How do I spec a coil spring?

[1800guy]

I need some advice on finding a replacement front coil spring. I need to lower the front of the car about an inch to an inch and a half, but keep the same spring rate (or close - a little stiffer would be okay). Here are my current spring specs: 5" coil diameter, .600" wire diameter, 8.5" installed (loaded) height, 11.25" free height. Both ends are ground flat - I count 8 1/2 coils, but I'm not sure about the tapered ends having the same load value. Should I be counting coils right to the very end? Car weight is 1360 each end. Any thoughts would be appreciated.

[wayne petty]

there are A LOT of variables....

to lower the car to the distance you want..

what would be the installed height of the spring at that point...

i am taking this is a conventional A arm suspension..

because most A arm springs are mounted around half way between the inner bushings and the ball joint pivot..

you are probably only going to need to reduce the installed height by 3/8" to 1/2" perhaps even less..

at this point.. one might even want to examine the places the spring is seated into.. is it a flat seat... or a form fitting seat that the spring coils fit nicely into...

I AM NOT a SPRING expert.. you might want to talk to a coil spring manufacturer...


http://www.eatonsprings.com/onlineordering.htm


there are a LOT of neat spring accessories on links at the lower right of that page also..

please check suspension travel left at the reduced install height... perhaps a SLIGHTLY shorter side wall would get you down to where you want it..

even lowering spindles.. so the suspension maintains its proper amount of travel..

these are only thoughts..

[enjenjo]

Your best bet would be to contact a spring manufacturer like Eaton to find what you need. They will need weight at each end to help you. There are books with spring specs in them that give you wire diameter, and installed height, I'll see if I have one.

Here is a chart that may help. http://www.classiccarsprings.com/coil-spring-specifications.html But without weights for the original application, and your weight, it's pretty much a guess.

[Warpspeed]

What I would do would be to remove the existing springs and set the car on a jack at the required ride height, and measure the new loaded spring height.
This is obviously going to be less than 8.5 inches, but you need to know by exactly how much less.
This will be far more accurate than trying to measure a non linear motion ratio and trying to calculate the new spring length.

Take the original springs around to a spring specialist and he can test and measure the exact spring rate on his spring testing machine.

He will most likely suggest resetting and re heat treating the existing springs, or possibly winding up some completely new springs.

The reason for making totally new springs might be the possibility of coil bind, but that seems unlikely.

All the spring guy needs to do is reduce the free length by the required change, and the spring rate will remain exactly the same as original.

[1800guy]

That's the plan for tomorrow - and hopefully, the cure.

The local suggestion was to re-install the a/c and the automatic, but I'll pass on that.

[GPster]

One thing to remember is a coil spring is a straight torsion bar coiled up. If you loose one coil you are actually loosing the diameter of the coil (not diameter of the wire} times Pie (3.1416... ) in wire length. Also the entire front suspension is designed as a unit so any change will effect everything else. You are going to get some suggestions according to areas of specialization and I'm not specialized in anything. Have you thought about air bags? GPster

[Warpspeed]

No need to lose any coils, or change anything other than the free length.

Just a case of very carefully heating the spring in a controlled oven while under load, to reduce it's length, then giving it a full new from scratch, heat treatment.

If it ends up finally being one inch shorter, it will sit one inch lower in the car, under the same original compressive load.
That will be because the original spring rate has not changed, so it will compress exactly as far, under the exact same weight as it did originally.
But because it started out slightly shorter, it will end up being shorter at ride height by the same amount.

It is important to realize that a one inch shorter spring will lower the car by a lot more than one inch. That is why measuring the required new spring length very accurately is absolutely critical to success.

It's not rocket science, and the professional spring guy will have all the equipment plus the knowledge and experience to do it exactly right.
You just need to make very sure you know exactly what to ask for, and have a clear understanding of why this works.

While it is possible do this very successfully without knowing the spring rate, or the weight of the car, ask the spring guy to test and rate your springs. It will be very useful information to have if you decide to make further changes later on.

[1800guy]

Warpspeed: Thanks for that comment. That was my original thinking, but two local shops said that it couldn't be done that way. I was about ready to grab a wheel and cut off a half coil and see what happened - but I'll try a few more shops in hopes of finding somebody that will do it. This car is a temporary week-end toy while the other week-end toys get finished, therefore I'd like to not spend money on it. I have more stock springs around so I can gamble a pair or two before I bit the bullet and get new ones made.

Improvise, Adapt, Overcome.

[Warpspeed]

Resetting a coil spring can certainly be done, but it is tricky.
Very likely the spring shops did not want to get involved in it.

The problem is the spring needs to be preloaded and placed in an oven.
How much height it loses is not easy to estimate for someone not doing a lot of this type of work.
It may take several tries to get it right before final heat treatment.
The spring guys probably figured this was going to be a lot of time and messing about, with a certain risk of stuffing it up, and there would be not enough money in the job to make it worthwhile.

Cutting a bit off each end should do it, as the amount of length reduction is not going to be great.

An angle grinder would be my choice, but take your time and allow long cooling down periods between many light grinds. If the spring never gets too hot to touch with bare skin, it will have no effect on the original heat treatment.

[river1]

if you decide to cut the coils make sure you don't cut to much as you can't add it back

i would cut 1/4 coils at a time till you get where you want

grinder, or porta band saw will do the job. if you have both i'd go with the band saw

later jim

[Mikej]

If you cut it don't get in a rush to cut it again. Let it settle in. Drive it. Wait awhile. I rush and ended up cutting to much. I fixed it with coil overs.

[wayne petty]

i ran across this while searching for something else..


http://www.timskelton.com/lightning/race_prep/suspension/springs.htm

it looks like it might explain but i am yawning so hard i cannot see the screen very well..

[1800guy]

Well, first let me say I've learned a whole lot more about springs than I knew before. Thanks to everybody that had suggestions, but I finally took the cheap way out - or the cowards way, maybe. Twice I got ready to cut a coil off but was really unsure about closing the resulting open end. While repeatedly procrastinating I cleaned up some of the shop mess and came across a pair of springs that had the same number of coils and were the same basic free height, but with 1/8" less coil diameter and .020 less wire diameter. I installed them just to get an idea of how they would look and the car now sits level. I would have liked a little rake, but it's good enough for who it's for - me.

Now back to my real project.

[Mikej]

You may need to have the front end aligned now as the the camber will change with a height adjustment. Let the springs settle in for awhile first.

[1800guy]

Good idea - the car was out of my ownership for about ten years and ran short on love and maintainence.
Any suggestions for a good alignment shop in the Muskegon area - not a franchise?