[pro-tour79]

shocks would be the problem not rate I have 800# in the front of my car, driving down the road the spring pressure is the same regardless of rate all the rate will do is affect how far the suspension will travel when hitting a bump, the shock will affect the speed of the suspension travel if the shock does not allow the spring to compress fast enough to support the added load caused by the bump the energy will not get absorbed by the motion of the shock and will transfer to the chassis

[pro-tour79]

couple more things, I HATE the word overkill it's meaningless at best
The other thing is the difference between 580 and 700 at the contact patch is only about 40# , not much of a difference

[Skip Fix]

FWIW my full sized Bronco was way stiffer with factory springs than the TA with 700+ springs.

[Z Code 400]

Thanks Guys...

I appreciate that information...My Koni's are single-adjustable, so not a lot of infulence there.

Ok...taking all my measurements into consideration, what springs do I need up front that will compliment the rear springs???

I am thinking I will eventually use a rear spring that will give me a 1.50" drop to try and make the car sit level.

Here are my current measurements with the springs out and the chassis setup where I would like it to be when it is finished:

Shop floor to fender lip: 28.0"

Spindle Center to Fender Lip: 15.50"

Lower Bumpstop to Frame: .500"

Spring Seat Clearance: 11.250"

In this position, as shwon in the photos below, the lower control arms and the tie rods are pretty much parallel to the floor. If you see anything wrong with running at this height, please chime in....Thanks....Robert

[Z Code 400]

Ok,

After talking with a couple of spring suppliers, I've pretty much been told that by keeping my period-correct 15"x8"4" wheels and 255/60/15 tires, it makes no sense whatsoever to do any suspension upgrades. So, I am back to looking for a good factory spring that I can use, hopefully, without having to cut them.

Which spring has the potential to have a higher ride height in my 1975 Formula, based on the above measurements:

#5662 a 748lbs/inch spring with 0.750 wire diamter, a 1690lbs rating with an advertised 10.750" loaded height and 13.01" free length

#5664 a 707lbs/inch spring with 0.765 wire diameter, a 1863lbs rating with an advertised 10.750" loaded height with a 13.18" free length

#5660 a 598lbs/inch spring with 0.718 wire diameter, a 1538lbs rating with an advertised 10.750 loaded height and a 13.26 free length.

Thanks....Robert

[Z Code 400]

Greetings,

Here is what I have come up with so far. We need a 11.250" to 11.500" installed height (based on our mock-up) and must account for each of these springs taking a slight 'set' after installation. Anything between 400-500lbs/inch would probably work good with the stock sway bars and rear springs, based on what Herb Adams was recommending.

All springs calculated with 1950lbs front end weight:

#584 457lbs/inch spring, 16.13" free OAL, 11.87" installed height

#586 432lbs/inch spring, 16.06" free OAL, 11.55" installed height

#6450 406lbs/inch spring, 15.93" free OAL, 11.13" installed height

#5534 500lbs/inch spring, 15.87" free OAL, 11.97" installed height

Thoughts????

[Z Code 400]

I talked with Coil Spring Specialties in St. Mary's, Kansas this morning. I gave them all my pertinent data, measurements taken from before we took the car apart, front and rear axle weights, etc. Currently, without springs, we are mocked-up at: 28.0" from fender to floor, 15.0" from spindle centerline to floor and 9/16" between bumpstop/frame. Right now, our control arms and tie rods are almost perfectly parallel to the shop floor.

With 15.0"x8.0"x4.0" and 255/60/15 tires, this is where I want the front suspension to be.

According to their engineer, to keep my car sitting at this height with everything assembled, we need a spring that has an 11.250" installed height under load. I also discovered that a second generation ront suspension has a 1.80:1 ratio. In the end, we settled on a 450lbs/inch spring, .760" wire diameter with 11.250" compressed height. They are going to make the springs for me, so no need to harvest junkyard springs or deal with Moog that might be produced offshore nowadays.

Just wanted to give you all an update....Robert

[Z Code 400]

Man,

Kevin at Coil Spring Specialties in St. Mary's, Kansas, is a fabulous technician to work with. As some of you know, with my large 255/60/15 tires and 15"x8"x4" wheels, most aftermarket springs will drop my car too much, as they are designed for lower profile rubber.

After some additional measurements, weight calculations and end-use considerations, we upped the rate to 500lbs/inch and dropped the installed height another .125" which gave us a full 1.00" drop at the front fender. The springs are .760" wire diameter with a 15.500" free length and 11.00" installed height. We specified a linear spring.

We are setting the static front ride height at 14.750" from spindle centerline to the shop floor (27.50" from fender lip to the shop floor) with an increase in front spring rate from 294lbs/inch (stock) to 500lbs/inch with the new springs. This setting puts our lower control arms and tie rods parallel to the shop floor.

