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Hi all,

I am about to shorten a 12 bolt from early a 70s Impala to the 62-67 length.
I just want to make sure I get the numbers right.

From what I found the housing end to housing end length should be 52.125.
That number should NOT be from the C/L of the pinion yoke to maintain the 1/2" offset, but rather centered from the C/L of the carrier location as best as possible.

The spring perches should be 43.5 at centerline.

This site below shows the distance from the "backing plate" to be 50.75, so I take it that is not taking into account the offset stamped into the backing plates?

http://www.novaresource.org/axle.htm

Thanks
 

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If this is going to be used in a 62 - 65 with rear disc brakes shorten it an additional .750" at each end. It will make wheel selection and tire fitment so much easier.

Not real sure about the 1/2" offset. The axles are both the same length on GM rear ends.
 

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I think you're going about this backwards. The wheel mounting surface (WMS) is really the width you care about. The backing plate and brake setup affects that. Either:

1) Mock up the tires and rims, and measure the WMS-WMS distance, measure the assembled Impala WMS distance, and work from there.

2) Measure a stock diff WMS distance, measure the assembled Impala WMS distance, and subtract to find out how much to cut out.
 

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I think you're going about this backwards. The wheel mounting surface (WMS) is really the width you care about. The backing plate and brake setup affects that. Either:

1) Mock up the tires and rims, and measure the WMS-WMS distance, measure the assembled Impala WMS distance, and work from there.

2) Measure a stock diff WMS distance, measure the assembled Impala WMS distance, and subtract to find out how much to cut out.
i agree with the above and also that shortening it by a tad extra as Philip suggested would be thinking ahead... if the diff is to be cut down anyways then why not center the wheel in the opening and not have to rely so much on the backspace of the wheel to get it to fit right?

meaning... why set it up for (example only) a 15x8 w5" backspace when by cutting it shorter you can use a 15x8 w4" of backspace? this would better center the wheel for distribution/bearing loads and leave you the equal distances on outside & inside clearances...

just a thought...
 
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