Difference in drum brakes A-B Body

[mopardude318]

What is the offset difference of small bolt pattern drums from an "A" body 8 3/4 to big bolt patter drums from a "B" body 8 3/4 rear axle?

From my understanding, "A" body SBP drums are 1 3/4" and the "B" body BBP drums are 2 1/2". So the difference is 3/4". Am I correct? And I assume that any "B or C" body drum brake will work just fine on my 8 3/4?

Sorry for such a dumb question, I know I'm over thinking this right now. The answer is simple.

-James

 

[340butterduster]

It doesn't matter what body style the drums came from. The backing plates are different from 1 3/4" to 2 1/2" drums, the bolt pattern you already know.
The offset is built into the backing plate.
There is also differences in drum diameters, 10"-11".


My understanding ( I haven't tried this) that backing plates from 8 1/4" will also bolt in.

Hope this helps.

 

[mopardude318]

It doesn't matter what body style the drums came from. The backing plates are different from 1 3/4" to 2 1/2" drums, the bolt pattern you already know.
The offset is built into the backing plate.
There is also differences in drum diameters, 10"-11".


My understanding ( I haven't tried this) that backing plates from 8 1/4" will also bolt in.

Hope this helps.

Ohhh Ok...So the actual overall length of the axle and wheel mounting surface doesn't change. The backspace of the backing plates change. Thanks for clearing that up for me.

As for the 10" or 11" brakes, it doesn't really matter to me which ones I use as long as they are the 2 1/2" pads, and large bolt pattern, so they will go on the B body 8 3/4 I'm getting.

So, now my mission is to find a donor car that has a drum brake setup I can snag off of it...

-OR- Couldn't I just use the small bolt pattern 1 3/4" brakes that came off my A body 8 3/4 and just have the drums redrilled?

 

[crackedback]

The axle length would be different because the standoff, from the bearing retainer to wheel mount surface, is about .25" shorter on an a body 8.75 vs the BBP B body axles.

That's why when you put the BBP A body aftermarket axles in an A rear, the track increase by about 1/2".

A body 8.75 brakes are their own animal. They don't play nice with any of the BBP axles/brakes.

The only way to use A body 8.75 brakes is if you special order a set of axles using the A body standoff distance. You also need to have the center turned to accept the redrilled A drum smaller center registe , or open the hole in the drum to BBP size.

 

[mopardude318]

The axle length would be different because the standoff, from the bearing retainer to wheel mount surface, is about .25" shorter on an a body 8.75 vs the BBP B body axles.

That's why when you put the BBP A body aftermarket axles in an A rear, the track increase by about 1/2".

A body 8.75 brakes are their own animal. They don't play nice with any of the BBP axles/brakes.

The only way to use A body 8.75 brakes is if you special order a set of axles using the A body standoff distance. You also need to have the center turned to accept the redrilled A drum smaller center registe , or open the hole in the drum to BBP size.

Ok thanks crackedback. I'll find a drum brake setup off of any B, C, E, F M, J vehicle..