The company does not charge you to design the spring and they will work from your custom weights/measurements, or from the factory suspension specifications. They will even 'prove' your current springs, work with your current measurements and develop a custom spring to put your ride height anywhere you want it to be. My springs cost me less than $150.00 made precisely to my specifications.

Hope this helps...Robert

[Z Code 400]

My new springs arrived yesterday and I installed them last night. The ride heigth is exactly where I specified it to be at 14.75" from spindle centerline to fender lip and 27.50" from fender lip to shop floor. This is a full 1.00" drop from stock.

Thanks to David Pozzi for the unsprung weight calculation formulas. It is great to be able to design a coil spring on paper, from a handful of measurements, and have the car sit exactly where you wanted it to be without any guesswork and/or coil cutting.

Hope you all have a great weekend....Robert

[vidguy]

Robert=
I apprecaite all of your research on this thread. All of the measurements have been very helpful. I emailed Coil Spring Specialties last week. He did reply and I'll now call him and tell him that I want what YOU bought!

BTW Is that measurement without the shocks installed too?

I ask because I had cut .5 inch in height off of my stock coil springs. Ended up being a full coil. I reinstalled them. When I put my motor and transmission back in the drop seemed to be imperceptible. Granted I dont have the radiator or hood on. Also I didnt put the shocks back on.

I think that the Monroe Sensa-trac 5801 shock with the 14.375 inch extended length would limit that travel/lower the gap somewhat when installed? I should check that first anyhow.

I was going to work on the car today and put some parts or weight back on it to see what happens.

[Z Code 400]

James,

My Koni shocks did not alter my ride height on my non A/C 1975 Formula. My custom springs are 500lbs/inch that you wouuld not need on a street car. Just for comparison, a stock Formula without A/C had a 294lbs/inch spring and a 1979 T/A with the WS6 pacakge and A/C had a 419lbs/inch spring.

Keep in mind that you need precise measurements from your car to get the front springs made correctly. This includes total vehice weight, front/rear axle weights, unsprung weights, fender to floor measurements, installed spring length at desired ride height and front suspension leverage ratio.

If you arrive at the desired front end height (distance from floor to fender lip) and you provide CSS with your stock spring wire diameter, number of coils and free-length dimensions, they can provide a custom spring for youbased on all the information they have in their database.

Hope this helps...Robert

[Z Code 400]

Originally Posted by vidguy

Robert I ask because I had cut .5 inch in height off of my stock coil springs. Ended up being a full coil. I reinstalled them..."

Cutting free length from the spring does not affect the ride height on an 'inch-for-inch basis. It does alterthe spring's rate, which does influence the installed height, but it is not a predictable change in every case. This was the first fact that Coil Spring Specialties explained to me. You can cut a full coil off a spring, and, depending on the rate and front axle weight, not alter the front ride height hardly at all, or, slam the crossmember into the ground.

The lower control arm on a second generation F-body has a leverage ration of 1.80:1. When you change the spring's installed height by a given amount, it will change the measurement at the wheel by an amount based on that computation. Most people will use 2.00:1 as the leverage ratio, which is close, but if you are having a spring designed, you must have exact calculations.

Hope this helps...Robert

[vidguy]

Right, I had read that. I expected a 1.5 - 2.0 drop based on cutting 3/4 inch off the free OAL.

So much for that.
Coil Spring Specialties sounds like they have it together.
I'll call him and give the data. He had quoted me About 150.00 a pair based on my preliminary data.
I'll measure it up and get that to them.
Thanks

[Z Code 400]

Kevin is great to work with. His extension is 113...Robert

[Z Code 400]

Vidguy,

I have my 294lbs/inch factory springs that have had 1 coil trimmed off and the lower coil re-shaped to fit in the lower control arm pocket. You can have them if you can use them....Robert

[Z Code 400]

Vidguy,

Did you get your springs yet??????

[vidguy]

Robert. THanks for the offer on those springs. I may take them for the heck of it...
What I really want now is to get the rear springs in line with the expected lower front..

I am going to buy the solid bushings from PTFbody too. I had replaced my originals with polys a few months ago but I think I'll go solid and use the lower position.

I have my specs in with Kevin At Coil Springs Specialties. Due to the holiday He expects a engineering design today or tomarrow.
I'll hear back soon i expect.

[Z Code 400]

I have the PTFB solid body bushings and sway bar brace. They are nicely made parts.

You cannot beat CSS for custom wound springs. PTFB offers a nice set of lowering springs, but if you want to retain the big tires and 4.00" offset that I am running, they drop the car too much. Once you have all your values and measurements, having a spring made to your specs is easy.

Mine fit perfectly and my ride height is exactly where my calculations said they would be....Robert

[Z Code 400]

Get your springs yet?????

[vidguy]

Not yet.
400 Lb 1.750 drop.
My Originals measured .700 thick 17 inches free height.

I told him I wasn't in a hurry. I expect them Next Week.