Rear Drum Brake Sizes

[70 Challenger Lover]

I was hoping to upgrade the rear drum brakes on one of my E bodies but I was surprised that there appear to be different sets used over the years. Or maybe I'm getting bad information. Couldn't find a lot of information through research so I thought I'd ask the experts.

My current rear drums are 10" and that seems consistent with all my current E bodies. I believe width is somewhere around 2" or so but I don't have a wheel off to verify.

I once owned an RT and I recall it having huge 11" finned drums and I thought they were 3" deep. At minimum, they were 2 1/2" but noticeable wider than the 10" drums for certain.

Now that I'm looking for a set, I find different back spacing on the inner plates yet the sellers all claim they are E body correct. One even said 11" brakes can only be used with 15" wheels but that doesn't seem accurate. My RT had 11" brakes all around with 14" road wheels.

On one friend's car, I found 11" rear drums with plain drums and the depth is fairly shallow. On a different friend's 318 car, he has the huge 11" finned drums in the rear and claims it came standard.

I'd like the largest rear drums I can find but I will need to also be able to buy new replacement drums so better to get 11x2 rather than 11x3 if those huge finned drums cannot be found new for purchase.

Please help me clarify so I can select a set and get moving. Thanks.

[moreparts]

My '70 R\T has the factory heavy duty 11' drums on all 4 corners.  Widths are 3" fronts and 2.5" rears. The car has stock rally 14 inch rims too.  The backing plates are unique front to back as well and it appears the last time I checked the fronts are getting harder to come by.  It seems the front drums are drying up too in the 11 inch variety.  I have heard some people say upgrading to 3" rears works and others say the backing plates won't work correctly for that upgrade.  I've just stuck with the factory brake layout since it's the fronts that do the hard work.

[70 Challenger Lover]

My '70 R\T has the factory heavy duty 11' drums on all 4 corners.  Widths are 3" fronts and 2.5" rears. The car has stock rally 14 inch rims too.  The backing plates are unique front to back as well and it appears the last time I checked the fronts are getting harder to come by.  It seems the front drums are drying up too in the 11 inch variety.  I have heard some people say upgrading to 3" rears works and others say the backing plates won't work correctly for that upgrade.  I've just stuck with the factory brake layout since it's the fronts that do the hard work.

11 X 2 1/2" on the RT rear. Good to know.

I checked my friends car and verified his E body rear end currently has 11 X 2 rear drums and the drum appears correctly indexed on the axle flange so either this particular E body came with 11x2 rears or they were transplanted from another car.

[blown motor]

I believe there was a difference between R/T or Rallye cars and the base models.
I'm thinking that I will buy shoes, drums and all the hardware now while it's available. I had all of that replaced two years ago and by the time I need it again who knows what will be available. Plus if I change it once more down the road that should be the last time for me.

[Mr Cuda]

B and E only have two rear brake sizes.
 10" ×2 1/2 
 11" x2 1/2
 10's came on 4 wheel drum base models i.e. 318 and 6,  and rear brake on disc equipped.  To my knowledge,  no E had factory disc and 11" rear.
 Performance models had 11" 4 wheel drum. (11x3 front 11×2 1/2 rear)
Only 71up B and  C wagons got 11"×2 1/2 rear drums.
C body got 11"×2 rear

Edit.   I just checked 11x3 front to 11x2.5 rear backspace,  and I'm going to say you cannot run 11x3 in the rear by using front drums.

[Skdmark]

T/A and AAR had front disc and 11x2-1/2 rear

[Mr Cuda]

T/A and AAR had front disc and 11x2-1/2 rear

Looks like they got smart....eventually,  never had one of those.
 Yet not on big block and hemi.

[bentpshrods]

Just rebuilt the rear drum brakes on my 71. It has power disc brakes up front and 11x2 1/2 drums.

[Skdmark]

Just rebuilt the rear drum brakes on my 71. It has power disc brakes up front and 11x2 1/2 drums.

HD brakes were not available with power disc in '71 from the factory.
Either the power discs were added or the rears were upgraded along the way. I'm doing something similar on my Barracuda

B11 HD brakes (11 inch drums) were standard on R/T's and non R/T 340.
They were extra cost on the other trim levels.

https://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1971/71_Challenger0018.jpg

[70 Challenger Lover]

Thanks everyone for the responses. My friends 70 Gran Coupe definitely has 11x2 rear drums with relatively light drums. Not heavy finned ones.

Perhaps someone swapped out the 10s for these off a C body car. I suppose the extra leverage provided by larger diameter drums could be beneficial even if the overall brake pad area doesn't increase by much.

The thing about his lightweight rear drums that I like is lower unsprung weight and less rotational mass to get moving. Not that it's a huge amount but I don't see a real drawback to them.