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f-body rear spring setup


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8.36.4. Springs of any origin may be used provided they are of the same number and type as originally fitted. Any spring used must install in the OEM stock unmodified location using the original system of attachment.


so what kind of setup are those running 3rd and 4th gen f-bodies using?

Just stiffer single pigtail type springs cut down to get the correct ride height w/ spacers for fine adjustment?


8.36.5 ... Any spring spacers/shims may be used. The spacers may NOT allow adjustment of the installed height of the spring without spring removal. The spring spacers/shims must install with the spring in the OEM stock location and no cutting, welding or other modifications may be made to the structure of the car to install these spacers/shims


above rule seems to say that the threaded spring seat adjuster available from Ground Control is illegal.


I was pondering sources for stiffer rear springs that would fit an f-body and fit the rules.

If you scroll down to the section starting 'Rear Coil Springs'

you'll see a list of springs


(note: this is a g-body web page)

specifically the moog 6377, 5659, and 5661 pigtail type 17 springs.

the table below that basically shows forces for a given compression of the spring in the g-body application.

The stock f-body springs varied a little over the years/generations but all are very close to the 5665 spring listed w/ the 113lb/in rate. For the 10.25" installed height of the f-body, spring 5665 & 5659 are pretty close in force i.e. for a given car the ride heights for the different should be close. I was thinking of using this spring, 5659, for the rear. maybe cutting 1/2 to 1 coil off to drop the ride height and increase spring rate (~10%). Talking to other f-body types it would seem 175lbs/in is about right for a 4th gen. the 5659 is a 162lb/in rating. cutting the spring, if necessary, could bring it up to the 175lb/in range.

The 6377 spring may also work, but the rate is a bit lower than the 5659.

The 5661 has the right rate, but the install height would just be too tall. Unless I wanted to cut a bunch off and run an even higher rate.




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Let me clarify. This is me assuming, through my interpretation of the rules, that the GC threaded spring seats are illegal. If they are legal.... then never mind. If they are illegal then see original post!

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Just about every roundy round speed shop can hook you up with legal f-body rear springs for about $50ea. They wont call them f-body springs, you have to tell them what you want (ie, pig-tail spring, 5"od (or is it 5.5"? I forget), X rate, y length)...There's some posts here about the length vs ride height you should look up.

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