porporting valve?..no front brakes

[lasvegas69charg]

i installed the right stuff 4 wheel disc brakes and noticed i dont have the greatest braking.  after looking at the rotors the rear are showing signs of wear where the front still has cross hatching on the rotors which is telling me that the fronts are not engaging during braking.  i have the porporting valve turned all the way out. does this mean i have full flow going to the rear?  i read somewhere on here about resetting the pin on the valve...what does that mean? i checked the push rod and its about 1/16" from hitting the booster when the master is mounted. everything is bench bled and all four corners has solid fluid with no air bubbles.  my neighbor said it sound like a bad master. any ideas?  thanks in advance.

[lasvegas69charg]

i did find out one thing today is that my booster is leaking vacuum...would this cause the front brakes from not engaging?

[WHITE AND RED 69]

The leaking booster is going to cause the whole system not to work correctly. The fronts should still engage just not very well depending on how bad the leak is. How does the pedal feel? Are you also sure the motor is producing enough vacuum for the brakes to work properly? A lot of disc brakes require more vacuum than the engine can produce. Especially if you have added a big cam.

I would get the booster leak free and than go from there. Since the proportioning valve is all the way open the fronts should be engaging first. Get the leak fixed and if that does not fix it then adjust the valve. Start at full open just as a starting point and test the brakes. You could also start it midway and test from there. Some instructions say either all the way open or half way? I did mine opened up. Closing the valve yields full pressure to the rear and opening the valve will reduce the pressure to the rear.

When you get the leak fixed and if the brakes still don't work you might have to add a vacuum pump or a hydroboost master cylinder to get the brakes working properly.

With the cam i'm running I could barely get the fronts to lock up with the low vacuum. I added a hydroboost master cylinder and my brakes have never felt better.

[lasvegas69charg]

thanks for the info. I have a electric vacuum pump so I have a constant 20 inches. I'm going to replace both booster and and mc see what happens.

[firefighter3931]

Read this thread as it applies to your situation :

http://www.dodgecharger.com/forum/index.php/topic,95452.0.html

I was having the same issue as were many other members. 

After some investigation it was determined that an improperly adjusted proportioning valve was a large part of the problem.

i have the porporting valve turned all the way out. does this mean i have full flow going to the rear?

The answer to this question is NO...in fact it is the exact opposite ! When the valve is turned all the way out you have essentially cut off all line pressure to the rear brakes and created a hydro-lock in the master cylinder. Turn the valve completely in (clockwise rotation) and road test. You can open the valve slightly until you achieve simultaneous lock-up on both the front and back brakes. In my case i ended up leaving the valve turned in all the way, which is fully open. 


Ron

[lasvegas69charg]

thanks Ron. I will try that and let you know. I thought the opposite that if I turned ccw all the way out that it would be fully open allowing full pressure going to the rear.

[lasvegas69charg]

Also if I had no pressure going to the rear wouldn't it cause only the front to engage and not the rear do to no line pressure because the portioning valve is closed?  I'm not understanding the hydrolock.

[firefighter3931]

thanks Ron. I will try that and let you know. I thought the opposite that if I turned ccw all the way out that it would be fully open allowing full pressure going to the rear.

I thought the same thing too....conventional wisdom would be that adjusting the valve "out" would increase flow but this is not the case. Lots of us have made the same mistake so don't feel bad. 

Also if I had no pressure going to the rear wouldn't it cause only the front to engage and not the rear do to no line pressure because the portioning valve is closed?  I'm not understanding the hydrolock.

Read through my link above and the hydro-lock theory is explained. 

The short version ; with the prop valve closed the plunger in the master can't move so the front brakes won't get enough line pressure to properly stop the car. 

Trust me, adjust the valve and you will notice a huge difference ! 


Ron

[six-tee-nine]

On a side note, if you have a vacuum leak or a bad vacuum booster, your brakes should still be working like they should, they just are'nt power assisted anymore (or less power assisted depending on the largeness of the vacuum leak).

[lasvegas69charg]

Ron, your the man    Not only does it lock up ALL 4 tires at the same time,  it stops on a dime.  Thanks again for the GREAT advice. This is truly a beautiful thing...

[firefighter3931]

You're welcome....glad to help 

I know all to well how you're feeling....it's a huge relief to have the brakes working as they should. 


Ron