Just finished installing HPs on the front of my 77 (also did all front end bushings, ball joints and tie rod ends), when I put the wheels on and lowered her, she was/is conspicuously taller. It almost appears as if the engine is out, I am hoping there will be some settling. Comments....

In spite of carefull recording and resetting the toe in seems out of whack - I am thinking this is related to the growth spurt.

Got insight - please advise.

I'm not surprised that those of you with modern lowering springs haven't noticed this gas-strut effect. Those springs were likely designed after gas shocks became common, and so the spring rates have probably been adjusted to take that into account. So far the complaints have all (to my knowledge) come from people using factory springs - which had their spring rates determined assuming non-gas struts. So the only people who are really having this problem are those of us who would rather not lower our Zs. Unfortunately, instead we get to have them lifted!

Hi Arne (everyone):

Just a minor point of clarification.. Lets say that the OEM Stock springs are 14 inches free length, and have an installed height of 9 inches. The springs are pre-loaded, ie. partially compressed when installed on the struts (why you need a spring compressor to remove/install them).

After being compressed to aprox 80% of their free length - their spring rate is pretty constant - lets just say 82 lbs per inch for the stock front....

It is possible that aftermarket springs had their spring rates adjusted to compensate for the lift provided by gas pressure shocks - but that would mean lower spring rates would be used, which is not normally the case for after-market springs.

It is more probable that that after-market springs had their free length/installed height adjusted to compensate for the additional lift of the gas pressure shocks.

So we may need to shorten the OEM and Euro Spec. springs when used with gas pressure shocks..

FWIW,

Carl B.

LOL AH. just convert to coilovers....problem solved. FWIW, I had the same problem on my car when I went from KYB to Tokico inderts....it raised the car about 1in...like I said...installed coilovers, problem solved

FWIW I have the Eibach springs and HP shocks on my '71 240Z and they work well together.

The rod moving into the shock tube displaces quite a bit of fluid and will give them some spring action even without gas.... the high pressure gas is working against the rod displacement like a spring...

Hey Marty

We must be pretty busy guys - it takes four months to have a conversation.

Just to respond to your question - She looks a little like a mudder, but I'm a tall guy (6'2") so it fits ok:) . As for the handling - very good for street - I like it.

I did the bushings too, so she's a little stiff.

I'ld like to lower her for appearance but it's too time consuming and like I said she handles very well (up to 110 anyway (He He)).

Hey Marty

We must be pretty busy guys - it takes four months to have a conversation.

Just to respond to your question - She looks a little like a mudder, but I'm a tall guy (6'2") so it fits ok:) . As for the handling - very good for street - I like it.

I did the bushings too, so she's a little stiff.

I'ld like to lower her for appearance but it's too time consuming and like I said she handles very well (up to 110 anyway (He He)).

Yep, it's been very busy around here lately. And I am putting in a new engine in my track car, so I have not had a lot of time to check in here.

Marty

We installed Tokico's about 12 years ago on my 77 280Z and it definitely sits an inch or two higher than before. They never did settle in to their previous height. My car was in storage for about 11 years and my husband just rebuilt the engine for me. I don't like the way the car looks with the Tokico's so we may get rid of them now that it's back on the road. I never noticed an improvement in the ride or handling either with the Tokico's so I'd rather have it back at the stock height.

t is possible that aftermarket springs had their spring rates adjusted to compensate for the lift provided by gas pressure shocks - but that would mean lower spring rates would be used, which is not normally the case for after-market springs.

It is more probable that that after-market springs had their free length/installed height adjusted to compensate for the additional lift of the gas pressure shocks.

So we may need to shorten the OEM and Euro Spec. springs when used with gas pressure shocks..

FWIW,

Carl B.

A couple of thoughts on this to add:

You're right Carl, it is more likely that the free length has been changed on the lowering springs, if they are linear rate as the OE springs are/were. But if they are progressive rate - which is the case for Tokico and Eibach, to name two - they could easily have tweaked the initial rate without having to make big changes to the free length.

Also, installed height is not an issue here, as the installed height is determined by the amount of shock travel. Since the springs are pre-loaded (i.e. you have to use a compressor to install them) the installed height will always be as much as the shock travel will allow. It is still a factor for the spring engineers, but it will not change from spring to spring on the same shock.

