Mustand II front coil springs

[Bob Paulin]

While we're on the subject, I think I'm going to have to change the springs on the Mustang II front end under the Rambler wagon.  The ride height is real good but the ride is too firm.  My question is, can I tell what the current spring rate is by the number of coils, wire diameter, and length? ....or are there other factors that determine spring rate too?  

I need to find out where I'm at before I can pick a set of springs that will improve the ride but not change the ride height.

The absolute easiest way to determine a spring's rate is to find an oval-track racer with a spring rater....many teams have them, since they are always changing springs, and very few springs are *exactly* what they are supposed to be.

If you were a few blocks closer to me, I'd say bring them over here.

Now......

The basic equation for spring rate is a function of the outside diameter of the coil (D), the wire diameter (d), the number of active coils (n), and the constant/modulus for spring steel (1,500,000).

The spring rate is calculated using the following formula:

1,500,000 X d(4)
---------------- = Spring rate
n X D(3)

That's "d" to the fourth power and "D" to the third power.

I can't get my browser program to do the superscripts I can do in MS Word.

Active coils means those coils that move and are not touching when the spring is installed with the car's weight sitting on them. Coils that are touching are not active....they're dead from the point of contact.

And....this equation is valid for both new and used springs - which should put to bed those myths about spring steel losing its rate.

Springs can lose height, but spring steel does not lose its rate.

The "loaded" or "ride height" seen in the catalog refers to the height of the spring as installed in the assigned application. Put it in a different car with a different weight, and you will get a different loaded height.

An 800 pound spring may result in a nine-inch ride height in a Mustang II while it might take a 1000 pound-or-more spring to come up with the same ride height in a Caddy.

In the case of your Rambler....in order to soften the spring and maintain the same ride height, you'll need smaller wire diameter but a slightly longer free height.

You can figure out what sort of load is on the current spring by determining what its rate is and how far it is compressed under load.

Then, you can figure another spring's rate and how far it will compress under the same load.

When you find a new, softer, longer spring that will compress to the same ride height as the current spring under the known load, that should do the trick for you.

IOW - if you have an 800 pound spring rate that compresses two inches, it has 1600 pounds of load. A 400 pound spring would compress four inches under the same load, so would have to be approximately two inches longer in free height in order to end up at the same ride height.

If you're fortunate enough to hook up with a racer who has a rater, he can, most likely, load your current spring to its ride height, then load potential replacement springs to the same ride height to see if they match under the same load conditions.

B.P.

[GPster]

I think that all the questions and answers about Mustang II front ends should be taken from our archives and put in a special spot so all of this information can be reached without having to ask these questions again. I think that this section should be opened by Bob Paulin's excellent explanation of coil spring theory. Maybe we should also find a place in the BBQ trailer for one of those spring raters (this asside is only a try at humor and not meant to detract from the sinceraty of the first statement). That way we could supply an additional service to or members. Shut up now, GPster

[PeterR]

And....this equation is valid for both new and used springs - which should put to bed those myths about spring steel losing its rate.

Springs can lose height, but spring steel does not lose its rate.

Bob, I suspect no matter how hard we try to get this message across it just falls on deaf ears.

Steel makers would dearly like to be able to tailor the value of the elasticity of steel to suit particular applications but the fact is that while the strength varies considerably for different types of steel, the elastic rate is virtually the same across all steel whether it be the steel plate on an aircraft carrier deck or the spring in a ball point pen.

The only way the spring can lose rate is by losing section either by rusting or developing cracks, and even then the properties of the steel have not changed.

If a person believes a spring has "gone soft" they should compare the free length with a new spring of the the same part number, and you can bet the old spring will be shorter.

[Bob Paulin]

And....this equation is valid for both new and used springs - which should put to bed those myths about spring steel losing its rate.

Springs can lose height, but spring steel does not lose its rate.

Bob, I suspect no matter how hard we try to get this message across it just falls on deaf ears.

Steel makers would dearly like to be able to tailor the value of the elasticity of steel to suit particular applications but the fact is that while the strength varies considerably for different types of steel, the elastic rate is virtually the same across all steel whether it be the steel plate on an aircraft carrier deck or the spring in a ball point pen.

The only way the spring can lose rate is by losing section either by rusting or developing cracks, and even then the properties of the steel have not changed.

If a person believes a spring has "gone soft" they should compare the free length with a new spring of the the same part number, and you can bet the old spring will be shorter.

Peter:

The analogy I use - and often demonstrate at my shop bench - is the steel paper clip.....

If you straighten out a steel paper clip, hold one end at the edge of the table, and push downward slightly on the other end, the clip will spring back to it's original position.

If you push too far, you distort the clip, and it does not return to the original position....but, the spring rate of the steel remains the same.

In its bent condition, it will still have the same "spring" as in its original straight condition.

Coil springs that are continuously bound up - or have the coils twisted too tightly when compressed - will eventually do the same thing - resulting in a loss of ride height, but not spring rate.

Of course, the loss of ride height will often result in the spring coils binding or the spring "bottoming out" since the coils are now running closer to each other.

Another thing that I often run into - which probably serves to perpetuate the myth - is the oval track racer who puts a coil spring on the rater after running it for a year, finding that a supposed 350 lb/in spring actually rates in at 325 lb/in on his rater.

He assumes that the spring "lost" 25 pounds of rate, when in fact, if he had rated the spring new from the box, it would have rated in at 325 lb/in on that particular spring rater.

I always get that blank stare when a racer complains about his 350/325 spring, and I ask him what it rated at fresh from the box.


B.P.

