Author Topic: Diff Ratio recommendations  (Read 1622 times)

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Offline 1bigdog

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Diff Ratio recommendations
« on: February 02, 2012, 03:58:09 PM »
Hi All, new to this forum.  I just purchased a 65 Sky Convert. and am planning some running gear updates for it.  I was surfing the local craigs list  and found a couple of posi rear ends, one out of a 75 el camino with 3.25 ratio and another from a GN with a 3.73 ratio, both are 8.5" units.  I plan on getting a 200-4r tranny.  So a couple of questions:

1) which gear ratio would you all recommend for this car
2) which of these to rearends would be the easiest to install in the 65?

I don't plan on hitting the strip just want something that is nice to do some crusin around with decent performance and milage.  Currently the car has a 300 in it for a motor, but that could change down the road as well.


Offline WkillGS

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Re: Diff Ratio recommendations
« Reply #1 on: February 02, 2012, 11:17:57 PM »
Neither rear will bolt right in since the control arm mounting points are different. There may be adapter control arms avail to put in the GN rear, but that adds a lot to the cost.  But maybe those are adapter control arms to put an old rear in a GN? :icon_scratch:

An 8.5 inch rear from a 71-72 Skylark or cutlass are the ones to look for. Gears are easy to find for those.
Or just get gears and a posi for your 8.2 rear.
Walt K
Eastern Pa

66 GS Astro Blue/blue 425 auto
66 GS Silver Mist/black 401 4 spd
66 GS Flame Red/black 401 5 spd
66 GS Saddle Mist/black 401 L76 auto
66 Special Flame Red/black 300 5 spd
65 GS vert Verde Green/ Saddle buckets 401 4 spd
79 Turbo Regal

Offline Brian

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Re: Diff Ratio recommendations
« Reply #2 on: February 03, 2012, 07:05:01 AM »
Your car most likely has a set of 2.78 gears in it.  As Walt said, the 72 and older rears out of any GM A-body car will fit.  Keep in mind though that andy 68 and newer rear end is about 1" wider and will give you a wider rear track width.  I am with Walt--change the gears in you existing rear.  With an overdrive transmission, you can get a set of the aftermarket 3.90 gears and Auburn posi to go with it. 
'64 Skylark 2dr ht 4 speed, 300-4
'65 GS ht, 4 speed,2-4s,AC,PS,PB,PW,Pseat,Tilt
'66 Skylark 2dr ht 300-2 automatic
'78 Yamaha DT 400 2 stroke
'88 Ford F-150 4x4 (used to be 4x2)
'89 Ford F-350 4x4
'03 Honda Accord Coupe V6 6-speed manual (daily driver)

Offline 1bigdog

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Re: Diff Ratio recommendations
« Reply #3 on: February 03, 2012, 10:29:25 AM »
Great insight, thank you.

Offline WkillGS

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Re: Diff Ratio recommendations
« Reply #4 on: February 03, 2012, 12:50:05 PM »
Jim 'Monzaz' has extensive experience with the Buick rears. Check out his site here:
http://jdrace.com/
He's likely to have some used parts or can set you up with new stuff at a great price. :thumbsup:
Walt K
Eastern Pa

66 GS Astro Blue/blue 425 auto
66 GS Silver Mist/black 401 4 spd
66 GS Flame Red/black 401 5 spd
66 GS Saddle Mist/black 401 L76 auto
66 Special Flame Red/black 300 5 spd
65 GS vert Verde Green/ Saddle buckets 401 4 spd
79 Turbo Regal