Cobra Hydroboost bleeding problems

[Cortez]

I'm installing the h-boost brakes this weekend and have it all installed, but having a helluva time bleeding them. I can pump them up to moderate stiffness but can't seem to get them to pump up to a solid stiff pedal feel. I've tracked down a couple leaks and resolved them but still can't seem to get it.

- is a leak the only reason it won't get a firm pedal feel or does that mean I still have air in the lines. I've pumped through about 3 cups of brake fluid.

- I jacked the front off the ground and pumping the pedal doesn't engage my pads to stop a spinning wheel. Is this just because I don't have them bled out good?

- What else should I be looking for??

Any help would be appreciated - thanks!

 

[TOFIC]

some suggestions for you
check your hboost itself, is the front spinning wheel just one or both??
check the length of your actuating rods (not likely as you get a semi firm pedal) a little slack but not much.
ON a guess its your master cylinder not working right- - - look at this.
Also your forgot to mention, do you have power steering or is it still fell stiff and like manual steering. if the steering is right the hboost bypass is working and the air is out of the hboost system. if not, you have problem with blockage in the system(contamination in the spool valve of the Hboost) which is causing problems
anything else you can tell us??
What master for example.
TOFIC

 

[rjrobin2002]

What kind of front/rear brake set up are you running? What diameter is the master cylinder bore? How does the pedal feel when the vehicle is running versus when the vehicle is off? Did you bench bleed? I do not know much about hydroboost, but I know that these things are going to need to be known for you to get lined up with the right master cylinder and for TOFIC to give you a good answer. Hope it works out.

 

[Cortez]

Power steering is working fine.

When the engine is running the pedal is super soft to push and a slow return.

I did the bench bleed 3 times before I felt like I got it good.

I've got Chevy conversion discs in the front, drums in the rear

the h-boost conversion plans on classicbroncos.com indicated to use the master cylinder that came with the h-boost and so that's what I have, from a 97 cobra mustang.

I have a rear adjustable pro valve with the standard h-block on my bronco

 

[Cortez]

I have the adjustable pro valve for the rear in line ahead of my H-block...should it located after the h-block in the rear line?

 

[toddz69]

I have the adjustable pro valve for the rear in line ahead of my H-block...should it located after the h-block in the rear line?

Where you've got it is fine.

Todd Z.

 

[Cortez]

I think I'm leaning toward a bad master cylinder. When my buddy is pumping the pedal I can hear what sounds like fluid or air leaking inside the MC. That combined with the fact that it won't pump up any significant pressure leads me to believe the seals in the MC are failing.

Can anyone help with other symptoms of a bad MC?

What's confusing is that I replaced all the brake lines so I have a lot of new potential points of failure...but I feel fairly confident that I've located and resolved all the leaking areas and don't see any more fluid drips...yet it still won't drive any pressure.

I do get some fluid flowing from all the bleeders when pumping...but you can pump forever with the bleeders closed and it never gets a firm pedal.

 

[G's Baja Bronco]

Cortez, dealing with similar problem, did you figure out the issue??
Thanks for your time!

 

[TOFIC]

I think I'm leaning toward a bad master cylinder. When my buddy is pumping the pedal I can hear what sounds like fluid or air leaking inside the MC. That combined with the fact that it won't pump up any significant pressure leads me to believe the seals in the MC are failing.

Can anyone help with other symptoms of a bad MC?

What's confusing is that I replaced all the brake lines so I have a lot of new potential points of failure...but I feel fairly confident that I've located and resolved all the leaking areas and don't see any more fluid drips...yet it still won't drive any pressure.

I do get some fluid flowing from all the bleeders when pumping...but you can pump forever with the bleeders closed and it never gets a firm pedal.

a leaking rear seal on the back of the Master cylinder comes to mind.
unbolt the MC and look at the rear of the MC,, if its wet replace it.
TOFIC