Do factory equipped vehicles always have same size drums front/rear?

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dibbons

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My '65 Valiant Signet V-8 currently has 10 inch front drums and 9 inch rear drums. A previous owner swapped in the current 7 1/4 inch rear end from a '74 Dodge. I was wondering what my vehicle originally must have had factory installed for rear drums 9 or 10 inch? And then the question in the thread title: Did drum diameter not match front/rear on some factory vehicles? Thank you.
 
My 66 Valiant Signet V8 had 10 inch drums all around. I don't know if Mopars mixed up the sizes, sorry.
 
Best I remember, front drums were bigger because of weight bias to the front and weight transfer towards the front. Meaning the front drums did more work. More braking power on the rear would just tend to lock up the rear wheels.
 
They were always the same size, they would never interchange safety features like that. And, there is no rhyme or reason to what got what. Most people say slant 6 cars all came with 9” drums, but you could order any size brake that was available on a particular model, if YOU wanted to spend the money.
 
Best I remember, front drums were bigger because of weight bias to the front and weight transfer towards the front. Meaning the front drums did more work. More braking power on the rear would just tend to lock up the rear wheels.

that’s what the proportioning valve was for, to limit the pressure going to the back brakes. Or in the early cars, the secondary valve did that before the prop valve came into play. 9” and 10” brakes were never mixed, and are 2 completely different setups.
 
Too many forum members are eager to chime in to help despite their lack of knowledge on a subject. It is nice to want to help but passing out incorrect information helps no-one.
4 wheel drum systems have NO proportioning valve. They have a distribution block that only serves as a multi-port unit to distribute the fluid. The wheel cylinder sizes determined the proportioning.
I have never seen a staggered drum diameter front to rear but I have seen wider shoes used on the front.
R/T B bodies used 11" drums F/R as standard equipment. My '70 Charger had 4 wheel 10" drums. Of all the A body cars I have owned, I have never seen a 10" front, 9" rear drum arrangement.
If they ever were built that way, I have never seen it.
 
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Four wheel drum are not always the same size. They may have been the same diameter, I'm not positive, but at least one car I owned had 11" and wider shoes on front than rear, and it seems like they were smaller dia. on rear. So they are "at least" sometimes different width.

Here's a random example out of the Raybestos catalog, page 121, for elderly Coronet

https://www.brakepartsinc.com/dam/i...-0c6474260927/2019-Pads-and-Shoes-Catalog.pdf

Notice that the upper section is front, and the bottom section rear brakes

Notice that some used 11x3 front, but no such width is listed for rear Also notice some rear are 10 x 1 3/4 and that width was not used on front

brakes.jpg
 
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My '65 Valiant Signet V-8 currently has 10 inch front drums and 9 inch rear drums. A previous owner swapped in the current 7 1/4 inch rear end from a '74 Dodge. I was wondering what my vehicle originally must have had factory installed for rear drums 9 or 10 inch? And then the question in the thread title: Did drum diameter not match front/rear on some factory vehicles? Thank you.
Yes!
 
Front drums were usually 'wider' than the rears but were the same diameter front and rear. I've never seen 10's on the front and 9's on the rear.....or 11's and 10's for instance.
 
My Chilton's Dart & Demon Repair & Tune-up Guide 1965-1972 page 205 shows 1970 6 cylinder cars had 10" front drums and 9" rear drums. All other years had 9" drums front and back. My 1970 Dodge Challenger Dart Service Manual page 5-54 also shows 6 cylinder Darts had 10" front drums and 9" rear drums.
My Chilton's Valiant Duster Repair & Tune-up Guide 1968-76 page 183 shows 1970 6 cylinder cars had 9" drums front and back, however, 1973-76 all drum brake cars had 10" front drums and 9" rear drums. For some reason 1970 Dodge and Plymouth A-bodies were different in 1970. I don't know for sure but 1973-76 Darts were probably the same as Valiants and Dusters.
 
I've only had a couple of 'A' body cars and have parted a couple and don't remember them having different diameter drums on them......oh well. Learn something new all the time. My 66 /6 Belvedere had 10's.....10x2 on the front and 10x 1 1/2 on the rear. My rears were grooved to the max and couldn't find any replacements in 1990 so I cut them myself. Took .100" out of them and they didn't clean up but ran them anyways until I could swap out the 7 1/4 rear for an 8 3/4. The over cut drums worked and never blew apart even after 'testing' them :D
 
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