Does she have a nice rear end or what?

Communik8r

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Nov 18, 2019
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I have a rear end that may or may not be original to my 1969 Mustang. Engine and transmission are not original. Car came with a 302, but was replaced with a 351C. Transmission is a C4.


The differential is leaking, so I need a gasket at minimum, but I would sure like to know if I have a limited sllip, and what gear ratio is in there. There are lots of numbers in the casting, but no tag.


It is a 9" for sure. Any suggestions on how to identify what I have?
 
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rbohm

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Apr 12, 2002
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if you can get a socket on two of the lower pumpkin bolts, its not a 9".

as to whether or not its a limited slip diff, jack up one wheel, and with the trans in neutral try to turn it. if it turns easily then you have an open diff.
 

Olivethefet

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May 17, 2018
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With the wheels off the ground when you rotate one wheel the other should rotate in the same direction. If it does not I believe that is also an indication that it is open.

As for the ratio. Mark the wheel and mark the drive shaft. Rotate the drive shaft and count how many times you have to rotate it for the wheel to make one full rotation.

All of the above is true for a fox rear. I'm not sure how different the 9" is. Hope it helps.
 

Communik8r

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Nov 18, 2019
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Cool. I will do both of those things tomorrow. I still need to get a gasket tho. Which numbers on the casting would be the ones to look for? And is there any way to tell what year it is without the tag?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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You are gonna pull the pumpkin to fix the leak anyway, the ring gear will tell you the ratio, the carrier will tell you open or not.
 

Communik8r

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Nov 18, 2019
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Post a pic of it
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