8 3/4 SBP 10x1.75” Drum Help*

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b-body fan

b-body fan

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I have a fully rebuilt A Body Rear end with SBP axles and have purchased 2 sets of drums which don’t seem to recess into the backing plate. What is going on with this setup? I didn’t build the rear but someone said the bearings could be on backwards, is that even possible? Here’s a picture of one of the axles and both drums from different sets. Does the axle bearing look like its put on right? I haven’t checked my service manual yet. Finding the drums was ridiculous of course as you all know too well. I want the SBP axles but this is frustrating me to no end. I measured drum to drum the best I can and it looks like 57 1/4
Thanks in advance for any insight.

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Can't see if the axle/drum registers clear. Need a photo from the front. 65
 
When you install the drum does the axle/drum center registers clear each other? If not, the drum won't seat. 65
 

b-body fan said:
My shoes are part number 331 and are 1.75” which should be right for the car.
I have a 10x2.5 backing plate with brakes assembled from the LBP rear I took out and will slide the drum over it to see what that looks like. Thanks
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You can’t use those 2.5” backing plates, or any other backing plates from a large bolt pattern axle. They MUST be from a small bolt setup. The small bolt axle and corresponding brake setup has a unique offset that is only available in a small bolt axle. You need to either find a pair from an A body 8 3/4” axle, or you can use the 7 1/4” small bolt backing plates from a 10” brake system, but you would need to drill the 5th mounting hole, as 7 1/4” backing plates and axle mounting plates only have 4 studs, the 8 3/4” has 5 studs.
 
cosgig said:
You can’t use those 2.5” backing plates, or any other backing plates from a large bolt pattern axle. They MUST be from a small bolt setup. The small bolt axle and corresponding brake setup has a unique offset that is only available in a small bolt axle. You need to either find a pair from an A body 8 3/4” axle, or you can use the 7 1/4” small bolt backing plates from a 10” brake system, but you would need to drill the 5th mounting hole, as 7 1/4” backing plates and axle mounting plates only have 4 studs, the 8 3/4” has 5 studs.
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Maybe I said it wrong and caused confusion. The backing plates on the car are said to be for the 1.75 A Body brakes and the axles on the car are SBP.

The 2.5 backing plates are not on the car. They are what I took off along with the LBP axles. These are not going back on the car.
 
Here is a picture of an A body 8 3/4” backing plate. The flange offset is 1 7/16” or 1 3/8”, I would check the offset of your current backing plates to confirm that you have the correct backing plates. Did you get the complete set of 1.75” drums and backing plates together, or are these pieces that were put together separate? Most people don’t know anything about the small bolt pattern stuff, which is all I run on my A body cars. I have a few extra sets of everything if you find out you need any or all of the components to make up a complete set. Including the original style bell flanged drums.

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cosgig said:
You can’t use those 2.5” backing plates, or any other backing plates from a large bolt pattern axle. They MUST be from a small bolt setup. The small bolt axle and corresponding brake setup has a unique offset that is only available in a small bolt axle. You need to either find a pair from an A body 8 3/4” axle, or you can use the 7 1/4” small bolt backing plates from a 10” brake system, but you would need to drill the 5th mounting hole, as 7 1/4” backing plates and axle mounting plates only have 4 studs, the 8 3/4” has 5 studs.
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Not entirely true. If we're just strictly talking A-body, then yes, but some '66-70 6cyl B-bodies used 10 X 1 3/4" rear brakes too and use the same backing plates as the 8 3/4 SBP A-body. The early numbers are 2533840-1 and by 1968 they are 2880582-3. Must have been a slight design change, but, I've swapped early and late with no issues. It's just that the B-body ones are pretty rare.....even more so than finding A-body ones.
 
b-body fan said:
? I didn’t build the rear but someone said the bearings could be on backwards
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If the outer race is trapped by the bearing and the axle retainer it's on correctly.

Possibility that the bearing is not pressed on far enough?

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cosgig said:
Here is a picture of an A body 8 3/4” backing plate. The flange offset is 1 7/16” or 1 3/8”, I would check the offset of your current backing plates to confirm that you have the correct backing plates. Did you get the complete set of 1.75” drums and backing plates together, or are these pieces that were put together separate? Most people don’t know anything about the small bolt pattern stuff, which is all I run on my A body cars. I have a few extra sets of everything if you find out you need any or all of the components to make up a complete set. Including the original style bell flanged drums.

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Great info thanks for sharing this.
I’ll disassemble everything tomorrow, measure the backing plates and post pics tomorrow.

The shoes and cast color drums are from a local guy on Long Island who sells Mopar parts and the black drums are from an ebay seller who had already sold 28 drums neither set was cheap and both sets appear to be identical.
“If” the plates I have are good A Body plates I’ll pull the axles to look at the bearings to see if they are pressed on properly. If I need to purchase backing plates/drums I will send you a message, thanks for mentioning that you have them
 
This is how my brakes look.. I would think ya don’t want the drum to touch the backing plate for obvious reasons. These are the Centric brand drums. I bought them from summit but can be found there and rockauto. Small bolt pattern for an a-body on a 8 3/4 axle. This is on a ‘68 Dart GT and in the photo I was swapping the axle to a 8 3/4.

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Hmmm.. just spitballing but I’m guessing the axle shaft length is correct? I didn’t use OE style bearings either. Not that it makes a difference. I used green bearings from Dr Diff. Offset of the axle? I’m stumped..
 
Dana67Dart said:
If the outer race is trapped by the bearing and the axle retainer it's on correctly.

Possibility that the bearing is not pressed on far enough?

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Can anyone tell from this picture if its pressed on far enough? Passenger side axle length 27 1/2” splined end to the back of the flange. 25 3/4” splines to the mounting plate.

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