HydroBoost - Please help diagnose a soft pedal and weak brakes.

[mynameisjonas]

I am looking for some help to diagnose a soft brake pedal and mediocre brakes after I replaced all of the brake lines and master cylinder. The Bronco has 4-wheel disc brakes, and it had the HydroBoost brake system already installed, and it was wokring. fine The brake lines and hoses were corroded and in real bad shape from sitting outside at the beach, so I replaced them, along with the brake master cylinder. I have bled the system several times and confirmed there are no leaks and no air, but the brake pedal is soft and although the brakes work, they don't work very well, and nowhere how they did before I replaced the parts. I am leaning towards the new master cylinder, as I look at the specs for other complete kits include a 1 - 1/8 inch/ bore master cylinder, and I know mine is 1". I could not find a part number on the old one, so I just relied on the local NAPA to match it up. I suspect the old one could have been a 1 - 1/8 inch bore. Would the difference of the master cylinder bore be what is causing this problem?

 

[toddz69]

Definitely a possibility. A smaller bore master will make the pedal feel softer/squishier. Does the pedal height when the brakes are applied feel/appear to be lower?

Todd Z.

 

[mynameisjonas]

Definitely a possibility. A smaller bore master will make the pedal feel softer/squishier. Does the pedal height when the brakes are applied feel/appear to be lower?

Todd Z.

The brake pedal will go to the floor if you push hard enough and the brakes are not locking up. Everything worked fine before, the only change is the master cylinder and the prop valve. There were no part numbers on the old master so we best matched it up, but I do know it is a 1" bore. Most of the HydroBoost kits spec a 1 1/8" bore master, so that is what has led me to think it is the master.

 

[ntsqd]

I would consider a 1-1/8" master to be the smallest that you should run. 1-1/4" would be and is my choice for Ford or GM front calipers.

Do you know which master cylinder mount stud spacing you have? The H-B unit will either be from a Ford or from a GM and the distance between the studs is different. This will matter as to what suggested masters will fit.

Is the new prop valve an OEM type? If so, were you able to get brake fluid flowing freely at all four calipers?

 

[ksagis]

Do you still have old master cylinder? Would be simple to check its bore.

But as said above 1 1/8 is smallest bore I would consider and would reco 1 1/4

 

[hunter1]

Bleed, bleed, bleed.

 

[hunter1]

I actually had an aftermarket master cylinder that the piston stuck partially depressed. Caused all sorts of frustration until i took it off and saw what had happened. Same symptoms.