New Disk Break Problem! HELP!

[wrestler5]

My uncle and I just put a new power disk break set up on my 73 mustang. We got everything set up and in place, bled all the lines, and check for leaks and we didn’t find any. After we bled all of the breaks we had some break pressure, but it was spongy. Once i started the car and the break booster kicked in I lost all of my pressure altogether and the pedal slams to the floor. It still stops once it hits the floor but it is a sudden stop. There is no slowing down. I went from manual to power breaks so can this be because I didn’t change pedals? or Is it possible that my master cylinder or break booster is bad? or Is it something else completely? I would appreciate your help. Thanks Guys.

 

[1965pony]

brakesssssssssssssss

Well there could be several problems.
Air still in system.
loose rear adjustment
Wrong combo valve ( if it uses one)
wrong push rod position at pedal.
my favorite and most common, bumb master due to dirt getting into seals during bleeding process.
You guys did bench bleed the master right? Crack open the lines at the master, slowly depress pedel down and hold down. Do not release. During the down ward stroke observer fluid coming out...
good pressure out of both ?
good pressure out of rear none in front?
visa versa?
no fluid at all or just spurts?
let us know what you come up with. Vince

 

[GeorgiaBadger]

I have a similar problemm in my 69 with factory disc, but my pedal is hard until I start the engine and vacum gets applied. At that point it will get spongy. When I hit the brakes the rears lock when the pedal goes halfway.
I dont want to think about how many times the brakes have been bleed. Master Cylinder has been changed 3 times( all bench bleed). I am running a new distribution block, new prop valve in the rear line, new wheel cylinders in the rear and new calipers in the front. What else is there? Oh yea, I have all new brake lines also

Well there could be several problems.
Air still in system.
loose rear adjustment
Wrong combo valve ( if it uses one)
wrong push rod position at pedal.
my favorite and most common, bumb master due to dirt getting into seals during bleeding process.
You guys did bench bleed the master right? Crack open the lines at the master, slowly depress pedel down and hold down. Do not release. During the down ward stroke observer fluid coming out...
good pressure out of both ?
good pressure out of rear none in front?
visa versa?
no fluid at all or just spurts?
let us know what you come up with. Vince

 

[TT670]

I have a similar problemm in my 69 with factory disc, but my pedal is hard until I start the engine and vacum gets applied. At that point it will get spongy. When I hit the brakes the rears lock when the pedal goes halfway.
I dont want to think about how many times the brakes have been bleed. Master Cylinder has been changed 3 times( all bench bleed). I am running a new distribution block, new prop valve in the rear line, new wheel cylinders in the rear and new calipers in the front. What else is there? Oh yea, I have all new brake lines also

Are you sure its a disc brake M/C? M/C piston diameter plays a major role in pedal feel.. smaller the piston the softer the pedal and power assist amplifies the soft feeling.

 

[wrestler5]

Are you sure its a disc brake M/C? M/C piston diameter plays a major role in pedal feel.. smaller the piston the softer the pedal and power assist amplifies the soft feeling.

What do you mean by disk break M/C?

 

[wrestler5]

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