Eibach psrings arrived, WAY SHORTER than stock?????

[Zs-ondabrain]

So I just opened the box from MSA and the Eibach pro Rate springs are WAY Shorter than stock.

The 260Z springs are 15.5 inches tall (all 4, unmounted)

The new Eibachs are.....

Fronts.. (189710) (6303.001) is only 10.75" tall ( 4.75" shorter than stock

Rears....(189712) (6303.002) is only 12.625" Tall ( 2-7/8" shorter than stock)

Is this correct? Are the fronts springs supposed to be almost 5" shorter than stock? And if they are, how does this only drop the car 1" to 1.5" ?????????

I'm don't want to install them until I hear from someone who has dealt with this before and can reassure that I'm not crazy.

Please help before I get overambitious and instal them just to see.

Dave.

Edited November 6, 2008 by Zs-ondabrain

[Oiluj]

I don't recall how much shorter the Eibachs I recently installed were, but they were significantly shorter than the stock springs.

I seem to recall that they were 2-3" shorter, but don't go by this info alone...

[Sailor Bob]

They are shorter for the 280s, not so much for the 240 - I wondered befor I installed them. For the front I don't think you will even need the compressors. I can assure you when I matched them with HPs they were very nice - lowered her about 1" from stock. The 240 version is a different bag of nails altogether.

Edited November 6, 2008 by Sailor Bob

[Zs-ondabrain]

I called MSA and spoke with one of the guys there, Garrett? I think. He said that the front's would go on without the use of a spring compressor and would have a little slop to them.

You can see that there is about 1/2" of space between the top perch and the spring. I took the picture while tugging on the spring, letting gravity pull the strut assembly away from the spring.

The other shows the full assembly just sitting there but the top bearing is resting on the top of the upper perch but still about 1/2" away from the top 3-bolt assembly.

After the POR15 dries on the rear strut assembly (tomorrow) I'll load the old strut in (because I don't have the rear struts yet) and see how the spring looks.

Dave

[Carl Beck]

The 260Z springs are 15.5 inches tall (all 4, unmounted)

The new Eibachs are.....

Fronts.. (189710) (6303.001) is only 10.75" tall ( 4.75" shorter than stock

Rears....(189712) (6303.002) is only 12.625" Tall ( 2-7/8" shorter than stock)

Is this correct? Are the fronts springs supposed to be almost 5" shorter than stock? And if they are, how does this only drop the car 1" to 1.5" ?????????

Hi Dave:

Let's start with the Stock Front Spring.

If you look at the Field Service Manual (FSM) you will see that the spring's Free Length is 15.5". ( I don't have a FMS for the 260Z - so I'll have to use figures that are guesstimates for this discussion).

Your FSM will also list an "Installed Length" or "Installed height" - it will most likely be something like 8.72".

Your FSM will also tell you how much weight is sitting on the spring, when the car is sitting on the ground. That will be something like 685 lbs.

Your FSM will also tell you what the "Spring Rate" or "Spring Constant" is. It will tell you how many pounds of weight will compress the spring one inch. As a guess on the 260Z that spring constant will be around 101 lbs/in. (might be 112 lbs/in... but we'll use 101 for now).

So if you have 685 lbs... divided by 101 lbs/in - the spring will be compressed 6.78 inches.

15.5 minus 6.78 = 8.72". ( this is just an example of how these numbers are arrived at)

Now if you install a spring with a shorter Free Length to begin with - but one with a greater Spring Rate.. that same 685 lbs will not compress it as much per inch.

So if you start with a spring that has a free length of 10.75" and you intend it to be 1" shorter than stock when installed.. your installed height would be 7.72" (rather than the stock 8.72").

10.75" - 7.72 = 3.03" So you would need a spring that would compress only 3.03" with a weight of 685 lbs sitting on it. A spring rate of 226 lbs/in would get you there. (685 lbs divided by 226 lbs/in - Spring Constant = 3.03)

Another thing to keep in mind is that a coil spring has a more or less constant rate of compression - once the spring is pre loaded and compressed to 80% of it's free length. So starting with a spring 10.75 in free length - then using it compressed to 7.72" will give you a pretty constant spring rate in use.

The fact that the spring is loose with the tires off the ground - isn't a big deal really. What matters is that the spring is held in place with the weight of the car sitting on it. To have the spring shift - you would have to get the entire weight of the car off the spring, at the same time the shock rod is fully extended, and the wheel/tire is off the ground. Unless you are running high speed Pro Rally events and making long high jumps .. you aren't going to have the entire weight of the car off the spring... (if you are running Pro Rally events you have to have travel stops on the suspension to keep it from dropping down to full extension when the tires come off the ground).

FWIW,

Carl B.

Edited November 7, 2008 by Carl Beck

[Zs-ondabrain]

Thanks Carl, Great help as usual. After a few emails, describing in essence, the same thing, I've used my engineering brain (Self taught) to figure out that The stiffness of the aftermarket spring more than compensates the weight of the vehicle under normal loads. The preloaded, soft steel, stock spring was only able to do it's job after being compresed and keeps the full assembly tight when not under a load.

I'll never plan on "Jumping the vehicle" and I'm installing the lowering Progressive rate springs because I like the feel and every once in a while, I like to hit the corners hard and come out level without bouncing down the road. I have the same set-up in my 70 and it rides like a limo (comfortably) but can out corner and manuver most Ricers when it wants to.

I'm gonna stop stressing on this until I get everything on the car and it's rolling down the road, Hopefully to the Z Nationals (Anaheim) next spring. Or at least that's the plan.

Thanks again guys. And hopefully this thread will help other people in the process. Not a total waste of time when you learn something.

Dave.

[fixitman]

Just in case you still need it, the spring data from the FSM for an early 260Z is attached.

Fixitman

SpringData-FSM.pdf

[Carl Beck]

Thanks David!! I appreciate that...

Carl B.

[Oiluj]

That's interesting... I did need to use a spring copressor to get my eibach's re-installed in my 72 240. Only a little, but I could not have done it without the copressors. I wonder if I got different springs?

I'll be lowering the car back off the jack stands this weekend and can see what my drive height looks like...

[TomoHawk]

I was thinking of this swap on a 280Z. Should I expect the same kind of thing?

thxZ

[Sailor Bob]

As I said earlier - I have done it (Eibachs) on both the 240 and the 280 - they are not the same springs. In the 240 the fronts are (IIRC) the same length as the rears but as stated above the 280s are a different set of springs, but work perfect. See attached pic.

As a matter of fact the 240 type stand too tall for me - I am thinking about cutting them at least 1 coil in the front.

77Z.bmp

Edited November 7, 2008 by Sailor Bob

[Zs-ondabrain]

That's interesting... I did need to use a spring copressor to get my eibach's re-installed in my 72 240. Only a little, but I could not have done it without the copressors. I wonder if I got different springs?

I'll be lowering the car back off the jack stands this weekend and can see what my drive height looks like...

Apparently, The only difference in the front strut assemblies on the 240Z and the 260Z is the lower spring perch. It sits one inch lower on the 260Z.

So if I had 1/2" of slop on my 260Z when installing the Eibach PR springs, You would only need to compress your Eibach's 1/2 inch to install them on your 240Z. Nothing to worry about there.

A stock early 260Z looks like this.. Thanks Clayton 260Z.

And after using the Eibach PR springs, It looks like this...

I hope mine looks this good when I'm done.

Dave.

Edited November 7, 2008 by Zs-ondabrain