8.25 Vs 8.75

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V8 Sam

V8 Sam

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Howdy again peeps!

Another question.


I'm narrowing my b body 8.75 to abody width.

The b body 8.75 has no brakes jist big bolt halfshafts

obviously the b body halfshafts won't fit once it's narrowed but I have 8.75 half shafts in small bolt pattern a body form to use as I want to keep my SBP wheels.

I also have a complete a body 8.25 that's big bolt battern

Can I use the a body 8.25 backing plate on a 8.75 that WAS big bolt but now.small bolt?

Or does bolt patterns etc not even come into play?
 
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Small bolt pattern axles will have a different bearing position to match the corresponding offset of the backing plate/brakes that came with them.

You can't mix parts between small and big bolt pattern axles. They need their corresponding brake assemblies.

Big bolt pattern 8 3/4" brake assemblies (B-body) will interchange with big bolt pattern 8 1/4" brake assemblies ('73+ A-body . They are the same size and backing plates have the same offset.

The drum register on the big bolt pattern axles is bigger also.
 
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re: 'half-shafts'. Ahh, the British slang. I'm well-versed on such dialog since I have a '71 Daimler ds420 limo so words like bonnet, wings, boot lid, sparking plugs etc. not strange to me. :D Sounds like a nice project - assuming you are replacing orig. 7.25". Just curious as to what ratios are the original versus the replacement and S.G. or 'open style'? And, consider that the drive shaft will need to be shortened by ?"
 
As Loco said, the BBP backing plates won't work with the SBP axles, different offsets. Once narrowed to A body dimensions, your SBP axles will fit the 8.75 housing without issue; you just have to find the correct pre-'73 A body brake parts. 8.75 rear will also require shortening the driveshaft if you are replacing a 7.25, as well as addressing possible u-joint differences.
 
Perhaps, my swap parts were previously swapped? IDK, I haven’t owned them since new... LOL! I could be wrong. I would not have said what I did if I did t do it or know of someone I trust that said they did it themselves. I don’t like to give third hand, I heard... someone on the internet.... etc advice or say it works.

You have two guys saying different and I myself will be wary the next time around.

When I did a set of Dr. Diff axles, he said I had to use B Body drum backing plates. That wasn’t a problem since I just swapped out a 8-1/4 for a 9-1/4 in my (B body) ‘79 Magnum. The 8-1/4 backing plates went right on the A body rear end with Dr. Diff’s axles.
 
I been thinking

What if I was to use my current 7.25 backing plate and brakes (that are fully working) and just drill the extra mounting hole out? Is that workable?
 
V8 Sam said:
I been thinking

What if I was to use my current 7.25 backing plate and brakes (that are fully working) and just drill the extra mounting hole out? Is that workable?
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Yup, that'll work; but I don't think I'd bother if they're 9" brakes- but the 10' may already have the extra hole.
I think Rumblefish and I are on the same page- if I understand correctly he said he used B body brakes on his Dr. Diff axle swap- which is exactly right. But in order for you to use your stock small bolt axles in a cut down B body housing, you'll need A body brakes. We're just talking about two different setups.
 
Professor Fate said:
Yup, that'll work; but I don't think I'd bother if they're 9" brakes- but the 10' may already have the extra hole.
I think Rumblefish and I are on the same page- if I understand correctly he said he used B body brakes on his Dr. Diff axle swap- which is exactly right. But in order for you to use your stock small bolt axles in a cut down B body housing, you'll need A body brakes. We're just talking about two different setups.
Click to expand...

I've read 7.25 sbp backing plates have a different offset to sbp 8.75 extra drilled hole or not.

Think I'm gonna have to find some sbp 8.75 backing plates with 10 or 11" brakes
 
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