Brake problem, spongey pedal.

[UK Mach1 dude 13]

I've got a strange problem with the brakes on my 70mach1, it has stock fronts and a rear

disc conversion.

Recently it felt as if the master cylinder had worn out allowing the pedal to slowly drop,

so I fitted a new m/c assembley which I bench bled beforehand.Now, I;ve been unable to get

a decent feeling pedal for about a month, I've re-bled it, re-bench bled the m/c checked

everything but its the same as it was with the old master cylinder.

This is how it is, with the engine off the pedal feels not to bad, not maybe as hard as it

used to but if you start the engine then the pedal goes real spongey as if there is lots of

air bubbles in the system.

You can press the pedal down through this spongeyness to a certain point were you can feel

it connect against something, as if the springs in the m/c are compressing and you can feel

them coilbind? is this possible?

I have checked the rubber flexy hoses and they are all good, and new about 6 years ago,

is it the servo acting up? I used to get a slight sinking of the pedal when I started the

engine followed by a rising when I stopped the engine but no longer get this, I read

somewhere that this was a good test of a servo's health?

I'm getting totally baffled by this, can anyone help please?

[69in2006 11]

Hey man...when you bled the brakes do you have good flow form the front and rear calipers..If not I have seen the proportioning valve stick adn cause similar problems...

Hope this helps..

[SELLERSRODSHOP 13]

which master cylinder are you using? did you replace with the same thing?

 

also, are you running a booster or manual?

[Grabber70Mach 107]

If you are using the stock disc setup on the front. I ran into a simular problem with mine at one time. The bleeder screw is postioned at around the 10 o'clock position this allows air to stay in the system. Remove the bolts from the caliper and position the screw at 12 o'clock then bleed. If you have someone pumping the pedal, make sure that the pads are still on the rotor, then do the other side. Hope this helps you.

[Cheo69GT 1]

Could it be the booster? I had a similar problem, it was a bad booster, also, re-check the rod length, with the engine off and the MC cover off, you should see brake fluid squirt up when you slowly push the pedal down about 1/2", if it takes longer before you see fluid squirt, the rod may be too short.