Technical Differences between early Ford juice backing plates

Lots of reading on here but can someone explain the differences between 39, 40-42 and 46-48 front and rear backing plates. Also, pictures would help us mentally challenged.
Thanks

 

40-42 have eccentrics on the bottom of the shoes for a finer adjustment. 46-48 are cotter pined on bottom, with no adjustment there. 39 I believe were a different diameter, someone else will surely correct me.

 

The later42-48 are as jkeesey states have no lower adjustment as well as dimples around the perimeter, shoe lands if you will. 39-48 are all the same size dia.

 

The only different diameter was the lug spacing on the drums, 5 on 10 1/4 on '39 and 5 on 5 1/2 on '40-'48. The hydraulic pre war backing plates were all the same.

Charlie Stephens

 

40-42 - SMOOTH - more adjustment
They look better.
my .02

 

Anyone know why ford took a step back away from adjusters?

 

probably found that it wasn't worth the effort. it is much faster and easier to adjust the later style shoe (anyone can do it) and the early style brakes have to be adjusted perfectly to notice any difference at all.

for our purposes its a non issue anyway. most of us are running light cars with bias ply tires, you could drag a stick and have brakes that are effective enough to lock the narrow little bias plys

 

The lower adjustment is to center the shoes after a relining. The later backing plates use an eccentric, the later have to be done manually. There is a specific sequence to center the shoes using top and bottom adjusters on early plates. Later center shoes automatically. After this initial centering, the only required maintenance is the upper adjusters.....

 

For a good read on this, with adjustment instructions, go to Rumbleseat's online book http://www.flatheadv8.org/rumblest/intro.htm and click into the brake chapter.
As with Lincoln Lockheed brakes, there is a major adjustment with centering used when new linings go in, and a minor adjustment used for taking up wear in use.