I have a few brake questions as I'm wanting to convert my '71 Challenger to 11 inch drums. The car has the original 8 3/4 with 10 inch drums.

I read that '71 E-bodies with 11 inch rear drum brakes only used 2 1/2 brake shoes, is that correct or would 2 inch also be used in some cases. Any suggestions on aftermarket 11 inch drums?

Also, are rear backing plates from '73-'74 B-Body the same as E-Body?

Thanks in advance!

I think you will need a 11.0 inch complete set up, drums, backing plates and so on, from a C body to get the 11x3.0 brakes.
I have seen and think I have a complete set of 11x2.5 rear drum set up(which I believe came off of a 1968-1970 B body) in the shop to use on a faster race car in the future.
On your deal you may need to swap the emergency brake cables from the old backing plates to the ones your going to use, maybe not

I put some 11" from a truck. just grabbed the backing plates and a few parts. Everything else was new.

It works best to get a set that has been kept together...

It's real easy to accidentally end up with the wrong backing plates for the wrong drums...

All of the internal hardware can be purchased new...

Not sure what the OP is trying to gain here.

Have the 10" brakes been overheating in heavy use?
Are we trying to add more rear weight?
Are you lacking rotational inertia?
Have the fronts, that do 70% of the braking, already been significantly upgraded?
Is there something amiss with current rear brakes that prevent rear wheel lockup? ( implying any brake capacity after lockup is useless)
Does your car have a Class 3 trailer hitch?

Seems like a low pay off "upgrade".

Others will chime in, "if its your car, do want you want", absolutely.

the only thing i can add is this.
any chrysler, truck, van, or station wagon with 11" rear brakes with a 4 1/2" bolt pattern between 1965 to around 1980 will work. 8 3/4, 9 1/4, and dana 60.
as has been stated, try to get the drums and backing plates from the same vehicle, then source the internal parts from your place of choice.
one thing you may have trouble finding is the e-brake tie bar, so be sure to keep it with your donor parts. it is being reproduced, but it won't be available at your local parts store [to my knowledge]

I've seen the e-brake bar in the help section...Just remember there is a right and a left...

Bought about 8 of them 50% off when a local Advance closed down last year...

Of course it wasn't four left and four right...

well of course they wouldn't be paired up ! thanks for reminding me of the R&L differences !

i am guilty of buying up mismatched sets of items i "might" need "someday" as well, so i definitely know how you feel.
and to top it off, i usually NEVER acquire the needed mate.........

The C-bodies had the 11 x 2-1/2" rear drums. The Imperials had the big and heavy 11 x 3" rear drums

My 65 Fury has 11 x 3

11x2 1/2 here on the back of my '63.

I used them because they were on the shelf from a '71 Chrysler 300 I parted years ago.

Not sure they work better or worse than 10". They are just what I had. The weight is in the correct place so it doesn't bother me. I need all the help I can get for traction back there! I was able to source all the replacement items from the local Autozone.

Are your 11 x 3 rear brake drums "finned"?

My 65 Fury are not finned.

Imperials had 11 inch brakes also.Cant use the drums because they have different bolt pattern but the backings are thes same.Rocky

https://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1965/65_Fury0033.jpg

Standard was the 11 x 2
I'm now seeing in the 1965 parts book that 11 x 3 rear brakes were optional on C-bodies.

Good thoughts, and I agree that it's probably not worth the time or money since my brakes are working fine. Also, my front brakes have recently been upgraded to factory discs so it stops great. My thinking on this is because I am changing my chunk to a 3.23 posi unit, now would be a good time to upgrade the brakes since everything will be apart. I was just thinking it would enhance the car.

Just in this case, I think that might be a hard case to make.

Of course, its up to you.

I have 11.75 discs up front and 11x2.5 drums in rear.
Changed the rear brake cylinders to smaller 7/8” and rears still locked up first.
I now have put in 2” brake linings instead of the wider 2.5” to reduce contact area and rear bias.

So the larger drums are not needed, but the larger finned drums look much better behind the rims compared to the smaller 10” drums.

Yes the 11 inch definitely do look better, but I guess I just need to decide if it's worth it to swap. A complete setup is likely to cost $250-$500 depending where and how I purchase. The other option is a super nice complete setup that I could rob from another car I own for free, but that's creating double the work since I'd need to swap my 10 inch setup to it...

The M body cop cars came with the small rotor and 11" drums.

When I updated my Dart and my Cuda to the 11.75" discs I also added the 11" drums from an M body using the M body combination valve. Very nice package, well balanced braking. But M bodies aren't as plentiful in the yards anymore. Once thing to remember is that the M body came with one of two possible combination valves, the only difference aside from the valve was the diameter of the rear drums. So Chrysler thought it important to have a different combination valve for the 11" drum setup. The FSM detailed the differences between the two valves operation.