My name is Dale.
Here are some specific instructions about adjusting the rear brakes that may shed some light on how the system functions:
Major Brake Adjustment
To make a proper major adjustment on any De Soto or Dodge brake a shoe-centering gage, axle-type lining grinder, or dummy drum is required.
The anchor pins are eccentric and are adjustable only with the drum removed. This means that it is impossible to adjust the anchor by making the heel of the shoe contact the drum since the drum is not on when turning the eccentric.
Where a centering gage or a dummy drum is available the shoes are adjusted so that the heel of the shoe (nearest the anchor) is adjusted to 0.005 inch and the toe of the shoe (farthest away from the anchor) is adjusted to 0.010 inch. This is accomplished by turning the eccentric anchor in the required direction to adjust the heel of the shoe and turning the eccentric adjuster cam (half way up the shoe) to adjust the toe.
Where a dummy drum or centering gage or axle-type lining grinder is nnot available and it is absolutely essential that the anchors be adjusted, the following procedure has been found to work out fairly well.
Remove the anchor pins from the car and, using a thin grind stone grind a screw driver slot into the back end of the anchor pin (threaded end).
Now replace the anchor pins and mount the shoes. Do not tighten the anchor pins so tight that the pin cannot be turned with a screwdriver. Just snug it up enough so that it can be turned stiffly with a screwdriver.
Mark the anchor pin at the inner end to show the position of the high spot of the eccentric so that its position will be known while turning the screwdriver.
Mount the wheel and drum on the axle and spin the wheel. Turn the eccentric cam (half way up the shoe) until the lining drags and then turn the anchor pin with a screwdriver in a direction that the eccentric will move in towards the other shoe, and down towards the brake drum until the shoe no longer drags. Again turn the eccentric adjuster until the shoe again drags and again turn the anchor in the same direction until it is free. Keep repeating this until it is impossible to turn either the anchor or the eccentric without making the shoe bind. At this point, lock the eccentric anchor adjustment. Now develop clearance between the lining and shoe by turning the eccentric adjuster in the opposite direction until the wheel is free. Repeat this process at all four wheels.
It has been found that if the above procedure is followed very carefully a perfectly good adjustment can be had.
Here is the brake shoe inspection instructions as well.
> Rear Drum Brakes
> Brake Shoes
Next examine the brake lining. Most states require that brake lining be replaced when sixty percent of the original thickness is worn away.
Lining which is cemented to the shoes can, in many cases, be used until as much as seventy percent has been worn away.
Improper adjustment of anchor but shoe has worn to fit drum. Should not be readjusted until new lining is installed
Notice particularly if the lining is wearing all over the surface. If the lining is wearing evenly all over its surface and the entire surface is in contact with the drum as indicated by the wear on the lining, the anchors probably do not require adjustment.
On examining lining, mechanics frequently find a condition where the lining is wearing more at one end of the shoe than it is at the opposite end of the same shoe, but, in spite of this, the lining has worn so that the entire surface contacts the drum. When this condition is found it indicates that the anchors were not properly adjusted when the lining was first installed. However, the lining has worn itself down until it is finally in complete contact with the drum. When this condition is met with it is advisable either to leave the anchor adjustment as it is, or replace the lining and reset the anchors properly.
Improperly adjusted anchor bolt. Shoe has not worn to fit drum. Lining should be replaced and anchor bolt readjusted
Where examination shows that the lining is wearing at one end only and the opposite end has not yet come in contact with the drum, the lining must be replaced since it no longer has a true arc and cannot be properly adjusted. This condition can be corrected, however, if an axle type lining grinder is available. Axle type lining grinders are mounted on the spindle or axle of the car and are so arranged that they will grind the lining into a perfectly true arc.
Distorted brake shoe and improper shimming of lining. Shoe and lining should be replaced
Many successful brake shops prefer to use the axle type grinder on relines to insure perfect brake contact and also eliminate the wear-in which may be required if unground lining is used.
Running clearance for brake lining is carefully calculated so that when the brake is applied, all of the lining will contact the drum at the same time.
Axle type lining grinders insure even contact in the applied position.
I hope this gives you enough information to be able to get in there and change them out.
Note: Some of the older vehicles required that the new shoes be "Arc Ground" and fitted to the drum. Any good brake man will know how to use the arc grinder on his Anco brake machine to do it properly. If you do not do this you may and probably will end up with a spongy pedal.
PS-I am partially disabled and I subsidize my income by the earnings I get from my customers. I am available about 50% of the time and I must rest when I am not working for you.