Rear suspension spring rates on 68 Mustang

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Author Topic: Rear suspension spring rates on 68 Mustang  (Read 736 times)

Offline AussiePhil

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Rear suspension spring rates on 68 Mustang
« on: July 30, 2021, 07:11:25 pm »
Hi all,
I’m running a Helix brand four link on the back of my 68 Mustang street car.
I find it very good, smooth, good movement, no interference, but have a question about spring rates.
I have two sets of springs, the originals were progressive 180 - 200lb/in. (a bit soft) and 400lb/in. (very stiff)!
I run the car pretty low and scraps a bit with the soft springs on reasonable bumps, and the wheels skip on low speed bumpy street turns with the heavy springs. I probably have 2 1/2” of travel.
When buying the 400lb I wanted 350lb, but they were out of stock, I should have gone down to 300lb.
So 250lb/in. Sounds right to me?

I know it’s apples and oranges leafs and coils but it’s basically the same, weight and movement!
I’ll go to our Council weigh bridge tomorrow and get everything weighed.

My question is what sort of spring rate do you use for your similar weighted car.

The heavy springs are no good to me so I was thinking of grinding the entire length of the 400lb spring coils to lessen the spring rate (tension?)
Cheers Phil.
« Last Edit: August 01, 2021, 01:53:18 pm by AussiePhil »
If you've never buggered anything you've never done anything!
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Offline AussiePhil

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Re: Rear suspension spring rates on 68 Mustang
« Reply #1 on: July 31, 2021, 07:06:34 pm »
Hey all,
I had the car weighed today and it came in at 1410kg total and 635kg rear.
I bought a pair of AVO coilover dampers.
Now I need to find a pair of springs to suit, 1.9”id. X 7”, I’m guessing about 250lb/in. (4.5kg/mm)
Cheers Phil.
« Last Edit: August 01, 2021, 02:17:04 am by AussiePhil »
If you've never buggered anything you've never done anything!
But if you've buggered a lot maybe you're not very good at it!

Offline Haggspeed

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  • Car: '#03967 Mustang Fastback
Re: Rear suspension spring rates on 68 Mustang
« Reply #2 on: July 31, 2021, 10:12:38 pm »
Hi Phil,
While my cars not yet finished, we've built a custom parallel Four-Link in my '67 Fastback, which I estimate will be a similar weight to your car.  I was advised to start with 225 lb/in springs in the Coil-Overs.  So your guestimate of about 250 lb/in sounds pretty close to me.   

Offline AussiePhil

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Re: Rear suspension spring rates on 68 Mustang
« Reply #3 on: August 01, 2021, 02:14:58 am »
Hi Phil,
While my cars not yet finished, we've built a custom parallel Four-Link in my '67 Fastback, which I estimate will be a similar weight to your car.  I was advised to start with 225 lb/in springs in the Coil-Overs.  So your guestimate of about 250 lb/in sounds pretty close to me.   
Hey Jeff.
Glad to hear, you won’t be sorry changing to four link!
With that and fitting Unisteer power steering the car’s far better.
Thanks for your reply!
Cheers Phil.
If you've never buggered anything you've never done anything!
But if you've buggered a lot maybe you're not very good at it!