7.25 to 8.75 swap brake issues

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Mopar2

Mopar2

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(68 dart 340) I am swapping 7.25 to 8.75. I bought correct A-body housing and axles staying with the 5x4 sbp so my cragers still fit. Problem is my old 7.25 backer plate wont fit due to wrong bolt patter and center hole to small for axle bearing to fit though hole in middle of plate. I do have a set of older backer-plates that I had on a donor 8.75 that fit fine but have NO shoes,springs, or drums. My question is how do I figure out what size drum i need to buy to fit these and will it have sbp on it and how to I measure the one spring that was stuck on backerplate to figure out what size to buy. I can take pics of what i have if needed.

thanks
 
Measure the diameter of your backing plate for your 8 3/4. I believe it should be minimum of 10" if it came from an A body. Then you can buy drums online in SBP, correct for your 8 3/4. I bought 10" drums with SBP on www.nationalmoparts.org, and you can also buy a new spring set from manciniracing.com for it as well. You should also buy new wheel cylinders, as I don't think your old ones will fit?
 
Compare the diameter of your old backing plates (which you know the size of) to the ones you want to use. If they came off an 8 3/4, it's most likely a 10 or 11" brake unless you took it off an Imperial or early C-body with 12" brakes. The problem is figuring out the width of the brake shoe. They made them in 1 3/4", 2", and 2 1/2" widths in the 10" and 2", 2 1/2", and 3" in the 11". They used different backing plates for each one. The most common was the 2 1/2" in both 10 and 11" brakes. Take a plate down to the auto parts store and set a new shoe in position against the center of the wheel cylinder push rod, and upper anchor pin and see if it sits square and not at an angle. Once you find out the width, you can order a hardware kit for it.
 
If the backing plate is close to 11" in diameter, it's a 10" drum. If it's 12", it's the 11" drum and you need to find the 10" version. There's 10x2" which is A body sized, and there's 10x2.5 which is many other body styles. There are no 11" drums for the small bolt pattern.
 
my donor axle had two backer plates on it which im using and one brake shoe rusted to it, so I measured it and it was 2", so I will buy 10" sbp drums and 10x2 shoes.

thanks for the helpfull info about the shoe sizes!
 
anyone know of a good donor vehicle I can get all these parts from junk yard out of like a newer car that would be a direct swap so all I gotta spend big bucks on is the sbp drums? I have lots of salvage yards around I can get good shoes, cylinders, springs etc from. Im way over budget already!
 
If you're using the stock 10 X 1 3/4 drums and shoes, you have to use the matching backing plates too or the shoes won't sit square. Those backing plates were only used on A-body 8 3/4 and '65-70 B-bodies with the wimpy brakes.....mainly 6 cyl. cars.
 
here is how you ID what backing plates you have..


backingplateID.jpg
 
personally i would go to a yard and grab an entire brake set up from a donor car. that way you know exactly what your working with.
 
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