Brake Drum Identification

I am converting my 56 CJ5 to 11" brakes and drilling them to remove water. I bought all 4 brakes off a 72 Wagoneer. Three of the drums have a groove around the edge that goes near the backing plate. The fourth one seems to be a little larger in o.d. and is machined flat where the others are grooved. The flat does not appear to be just a grooved drum that was machined as the diameter of the flat surface is larger than the bottom of the groove on the others. Can anyone identify this drum? I'm thinking that it may be a CJ5 drum whereas th others are Wagoneer drums. All 4 drums appear to be interchangeable. The max i.d. on the Grooved drums is 11.090", whereas on the other drum it is 11.060" which is curious as this drum has a larger o.d. than the others. I will post this on the jeep forum under full size jeeps (Wagoneers) in hopes that someone there will also have some ideas about this. Here is a picture of what I'm talking about. The drilling is going well. I put n three rows of 24 1/8" dia. holes to balance the holes across the width of the shoes.

 

different make of drum?

 

I have two pair of mismatched drums like you describe (two of each type), I just figured it was different manufacturers. Nice setup to drill the drums, what size drill bit and row spacing did you use?

 

A postal Jeep makes sense. They do a lot more braking and would have to be heavier duty. I've got a Dremel but I need to buy the cone shaped stone.

For drilling, I used a 1/8" drill bit.

 

I used a 1/8" drill bit running at 2600 rpm for proper drill speed in cast iron. (about 90 to 100 fpm of the outer edge of the bit) I wrapped a wire around the drum in the groove and marked the circumference on it. (see photo) It came out at just over 36". I figured that 24 holes per row would be 1 1/2" per space and I could divide that by 3, or 1/2" offset between holes in each row. I made a gage that I could hold against the flat side of the drum and spaced my rows at 3/8" from the flat side of the drum (the bottom of the groove), 1 3/16", and 1 15/16" . See photo. It was easier to do than to explain. I hope the photos help. The flat drum (no groove) is a bit larger in diameter (the outer mark on the wire in the photo) so the spacing of 24 holes won't be an easy 1/2", but more like17/64" or so. It'll just a bit more work setting it up but the principle's the same. The last picture shows the drilling setup. In it you can see thespacing marks.