In tech section it talks about removing valve to obtain 100% pressure to all four brakes. I want to do this. But on mine I have two lines from MC to valve then only three lines leaving. Two to the fronts and only one to back(I think).

How and what do you use to you connect directly to MC with this situation?

Other option is buy self adjusting valve. Where can I find one? THX

 

When I had manual brakes the best thing I did for them was remove the proportioning valve. I allowed the back wheels to finally do their share of the work. It was like night and day difference. I went and removed it also from the power braked mustang and once again a big difference.
A real advantage is that if you loose one end like a blown line the brake pedal still feels normal and no going to the floor.
Now how was it done.
The back is easy , unscrew the rear line from the valve and buy a short length to splice it directly to the rear of the master cylinder. Easy
For the front I did install a line lock so it just involved running one line from the front of the master cylinder to the line lock and the line lock has 2 seperate lines comming off it.
You don't want a line lock? How about buying a Tee . A short line off the front of the master cylinder into the Tee and 2 seperate lines off the Tee to each of the front brakes.
You will find bleeding the system alot easier without the proportioning valve. If you just bleed the front and take it for a drive and remember you have 2 seperate independent systems now the car will stop just fine. Once the backs are also bled the car will feel like someone is holding the back bumper.
I DO NOT DRIVE IN THE RAIN OR SNOW. You could get wheel lockup in the rain so be careful.
Next came the hydraboost and incredible brakes. Compared to my wife's new Bonneville SSEI Supercharged my brakes are FAR stronger. This is with stainless calipers and stock drilled rotors.
Hope this helps. If you need more just ask

 

Well, here we go again with the proportioning valve nonsense...

First of all, there is NO proportioning valve to remove on a 68/69 vette.

Second, the item thats being called a 'proportioning valve' is a distribution
block with a switch in it that will illuminate the brake light if the front or
rear brake pressure is lost.

Third, brake proportioning is done by using much smaller rear brakes as
compared to the front brakes. Take a look at the difference in size of the
front and rear caliper pistons.

Both the front and rear get equal pressure, however, since the rear pistons
are so much smaller, they exert a whole lot less force against the pads.
Thats why the front brakes do a lot more of the braking.

If you truly wanted all 4 wheels to exert the same braking force, you'd need
the same size brake calipers on all 4 wheels. After doing this you would
immediately need a REAL proportioning valve to limit the pressure to the
rear brakes unless you wanted a very dangerous handling car.
You'd probably come out with about the same front/rear braking bias as
the stock system.

 

Wether its a valve or a switch, its always been called porportioning valve regardless on any car when talking to other people I know. Since it's not acting as a valve or a circuit protector then why not remove it since different caliper sizes makes it a wash anyway? Why have something disfunctional on such an important system? What about a real valve, was the other question.

 

I think the reason most people call it a proportioning valve is because they dont know what it really is. Some can be combination valves but on the early C3's like Gwilliam said, "its a distribution block". There is no proportioning valve in your car right now so you are getting the same pressure to your front brakes as your rear brakes. like said before because of the smaller piston area on the rear calipers that is how your braking power to the rear is limited. There is no reason to get rid of your distribution block. If you do the only thing accomplished is that you will have no pressure diffirential switch which means if one half of your brake system fails your warning light wont go on.

 

Believe we do have proportion valves on our vettes. Here is a good overview on how it work:

http://www.howstuffworks.com/master-brake2.htm

With the vette be almost 50/50 weight ratio, under light to mod braking having no proportion valve would give a better breaking feel and less front end dive while under heavy breaking the rears would lock up since you would get greater weight transfer to the front end. Would be optimal to have a proportion valve that was progressive meaning no proportioning under light pressure and greater and greater proportioning as the pressure increased. Of course anti-locks are the ultimate but not sure how much $ it would take to retro-fit a system to our c-3s.


Not sure if tis means anything but:
http://store.yahoo.com/zipproducts/b...ng-valves.html

Seems if they where just dist blocks then they would be labled as such but I am not sure. :confused:


[Modified by Fevre, 3:39 PM 11/26/2002]

 

Calm down now but your post asked how do I get 100% pressure on all
4 brakes, right?

News flash - you have 100% pressure at all 4 brakes now!

You don't have the same braking force because the rear brake pistons are
a lot smaller than the front ones.

How viable do you think it would be to make up for inadequate rear brakes
by using a proportioning valve?

If the purpose of all this is because everyone says it's needed even though
they don't know why and it looks cool then go for it!

 

I forgot to mention before that if you take this valve out your brake pedal will act the same when you have a failure in one half of the system(it will still go almost, or completely to the floor). The way the master cylinder is designed it is impossible to have the same pedal reserve when half the system fails.

Fevre: Thats interesting how zip has called them all proportioning valves. Im pretty sure they have just mis labeled them. From the pictures they provide those "valves" dont have any exterior features to indicate that they are proportioning valves. All those valves are simply pressure differential valves.


