69 rearend help
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Joined: Jan 2011
Posts: 99
From: Western PA
69 rearend help
This is my 69 cutlass covertible rearend which I believe is a O rearend 12 bolt cover/10 bolt ring gear with a 2.73 one legged gear. 350 turbo with a 350 motor. the Drive shaft is 56" center to center of drive shaft cups. Im planning on dropping a 455 with a 400 turbo in her in the next 2-3 weeks. She wont be down the strip but do want to do some work to help traction. so is this a 8.5" ring gear ? Also i picked up a couple driveshaft bodies from A bodies one is 54" center to center cups and the other is 53 3/8. do these sound ok ? I just didnt want to wait until i have her tore down. 
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Last edited by 69OLDSCUTCONV; Jun 25, 2011 at 09:23 PM. Reason: picture
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Joined: Oct 2009
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From: Erie,PA
The 12-bolt o-axle is unique to itself.It is an 8.5" ring gear,but it is NOT the same as the 8.5" 10-bolt,which is also known as teh 8.5" corporate.
As for the driveshafts,if you keep the existing rear,and install a short-shaft TH400,the 54" drivehshaft could work,but will be slightly short.
If you install the short-shaft TH400 with a 71-72 8.5" 10-bolt,the 53 3/8" shaft will be correct.
As for the driveshafts,if you keep the existing rear,and install a short-shaft TH400,the 54" drivehshaft could work,but will be slightly short.
If you install the short-shaft TH400 with a 71-72 8.5" 10-bolt,the 53 3/8" shaft will be correct.
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Joined: Jan 2011
Posts: 99
From: Western PA
More Questions
Whats tha advantage of going to the 10 bolt 8.5" from a 71-72. are parts easier to find or is it stronger? How hard is it to find a 10 bolt housing.
I would really like to end up with a decent posi with a low 3.?? gear nothing numerical higher than 3.42.
I would really like to end up with a decent posi with a low 3.?? gear nothing numerical higher than 3.42.
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Joined: Jul 2006
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From: Richfield, Oh
rear end help
Well if BT got the length correct on the drive shaft (which I am sure he did since he builds these cars) 10 bolt 8.5 wil lvery easy to get parts for in MANY different ratios. 2.93 3.08 3.23 3.42 etc. Posi you can use a stocker from any mid 70's car. Aftermarket is the way to go if you have the little extra money.
12 bolt olds option you have - We have posi units that will fit these rear ratios stock GM 3.08 -3.23 and aftermarket 3.42 and 3.90 Richmond gears.
Rebuild kits etc are always available too.
Both the 10 bolt 8.5 and 12 bolt olds rear are 28 spline both are 10 bolt ring gear the 8.5 does have a larger pinion spline yoke area which will handle more power like a 12 bolt chevy... If your not going to the track doubt it will make that much difference especially if your using aftermarket better gears.
Jim
J D
12 bolt olds option you have - We have posi units that will fit these rear ratios stock GM 3.08 -3.23 and aftermarket 3.42 and 3.90 Richmond gears.
Rebuild kits etc are always available too.
Both the 10 bolt 8.5 and 12 bolt olds rear are 28 spline both are 10 bolt ring gear the 8.5 does have a larger pinion spline yoke area which will handle more power like a 12 bolt chevy... If your not going to the track doubt it will make that much difference especially if your using aftermarket better gears.
Jim
J D
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