Question about 7 1/4" rear end differences

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1968 Dart 270

1968 Dart 270

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Looking at 7 1/4" rear ends for a 68 dart and noticed that this 71 duster rear has some sort of fluted or bell shaped flare behind the brake backing plates. 68 doesn't have this. When did this change occur and what's the purpose of it?

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At one time the 7 1/4 with 9'' brakes had drums with a Bell design. Not sure of years.
Found that out when looking for the 10x1 3/4'' drums thinking they only had the Bell design.
 
I have no idea. Rear is out of a 71 duster. Just saw it online. My 68 doesn't have a bell shaped design and neither have the others I've seen. I wondered why it's there and when it first appeared
 
Darter6 said:
At one time the 7 1/4 with 9'' brakes had drums with a Bell design. Not sure of years.
Found that out when looking for the 10x1 3/4'' drums thinking they only had the Bell design.
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What's the purpose of the Bell design. Did brake drum sizes change from 68 to 71? Bolt pattern should be the same right?
 
Have no idea. Just guessing more surface for cooling. The 9'' drums were known for squealing noisey brakes too.
 
10'' drum brakes were optional depending on engine size.
Most Slant 6 cars came standard with 9''.
Most disc brake optional cars would have had 10'' rear brakes. Also the optional 8 3/4 rear axle could be ordered. They had 10x1 3/4'' rear brakes
 
Darter6 said:
10'' drum brakes were optional depending on engine size.
Most Slant 6 cars came standard with 9''.
Most disc brake optional cars would have had 10'' rear brakes. Also the optional 8 3/4 rear axle.
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My car is a 273 v8. It would have 10" brakes tben,right?
 
Not necessarily. All depends on how the car was originally ordered.
 
the darth vader helmet drums were typical to earlier 10" 8.75's and some 7.25's that got 10" drums.

you can swap stuff around, but you need to keep all the pieces matchy-matchy.
 
So the “Vader drum” is a barrier for water as well as an increase in surface area for cooling. Both nine and ten inch drums were made that way starting in 70.
Not sure if it adds to the discussion any but AMC used the same thing on some of their drums.
 
Interesting and would make sense then since it's a 71 Duster rear end.
 
junkyardhero said:
the darth vader helmet drums were typical to earlier 10" 8.75's and some 7.25's that got 10" drums.

you can swap stuff around, but you need to keep all the pieces matchy-matchy.
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So all of the 7.25s with the flared drums are 10"?
 
Not too hard to figure out. As was said, the extra metal aids in cooling, shedding water AND also helps to dampen extra noise sometimes created by brakes like squealing and such. I would also make a guess that the extra weight could dampen vibration as well. @Charrlie_S is a wealth of knowledge on these little rear ends. Maybe he will chime in with some more info.
 
Darter6 said:
Nope. There were 9'' too.
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Now this is something I didn't know. I've seen them only on 10" brakes but none on 9" brakes....like that means anything. lol Thanks!
 
Yeah, I was hunting drums for a 8 3/4'' 340 car. Went to the pick and pull and was like,
"Wow I can't believe I found some !" Got home and they were 9''ers.:BangHead:
 
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