70 Challenger. New rear brakes, drums turned, linings arc. All new self adjusters. Very hard pedal at top of travel when braking. Emergency cable adjusted tight. Everything good shape and well lubed.

Parking brake on anything more than a very modest slope,,,going forward or backward almost worthless.

Our 300B with a no park torqueflight and driveshaft actuated brake will lock the rear wheels at 30mph and hold on any slope.

How well does your E Body or any other rear wheel brake system perform. If good, what is the secret?

If all else is correct and well it may be that the new shoes have not seated or worn into the drums. meaning the shoes are not achieving full surface contact.

Sometimes setting the e brake and then stepping on the brake pedal will better center the shoes and apply more holding power to the e brake.

As already mentioned if your new shoes weren't arc on both tips it will take some time and wear to break them in. I have a freind who use to push his emergency brake pedal about half way down for 2 to five miles on the road on his 1968 Charger that he used to tow his ski boat with after he had back the car into the water on the boatramp to reload it. Applying the E brake helped dry out the shoes, drums and backing plates
You might want to try doing that some to help breakin the new shoes.

Have you confirmed that ALL the cables in the parking brake system function as they should?, nothing seized?, that all the hardware needed to connect the cable ends to the rear shoes is in place and functioning,?

Been using my parking brake on my 70 RR every time I shut the car off since I have owned it (1981). Still works like new.

Do you set the parking brake without using the service brakes?

If so, that might be the issue.

Several good points.

Even though I did have my shoes arc' to the drums, when I pulled my drums to inspect, I find that the last inch or 2 of the shoes on each end show zero sign of contact. Only the centers show moderate wear,,,,so if I should disconnect my emergency brake on warning light,,,it would not be long before I had given these shoes the wear toward ends that the deserve.

Don't recall if I stand on service brakes before setting emergency. Will be at Goodguys Nationals all weekend, so will make a point to check this out and also do some cruising about with the emergency set.

I have checked closely the cables, pulleys(or sliders) and all else. All almost new and appear good.

Had considered this product for wife's 55 TBird. Emergency on this is one of those 'T' handled jobs on the left of steering wheel. Very hard to pull to get any holding power. Somewhat gave up on idea as mounting on cables and other required hardware was going to be a nightmare for me on this car. Have seen demos of them,,,they do a hell of a job if you can fit it.

http://www.estopp.com

You do not have to step on the service brake to set the parking brake, they are independent. Question, do you have any idea where the cables came from if new?

You don't have to, but it is the proper way to do it.

It is not an emergency brake, it is a parking brake. It isn't designed to stop the car, though it generally will, it's designed to hold it already stopped.

FWIW on my '70 Challenger the OE park brake held fine with stock rear drums. As I run an manual transmission it matters and is noticeable. Good parking brake needed!

After upgrade to a Dr Diff rear disc setup it also holds fine.

It sounds like you have the wheel stations and basic brake adjustment in good shape so I wonder what is wrong? Maybe try tightening the E brake cable adjustment until it causes drag then back it off a little to make sure the cables are as tight as possible.

For basic brake adjustment, move the star wheels until you have slight drag after fully applying the brakes a few times works for me.