I have a E-body 8 3/4 with only the BP. how do I measure them for correct shoe and drum size.

across for 10" or 11" drums

measuring the offset for shoe size, measure from flange to back side of BP?

what's specs for 10x2 or 10x2.5 ?

straitedge across raised 5 hole flange then measure down to one of the (6) shoe contact rub areas. I have some regular (2&1/2" I would assume) plates I can measure later on today & for shoe size also..

10's and 11's are a very noticeable diameter difference. Any old 10 or 11" drum will confirm what you have. The flange measurement Robert talks about will confirm the shoe width. It might not hurt to have and old housing and axle laying around to double check the b/p fit with the drum...
I've got a couple laying around I can double check if you find out what you have and maybe need a application to order everything else for...

My axle doesn't have backing plates on it anymore. I'm exploring making disc brakes for the rear. How thick were those backing plates? They look pretty thin in the pictures. 3/16"? 1/4"?

more like 3/32??? Not very thick...
Just mic'd one out of curiosity 0.100...
10x2 1/2" removed from a 65 Coronet...

Sent in my A-Body 10" backing plates for powder coating a couple decades ago, got them back a year later, installed them, the 1-3/4 shoes would not fit! Found out the company shipped back some B-Body plates, I am sure another customer was just as mad...

I just got .130" thickness on a 11" backing plate (I'd think all of em would very close to that dimention). You might go ahead with the rear rotors & here are some 4" SBP and 4 &1/2" BBP ones. I gotta get some oil on em before they rust further.

here's what I am scratching together for the 85 stepside now that I removed the nv4500 5 speed and went back to a 727/CRT-TF2 VB.

I measured till I am blue here.

I was told this 8 3/4 was from a 67 polara C-body

which the 67 742-3.23 open 10 spline pinion with a 1330 yoke was listed in a 67 polara behind a 426/440

housing measures 56.5 flange to flange/axles 30" with 46 perch centers.

67 c-body does have 46 perch centers but housing and axle shows in chart to be different.

all E-body show 56.5 housing with 30" axles 46 perch centers.

now the backing plates that came with it are 315969-L 315970-R

E-body brake lines/vent bolt/tee all fit perfect.

so I ASSume its E-body 8 3/4 housing/axles.

I measure 12" across the backing plate, my 11" 5 on 5.5 drums SEEM to fit eyeballing. my new 11x2.5 shoes seems to fit but wont need muck of a slack adjustment (think they are 10"?)

I seem to have measured the wrong way for offset so I will recheck it.

here are some pics of what I am scratching together. should tuck 10" rims in the fender easy.

more pics

last 3

Read above attachment,

Diameter is measurement MINUS 1"

Whew. .100-.130"?! That's really thin! Makes the 1/2" and 7/16" brackets I made for the brembos on my Dakota seem like ridiculous overkill.

A stamped backing plate with all of the bends is much stronger than anything in a "flat plate". I'd think 1/4" in a flat plate would suffice. I know the Wilwoods I just put on the Duster are about 1/4" and are aluminum.
Scratchin it definitely sounds like you have 11" backing plates...now you just need to determine which shoes and drums are correct. The magazine add above may be the way to determine that.
I'm not positive from the pics but it sure looks like a deep recess from the axle flange to the back of the plate. Could be 11x2.5 or maybe even 11x3...

For overall rigidity, I agree. A stamped piece with contours is better than flat plate. However, when it comes to the sheer loads generated by the brakes, all that holds it from ripping away are the 5 studs pressed into the axle, and the cross section of the plate; which at .100-.130 isn't a lot of area.

I measured from outside flange area to shoe contact pad and get 1.5"

1.5" + 1.35" = 2.85

so is that a 2.5" or a 3" wide shoe?

I do see a set of 11x2 3/4" shoes for a c-body or truck.

would the 2.85 be a 2 3/4 wide shoes?

measure across and get 12" and subtract 1" = 11" drums

Through deductive reasoning didn't you maybe think the housing was for an E body? Were the backing plates from the same housing? If so maybe see what was offered on an E body...
At 2.85 I'd think they are 2 1/2" shoes...

yes I kinda think it is a E-body housing at 56.5 flange to flange with 46" perch centers 30" axles.

the 742-3.23open with the 10 spline pinion 1330 yoke is dated 67 on the ring gear.

that chunk was an option on a 67 426/440 polara which also shares the 46" perch centers. found this looking up the 1330 u-joint.

maybe someone swapped the e-body housing in the polara. would not be that much of a difference in trac width. maybe 1" from the chart specs.

or the junkman was referring to the chunk only?

11x2.5 sound right for a BB auto/4 speed E-body but I never looked at many of those e-bodys myself to know.

IIRC I can run a 2" shoe in a 2.5 drum correct?

Make sure you measure from the raised portion that the brake pad rests on

On a side note, I put 11x2 pads on my 11x2.5 set-up to fix my rear lockup issue.
You can go smaller, not larger

that is an interesting novel idea. & that is a problem issue. is there 10x2 shoes for the common 10x2&1/2 setup?