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Do Coil Springs Go Soft?

Old 11-16-2018, 02:18 PM
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Do Coil Springs Go Soft?

I put new KYBís on my 89 IROC Vert and itís ride height seems perfect or near stock but the car seems floaty. Too floaty from what I remember. In fact on certain types of dips it bottoms out in the rear.

Wondering if a fresh set of coils front and back would transform the car or just be wasted.

If if so, any recommendations?
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Old 11-16-2018, 02:28 PM
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Re: Do Coil Springs Go Soft?

Yes. I got acces to a friends wrecked 16k mi Z28. I got the springs and rear off it and put on my car. There was almost an inch difference in spring height between the 16k mi car and mine had maybe 89k mi at the time. I did new shocks and sway bar bushings and such at the same time and it made a lot of difference and the car is much more quiet. How many miles are on your car?
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Old 11-16-2018, 06:52 PM
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Re: Do Coil Springs Go Soft?

Coil springs don't really change spring rate over time but they do "take a set", meaning the compressed height can change over time. If the car got more floaty then that is due to shocks, not springs.

There were a whole lot of different front springs offered in our cars with different free height and spring rates. It is of no surprise that you take springs from a random Z28 and end up with a different ride height in a Trans Am.

https://www.thirdgen.org/forums/susp...ring-info.html
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Old 11-16-2018, 08:24 PM
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Re: Do Coil Springs Go Soft?

Qwktrip how many miles on these cars usually wears out a set of springs? I've always changed them out at 100k or so and have usually has around an inch difference on other cars of mine in the past. Struts i don't seem to get as many miles out of.
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Old 11-17-2018, 12:02 AM
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Re: Do Coil Springs Go Soft?

In the case of steel spring, the spring will never fail as long as the stress in the spring is low enough (it is a property called the endurance limit). Suspension coil springs are expected to last for millions of load cycles, and the only way to last that long is to be below the endurance limit. And once below the endurance limit the spring never fails. Over loading springs (higher stress), or compressing too far (buckling) can cause damage. And the real world has things like corrosion that cause problems too.

The sag you're seeing is due to spring set. The spring rate didn't change but the compressed height did. I can't remember why this occurs. I haven't used or looked at this kind of stuff for 25 years.
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Old 11-17-2018, 12:11 AM
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Re: Do Coil Springs Go Soft?

For what it's worth, things change when using small diameter wire, such as valve springs, and it becomes a more complicated topic.
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Old 11-17-2018, 01:09 AM
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Re: Do Coil Springs Go Soft?

Whoa. That thread starter was my 1,000th post!

Good info here. I am going to look into this further. I suspect I have the original springs in there.
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Old 11-17-2018, 02:31 AM
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Re: Do Coil Springs Go Soft?

Originally Posted by QwkTrip View Post
The sag you're seeing is due to spring set.
The proper term just came to my mind. It's called spring creep. Now that I remember the proper term I might be able to find something about it in my old textbooks.
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Old 11-18-2018, 10:30 AM
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Re: Do Coil Springs Go Soft?

Short answer:

YES

Change em out. You won't believe the difference. They're CHEEEEEEEEP and EEEEEEEEZY. Just do it. You've already wasted more time posting on the Interwebz than it takes to do the job.

Replace the rear shocks at the same time since it only takes acoupla minutes more.
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Old 11-18-2018, 03:34 PM
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Re: Do Coil Springs Go Soft?

You can buy springs from Eibach direct. Believe you want a 5.5" OD and for a slightly lower height than stock I think they have an 11" or 12". You can get rate between 800-1050 depending on how much harshness you'll tolerate. They are $60 a piece or so.
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Old 11-18-2018, 07:18 PM
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Re: Do Coil Springs Go Soft?

All springs wear out over time from cycling.
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Old 11-19-2018, 12:09 PM
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Re: Do Coil Springs Go Soft?

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Old 11-19-2018, 06:28 PM
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Re: Do Coil Springs Go Soft?

I was speaking of just the fronts. You click on the race spring menu and choose the correct options.
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Old 11-20-2018, 02:47 AM
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Re: Do Coil Springs Go Soft?

