8-3/4” axle conversion

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ricker4444

ricker4444

Some Day
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I need to swap out my rear axles from the 5x4 to the 5x4.5 on my 8-3/4. I thought it would be easy but I get more confused every time I reach out to a manufacturer. I understand that the offsets are different and was told I need to change the backing plates as well. I asked Dr. Diff but he did not have the backing plates for the axle package he had to convert me over. I hope I am just overcomplicating this and someone can simplify it for me. Can someone enlighten me? I am not the one doing the work and I was hoping to stay closer to stock rather than throwing on something like the Wilwood aftermarket. Any insight would be appreciated
 
No, you're not overcomplicating it. If you're using DoctorDiff 5x4.5" axles they use the standard Mopar BBP axle flange offset, which is different from the SBP flange offset.

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Which means you need the entire 10x2.5" drum brake set up, including the backing plates. You can't reuse the SBP backing plates.

You can find backing plate measurements here Converting rear drum brakes from SBP to BBP , which will also show why you can't reuse the SBP backing plates.

You'll have to find a set of 10x2.5" BBP backing plates.
 
I usually use the 10 by 2.5-inch stuff. Stock B Body stuff after 65 are usually the easiest to get or E Body backing plates and parts will work just fine. 1/2 ton pickup trucks with an 8 3/4 and 10 by 2.5-inch stuff will also work. There are others but to be honest I do not remember which I usually just stay with the B Body stuff. The last car I did was a 67 Barracuda. The backing plates and drums etc. All of the parts I used came off of a 68 or 69 satellite. Then you will need all the brake parts, shoes, hold down hardware etc. Make sure you get the emergency brake levers and parking brake struts from the donor car. If you can find an old car with everything on it that would be the best way. I reused the wheel cylinders and emergency brake cables from the old Barracuda 8 3/4 rearend. If you have questions send me a p.m. and we can exchange phone numbers and I can walk you through it.

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Backing Plates.jpg
 
10x2.5 is the most common, but don't rule out other options, like 11" brakes from C bodies, trucks and vans; 10" units from F/M/J bodies, early 5 lug Dakotas, and Jeep Cherokees, and Grand Cherokees up to late 90's. But whatever you do, get the entire brake assemblies as others have already said. And then write down what you used so you know what to order when service time comes around.
 
Last trip I made to junk yard plenty vans,trucks cars with 10 and 11 inch 8 3/4 and 8 1/4
 
Thank you to everyone for your feedback and to Steve “SMCARNUT” for the in depth phone convo. Very much appreciated!
 
Doesn't anybody make big bolt pattern axles that are a direct swap?
 
str12-340 said:
Doesn't anybody make big bolt pattern axles that are a direct swap?
Click to expand...

Yes, but then you’re stuck with re-drilling the SBP drums, and sourcing the 10x1.75” brake parts that are frequently out of production.

The BBP brakes are the far better option.
 
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