I recently purchased this 70 Bee and it has an aftermarket power brake system on it. When I purchased it the brakes were still set up like this picture attached. I was assuming the second canister was installed due to the high compression engine that was removed prior to me purchasing the car.
I removed the second canister and have ran one line directly to the intake.

I have had issues on factory setups where the pushrod was not adjusted right and the car would not roll at all even when not running.
This one is acting a little different. It will roll perfectly when not running. It will also roll fine when running unless you hit the brake one time. Once I apply pressure the pressure will not release and the rear tires lock up. Once I shut off the car you can hear the air leaking out of the booster or hose from some point. Added info is that it does have a line lock system installed but it is not powered. I am assuming this is not an issue as it would affect the front brakes and not the back. ??
Any ideas. The booster did have a bunch of shims installed between the booster and the firewall however I have replaced them when changing the pedals back over to a manual set up from an auto.
Thanks for any help.

Now.

Canister removed.

I think I would try, starting at the master and working back, loosening the rear brake line connectors one at time to see where the pressure is blocked at when the brakes are locked up. That way you eliminate collapsed lines, bad line lock, master cylinder issues etc.

I think it is typically of either a bad booster, or your pedal doesn't go back far enough.
which would be why the guy put in shims.

There is a valve internal to the booster that "breaks" when you hit a certain point. It is supposed to be gradual but on one of mine, it gave away suddenly and would jerk the brakes. if you cannot let up enough to close it, the brakes won't disengage.

Try disconnecting the pedal and see if you pull back a little further, if you can't get it to release.

Also, you might unbolt the brake light switch, which is probably stopping it from moving back further instead of unbolting the pedal. you might be able to adjust it to allow further movement.

forgot.
the easist way to prove it is the booster or not is to unplug the vacuum source. try it without vacuum assist and if the problem goes away, it is the booster.

The front reservoir feeds the rear brakes.

Where is your line lock plumbed?

The front reservoir, which usually means it blocks brake pressure to the rear when on. You may want to make sure the line lock isn't acting like a one way valve.

It appears to be hooked to the larger front reservoir of the master. You can see it just above the master in the pic attached.

I believe the line lock is supposed to be below the master cylinder, not above it. Think that would cause drain back problems. dave ss/ea #1355

In the garage and trying to figure this out.
I added the extra vac can back on as it is pictured above.
I now have brakes that dont lock up however I only have
about a 1/2 " of travel and they are hard as a rock. Almost
as bad as it is when I pull the hose off and use them.
The line lock pictured is still not hook up. Any ideas?
Also my brake pedal is 2014-13" lowers than my clutch pedal

Trying again to load photo.

so I just played this game if you see my post on swapping in the 11 inch rotors.

I broke down the pieces and tested them individually, and found chevy puts their masters backwards, front port to front brakes and rear port to rear brakes. The exact opposite of how mopars wire them up.

I seperated the master from the booster and made sure I had full pedal.
put it back together, cracked open a bleeder to see if the master moved any further.
It did not for me. So I replaced the master with a manual master cylinder to get the smaller diameter piston.
I then put the fronts to the front port and rears to the rear port and it was all good.

I had to put in a new adjustible rod to fit the manual master, and port adapters, but it works like it should now.

Ok. Unhooked booster from master and pedal works fine so I
I am assuming its not a rod issue. Why did changing to a mopar
master help cure the issue. The master I have still has the big reservoir
on the front brakes.

I didn't change to a mopar. I got a new master, but for manual disc instead.
it changed from the over 1 inch bore to a 1 inch bore. gives more pressure at the brakes.

I also redid my lines so the front port went to the front brakes instead of the rear they way chevy does it instead of mopar.

the bigger resevior should be for the disc brakes.
you can also see the piston moves fluid on the front port before the rear port.