My stock rear spring replacement w/MOOG CC223 springs

[Hardway]

Ever since I bought my '71 240z in June 2014 the rear of the car would squat down at take off but never rebound.  I could tell as I was driving down the highway the car was nose high.  I witnessed just how bad it was when I had to take the car for its annual inspection watched the inspector drive it.  Even sitting still the rear always sat lower than the front of the car.  At first I thought the strut inserts were shot (and they were) but even after replacing them there was very little improvement.  Seeing that the springs were at least 47 years old I was sure they were fatigued.  Not wanting to lower the car with Eibach or Vogtland springs but still wanting a new spring I went on the hunt to find something that matched up.  Some of you may remember with my lime green '72 240z I went through a lot of trial and error with a full set of Moog 6558 springs that are designed for a Chevette.  In the end they were too stiff and no matter how much they were cut down it was never right.

Going back to Moog's giant spring chart and knowing I needed to stay within the inner and outer diameter of the stock springs which is 3.5" ID and 4.5" OD respectively I narrowed it down to the CC223.  I placed an order for a pair on Rock Auto which ran less than $50 with shipping.  The stock springs have a free height of 14.25" and an installed height of 10.5".  The CC223's have a free height of 14.5" and and installed height of 12".  The CC223 has a ID  3.5" and a OD of 4 3/8". The stock springs have a wire diameter of 11.46mm and the CC233's wire diameter is 12.56mm.  I am unsure of the stock spring pressure but the CC223 is 130 PSI.  Here is a picture of the original on the left on and the new CC223 on the right.

You will see the CC223 is a variable rate spring while the original is progressive.  Personally I did not care as long as it worked so I installed them but installed the variable end on the top.

Once both sides were done I put it back on the ground and unfortunately it made the Z look like a shackled up muscle car.  It had some compliance as I could push down on it but there was no way I could run it like this.

So off they came and through some trial and error I cut three coils out of the variable side and put everything back together.

The end result is exactly what I wanted.  The car sits level, has good compliance and handling, and has very little rear end squat at take off.  Now I just need to get some taller tires and it will be spot on.

I welcome any questions or feedback you have.  Thanks!

Edited May 8, 2017 by Hardway

[Captain Obvious]

Looks great and hopefully it handles as good as it looks!  I got some questions/comments...

About your old Chevette springs - They will get stiffer each time you remove more material, so if they started already too stiff and you were trying to balance ride height by removing coils, they're going to get stiffer and stiffer as you cut coils.

Looking at the pic where you have the CC223 installed as shipped - Those top three coils are already pretty much bound, and I'm sure that even with the resting weight of the car on the struts, those top three were completely bound. The point is...  The only thing those top three coils were doing for you other is raising the ride height and cutting them off shouldn't do anything other than lower the car:

I ran some quick and dirty spring force calculations with the numbers you provided above and came up with the following:

• Stock spring, assuming 9 active coils - 100 lb per inch
• CC223 uncut, assuming 8 active coils and no binding - 185 lb per inch
• CC223 cut, assuming 6 active coils - 250 lb per inch

Ballpark based on rough measurements and metallurgical assumptions of the composition.

How do you think ride height compares to stock? And even after you cut coils off the CC223, did you have to use a compressor to get them back together?

[Hardway]

23 hours ago, Captain Obvious said:

Looks great and hopefully it handles as good as it looks!  I got some questions/comments...

How do you think ride height compares to stock? And even after you cut coils off the CC223, did you have to use a compressor to get them back together?

Thank you Captain!  I don't know what the pure stock ride height looks like but I believe this to be very close.  The front suspension has always made the car look nose high, partially because of the small tires but also because the rear was sagging.  Below are some pictures from February 2016.  The rear sag is not very noticeable but it had gotten worse going in to 2017.  The real difference is in the ride quality.  At speed I can tell I am sitting level versus before and going over bumps and general handling the suspension is absorbing what it is supposed to.  I can still push down on the rear a little but it is stiffer than before and pretty much equal to the amount of force it takes to push down the front.  Yes, even with the three coils cut off I still had to use the spring compressor to install them.  It didn't take much but they are under tension once the strut assembly is back together.

[Captain Obvious]

Sounds great. I was asking about needing a compressor because I would like to lower mine a little but I don't like the idea of the commercially available lowering springs that are so short that they actually lose contact with the spring perches when unladen. I want something that is under compression even when the struts are assembled. Even if it's just a little.

I ran the spring force calculations based on the info and pics you posted, but the results really aren't that close to the specs you quoted. How confident are you in your measurements?

[Hardway]

This update is a little late but I got the new tires on the Z.  I wanted something that would fill the wheel wells without making it look like an off road vehicle.  I ended up going with 195/70/14's made by Douglas.  They are sold by Wal-Mart and at $40 per tire, they had great reviews, and at only $9 per wheel for mounting and balancing, it was the best deal in town.  Plus, they are made in the USA!  I have not had a chance to drive it much as I am working on another project but I think its great way to wrap up the project.  I had seriously thought about buying some 15 or 16 inch wheels but by the time I added tires my total cost would be anywhere from $800 - $1,000.  What do you think? 

[Mark Maras]

Walmart? Made in USA? Two things I never thought I'd see together. BTW, the tires look good. Let us know how they handle, rain and shine.

[dmorales-bello]

Stance looks stock, nice. Ride quality and tracking report will be important.