7.25 drum to drum measurement
I just measured the thickness of a new drum.
0.136" thick each.
If you measured axle flange to axle flange add 0.272" (0.136 + 0.136) to your measurement.
I measured my loose 67 7 1/4 and came up with 57 outside of axle flange to outside of axle flange.
There was a slight deflection over the center of the diff.
That would make it all in 57.272"
The posts say 57 1/8"
Which is a little under an 1/8" less than I measured.
I bet if you measured 100 rears you would get 100 different measurements.
Oh boy.
A ‘67 7.25” may not be the same width as a ‘73 7.25. The BBP 7.25’s are not the same width as the earlier SBP 7.25’s.
The 57 1/8” measurement is the SBP 8 3/4 width, which definitely is NOT the same as
any of the A-body 7.25’s.
Using a tape measure and going over the center hump will make your measurement longer than the actual width, potentially by a significant amount. None of the A-body 7.25’s are wider than a SBP 8 3/4, so the 57.2” measurement is totally inaccurate.
And as for “measuring 100 and getting 100 different measurements”, that has not been my experience. I’ve measured dozens of Mopar 8 3/4’s, and all them were less than 1/8” from the specs in that list I posted when measured correctly. Their width is somewhat critical to the function, and unlike body tolerances they were held pretty tight.
Thank you, as ever, lots of good advice. Am thinking i need to measure in any case....but.....
Two things:
- Am not sure if i have a BBP, i think it might be SBP, as this is the stock 1973 axel. Am not sure why Quick Performance need the measurement but think best i get it up on a ramp and double check but going by your comments on the backspace this got me thinking! Am presuming it might be better to provide the 8 3/4 drum to drum measurement - see photos and point 2 for further reasons?
- If that does make sense - @72bluNblu I didn't see a measurement for a 1973 on your shared post link.
- So leading on from this, i have measured the outside of the wheel to the edge of the arch - the rear sits a long way in (second photo), so thinking i'd be better giving them the 8 3/4 measurements in any matter - as the rear wheel sits nearly 1.5" inside the arch.
What do you think - imagine i could come out a little wider on the rear?
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Your ‘73 could be either SBP or LBP, depending on whether or not it came with factory front disk brakes. In 1973 the disk brake cars went BBP, and all factory V8 cars got front disks in ‘73. A /6 car could be drum/drum, and those care remained SBP. So, just knowing that it’s a ‘73 with a 7.25” doesn’t confirm which bolt pattern it is.
You can definitely use an axle wider than the A-body 7.25” regardless of its type, but your clearance to the quarters also depends on your wheels backspacing. And if you’re going from SBP to BBP that could be changing!