Brakes locks but loosen if you help the pedal up.

[__Larsson____]

First sorry for my bad English,

The thing is tha i was about to take the first jurney after the restoration but when i brake the pressure dosent get back without helping the pedal up again,

The brakecylinder is "newisch" but the booster is old, the onlything i have done is cleaned it and painted it. he adjuster nut on the buster dosent move casue of the age so that cant be the problem.

 

[Ron H]

The booster may not be holding vacuum; a fast check is to disconnect the vac hose after you've run the car for a few minutes pumping the pedal a few times. Shut the car off and disconnect the hose to determine if you hear pressure escape. An old booster could have a bad diaphragm. Another check is to simply hold the brake pedal down with the car running and see if the pedal looses pressure...seeps down. Next step may be doing a vacuum-hold check with a gauge.

 

[Lefty71]

I had a Frod do this once. It was a booster problem, caused by lack of use. What vehicle are you working on, 70RR?

 

[__Larsson____]

I mean the pressure dosent release the brakes until after the 2 minutes or if i help the brakepedal up. I dont think its vaccum related, you would still have brake function.
Its a 70 Charger

 

[Ernie ingling]

Suspect master cylinder at fault. Spring in master moves piston back opening relief port. The apply rod from booster maybe to tight also. Check free play in pedal 1/2” if not adjust if good internal probem in master.

 

[Lefty71]

I mean the pressure dosent release the brakes until after the 2 minutes or if i help the brakepedal up. I dont think its vaccum related, you would still have brake function.
Its a 70 Charger

Well, does it do it when the car's not running?

 

[__Larsson____]

Well, does it do it when the car's not running?

unfortunately yes, and when the MC was unmounted even then the pedal actead strange

 

[Ron H]

I'm having my own hassles with my brakes since disc brake install I've posted about. Here's the possible deal(s): If I followed your posts, you or someone, put in a MC but the booster is old or untouched. Was the MC bench bled before installing? This is one possible issue, maybe not; but the other thing is the (rod) between the MC and booster; there's a tolerance there that I'm going to explore further with my hassle. Tip from my brother an old mechanic. If this is maintaining contact with the MC with no pressure on the pedal, naturally the brakes wouldn't release. Yet another check is to look at the rod from the pedal to the booster as this was/is another thing with my hassles. I've found this a rather touchy issue between brake lockup and release - with pedal travel...could be this adjustment isn't allowing a complete release of the brakes. I ended up checking this with the car off the ground for a closer inspection.

 

[miller]

unfortunately yes, and when the MC was unmounted even then the pedal actead strange

Sounds pretty simple. Brake pedal itself hanging up?
Un-fasten the brake rod from the brake pedal, and see if it swings freely. It should. If not, check the mounting hardware, and make it right.
Like said from the other guys, with everything in place, need small clearance, from the rod end, to the MC piston.
I'll toss in, on your MC, pushing in on the MC piston, it should return fully to the stop (retaining clip) on it's own when released. If not, it probably needs a seal kit put in it.