8 3/4 Rear/Brake Line

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ConValiant64

ConValiant64

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I'm finally getting around to putting an 8 3/4'' rear into my 1964 Plymouth Valiant. The one I bought has a damaged metal brake line. Since I'm ousting it anyway, would the line off my 7 1/4'' fit? The rears are the same width and I'll be reusing the 9'' drum brakes, but just didn't know if the bends in the line were different to conform to the new Hotchkiss style rear. If they're different and I had to replace the line (wheel cylinder to wheel cylinder), where would you recommend I purchase this item? Thanks.
 
You can bend one yourself or buy one from Fine Lines pre bent....
 
You can’t use your existing 7 1/4” lines, the splitter block is a different configuration. You also can’t use your existing 9” brakes, as the A body small bolt 8 3/4” rear has a unique offset axle flange that will only work with the 1 3/4” with 10” brake setup! The backing plates from the 7 1/4” are also different and only have 4 bolt holes instead of the 5 that the 8 3/4” has. Now, if you have aftermarket large bolt axles, there are many other brake options for that setup!
 
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Not sure about the guy below me? He could be a lil shady? Lol ( Just kidding)
 
cosgig said:
You can’t use your existing 7 1/4” lines, the splitter block is a different configuration. You also can’t use your existing 9” brakes, as the A body small bolt 8 3/4” rear has a unique offset axle flange that will only work with the 1 3/4” with 10” brake setup! The backing plates from the 7 1/4” are also different and only have 4 bolt holes instead of the 5 that the 8 3/4” has. Now, if you have aftermarket large bolt axles, there are many other brake options for that setup!
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Very helpful. Thanks for the info.
 
cosgig said:
You can’t use your existing 7 1/4” lines, the splitter block is a different configuration. You also can’t use your existing 9” brakes, as the A body small bolt 8 3/4” rear has a unique offset axle flange that will only work with the 1 3/4” with 10” brake setup! The backing plates from the 7 1/4” are also different and only have 4 bolt holes instead of the 5 that the 8 3/4” has.
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So Cos.....before I get too far into it....can I install a complete 10" x 1-3/4" rear drum setup from what I believe came from a 1970 SBP onto my 1964 a-body 7-1/4" rear end?
 
KosmicKuda said:
So Cos.....before I get too far into it....can I install a complete 10" x 1-3/4" rear drum setup from what I believe came from a 1970 SBP onto my 1964 a-body 7-1/4" rear end?
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So, here’s the scoop, the 8 3/4” backing plates have 5 bolts to mount to the housing, the 7 1/4”only has 4. There has been word that you can drill the 5th hole and use 7 1/4” backing plates, I don’t believe that’s possible. That assumes that the other 4 bolt holes are in the correct location. However, 10x1 3/4” brakes will swap to 7 1/4” from 8 3/4” if you have 10” backing plates from a 7 1/4”, even the drums and hardware are the same.
 
cosgig said:
So, here’s the scoop, the 8 3/4” backing plates have 5 bolts to mount to the housing, the 7 1/4”only has 4. There has been word that you can drill the 5th hole and use 7 1/4” backing plates, I don’t believe that’s possible. That assumes that the other 4 bolt holes are in the correct location. However, 10x1 3/4” brakes will swap to 7 1/4” from 8 3/4” if you have 10” backing plates from a 7 1/4”, even the drums and hardware are the same.
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Another question: Am I able to use the same driveshaft, or is the one from my 7 1/4 different?
 
ConValiant64 said:
Another question: Am I able to use the same driveshaft, or is the one from my 7 1/4 different?
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Your existing driveshaft will be about 2” too long, and if you’re running the original trans with the ball and trunnion front coupler, you will need to have your existing driveshaft shortened!
 
cosgig said:
Your existing driveshaft will be about 2” too long, and if you’re running the original trans with the ball and trunnion front coupler, you will need to have your existing driveshaft shortened!
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Thanks again. Just one more: Am I also able to use 11'' brakes off of, say, a B body?
 
ConValiant64 said:
Thanks again. Just one more: Am I also able to use 11'' brakes off of, say, a B body?
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11" brakes on the rear of a 64 Valiant will slow you down alright. Decelerating and accelerating.The drums are VERY heavy. Guaranteed if you use those you'll be at least a couple tenths slower in the quarter. You now have to accelerate those heavy flywheels.
 
cosgig said:
So, here’s the scoop, the 8 3/4” backing plates have 5 bolts to mount to the housing, the 7 1/4”only has 4. There has been word that you can drill the 5th hole and use 7 1/4” backing plates, I don’t believe that’s possible. That assumes that the other 4 bolt holes are in the correct location. However, 10x1 3/4” brakes will swap to 7 1/4” from 8 3/4” if you have 10” backing plates from a 7 1/4”, even the drums and hardware are the same.
Click to expand...

RATS! Another thing is that quite possibly the axle flange width may be different between the two. Pretty sure the brake setup came off a 70 Dart 8-3/4.
Sorry to hijack this thread.
 
ConValiant64 said:
Thanks again. Just one more: Am I also able to use 11'' brakes off of, say, a B body?
Click to expand...

Not without buying aftermarket axles. The A body 8 3/4” small bolt axles have a unique axle offset that is specific to the 1 3/4” wide brakes. The offset is different, the brakes from a B body are wider, have the large bolt pattern on the drums, the center register is larger in the B body so the hole is bigger in the center of the drums!

The rule here is pretty simple for A body 8 3/4”, you either run small bolt axles and the original 1 3/4”x10” brakes, or you get aftermarket axles which will be large bolt, and use any large bolt brake setup! You can use your 7 1/4” 10” brake stuff provided you have the proper backing plates, and vise versa.
 
cosgig said:
Not without buying aftermarket axles. The A body 8 3/4” small bolt axles have a unique axle offset that is specific to the 1 3/4” wide brakes. The offset is different, the brakes from a B body are wider, have the large bolt pattern on the drums, the center register is larger in the B body so the hole is bigger in the center of the drums!

The rule here is pretty simple for A body 8 3/4”, you either run small bolt axles and the original 1 3/4”x10” brakes, or you get aftermarket axles which will be large bolt, and use any large bolt brake setup! You can use your 7 1/4” 10” brake stuff provided you have the proper backing plates, and vise versa.
Click to expand...
Good stuff! Thanks everyone.
 
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