Rear backing plate size?

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74RR

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How do I determine what size backing plate I have? I bought a 8 3/4 housing and it came with backing plates. I need to install all the hardware now so I need to figure out what size I have.

Thanks.
 
First measure the diameter, that will tell you if you have 10" or 11" brakes. 11" drums have backing plates that are about 12 1/8" in diameter, 10" brakes have backing plates that measure about 11" in diameter.

If the backing plates are for 10" brakes, next measure the depth or offset of the backing plate. That will tell you if you have BBP or SBP brakes, because they used a different offset. SBP brakes have about a 1 1/4" offset, BBP brakes have a 1 3/4" offset. SBP backing plates can't be used with BBP axles, or vice versa.

This thread has pictures of the measurements...

http://www.forabodiesonly.com/mopar/showthread.php?t=258919
 
im restoring a 70 Duster 340, can someone reccomend a quality vendor for a complete brake line kit? fronts are factory disc, rear drum
 
Was there a big difference in quality between the SBP & BBP? Or does it just stand for Small Backing Plate & Big Backing Plate? Looks like I have the SBP 11" backing plate and that equals to a 10" drum correct?
 
Bad Sport said:
Small bolt pattern.

Big bolt pattern.

These refer to the bolt pattern of the lugs.
Click to expand...

Exactly. Small bolt pattern is 5x4", and uses 10x1.75" brakes. Big bolt pattern is 5x4.5", and uses 10x2.5" brakes.

If your backing plate measures 11" in diameter, then you have 10" brakes. And if the offset it 1 1/4", then you have small bolt pattern, 10 x 1.75" brakes.
 
Hmm. I measured the backing plate and it is 11" and 1 1/4 offset. But the brake pads themselves are measuring 2 1/4 if I remember correctly and not 1 3/4 as stated above. Maybe someone put the wrong pads in? I'm going to be getting a rebuild kit for the front drums and want to make sure I grab the right stuff before walking out the door.
 
The 1 1/4 offset that most of the posts are about is referring to the rear drums. Fronts had wider pads than the rears.
 
66Dart273 said:
Hmm. I measured the backing plate and it is 11" and 1 1/4 offset. But the brake pads themselves are measuring 2 1/4 if I remember correctly and not 1 3/4 as stated above. Maybe someone put the wrong pads in? I'm going to be getting a rebuild kit for the front drums and want to make sure I grab the right stuff before walking out the door.
Click to expand...
Sounds like you have 10" x 2 1/4" FRONT drums. Front and rear shoe widths are not going to be the same.
 
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