Mustang Owners Club Australia Forum

Technical & General Discussion Area => Restomods => Topic started by: AussiePhil on July 30, 2021, 07:11:25 pm

Title: Rear suspension spring rates on 68 Mustang
Post by: AussiePhil 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.
Title: Re: Rear suspension spring rates on 68 Mustang
Post by: AussiePhil 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.
Title: Re: Rear suspension spring rates on 68 Mustang
Post by: Haggspeed 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.   
Title: Re: Rear suspension spring rates on 68 Mustang
Post by: AussiePhil 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.