I think I just want stock suspension performance again. Those racing springs might be too stiff?

IIRC, Eibach sets back in the day were known for their ride quality and handling. Though it would lower my car about an inch, I would really like stock ride height. Maybe Moog OEMs?
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Old 11-20-2018, 08:50 AM
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Re: Do Coil Springs Go Soft?

yes. moog. try rock auto. you may also be able to get them thru Advance, AZ or one of the others that always run some kind of online discount.
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Old 11-20-2018, 01:41 PM
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Re: Do Coil Springs Go Soft?

So it appears the Moog CC635 (rear) and 5642 or 5664 (front) for my 89 IROC auto Vert

Specs are here:






https://www.motor-talk.de/forum/akti...hmentId=740605

Last edited by Tootie Pang; 11-20-2018 at 01:44 PM.
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Old 11-20-2018, 03:22 PM
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Re: Do Coil Springs Go Soft?

Originally Posted by Tootie Pang View Post
I think I just want stock suspension performance again. Those racing springs might be too stiff?

IIRC, Eibach sets back in the day were known for their ride quality and handling. Though it would lower my car about an inch, I would really like stock ride height. Maybe Moog OEMs?
You can get them in whatever height and poundage you want. This eliminates the idea of buying a factory spring and taking a cutoff wheel to it. You can buy the tears this way also but I think it's blue coil or a like spring company, you need a pigtails spring. Buying race springs isn't much more than the three parameters. Also allows you to run different poundage on one side. In my case my battery, subwoofer and I all sit on the drivers side...
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Old 11-21-2018, 08:23 PM
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Re: Do Coil Springs Go Soft?

Surprisingly all these years, the rear springs on my 82 Trans Am are about right. I did put new shocks on it around 2008. My 89 Firebird was sagging in the rear when I bought it with 161k. New factory style springs and new shocks jacked it right up and made it ride a whole lot better. The 90 Formula I just bought is also sagging in the rear with only 69k miles on it, so it too will be getting new rear springs and shocks. You can feel the sag in this one as you drive it, as it has this "low slung" feel. I can feel the back of the car lower.

Miraculously for whatever reason, the rear springs on my 82 are well built and still standing tall and that car has 181k on it now. The 82 sits just about 1/8" higher than my 89 in the rear. The 82 also rides better than both my other cars and better than any thirdgen I've ever owned or rode in ever. I can go over the same set of tracks with either car and both the 89 and the 90 are a little jarring and both creak in the ttops and doors. The 82 does not do this at all. It takes tracks like a full frame car with body bushings and it's always rode this way with no creaks anywhere. It's baffling really. It's a Norwood car and the other two are Van Nuys.
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Old 11-21-2018, 10:11 PM
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Re: Do Coil Springs Go Soft?

Some people pay big money to lower their cars and you got it for free. Maybe sell your 2" lowering springs for $75.
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Old 11-21-2018, 10:32 PM
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Re: Do Coil Springs Go Soft?

Originally Posted by QwkTrip View Post
The proper term just came to my mind. It's called spring creep. Now that I remember the proper term I might be able to find something about it in my old textbooks.
I couldn't find information about creep in my mechanical engineering design book. My guess is it is in the mechanics of materials book but it is not popping off the page in the index. I'm too lazy to keep looking. Maybe a younger engineer with higher energy level will speak up.

Basically creep is yielding of material due to a constant load being applied. Your springs keep dropping height because there is a load on it. Doesn't matter if you drive or not. You can slow down the process by storing the car on jack stands in the off-season.

Spring "presetting" is a manufacturing process to induce useful residual stresses. It is not used when springs are subject to fatigue, such as suspension springs. So forget I ever said that word earlier.

Whew! That's the most use I've gotten from that book in over 25 years!

Last edited by QwkTrip; 11-22-2018 at 01:34 AM.
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Old 11-22-2018, 08:56 PM
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Re: Do Coil Springs Go Soft?

