Are the rears the same,what are the differences?

 

There are variations in both but they are both 10 bolt diffs. In 1990 they went to 28 spline axles and I think it was in 87 when they went from 7.5 to 7.625" ring gears.

The biggest difference is that a 4th gen diff is 2" wider on each side. A 4th gen is a direct bolt-in for a third gen once you figure out the wheel backspacing.

 

It was earlier than 87, because my 85 Z has the 7.625 ring gear.

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Ludicrous Speed GO!!!
If anyone knows what movie this quote is from, you win a special prize!!!

 

I thaught 86 was the first year.I have a list
of gear ratios from gm and 86 is the 1st year
i see on my list for the 7 5/8.

 

Check the Tech Articles on this site, it says that they switched in '85. This is corroborated by the mechanic who inspected my car when it came in to the dealership. Your list must have a typo or something.
------------------
Ludicrous Speed GO!!!
If anyone knows what movie this quote is from, you win a special prize!!!

[This message has been edited by MartyMcFly (edited July 28, 2001).]

 

So the ring and pinion are the same for 1990 to 2001?And the hangers trans arm placement is the same also.
Thanks all