (as opposed to
a C2 with a single reservoir) , and you crack only one
bleeder, the pedal goes to the floor.

Lets see what happens when one output port is wide open,
simulating a ruptured brake line as occurs with rusty lines in
the snow/salt belt. (which I have personally experienced).

Tom454
Senior
Member

2035 posts [100%]
Raleigh North
Carolina

Update

5:47
AM 6/27/2002

The project has begun... while I disconnected
the brake lines, Jenny removed the Master Cylinder and all 4
calipers. Caliper Kits were purchased at AutoZone, while a M/C
rebuild kit (Bendix) was ordered & received from Advance
Auto. I already have several quarts of silicone fluid (DOT 5)
in stock.

The distribution switch did not come out without a
struggle... the bottom inverted flare nut & tube twisted
off due to rust, so I have to repair the damaged line..... and
this will add a little time to the project. I expect to just
splice in a piece for the test, but will order new stainless
line(s).

I expect to have the brakes re-installed and the test
completed by Monday, because I intend to drive the car to the
Stars & Stripes event being held at Performance Chevrolet
in Chapel Hill on Monday ( http://www.grammonline.com/starsandstripes
).

The switch ("proportioning valve" ) has been disassembled,
sandblasted and refinished.

It did have some sludge in it, and the electrical contact
portion of the switch was obviously malfunctioning..... it had
a thick, non-conductive coating of sludge on the exact spot
where the circuit would normally complete (inside the switch)
to turn the light on in the event of a hydraulic pressure
loss.
I know several people have recently asked if this
switch can be rebuilt...
The answer is yes for a 1970 OEM
brass switch... it has two O-rings inside, and two o-rings to
seal the switch post insert. To disassemble it, we tapped the
inverted flare seats in both ends with a 6-32 tap, mounted the
switch in a bench vise, and used a machine screw to (very
carefully) pull the seats out of the ends of the switch. Once
the seats are out, and the switch contact post is removed, the
internal parts can be pushed out of the switch. If the switch
post is not first removed, you will destroy the valve trying
to get the internal parts out. Here are the
parts....end-to-end...

inverted flare seat
spring
piston with
o-ring
"dog-bone" switch contact slider
piston with
0-ring
spring
inverted flare seat

The switch contact where the wire connects does not move...
it remains stationary. The center post is isolated (insulated)
off ground, and as the internal hydraulic parts slide off to
one side during a system failure, the "dog-bone" touches the
switch post and via the all brass internal parts, goes
(connects) to ground. There is no provision for
"proportioning" of fluid pressure whatsoever in a 1970 OEM
brass "proportioning" valve. Not that I can discern.

The hydraulic portion of the switch appears to be working
properly.... no pits or scoring is evident.

We have pictures and will post when the job & test are
complete.

FYI- The OEM Chassis Service Manual has a good description
of how the dual master cylinder is supposed to save our lives.

If I can find the time, I will post that as
well.
Tom

Fevre
Senior
Member

1467
posts [100%]
Ann Arbor MI

Re: Update
(Tom454)

5:57
AM 6/27/2002

I appreciate you taking the time to do some
research to benefit all of our knowledge bases. I am going to
do some extensive dyno testing on my current engine and 383. I
will post a list of things I plan to change and dyno after
each just to see what it does. I want to see hard data on what
changes I make have the most/least affect on my power ratings
and which ones are worth the trouble and expense.

_______

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

norvalwilhelm
Senior
Member

1827
posts [100%]
Waterloo ontario Canada

Re: Update
(Tom454)

6:51
AM 6/27/2002

Tom and Jenny. You guys are really getting into
this. Removing the master cylinder and all 4 calipers plus
rebuilding the proportioning valve. Hope this is needed and
not just done to find out what works and what is needed. I
thought you would just remove one or open a bleeder valve to
simulate a ruptured brake line and take it for a drive. If you
get the chance and you ARE going to alot of work for us try
the system with and without the proportioning valve and see if
the back brakes work that much better.
If you were local i
would gladly send you the replacement silicone. I have it by
the drum full.
Good luck in testing and thank you for the
effort you and Jenny are making for the rest of
us.
_______

Norval

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