Springs do not creep from constant load without heat. The cycling is what wears out a spring in this situation

I found this quickly; "
  1. Decide whether creep is seriously a consideration for you. Most springs operate no where near the UTS of the material they are made from and if you are orders smaller then I'd question whether creep is something you need to worry about at all. Your car sits on its springs for decades and doesn't lose appreciable ride height. Even if you do get some change, does it influence on your design at all if your spring grows fractionally shorter over the space of a decade?"
Another;
"The spring steel is designed to have a large elastic extension before it platically deforms. Plastic deformation involves dislocation(1) creation and motion. In the long term, spring steel will tend to coarsen its grain structure, and flow slightly, and will over time plastically deform.

That is also why it is very difficult to make a high temperature spring--most spring steels I know of stop working at about 400 C, at best. Too much diffusion allows creep.

The second property required for spring steels is to find their fatigue limit. Over time, multiple cycles of loading/unloading of a spring will cause crack propagation, and eventual failure. As it turns out, roughening the surface of a spring drastically enhances lifetime--likely because cracks propagate in from the outer surface, and shot-peened steel has a compressed (crack healing) outer surface.

A common spring steel is .5% C, 1% Cr, .15% V, balance Fe. Usually cold drawn (elongated grains, small grained). Tensile strength is on the order of 1.7e5(d)^(1/6).

So to answer the question completely--long term compression will not affect the spring badly, though eventually, the system will reconfigure itself. That is very long term becahior. The loading-unloading cycle will fatigue the steel over time, and it is worse if (as ina car) it isn't a load/reverse load cycle."

Last edited by scooter; 11-22-2018 at 09:11 PM.
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Old 11-23-2018, 12:46 PM
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Re: Do Coil Springs Go Soft?

This is turning into a good old-fashioned tech thread

Yeah, you're right, heating it up will definitely cause creep to happen. But I think that is for a little different reason at fairly elevated temperatures. Creep happens at room temp too but at a much slower rate and magnitude.

I'm not very educated on this matter and pretty much at the end of my knowledge. It is entirely possible that load cycling causes the springs to wear out if the load is high enough. You're probably right, Scooter, that the real world pushes the springs that hard. And in that case it might be possible that higher spring rates last longer.

Another thing to consider is the front springs are curved when installed in the car and that can't be healthy for it!

It would be fantastic if someone with deep expertise could weigh in. But they are hard to find!

Last edited by QwkTrip; 11-23-2018 at 01:59 PM.
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Old 11-25-2018, 07:23 PM
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Re: Do Coil Springs Go Soft?

The thing that seems to "wear out" stock springs, besides their overall ... value engineering ... ,, is, repeated flexing.

The talk about heat is very appropriate: heating metal up destroys the heat treating that makes it into good spring material. But that's hardly ever an issue with suspension springs. Valve springs, sometimes; sometimes even ones in transmissions and such; but not ones holding up car weight.

Think about what happens if you bend a coat hanger about a million times. Sooner or later, it goes soft. Even if you don't bend it a whole lot at any one time; the repeated, over and over again kind of stress, eventually takes its toll in the metal. Acoupla hundred thousand, coupla million, maybe a billion back-and-forth bends; just keep on bending. The springs in your car suffer the same fate.

And to that point, dysfunctional shock absorbers are the biggest contributors. They allow the suspension to flop ruthlessly up and down, stressing out the springs. Repeated bending. Repeated over and over several more times redundantly and overflowingly too many times to count. Pay attention to the Xler minivans driving down the road sometime... the ones whose rear tires look like they're a basketball dribbling, are also the ones that sag. Same deal with our cars.

All I can say is, all you have to do to experience first-hand whether suspension springs "wear out", is change a set. ONCE. That's all it will take. I'm telling you, it will literally KNOCK YOUR D*** IN THE DIRT how much difference it makes. Just try it and see. One time. You will NEVER AGAIN believe the people that say they don't wear out.

Last edited by sofakingdom; 11-25-2018 at 07:42 PM.
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Old 11-29-2018, 01:44 PM
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Re: Do Coil Springs Go Soft?

I also have a 63 Impala and spend a lot of time on the early 60's impala boards. A lot of people on those boards complain when they get the new 2" drop springs for their car and it actually lifts the car up higher than the 50+ year old worn out springs their car came with.
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