Info needed……

[Red63440]

I’m at wits end…….new disk brake conversion on the front, new rear end housing including heavy duty brakes. New lines and hoses front and rear including a new power brake master cylinder mounted on the factory 1964 booster. Bled the whole system and have a hard peddle with the engine off but as soon as the engine is started the peddle goes to the floor and the engine wants to stall. I’m thinking it’s the booster but…..this is my first rodeo with boosters.

 

[davek]

plug the vac line of the booster and see what happens. Sound like vac leak.

 

[Red63440]

Check valve maybe?

 

[Ron H]

Aside from possible leaks or CV, could check engine vacuum with a gauge. Boosters typically require 15+ inches...more in the range of 17. If your motor has a hotter cam this can be an issue. Can also double check the booster condition vac for bleed down and if holds vac. Was the MC bench bled? Other quick thoughts - booster to MC gap checked...there's more...sad to report..

 

[Red63440]

Master cylinder was bench bled, and with the engine off the pedal feels excellent. Cam isn’t much hotter than a factory 383 magnum cam so I don’t think that would be the problem.

 

[snakeoil24]

Got to look for a leak in booster bladder

 

[pnora]

I’m at wits end…….new disk brake conversion on the front, new rear end housing including heavy duty brakes. New lines and hoses front and rear including a new power brake master cylinder mounted on the factory 1964 booster. Bled the whole system and have a hard peddle with the engine off but as soon as the engine is started the peddle goes to the floor and the engine wants to stall. I’m thinking it’s the booster but…..this is my first rodeo with boosters.

The thing you need to remember is the booster is an assist. If your pedal goes to the floor starting the engine it is only because the booster is making the pedal easier to push. The masters hydraulics and pedal height and ability will be the same with or without the assist.

 

[pnora]

Post some pics of your front conversion. I assume the rear are still drum?

 

[Red63440]

Rear are drum and everything for the conversion is new except the booster which is factory. The conversion was made to be used with the factory booster.

 

[pnora]

Are the rears adjusted properly? With someone pumping the pedal what kind of pressure or flow are you getting at the bleeders?

 

[Red63440]

Good flow and pressure with a solid peddle.

 

[pnora]

Good flow and pressure with a solid peddle.

Does it keep the wheel from turning when stepping on the brake?

 

[Red63440]

No it doesn’t

 

[RemCharger]

Best case is to get it close to driveable and break in the new shoes and pads. Then bring it back to re bleed the brakes and adjust the shoes on the tighter side.
Then you can start diagnosing

 

[4mulas]

What hubs and rotors are those?

Or what kit is this?

Looks like stock A Body 4 piston calipers to me so I’m just trying to figure it out. Most people convert to single piston floating. Slipper design

 

[Red63440]

Best case is to get it close to driveable and break in the new shoes and pads. Then bring it back to re bleed the brakes and adjust the shoes on the tighter side.
Then you can start diagnosing

With the way it is now it won’t leave the garage. Trying to drive it the way it is would be suicide.

 

[Red63440]

What hubs and rotors are those?

Or what kit is this?

Looks like stock A Body 4 piston calipers to me so I’m just trying to figure it out. Most people convert to single piston floating. Slipper design

They are mustang hubs and rotors and are a Leed brake kit.

 

[Demonic]

Factory used different boosters for drum vs disc. Could be a travel issue.

 

[Red63440]

Factory used different boosters for drum vs disc. Could be a travel issue.

Conversion was designed to work with the original factory booster.

 

[Ron H]

Couple a things as I had a helluva time with my conversion. I swapped from manual to power though. Ensure your pedal isn’t pre-charging the booster having to do with pedal rod adjustment into the booster. There needs to be a bit of free play with the pedal in home position – not binding against the brake light switch. Had a ‘time’ putzing with this. The booster has to be of a compatible size for the setup. Though sounds like this isn't an issue. As well, the MC bore is different btw a power and manual setup. You likely know all this; just throwing out some things I remember with my conversion. Other thing here, is checking booster to MC gap.

As posted, there are three vac checks you can do on the booster with a pump vac gauge. Also I had issues with the rear brakes not an issue for you other than assuring the linings are adjusted (in my case the drums were maxed so had to get new ones).

Another thing I found is the pads were binding a bit, not backing off/sliding freely in the calipers, so did a better job deburring and lubing those..