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I am rebuilding my rear suspension, the rear end was sagging pretty bad. My question is when rear springs are worn out is the arch greater are less. The reason I ask this is because I went to NPD today and bought some new springs, I bought the Ford OE spec. springs, and went with the GT version with the 1" lowering option $179.00 for the pair. When I brought them home and compared them to the old springs there was a huge difference, from the floor to the top of the arch, the new springs are 3 3/4"(from the floor to the top of the arch) shorter than the old worn out springs. Is this right or do I have to make a trip back to NPD?
Thanks
 
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The 5 leaf rear springs I bought from Mustangs Plus had less arch on the garage floor than the OE spec GT springs I pulled off of my 65 2+2. So I think you are all right...except...

From the other details on your post about your Mustang, you might consider returning these OE spec springs and taking a look at the offerings from Mustangs Plus. I found the GT rated springs still allowed my Fastback to sag in the rear at rest, and didn't give me the performance I wanted in the turns or with straight line acceleration. For the price, I think you're better off with a stiffer spring.

Good luck.

Matt
 

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Generally, a softer spring will have a larger free arc than a stiff unit. The stock springs for 2V cars generally had a 6-7" arch, but the performance cars had spring free arc in the range of 3-5 inches. The greater arch makes up the difference because of the spring rates to obtaint he correct ride height. A spring that has a 120lb rate compresses 1 inch with a 120lbs placed upon it. a spring with a 240lb rate will only compress 1/2" with the same 120 lbs, hence the reduced free arc on the higher rate spring.
 

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I bought the same ones without the lowering option. I'm happy with them in combination with Eibach's up front.
 
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