determining leaf spring height
#1769393
03/02/15 07:00 PM
03/02/15 07:00 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
OP
master
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OP
master
Joined: Jul 2006
Posts: 4,179
California
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i have the mopar rear springs on my car, and they have sagged over time. i'm going to order eaton springs, but i want to figure out what i need to order to get the correct stance that i want.
if you look in my sig picture, that is the car with the stock mopar hemi springs, and 28" tall tires. the measurement from the ground to the wheel well is about 25". i think my front end sits a little lower than normal, which helps the stance.
right now, again with 28" tires, the measurement at the wheel well is 24". i jacked the rear end up to 25", and that is what i want. 26" was too much.
so the question is, will stock height springs, plus my 28" tires put the car back where it was, or do i need an extra inch of arch?
i'm assuming that since the stock mopar springs put the rear where i wanted it, that stock eaton springs will do the same, but want to make sure. that's an expensive mistake to make.
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Re: determining leaf spring height
[Re: mickm]
#1769394
03/02/15 08:00 PM
03/02/15 08:00 PM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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Since the springs ain't new & have sagged over time I'm thinking it'd gonna be hard to get a baseline anywhere to start from. What I'd do is remove the springs and set em on the ground (reversed) & measure the arch from the nub bolt down to the concrete the order ones with an additional inch of arch & maybe another inch if there is a possibility of them sinking a bit right off the bat when new (ask them). Downside would be the car would be up on stands for awhile unless you immed reinstalled em after measuring. If it ends up being a bit too tall with 2" then you could redrill the side to side holes in the front perches higher and possibly raising the rear shackle or shortening the 2 vertical bars. Nothing definite but here's a BTT for ya
live every 24 hour block of time like it's your last day on earth
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Re: determining leaf spring height
[Re: Mattax]
#1769400
03/03/15 01:54 PM
03/03/15 01:54 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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OP
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Joined: Jul 2006
Posts: 4,179
California
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Quote:
You need to know two and preferably three things besides the current height.
Spring rate of existing springs.
Free arch of existing springs.
Weight on the springs.
Then you can spec the free arch for a spring if know its rate and get close to the same ride height you are targeting.
so where do i get all that info from? weight i assume i can get an approximation by weighing the back end of the car? just the rear wheels on a scale?
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Re: determining leaf spring height
[Re: dtedler]
#1769402
03/03/15 04:11 PM
03/03/15 04:11 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
OP
master
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OP
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Joined: Jul 2006
Posts: 4,179
California
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Quote:
Here is what I did with my Challenger. I was in the very same situation that you are. What is the "Stock" ride height at a given point? No answers. Since I was replacing everything from the hangers to the pivot brackets in front I decided to go with the +1 springs (I know they sag over time) and AR Engineerings (purchase from Mancini) spring pivot brackets that allow you to adjust the ride height. If I didn't like where it was setting - I figured that I could adjust it down if I needed to. I ended up with a perfect ride height with the +1 and the stock location on the pivot brackets. Best of luck to you!
thanks for the input, i may end up doing something like that. you are the second person to say they got the +1
as i stated earlier, i just have to assume that mopar springs and a 28" tall tire gave my car the stance i like.
if i get new eaton springs that are stock specs, that SHOULD give me the same height. but the only way i will know is to try.
i know there is no science to this, but wanted to get people's experience with this.
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Re: determining leaf spring height
[Re: mickm]
#1769403
03/04/15 01:15 PM
03/04/15 01:15 PM
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Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax
top fuel
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top fuel
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
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Yes. Rear wheels on the scale will be close. Obviously the springs don't carry the weight of the wheels and axle, so if you want to go the extra step, you can subtract them. Existing spring rate. Load spring with known weight and measure the deflection. wt/distance = rate This is close enough for your purpose, especially for determining static ride height. An arched multi-leaf pack will have some on-linear characteristics, but not important here. You need something that weighs at least 100 lbs! Be careful when you step off the arch, some friends of mine have been tossed as the weight shifts and the spring springs back.   The only ride heights I've seen in an FSM is the front end setting for the LCA. Like TC I've seen an old factory paper somewhere on the 'net, maybe the Hamtramck website, listing body heights. Considering what you're doing with the rear wheels, not sure this would be useful in anyway. One potential issue with the rear chassis higher, be it be wheel diameter or other methods, is getting positive caster. Factory caster specs were pretty conservative, like +1 degree, so you'll probaby be OK. Just a heads up on that, and also watch the pinion angle. Stengle Bros springs carries Stanley - another US made spring to consider. Stanley just don't have many retailers with on-line info (other than Stengle Bros). Arch and length dimensions are all there. In addition to the factors Supercuda mentioned, leaf thickness along with the shape and placement of the front end of the leaves also plays a role in durability. Engineers are taught to design springs for 1 million cycles. So if properly designed and made, they should not noticibley lose shape under normal loads and deflections until they've been through 1000s of cycles. Of course the aftermarket doesn't always make things that way. Also, with a multi-leaf, there is hysterisis between the leaves and in the bushings - a car sitting higher initially can be in part due to this as well. Quote:
Quote:
You need to know two and preferably three things besides the current height.
Spring rate of existing springs.
Free arch of existing springs.
Weight on the springs.
Then you can spec the free arch for a spring if know its rate and get close to the same ride height you are targeting.
so where do i get all that info from? weight i assume i can get an approximation by weighing the back end of the car? just the rear wheels on a scale?
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Re: determining leaf spring height
[Re: 5spdcuda]
#1769406
03/05/15 04:23 PM
03/05/15 04:23 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
OP
master
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OP
master
Joined: Jul 2006
Posts: 4,179
California
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Quote:
Overall I think you've gotten some good advice. In order to keep it simple I suggest that if you were happy with the way the car sat when the springs were new, just measure your existing springs and order new ones with 1.5-2 inches more arch. Since the modulus of elasticity of spring steel is all pretty much the same, if you order springs that have same number of leaves and are the same length,thickness and width as the originals the spring rate will be the same. The extra arch will restore the ride height. It may take six months or so depending on how much you drive the car for it to settle to the level you're happy with. It's a safe bet that it will settle some so you want enough extra arch to start with to allow for that. IMO it would be better to have it sit just a little high since you can always use a small lowering block if necessary, but if you don't get enough arch to start with you'll be right back where you are now and be out the price of the new springs.
ok, so how do i figure out that arch on the old spring? just lay it out on a flat surface and measure the distance from the surface to the first spring?
and yes, i agree, too high is probably better.
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