[xbrit]

After a complete restoration on my 72 Challenger I totally rebuilt the braking system. It has factory power Disks.
I replaced the front calipers the rear cylinders, master cylinder, proportional valve, and properly bleed the system. The only part not replaced was the vacuum servo. I did check the servo and it seemed Okay.
The issue is that the brakes do work, but when I apply pressure on the brake pedal they remain on until I just tap the brake peddle (you can hear them hiss) then they release.
This seems to be the last teething issue i have to sort.
Cheers.
Xbrit

[Eddie]

Rears or fronts? The fronts use the piston seal to keep the piston retracted, the rears rely on the springs. Did you have the rear hardware replaced as well when you re-built the brake system? The 'hissing' sounds like the shoes are sticking?

[xbrit]

I replaced all the mechanical parts in the rear drums, the front calipers are brand new, the hissing sound is air escaping from the power brake system (I think). They only release, unlock when I dab the brake pedal.

[Adrian Worman]

Check valve in the power booster ?

[xbrit]

Thanks Adrian.. what is or how do I check the Check valve in the power booster?
Cheers,
Xbrit

[christer]

The hissing sound is probably due to a leaking brake booster. The will cause bad engine vaccum and a bad (rough) idle. Nothing more than that, as I see it.

The sticking brakes has most likely something to do with the master cylinder; either you need to bleed the system once more or there is something wrong inside the master cylinder.

About bleeding the brake hydraulic system: It is important that you start with the wheel that is most far from the master cylinder and work yourself closer to the master cylinder for each wheel you bleed. On an ordinary left-hand driven car, this means starting with the right rear wheel, then the left rear wheel, then the right front wheel and finally the left front wheel. Maybe this is old news?

Another important thing when you bleed the brakes is to use a special (low-cost) transparent hose + bottle that is made for bleeding brakes. If you keep the end of the hose below the fluid level, no air will be able to enter the brake system backwards. Yet another old news?

I remember a long time ago, when we tried to fill up a master cylinder with brake fluid. This was not the easiest thing to to. To push the brake pedal back and forth did not do any good. Instead we filled the reservoirs with brake fluid and left the brake line connections open on the master cylinder. After an hour or two,the master cylinder had filled up itself.

About filler ports inside the master cylinder (directly written from a book I have got):
The filler ports permit puming up of the brakes if the pedal is low. If the brake pedal is pumped rapidly, the return springs in the master cylinder return the pistons quickly. At the other end, the brake shoe return springs return the wheel cylinder pistons a lot slower. The flow of fluid from the wheel cylinders is delayed and can´t match the fast return of the master cylinder pistons. As a result, the master cylinder pressure drops and becomes lower than the pressure in the reservoir. Fluid is forced out of the reservoir by atmospheric pressure through the filler ports, through the holes in the piston, and past the piston cup. These filler ports are necessary because the compensating ports aren´t big enough to handle the flow needed to pump up the pedal.

Good luck.

[Adrian Worman]

I have had sticking brakes on my nephews R/T Dakota, down to a faulty master cylinder, you could well be right.
If you do bleed the system because you think there's a fault then don't forget that you'll need to bleed the M/C separately, like when you bench bleed it before fitting.
This is very important and there was a thread here about Wayne's(Red Raven) brake rebuild that has that info, look it up