66 gto rear end swap for a 12 bolt posi

[gtobear]

I have a 1966 gto and want to swap the 10 bolt for a 12 posi. Everything matches up but the spring perch design. The 12 bolt rear is from a 1972 monte carlo. Anyone know what type of spring I should use? thanks

 

[melsg5]

what does the original 66 spring look like, same coil width top to bottom or like the later springs the ends are a smaller coil? What does the spring perch on the rear end look like? As far as Pontiac original springs in the 68 to 72 era there is no difference in the spring used whether 10 bolt or 12 bolt.

 

[gtobear]

Small on the bottom and large on top. The original spring perch is flat. There is clamp (washer) on the lower end of the spring with a bolt that goes through the clamp and the spring and the perch with a nut on the lower side of the perch.

 

[melsg5]

based on the link below you will have to make modifications to get this work, things changed in late 67. I also ran across references to differences in the width of the rear end and the attachment of the upper control arms. Seems like unless you have lots of power and do lots of racing it may not be worth the effort.
http://www.gtoforum.com/f154/66-gto-rear-end-spring-swap-question-91378/