Need a favor - Brake Pedal Travel with power 4 wheel discs

[buening 63]

If anyone on here has 4 wheel discs brakes and a factory brake booster, can you take a measurement of your brake pedal travel with the car OFF and also with the car idling? I am fighting what I feel is excessive brake pedal travel but need a sanity check from someone else. Its been so long since I've had good brakes on my car that I don't know if I'm just too used to new vehicles or if I truly do have excessive brake pedal travel.  So if ya think of it, grab a few measurements for me (preferably to bare floor pan but to carpet is fine) and let me know what brakes and M/C you have to keep things relevant. 

 

 

[Rsanter 152]

I’m not near my car (I’m in Australia on vacation right now)

i went from factory front disc brakes to 4 who disc.

the rear discs are off a Lincoln LSC.

i also went to a booster by tuff stuff (non concourse version of the boss429 booster and a willwood MC (same bore as stock)

the feel and travel for the pedal at least feels the same as it did stock and my brakes are great.

[RPM 1,190]

I don't have a power booster, but does not the rear disc caliper take more fluid than the stock brake cylinder? If it has to move more fluid, wouldn't that be the cause of the longer brake pedal travel?

[buening 63]

Sorry for the delay, had to leave out of state for work. So I have 0.2" of pedal play with engine off until resistance, which feels like booster or linkage slop. Then I have 0.8" of pedal travel and feels pretty firm. As soon as I fire up the engine and get vacuum on the booster, I can press it down with one finger and the slop is gone and measure roughly 1.2", so essentially the same. Not that it matters but measurements were to rubber insert of carpet and perpendicular to floor. Attached is a video.

 

Parking brake on or off has no effect on pedal travel, so that should eliminate small amount of pad movement on the rear if pads were retracting. 

 

I just pressure bled (Motive) 2 quarts of brake fluid through the front and rears and no change in feel. All in I'm probably 6 quarts and have tapped all lines with rubber mallet, no leaks anywhere, and booster-MC rod is adjusted correctly. Pumping the brakes multiple times and holding the pedal down does not cause the pedal to sink. I went through 3 new 70 mustang M/Cs and am now on a new 00 Mustang V6 M/C (1.00" bore, same as 69/70 stock M/C)) with same pedal feel. All were bench bled in many different ways (plugs and also with hoses to bowl). 

 

I can't get the wheels to lock up on panic braking, and it does feel nose heavy upon braking. An adjustable prop valve is installed to the rear and is currently wide open. I measured 800psi with a guage to the rear caliper with the car off. I haven't done the fronts yet.

Setup is 13.2" rotors from 2012 GT with 4 piston Brembos and on rear is 13" 2016 GT. As mentioned, stock booster and 00 V6 M/C

[buening 63]

With car off:

[buening 63]

Small update: I hooked up the pressure guage to the drivers front and rear caliper. Something is definitely off with the fronts, whether its another bad MC or still air in lines. I also found that the "less brake" arrow on the Wilwood proportioning valve is backwards. Turning it that direction increases rear line pressures (yes I have the IN and OUT lines correct), so I had the rears at the min which explains why it was nose heavy on braking.

 

Front: Engine off = 300psi, on = 860psi

Rear (min prop valve): Engine off = 340psi, on = 540psi

Rear (max prop valve): Engine off = 680psi, on = 1030psi

 

The above is me basically standing on the pedal. 

 

I unbolted the brembo calipers and tilted them vertically and bled again from both bleeders and both calipers...... with no air and no change in pedal.  So frigging frustrating. Going to find some fittings and try to get the gauge hooked to the M/C and get pressures from there. 

[RPM 1,190]

I fought my power booster lack of power frustration until I removed the booster and bought a manual pedal. Been happy since. 

[buening 63]

Another update: I pulled the line from the MC and hooked up the gauge directly to the MC ports. I'm getting 1200psi (firm leg but not standing on the pedal) for the rear brake and buried the needle past 1500psi for the front brake.  My understanding is the caliper shouldn't have an effect on PSI (piston size impacts clamping force but not line pressure), so the only thing I can think of is there is somehow STILL air in the lines.

[RPM 1,190]

Yep, I agree with you that there's still some air in there. 1500 psi at the front is really good.