[enjenjo]

And....this equation is valid for both new and used springs - which should put to bed those myths about spring steel losing its rate.

Springs can lose height, but spring steel does not lose its rate.

Bob, I suspect no matter how hard we try to get this message across it just falls on deaf ears.

Steel makers would dearly like to be able to tailor the value of the elasticity of steel to suit particular applications but the fact is that while the strength varies considerably for different types of steel, the elastic rate is virtually the same across all steel whether it be the steel plate on an aircraft carrier deck or the spring in a ball point pen.

The only way the spring can lose rate is by losing section either by rusting or developing cracks, and even then the properties of the steel have not changed.

If a person believes a spring has "gone soft" they should compare the free length with a new spring of the the same part number, and you can bet the old spring will be shorter.

I agree, despite what I typed the other day. I did not explain it properly. The spring rate doesn't change as the spring ages, but other factors play into  failure of the spring to do what is required of it.

If it's overloaded to the point that it exceeds the ability of the spring to return to the unloaded condition when the load is removed, it has permanently changed. When the wire rusts in use, reducing the diameter, the spring is permanently changed. I have noticed when you sand blast, or bead blast a spring, it changes, I suspect that it either heats the spring enough to change the heat treat, or more likely it stress relieves it like peening that changes the spring.

I have checked spring rates with a makeshift rater. I  measure the spring's free height, and then mount a lever at about the same height on top the spring. The lever is 2 to 1. I then add a known weight (usually Fatcat) , and see how much it compresses the spring. After doing the math, it usually comes out pretty close, within 10 lbs or so. The reason for the 2 to 1 ratio, it reduces the error.

[Bob Paulin]

Maybe we should also find a place in the BBQ trailer for one of those spring raters (this asside is only a try at humor and not meant to detract from the sinceraty of the first statement). That way we could supply an additional service to or members. Shut up now, GPster

You can buy a brand-new DECO spring rater from Speedway Motors for $250.

You can often find good, used raters at racer flea markets for less than $150.

If you're really clever, you can probably build your own with a bottle jack for $50.

And, there are some people using one of their four wheel scale pads and a hydraulic press to rate their own springs in the shop. Care MUST be taken to contain the spring and to keep it from sliding out under load.

Most shops of which I am aware, charge $5 to rate a spring.

B.P.

[purplepickup]

The absolute easiest way to determine a spring's rate is to find an oval-track racer with a spring rater....

Now......

The basic equation for spring rate is a function of the outside diameter of the coil (D), the wire diameter (d), the number of active coils (n), and the constant/modulus for spring steel (1,500,000).

The spring rate is calculated using the following formula:

1,500,000 X d(4)
---------------- = Spring rate
n X D(3)

In the case of your Rambler....in order to soften the spring and maintain the same ride height, you'll need smaller wire diameter but a slightly longer free height.

You can figure out what sort of load is on the current spring by determining what its rate is and how far it is compressed under load.

Then, you can figure another spring's rate and how far it will compress under the same load.

When you find a new, softer, longer spring that will compress to the same ride height as the current spring under the known load, that should do the trick for you.


B.P.

Thanks for the really detailed info Bob.  Be glad you don't live close by.  I'm sure I'd be over more often than you'd like, trying to absorb some of your knowledge....and using your spring rater     I know a couple of racers around here and they should be able to point me to someone that can rate the springs.  Also, we have an old two man shop that makes leaf springs and works on truck, bus, and car suspensions.  The guys know a lot and might be able to help me too.  

I'm saving this whole thread since I haven't started working on the Rambler yet but the front suspension is an area that I know needs attention.  It will be after the holidays before I can dive into it.

....and Rick, thanks for letting me jump on your post.  Hopefully we all are learning some good stuff here.

George

[GPster]

Putting all of Bob's advise together it might be advantageous to get the car to the height you want and measure the length of the springs in their compressed state. Maybe there is some way to figure backwards and come up with a closer idea of what you want. GPster

[Topsterguy]

I put a mustang front end in my 55 F-100 and they said to use the lighter 4 or 6 cyl springs - something to do with the engine place ment. I put them in and the truck went right to the floor!  I put the V-8 ones in and it was perfect!

[moondisc]

"Moondisc, Id like to buy those springs from you. For $30, even if they dont work, I cannot go wrong."

I emailed you Dirk but got no answer.
If you want em send me your addy, and I'll get shipping costs for you.
Charlie

[rick 36dodge]

I went down to my local Race car shop (H&H Racing) here in Columbus, Ga and asked him if he could fab me up some 1" spring spacers. He said that would be no problem. I think that Racers and Rodders are the most positive people on earth.  My Dad started drag racing when I was 8 and the next 10 years my life was the greatest (He was not rich so like many of us 18 year olds in 1968 I had to go into service, and I joined the Air Force and got out in 1972). I met some of the best people. All of them have the can do attitude.  I got my 36 Dodge when I was 16 and drove it to high school everyday. I was the only guy that had a Street Rod and I built it myself. I think the Checkbook Rods are nice , but those guys miss out on 90% of our hobby and that is building it your self. My 36 Dodge will never be in any Magizine, because it is not perfect, but I build it and that is all that matters to me.
I want to say a big THANK YOU to all of you that helped me with project. I know there will be more questions.

Rick Harris
1936 Dodge Coupe
Columbus, GA

[Bob Paulin]

I went down to my local Race car shop (H&H Racing) here in Columbus, Ga and asked him if he could fab me up some 1" spring spacers. He said that would be no problem. I think that Racers and Rodders are the most positive people on earth........  

An engineer can explain in great detail why something cannot be done......

A Racer or Rodder will show you how to do it.............


B.P.