Need some tech advice on front springs

[rzola]

I re-built my front suspension on my 1970 240Z. I used a set of front springs that were on my 1971 240Z. I blasted and painted them. When I installed them, the front ride height was much higher! Also the camber is way off. Top of tire leaned out (popsitive camber I belive). Before installing the springs, I compared the heights. The old vs. new were within 1/4 of a inch. After scratching my head, I belive these front springs may be too stiff and holding the front of the car too high? I just measured the coil diameter. The old spings are about 0.425" wire diameter. The "too high" springs are about 0.455-0.460" diameter. I am going to install the old springs tomorrow. Heres a question....

My 1971 service manual says the left spring is 373mm or 14.7" tall. The right side spring should be 386mm or 15.2" tall in free state. Should the shorter spring go on the left side of a US left drive car? I relize more weight is on the left side of vewhicle. Wouldn't ou want the taller (and maybe stiffer) spring on the drivers side? Why did Nissan have different height springs on the front of these cars. Any help from you Z suspension gurus would be appreciated. Thanks!

[zguitar71]

I would put the taller one on the drivers side. My 240's driver's front corner is the heaviest corner of the car (40LBS heavier than the passengers front corner). In theory the longer spring should be weaker (assuming the two springs have the same inside/outside diameter and wire diameter and the longer spring has more coil thus making it longer) but with the slight difference in lengths I do not think the longer one will be that much weaker and the extra length will give the proper ride height. When I had my car corner weighted (no driver) the LF was 628, RF 589, RR 588 and the LR was 510 totaling 2315. So the car is weighted so the driver increases the weight over the LR. I was not able to get in and record the weights on the corners, it was weighed at a race (to make sure I was not under weight for my class) and there was not time to let me experiment.

[Zeke72]

Springs are generally linear when force is considered. In other words, for every inch of compression you multiply it times the spring compression factor to determine the force exerted. If both springs have the same compression factor the taller spring would be exerting more force if the spring holders are the same distance apart. Logic would state the taller spring would be on the driver's side to accomodate the added weight when driving alone. If the springs have different compression factors it becomes more involved.

I would be interested in what an automotive design engineer would have to say on this subject. In the mean time, put the original springs back in. The 71 springs probably have much higher compression factors and your alignment and tire wear will suffer.

[Carl Beck]

rzola wrote:

>I re-built my front suspension on my 1970 240Z. I used a set of

>front springs that were on my 1971 240Z. I blasted and painted them.

Before you blasted and painted them - did you notice they were marked with red and blue paint dabs? That was done at the factory so they could tell which spring was which. If you didn't notice the paint dabs... is would be easy to get them mixed up when reinstalling them.

>When I installed them, the front ride height was much higher! Also

>the camber is way off. Top of tire leaned out (popsitive camber I

>belive).

That will happen any time you unload the suspension, then set the car back down. Did you drive the car around for a while after you put it back together - to let the suspension settle out?

Did you let the car down on the suspension "BEFORE" you set the torque on the control arm bushings & tension/compression rod bushings? If you torqued the control arm bushing and TC bushings with the car in the air - you pre-loaded them and that alone can hold the car up higher.

>Before installing the springs, I compared the heights. The

>old vs. new were within 1/4 of a inch.

Actually - you compared the "old" vs the "older". After 34 or 35 years, depending on a lifetime of use/load etc...the springs will hold different percentages of their original spec.'s...{one reason to note the marking from the factory and remark them the same after cleaning/painting}. Measuring the free length of old springs can be very misleading... you can only use the free length measurements of new springs to tell them apart.

>After scratching my head, I

>belive these front springs may be too stiff and holding the front of

>the car too high?

If both sets of springs were OEM on the 70 and 71 they are the same. However if you didn't notice and take note of the paint dabs.. you actually have no way of knowing what some previous owner did... They may have mixed a front and rear spring.. 83 in/lb vs 103.6 in/lb and they are both close to 15 inch when new. (15 vs 15.2). The OEM rear's are marked with white paint dab.

