11 inch drum brake ID

[Imndeep]

I am looking for the part number for the rear drum that is for 3 inch brakes. I can't quite determine if I have a 3 inch drum of a 2 1/2 in drum. All the hardware looks like it's for a 3 inch setup but I'm not sure of the drum itself. Part number on my drum is 36860? Thanks for any help.

 

[66Satellite47]

Well you can measure if the drum you have is approximately 3" in face width or if it's about 2 1/2" face width. There were a wide variety of applications, mostly in the '70 & 71 vintage. 3" is very obvious.

 

[69L48Z27]

From my experience B-Body with 11" drums are 3" wide on front and 2 1/2" rear. Hardware is all the same, shoes and drums are different.

 

[Cranky]

11" rear drums on the old hot rods are 2 1/2" and like 69L said, 3" on the front. Truck drums are usually 2" but those can vary.

 

[MarPar]

From my experience B-Body with 11" drums are 3" wide on front and 2 1/2" rear. Hardware is all the same, shoes and drums are different.

x2

 

[66Satellite47]

X3

 

[mobileparts]

All standard Big Block "B" & "E" bodies use 11" x 3" on theFront & 11" x 2 1/2" ontheRear.....
the only cars that had11" x 3" on the Rears --- were Police Cars and Ambulances.....
Measure the shoe width --- 2 1/2" is 2 1/2" and 3" is 3" -- there is always an extra 1/4" on the drum depth because
the shoe does not go "lip to lip" --there is always an 1/8" inch on both top and bottom to perfectly center the shoe on the drum....

 

[miller]

Right. I have the 3" police type on my rear...also takes a different backing plate.

 

[66Satellite47]

Those should be really good. Maybe close to some of the 4 wheel disc setups. Again I used cheap "soft" shoes. Not good for durability, but had good grab. The high quality shoes were good for durability & lack of fade with frequent application. With my drag racing application, the cheap brake shoes worked pretty good, even when I was going hot laps. Just don't try to lean on them too hard very often. I can't recall for sure if I put the 3" rear shoes on. Seems like when I went to big brakes, I went to the biggest possible. In those days stuff was pretty obtainable at the junk yards. Cop car stuff was available. Then I decided to go back to the lighter 10" drums. Somewhat lighter. The 10" still did stop just fine, long as I didn't lean on them too hard.

 

[BCBOUND]

Just to go further into it, is the brake offset the same for all rear brake sizes?

So the 2, 2 1/2 and 3" backing plates are all the same or is there more inside overhang of the backing plate as the drums get wider?

 

[66Satellite47]

Just to go further into it, is the brake offset the same for all rear brake sizes?

So the 2, 2 1/2 and 3" backing plates are all the same or is there more inside overhang of the backing plate as the drums get wider?

As I recall the backing plate position stayed the same. No difference in wheel position.

 

[BCBOUND]

So then, 10" and 11" rear backing plates differ only in diameter, correct?

 

[66Satellite47]

So then, 10" and 11" rear backing plates differ only in diameter, correct?

As far as I know.

 

[miller]

So the 2, 2 1/2 and 3" backing plates are all the same or is there more inside overhang of the backing plate as the drums get wider?

If you check part numbers, or actually measure the backing plate offset, you'll see a difference for each different brake drum width.
Backing plate mounts to the axle housing flange, right? Same location, no matter what the drum width. Wider the drum, takes a deeper offset backing plate.
Of course their different.

 

[BCBOUND]

That's what l expected when l asked the question.
If laid flat and measured from the register hole to a flat surface, what are the depths or brake offsets for each drum ?

 

[miller]

Sorry, don't have any real numbers. But, here's what you go by, without parts numbers for the backing plates. The one constant in it, is the measurement from the axle housing flange, to the drum mounting surface, at the axle flange (outer surface) itself.
So...if you lay the drum flat, measure from the inside of the mounting pad, to get the width of the drum. If it's a 3", should be a little wider, for shoe clearance. For the backing plate, the offset measurement will be even more, since the inside edge of the drum needs clearance, to the edge of the backing plate.
Differences will be about 1/2", since drums are 2", 2 1/2", or 3". Each width needs same drum to plate clearance. That's why the different offsets.

 

[70 RR]

Right. I have the 3" police type on my rear...also takes a different backing plate.

Do you happen to know the part number for that back plate? I have a set of 11 x 3 drums and shoes I want to install on the rea axle of my 63 Sport Fury.

 

[Fran Blacker]

 

[70 RR]

View attachment 715967

Fran, is that the inside of the drum? Looks like 2.5"

 

[Fran Blacker]

Yes 11x2.5".