[Modified by 71vettman, 5:48 PM 11/26/2002]

 

For what it's worth: even on my 75, the AIM manual calls this thing a switch. I also believe it does no "proportioning" whatsoever. It does sense an imbalance of brake fluid flow to either the front or rear wheels to trigger a warning light. Im my own opinion, removal could lead to a dangerous situation, but probably not any worse than having the warning light burned out or missing.

:cheers: :eek: :cheers:


[Modified by Big Fish, 6:11 PM 11/26/2002]

 

Thanks for the responses.

My light keeps going on. After reading quite a few posts many people say it is a good idea, some say it is not.

I'm still not sure.

 

As GWilliam so passionatly wrote, you do not have a proportioning valve and removing your distribution block will not solve a brake warning problem. It is relatively easy to remove the block and investigate its "guts" for yourself. All you'll find in there is a rod that has two ramps just off center on either side of the rod and two sealing rings on it. When there is a difference in brake line pressure, this rod moves and grounds the sender on the ramps on the rod which illuminates the warning light.

If you've recently opened the brakes and got the light, then you need to re-center the switch by opening either the front or rear brakes and cause the rod to center itself by slowly pressing on the brake pedal until the light goes out.

If your light is coming on and you haven't worked on the system, then you have a hydraulic problem as the switch itself rarely goes bad. It could be a very small leak in a caliper piston.

Finally, I think that it was 1977 when the Corvette got a real combination valve.

 

CHEVROLET POWER BOOK / CORVETTE CHASSIS SECTION

Adustable Proportioning Valve

The new adjustable proportioning valve is designed to control front to rear brake balance on race cars and other off-road vehicles.........and other types of racing where track surface conditions vary, neccessitating a change in brake syatem balance.

Installation

To achieve the maximum benefit from the adjustable feature,it is recommended that the valve be installed inside the car , within easy reach of the driver. Mounting attiude is not critical. The valve should be plumbed into the rear brake system, between the master cyclinder and rear brakes, downstream of any differential warning valve, if one is present. The brake tube from the master cyclinder is connected to the top port on th evalve (marked "IN), and the rear brake tube connected to the bottom port (marked "OUT"). Both the inlet and ooutlet ports are tapped for 7/16th-24 tube nuts and will accept 3/16 or 1/4" O.D. flared tubing. Mounting is accomplishihed by using the two 5/16" holes.

Adjustment

Brake balance is varied by rotating the adjusting know: clockwise to increase rear brakes, coounterclosckwise to decrease rear brakes. It is recommended that the valve be initially set at its minium position (fully-counterclockwise), and be adjusted upwards, under actual track conditions, until the front-to-rear balance is optimum. After this intial setting is made, only fine tuning will be required to compensate for varying track conditions.


------------------------------------------------------------------------------------

The only other recomendation the book gives is to upgrade to an early Chevelle master cylinder with a similar 1 1/8" cylinder diameter with a larger resivoir or an even larger 1 1/4" dia. cyclnder from a '74 or '75 C- 20 or C-30 series truck and that all brake hoses should be replacesd with stainless steel flexable brake lines.

Hope this helps, JIM :thumbs:

 

GWillaims. Have you ever made this modification? Are you going strictly on theory? I am answering on experience. Not a little experience but alot. I have solved braking problems on 3 different cars with removing this distribution/proportioning valve whichever you want to call it.
I can cut a line in the rear brakes and take the car for a test drive and I will stop just fine and my peddle will still feel normal and NOT go to the floor the first time it is pushed. Unless you have ever experienced a line suddenly failing you don't know what it feels like and if you have you don't want it to happen agian.
When the brakes fail this switch moves over towards the failed end and the pressure in the good end suddenly goes down causing the pedal to hit the floor. A few pumps later you stop with the pedal almost on the floor and your heart in your mouth.
Try this with this distribution block in place and you stop normal.
Also without this block in place bleeding some rear brakes is alot easier.

 

I tend to agree with most of the suggestions and opinions in here, but I would
just like to repeat: A brake system problem that keeps lighting the warning
lamp will not be cured by removing this pressure differential valve. Most
likely is that you have some air in the system (bad bleed, rotor runout, etc).
This would allow the switch to move over during braking, and slide back into
center when pressure is released.

If you simply want the warning light to go away, just disconnect the wire at the valve.
[This is NOT recommended. A poor brake system can place your life and other's in danger]

Norval, I have much respect for the work you've done and the knowledge
gained. I agree with all of the advantages that you state - as well as the warning.
One thing that has me confused is the big difference you experienced when
the valve was removed. Yours is a ? 75 ? I think. Perhaps Bubba had replaced
the valve before you bought it - with a later model valve, or a proportioning
valve from another GM ? With a true 'proportioning' valve, the difference
should be quite noticable. With the C3 brakes proportioned with the caliper
piston surface area, I can't justify any difference - unless the valve was
improperly restricted or replaced with the wrong unit.

The hydroboost system sounds great. Maybe after I get mine back together ...