>I just measured the coil diameter. The old spings

>are about 0.425" wire diameter. The "too high" springs are about

>0.455-0.460" diameter. I am going to install the old springs

>tomorrow. Heres a question....

You said you measured the "coil diameter".... In the Factory Service Manual, that term defines the distance from the center of the wire on one side of the coil spring to the center of the wire on the opposite side. {100mm or 3.94 inch} The Factory Service Manual also give the "wire diameter" as 0.417. So 3.94+ 0.417=4.357 inch outside diameter of the coil spring and 3.94 - 0.417=3.52 inch inside diameter. 4.357-3.52= 0.837 / 2 = 0.4185 {vs. 0.4170 just rounding errors}

If you used a metric ruler to measure the outside and inside diameter of the coil spring.. it's easy to be off a few hundredths of an inch. If you used a Micrometer to measure the wire diameter..it's easy to be off from the factory spec.'s because the wire is curved not flat.. Again it's easy to get readings that are a few hundredths of an inch, or several thousandths off from the stated factory spec,'s..

>My 1971 service manual says the left spring is 373mm or 14.7" tall.

>The right side spring should be 386mm or 15.2" tall in free state.

>Should the shorter spring go on the left side of a US left drive

>car?

Yes.

>I relize more weight is on the left side of vewhicle.

Interesting - I always realized that the battery was on the right side, and that the engine leans to the right.

>Wouldn't you want the taller (and maybe stiffer) spring on the drivers side?

No - I'd want it where the factory put it. On the heaver loading on the Right Side.

>Why did Nissan have different height springs on the front of these

>cars.

Depends on how you say that. They have different "Free Length" but the same "Installed Height".

The spring constant is given as 83 in/lb. 42 lbs. additional weight on the Right Side and the Free Length is .5 inches longer. 83 / 2 = 41.5 lbs. So the additional 42 lbs on the Right Side, brings the "Installed Height" of the Right and Left springs out level...

>Any help from you Z suspension gurus would be appreciated.

I'm certainly not a suspension guru.. but I have been looking at the spec.'s for OEM springs recently...

I don't know if we can be of much help to you at this point - I think there are a lot of unknowns here.

For anyone following the thread..

1. note the marking on the springs and see if they match the factory markings. This at least gives you some indication that the springs are OEM or not.

2. keep in mind that after 35 years the factory springs won't be at their full factory spec.'s - even spring steel weakens over time.

3. put the weight of the car on the suspension - BEFORE - you torque things down

FWIW,

Carl B.

Carl Beck

Clearwater, FL USA

http://ZHome.com

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[zguitar71]

rzola wrote:

>I relize more weight is on the left side of vewhicle.

Interesting - I always realized that the battery was on the right side, and that the engine leans to the right.

>Wouldn't you want the taller (and maybe stiffer) spring on the drivers side?

No - I'd want it where the factory put it. On the heaver loading on the Right Side.

>Why did Nissan have different height springs on the front of these

>cars.

Depends on how you say that. They have different "Free Length" but the same "Installed Height".

The spring constant is given as 83 in/lb. 42 lbs. additional weight on the Right Side and the Free Length is .5 inches longer. 83 / 2 = 41.5 lbs. So the additional 42 lbs on the Right Side, brings the "Installed Height" of the Right and Left springs out level...

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When I corner weighed my car the heaviest corner was the LF (drivers side) corner. I thought it would be the RF too, but the LF ws 40 LBS more than the RF and the heavies of all the 4 corners. One person at the scales speculated that the weight on the LF was due to the extra equipment on that side like the entire carb set up and the headers, distributer ect... When I looked at it that way it made sence to me, most of the equipment on the motor sits on that side and right over the wheel too.

"the LF was 628, RF 589, RR 588 and the LR was 510 totaling 2315. So the car is weighted so the driver increases the weight over the LR."

I said this in my post earlier, I think this is the reason for the corners to be weighted as they are. What do you guys think?