MG Car Repair: Weak brakes, rear brakes, sanding disk

Question
Good morning Howard, a while back you gave me instructions for cleaning the rust from the brakes on the '76 MGB that I'm reviving from long storage.  I did that, then replaced the hoses, drained and replaced the fluid, and bled the system.  As I bled the last brake (front left), the pedal stopped going to the floor and showed positive response.  I took this as a good sign.  Indeed, the front brakes do work, though not well, but the rear brakes don't work even well enough to stop the car from rolling out of the garage with the parking brake engaged.  Where should I go from here?

Thanks,
Billy

Answer
Billy, if the hand brake does not even hold, you need to hand sand the lining and the drum to get a clean surface on both. I was able to get the disks clean by first removing the pads and rubbing them on concrete floor and sand the disks with a rotary sanding disk in a drill motor and this would make the disk spin so I could hold a piece of sand paper on the back side while it was spinning to get the rear clean too.
I usually was able to just hand sand the drum and shoes to get them to work unless they had brake fluid on them which no amount of sanding is going to correct.

When the brakes are finished you should be able to easily lock up all four brakes on a dirt road and easily lock up the front brakes on pavement. The rear was designed to not lock up on a hard panic stop on pavement so as to make the car brake straight and since 80%+ of the braking ability of any car is on the front brakes, the lagging of the ability of the rear brakes was a small price to pay for stability during braking. However they should be good enough to hold by the hand brake.
Howard