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Rear drum brake question.

70 RR

70 RR

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When l bought my 70 Roadrunner in 2013 it had drum brakes. One of the first things l did was do the front brake conversion and swapped out my 11" x 3" drums for discs. A year later l bought a Dana 60 for the car and converted to disc brakes in the rear also. I sold my 8.75 complete drum to drum so l don't have them to use as a reference. My question is this, did Chrysler use 11" x 3" in the rear as well as in the front?
The reason l ask this is because l have a 1963 Sport Fury that l occasionally race and although l have 4 piston 11" discs in the front, it only has 10" x 2.5" drums in the rear. I saved the 11" x 3" drums and shoes from the front wheels on the Roadrunner and l would like to use them on the rear of my Fury. I have sourced a set of 11" back plates and I'm wondering if any of you guys have tried using or know someone that uses 11 x 3 drums on the rear axle of their B body? I see plenty of listings for 11 x 3 in the front but only 11 x 2.5 in the rear. Thanks!
 
Bought a dana out of a 67 GTX with 11x3's. Had a 70 Coronet 318 4 piston discs front 10x2.5 drums rear. Front drums with hubs removed on rear???
 
Far as I know the HD brake system (R/T) rear brake drums were 11 x 2.5. I'm not sure if the back spacing on the front drum will clear the back plate when you attach it to the axles. I would think it would be in contact with the back plate with a 1/2 inch remaining before it seats on the axle flange... That's a good question for the B body brethren
 
Not only do you have to have a 11" backing plate for a 11" drum but they have to be for the correct width drum also. Hope you already knew that :)
 
68Moparmaniac said:
Far as I know the HD brake system (R/T) rear brake drums were 11 x 2.5. I'm not sure if the back spacing on the front drum will clear the back plate when you attach it to the axles. I would think it would be in contact with the back plate with a 1/2 inch remaining before it seats on the axle flange... That's a good question for the B body brethren
Click to expand...


Yes, i wondered the same thing.
 
Fran Blacker said:
Bought a dana out of a 67 GTX with 11x3's. Had a 70 Coronet 318 4 piston discs front 10x2.5 drums rear. Front drums with hubs removed on rear???
Click to expand...

So at least i know that it's possible. l do not understand your question, can you refrase it?
 
70 RR said:
So at least i know that it's possible. l do not understand your question, can you refrase it?
Click to expand...
You were wondering if b-bodies came with 3" rear drums, that 67 GTX did. bought that dana in 1979. Had other dana's 11"x 2.5". Factory put 10" x 2.5" on front disc break cars, can't say if on BB cars with front discs whether they used 11 rears. My guess is no because of stopping power of discs and probably save a few bucks on smaller drums.
 
Fran Blacker said:
You were wondering if b-bodies came with 3" rear drums, that 67 GTX did. bought that dana in 1979. Had other dana's 11"x 2.5". Factory put 10" x 2.5" on front disc break cars, can't say if on BB cars with front discs whether they used 11 rears. My guess is no because of stopping power of discs and probably save a few bucks on smaller drums.
Click to expand...

OK, understood. I wish I had kept the original 8.75 out of my Roadrunner, I never measured the width however I know the were 11" diameter just like the front.
 
My '70 Roadrunner came originally with power disc brakes & came with 3" drums in the back (still on there). Hope this helps!
 
According to my parts book, B body Taxis, and some C bodies came with 11x3 inch rear brakes. Hemi drum brake cars came with 2 1/2 inch. 11x3 brakes in the rear would lock up way to early in my opinion. Plus they weigh a ton.
 
R/T Boy 67 said:
According to my parts book, B body Taxis, and some C bodies came with 11x3 inch rear brakes. Hemi drum brake cars came with 2 1/2 inch. 11x3 brakes in the rear would lock up way to early in my opinion. Plus they weigh a ton.
Click to expand...


I guess that is why the use adjustable proportioning valves to keep that from happening. You are right about the weight however. I may just stick with the 10 x 2.5" drums that are on there, Thanks!
 
PurpleBeeper said:
My '70 Roadrunner came originally with power disc brakes & came with 3" drums in the back (still on there). Hope this helps!
Click to expand...


Hi Beeper it does help, thanks! I guess I need to find out if going to the 11 x 3 from my current 10 x 2.5 is worth the trouble. I still have no idea if all 11" backing plates are the same or are they unique to different width 11" drums? Hell, I may just put disc brakes on the back like my 70 Roadrunner....
 
70 RR said:
Hi Beeper it does help, thanks! I guess I need to find out if going to the 11 x 3 from my current 10 x 2.5 is worth the trouble. I still have no idea if all 11" backing plates are the same or are they unique to different width 11" drums? Hell, I may just put disc brakes on the back like my 70 Roadrunner....
Click to expand...
Those rear drum brakes will be fine unless your flogging it around a track with turns and what-not or having to do back to back panic stops on the street. I remember racing dirt track and I always liked a 40-60 bias (front/rear) on the car but on the street I like them to be around 70-30 bias. Raced with drums for years, still have that pre-brake pedal pump today just to find out where the brakes are at that particular moment... LOL old habits die hard.
 
Last edited:
68Moparmaniac said:
Those rear drum brakes will be fine unless your flogging it around a track with turns and what-not or having to do back to back panic stops on the street. I remember racing dirt track and I always liked a 60-40 bias (front/rear) on the car but on the street I like them to be around 70-30 bias. Raced with drums for years, still have that pre-brake pedal pump today just to find out where the brakes are at that particular moment... LOL old habits die hard.
Click to expand...


Thanks for you input I really appreciate it!
 
Measured dia of front 11" brake hub 2.810 +/- .010. Rear 2.815 same +/-.
wid41.jpg
 
Wonder if you look on rock auto and see if the part numbers are the same. Notice how I passed on that to you.
 
PurpleBeeper said:
This is interesting....so....do you think the 11" front drums are the same as the 11" rear drums???? (I'm guessing I'm wrong on this, but I have to ask)
Click to expand...
Went to rock auto center hole spec larger on rear 2.836" front 2.813".
 
Last edited:
Fran Blacker said:
Went to rock auto center hole spec larger on rear 2.836" front 2.813".
Click to expand...

I found this on the 10" drums also. They look idential for the exception of the center hole. You don't want to use a rear on the front. They do fit loosely on the hub.

You think ma would have made them the same?
 
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