Drum brake size change

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ChuckDock

ChuckDock

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I'm replacing my 7 1/4 rear end to an 8 3/4. My current drums are 10 inch by 1.75"
Can I just change the drums to the 10x2.5"? And then just get some 10x2.5 shoes?
Both old and new rear's have the 5x4 pattern.

Seems like that should work but wanted to throw it out here.
Thx!
 
10x 1 3/4 Means you have a original small bolt pattern A-body 8 3/4? If yes than no you can't change brake size, not with the original SB axles. They use a different brake spacing than all the other 8 3/4 er's. You can order new axles with the B,C,truck brake spacing from people like Doctor Diff.
 
Before you spend money on any brakes you need to swap to big bolt axles first.
 
I was under the impression that as long as he has the correct backing plate to go along with the 10"x2.5" drums they will work on any 8 3/4".
 
SGBARRACUDA said:
10x 1 3/4 Means you have a original small bolt pattern A-body 8 3/4? If yes than no you can't change brake size, not with the original SB axles. They use a different brake spacing than all the other 8 3/4 er's. You can order new axles with the B,C,truck brake spacing from people like Doctor Diff.
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Yes, the axles are for the 8 3/4, but are the sbp. I bought the case from one guy, and the axles from another person.

So, sounds like I could just use my 10x 1 3/4 drums and shoes on the now new sbp axles, right?
 
I just measured the old shoes that came with the 8 3/4 rear end, and they are the 10x1.75 shoes and I have those backing plates...darn, that means I ordered all the wrong stuff from Cass, Dr. Diff...
Thanks for the info folks. I'm just going to use my drums and shoes from my 7 1/4 setup since they are in great shape.
 
Sublime Swinger said:
I was under the impression that as long as he has the correct backing plate to go along with the 10"x2.5" drums they will work on any 8 3/4".
Click to expand...

Not entirely true. The axle flange offset is different between the 8 3/4” SBP axles and BBP axles. 10x2.5” drums only work with BBP axles. So yeah, the 10x2.5” drums can be used on any 8 3/4” housing, but they must be used with BBP axles. They won’t fit with the stock A-body SBP axles no matter what backing plate you use.
 
72bluNblu said:
Not entirely true. The axle flange offset is different between the 8 3/4” SBP axles and BBP axles. 10x2.5” drums only work with BBP axles. So yeah, the 10x2.5” drums can be used on any 8 3/4” housing, but they must be used with BBP axles. They won’t fit with the stock A-body SBP axles no matter what backing plate you use.
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Good to know, thank you.
The wheel lug studs are a different diameter as well I see. The one's I got from Dr. Diff are a lot thicker in diameter than the ones in the 8 3/4 sbp axles I have. He is going to hate me...lol. Hope he is good about returns. I just got the stuff yesterday, and its all new in the box still so I don't expect it to be a problem.
I'm sure you guys are thinking - get rid of the sbp stuff and bite the bullet. So many doors open with the bbp pattern for sure. One day for sure...
 
72bluNblu said:
Not entirely true. The axle flange offset is different between the 8 3/4” SBP axles and BBP axles. 10x2.5” drums only work with BBP axles. So yeah, the 10x2.5” drums can be used on any 8 3/4” housing, but they must be used with BBP axles. They won’t fit with the stock A-body SBP axles no matter what backing plate you use.
Click to expand...
Can you shed some detail on "axle flange off set". My 68 Notch has 8 3/4 with skinny brakes. Diff has been shortened with aftermarket BBP axles. I want to ditch skinny brakes and switch to 2.5" everything. Thanks
 
IF they are BBP axles made for the original 10x1 3/4” brakes,they have a unique offset. You can’t use the wider brake plates.
 
SGBARRACUDA said:
IF they are BBP axles made for the original 10x1 3/4” brakes,they have a unique offset. You can’t use the wider brake plates.
Click to expand...
Well crap, before I saw your reply I went down to Az. Differential and talked to the owner, they shortened the diff and aftermarket axles. According to him, the axles he cut and sold me will work with 2.5" brake set up so I got some used backing plates out of his pile, turns out their 11 x 2.5, got a tester drum coming tomorrow from NAPA. Crossing my fingers. If this doesn't work sounds like expensive axle mods or $400 for NOS skinny drums on e bay plus the search for skinny pads. What's car building without another rabbit hole!
Sure glad for your input.
 
SGBARRACUDA said:
Did you have them in use with the 10x1 3/4” brakes?
Click to expand...

No sir. Car has been disassembled and under construction for 5 years. Job 1 on the build was the stance on this car, built around the Year One Ralleye wheels with 390's out back. This work literally began with new axles purely to get to BBP. Ive not gotten to brakes until now.
 
Jumping in here because I'm doing something along similar lines and need some direction.
My Barracuda was originally a SBP 8 3/4 and I've acquired a BBP 8 3/4 with 10 x 2.5 inch drums/. I am going to need to completely rebuild the brakes, replace the slave cyl. and the drums, and need all new brake lines.
Where is the best place to go for these parts and/or what is the equivalent Mopar I can tell the counter person I am putting them too?
TIA
 
It came with the car when I bought it last year.
The previous owner told me it was from a BB A-body.
I've checked the measurements and they all correlate with that.
But I don't have a year or anything to go with.
 
Argh!
Okay then.
I know that the housing is for an A-body by the measurements.
It had 10x2.5 drums on it.
It had one axle still bolted in place that is a 5x4.5
I am having a diff out of a different car built for this.
I'm just needing to figure out where to get the right drum brake parts.
 
Well maybe someone ordered axles for it in the past. More than likely they are B body 10 x 2 1/2” drums. But this is just a guess.
 
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