Is the pedal a "kit" or something that you put together?  I had similar symptoms on a car with that I had to build my own foot box.  I had the geometry of the pedal wrong and it would go "over center" for lack of a better description.  I had the top of the pivot arm too far back and there was a region further foot movement only produced very changes in actuation and it felt springy or spongy even though without boost it felt good..  If you bought a pedal assembly, which one did you get?  Could be that your master cylinder bore is a little small.  Other thing could be the adjustment of your rear drums.  If they are too loose you lose a fair amount of pedal pushing them against the drums.  Your setup may work well with a 10 psi residual pressure valve in the rear circuit.

I used to have a link that showed the over center condition.  I thought I found another one but can only find a reference with the wrong picture in this article.  I'll keep hunting.  I moved my brake pivot point about 1" closer to the master and it completely cured my problem but certainly check everything else.  Do you have any pictures of the pedal and actuator rod setup?

http://www.superchevy.com/technical/chassis/brakes/sucp_0110_wilwood_brake_system/master_cylinder.html

MustangSteve wrote:

Your pedal ratio seems kind of high for a power brake system.  A Mustang manual brake system uses a 6:1 ratio.  My modified ratio pedals use a 4:1, and the original 67-69 pedals have approximately 3:1.  In 70, they increased it slightly.  I used rounded numbers for this comparison.

If you have a booster that allows the pedal to go down very easily and then instantly fully applies the brakes in about mid-stroke, then you probably need to replace the booster due to a faulty internal valve.

Also, like GaryP said, be sure the pedal geometry is right so the rod travels in a near straight line as it applies the force to the booster.

Are your pedals the underfloor pivot type like 32's came with?  I have never dealt with that type of pedal setup, so maybe there are some other issues that could be affecting it.

Its a swinging pedal set up under the dash. WOW am i impressed with all of the help here. Now i am going to look at all of the ideas that have been given. Thank You Thank You.

mrputz1 wrote:

MustangSteve wrote:

Your pedal ratio seems kind of high for a power brake system.  A Mustang manual brake system uses a 6:1 ratio.  My modified ratio pedals use a 4:1, and the original 67-69 pedals have approximately 3:1.  In 70, they increased it slightly.  I used rounded numbers for this comparison.

If you have a booster that allows the pedal to go down very easily and then instantly fully applies the brakes in about mid-stroke, then you probably need to replace the booster due to a faulty internal valve.

Also, like GaryP said, be sure the pedal geometry is right so the rod travels in a near straight line as it applies the force to the booster.

Are your pedals the underfloor pivot type like 32's came with?  I have never dealt with that type of pedal setup, so maybe there are some other issues that could be affecting it.

Its a swinging pedal set up under the dash. WOW am i impressed with all of the help here. Now i am going to look at all of the ideas that have been given. Thank You Thank You.

Well : I replaced the master with one from a 78 3/4 ton ford pickup 1.062 piston . More volume checked to make sure the pedal was not over center. adjusted the pin between the master and the booster and rebled the disc cylinders up front. Total difference the pedal does not drop softly .its a 1/2 inch drop with the engine off and 3/4 withe engine on using the booster. PROBLEMS solved. Thank you so much for the support.

I like the hood side panels. Makes the car look sleek and adds a air of mystery: "What's in there?".

Really nice looking Ride!

Brents65 wrote:

It sure does! I am proud of you for not sticking a 350 in it. Too many people for some reason feel the need to do this. I think it here should be rules against this.

Chevy engines and engine  parts (ok, most Chevy parts in general) are cheaper than the Ford counterparts, and they are easier to assemble and tinker on...or least they used to be before all this variable valve timing, cylinder shut off crap they have out now. Chevys: Easiest to work on, Fords: 2nd easiest, Dodges:...PITA!!!!   try doing upper and lower ball joints on a 99 dodge pick up....riveted in!
I know, its a Ford Mustang forum, but I've always been a chevy guy, even though I got 3 Fords, a Chevy and a Pontiac.
 

Last edited by mainiac1 (3/24/2014 9:40 PM)