:seeya


[Modified by Daves_rusty_75, 12:41 PM 11/27/2002]

 

I always ran big slicks on the back with non power brakes and they sucked. While trying to bleed my mustangs rear brakes you could open the bleeder and jump on the peddle and nothing would come out. I went to my friends garage and talked to him about this problem and he said he run into this all the time and it was the proportioning valve that caused the problem. I then went to my Canscar racer friend who also operated his own garage and he told me to get rid of the valve/distribution block. The brake pressure would go up to the back but also the brakes would release quicker comming off them.
I removed the block and immediately found the rear brakes with the big slicks started to haul the car down alot quicker and the car squatted rather then nose divided, not that a vet nose dives but it felt like someone grabbed the back bumper. I really felt the difference.
I then wanted power brakes so I first tried a 85 1/2 ton hydraboost and really like the syestem. It was almost a bolt in. I then went to a 94 one ton hydraboost for $50 and it really put the power up.
I now have a one ton hydraboost, a nascar power steering pump, stainless calipers, organic wagner pads and drilled rotors and my brakes are STRONG. If I choose to lock them up at 60 mpg I can easily do this. All 4 wheels. I am very familiar with the difference between the calipers front and back and bleeding vet brakes.
I read alot of posts on bleeding problems and can't understand the problem. I do my brakes, at least remove all 4 calipers for cleaning and painting and new organic pads EVERY year and have to rebleed. I have a pressure bleeder and it doesn't take more then 5 or 10 minutes to do the bleeding. Also the old pads push back easily off the rotor.

 

Maybe everyone is right........... Would it be to far fetched to say that when the " Valve " in question is offset in its contact position that it impares the flow of fluid? Even if it was intended as a warning device could it restrict the flow when placed in an abnormal position? Does it have a flow restricter in the block much like an oil restricter plug for a lifter valley. Seems possible and undectable to me without measurments taken.

I also see mentioned that the brake line size to the rear is a restriction factor, however GM Power Book doesn't mention changing line sizes for race cars.

My '80 seems to be fairly well balanced in braking. I wish it was stronger and I am looking at getting the HydraBoost set-up myself. I was also intending on using the adjustable valve from the article I posted above.

When I worked in a Chrysler dealership many years ago we encountered this problem and the cure was to literally stomp the brake pedal to recenter the warning valve after repairiing the initial fault.

I wish I had one here to take apart and take pictures of to see what makes it tick. ANYONE have one and a camera?

I posted what was written in the Power Book about the subject and realize it is not the last word. But with the different viewpoints here it makes me wonder if the Warning Valve desn't have some type of restrictive measure in the port to the rear brakes besides being a warning device. JIM

 

http://forums.corvetteforum.com/zerothread?id=410142

 

Did Tom454 ever post those pics?

 

Well, this has bugged me and so I got up and went to the shop and pulled out the 1980 GM Corvette Shop Manual and looked this up. Hmmmmmmmm seems I might have been right ! well at least on the '80.

OPERATION OF COMBINATION VALVE

The proportioning section of the combination valve proportions outlet pressure to the rear brakes after a predetermined rear input pressure has been reached. This is done to prevent rear wheel lock up on cars with light rear wheel loads.

The valve is designed to have a "by pass' feature which assures full system pressure to the rear brakes in the event of a front brake failure, full front pressure is retained in the event of rear failure.

The pressure differential warning switch is designed to constantly compare front and rear brake pressure from the master cyclinder and energize the warning light on the dash in the event of a front or rear system failure. The valve and switch are so designed that the switch will latch in the "Warning " position once a failure has occured. THE ONLY WAY THE LIGHT CAN BE TURNED OFF IS TO REPAIR THE FAILURE AND APPLY A PEDAL FORCE AS REQUIRED TO DEVELOP UP TO 450 PSI LINE PRESSURE.

Like I said, seems that most everyone was right in some capacity.

JIM :seeya


[Modified by PROSOUTH, 11:45 PM 11/27/2002]

 

Chris... I have not posted the pics... my "helper" has been too busy with other interests. Maybe I can find someone else to help me.

On thing I did find out is that the valve/switch (whatever) varies quite a lot from year to year. For example, the 1970 switch does not have "ramps" in it as described above. It has a "dog-bone" shaped brass slider that moves in response to lack of pressure on one side... it then contacts a stationary pin protruding from the middle of the assembly. When it hits the pin, the ground circuit is completed for the brake warning light through the brass internal parts of the switch. The pin does not move in any direction... it is stationary.

The 80 switch is designed completely different.
Bottom line... if you want to discuss this item intelligently, your comments must be limited to a single year design. You can't make generalizations about the C3 switch. Some years are probably the same... but don't make any assumptions or statements unless you have personally disassembled one for that year. This is the lesson that I learned by taking these things apart.

The other lesson that I learned is that the device will most likely not save your butt if you lose pressure in one side. Now remember... this is for a 1970 version of the switch. I didn't test the 80.

Please see the link Kelly posted above for my test.

Tom