How to identify rearends & Differentials

jcode68 · Apr 14, 2008

I am heading to Carlisle next week and hope to find either an upgrade to my existing 8" rearend or a replacement 9". I currently have 2.79:1 open differential and would like to get something in the 3.73:1 ratio with a True Trac or comparable. So I guess what I'm asking is - how do I identify the parts that I'm looking at as a True Trac versus something else? Is there an way to tell by looking (other than gears missing teeth) that a differential is good or bad? I know how to identify a 9" rearend, but what markings do I look for to ensure it is the right size and will not require any trimming and or fabrication? I did a search, read the sticky on rearends etc, but couldn't find what I was looking for. Thanks for any info provided, maybe we can add it to the sticky as well.

red65 · Apr 14, 2008

Steve has the best (imo) compilation of info on the Ford 9-inch at this link:

http://www.ultrastang.com/

There's also an excellent discussion of the True-Trac at corner-carvers here:

http://forums.corner-carvers.com/showthread.php?t=4246&highlight=true-trac

ultrastang · Apr 14, 2008

red65 said:
Steve has the best (imo) compilation of info on the Ford 9-inch at this link:

http://www.ultrastang.com/

There's also an excellent discussion of the True-Trac at corner-carvers here:

http://forums.corner-carvers.com/showthread.php?t=4246&highlight=true-trac

There weren't any factory-issued 3.73 gears in either the 8- or 9-inch rear ends from Ford. The 3.73 ratio wasn't available until the Spicer 7.5" & 8.8" rear ends came out for the Ford trucks and the Fox-bodied Mustangs (the rear ends with the bolt-on rear end housing covers) . In aftermarket gear offerings though, you can get 3.73 ratios for a 9-inch , but as I said from the factory, Ford didn't offer these in the 8- or 9-inch rears.

If you are looking for a (used) 9-inch and are wanting lower (numerically higher) gear ratios, the best place to look would be in the '60s-'80s Ford half ton pickups. 3.50 and 3.70 Ratios were very common in those models. --3.89s were fairly common in the pickups up until '67.

Any 9-inch 3rd member will fit any 9-inch housing and will work so long as the axle spline count of the 3rd member is the same as the spline count on the axles you will be using.

Some links from my site on the subject:

1. http://www.ultrastang.com/Page.asp?PageID=6

2. http://www.ultrastang.com/Page.asp?PageID=7

3. http://www.ultrastang.com/Page.asp?PageID=11

4. http://www.ultrastang.com/Page.asp?PageID=10

5. http://www.ultrastang.com/Page.asp?PageID=8

jcode68 · Apr 14, 2008

Thanks for the responses guys. I spent some time on Ultrastang's site and no doubt, he has the 9" info covered extremely werll

I was originally planning to just purchase a rebuilt 8" center section with 3.73 or 3.89 gears (have seen on eBay from various sellers) with traction lok for about $600. But then I got to thinking that I might find this cheaper at Carlisle or better yet, maybe find a good 9" ready to go. Just want to make sure if I buy something, I know what it is. Any info on identifying 8" center sections?

How to identify rearends & Differentials

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How to identify rearends & Differentials

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