Lastly, I have finally started installing my Euro Stage 1 springs, and I now believe that the increased ride height issue on those is not solely caused by the gas shocks, but also that we are comparing to old, sagged out stock springs as our reference point. I have not done the rear yet, so I won't share all the measurements yet, but I have replaced the 35 year old stock springs on the front of my car with the Stage 1 springs. I did NOT change the shocks at all. The Stage 1 springs alone raised the front ride height about 1/2" when compared to the stock springs on the exact same shocks. My car still has non-gas shocks in it, but that is immaterial here, because I am comparing changes from the springs only.

More details on this when I finish the spring swap.

It is more probable that that after-market springs had their free length/installed height adjusted to compensate for the additional lift of the gas pressure shocks.

So we may need to shorten the OEM and Euro Spec. springs when used with gas pressure shocks..

Seems fairly obvious to me that if you put a stiffer spring in that is the same length that the ride height you get will be higher than the original spring.

You're right Carl, it is more likely that the free length has been changed on the lowering springs, if they are linear rate as the OE springs are/were. But if they are progressive rate - which is the case for Tokico and Eibach, to name two - they could easily have tweaked the initial rate without having to make big changes to the free length.

Also, installed height is not an issue here, as the installed height is determined by the amount of shock travel. Since the springs are pre-loaded (i.e. you have to use a compressor to install them) the installed height will always be as much as the shock travel will allow. It is still a factor for the spring engineers, but it will not change from spring to spring on the same shock.

Also, with respect to the Tokico springs, Arne is correct that the free length is shorter. I don't think they're preloaded at all. In fact I think they're a bit shorter necessary to hit both spring perches, which is why you occasionally see posts asking if the springs are going to fall out. I believe the Eibachs are the same way, as are the Suspension Techniques springs.

...we are comparing to old, sagged out stock springs as our reference point.

This is absolutely the case.

Also, with respect to the Tokico springs, Arne is correct that the free length is shorter. I don't think they're preloaded at all. In fact I think they're a bit shorter necessary to hit both spring perches, which is why you occasionally see posts asking if the springs are going to fall out. I believe the Eibachs are the same way....

I just pulled a set of Eibachs off my parts car (posted on eBay right now as #120017599781, shameless plug) and I can tell you for certain that the Eibachs are definitely preloaded. In fact, the free length of the Eibachs is very close to that of the stockers. I don't know about the Tokicos first hand, but I too have heard that they have no pre-load.

I just pulled a set of Eibachs off my parts car (posted on eBay right now as #120017599781, shameless plug) and I can tell you for certain that the Eibachs are definitely preloaded. In fact, the free length of the Eibachs is very close to that of the stockers. I don't know about the Tokicos first hand, but I too have heard that they have no pre-load.

Ha! I was just looking at those yesterday! I'm not sure taht I trust my old shocks too much, I may look into those!

Hi Guys:

During our discussion, we may be introducing some misunderstanding or errors in terms... So this is how I understand it...

Stock Ride Height:

Measured from the garage floor - to the bottom of the rocker panel, at the front and rear jacking points - a stock 240-Z sits about 7 3/4 to 8 inches high (the 73's actually sit a bit higher than the earlier cars do to the headlight height standards and bumper height standards for that year). Bottom of the rocker panel - means just that - NOT to the pinch weld that sticks down farther... (this is from the Factory Service Manuals, not from older springs..).

Installed Height:

"Installed Height" = the height as installed on the car. This is not the compressed or non-compressed length of the spring on the strut before it's installed on the car. So shock travel doesn't effect installed height. Free Length, Spring Rate and the Load placed on the spring does. (that way the shock can travel higher than the installed height - as well as lower).

Coil Springs compress at a "more or less" constant rate - once they are pre-loaded to about 80% of their length. The rate will vary greatly during that first 20% because the distance between the coils and shape of the spring wire at the top or bottom are made to sit in the different types of spring perches. So Free Length and Load are managed to provide the desired Installed Height at any desired spring rates.

Once the spring is installed on the strut, and the car is sitting on the strut - from that point forward the spring rate will be more or less constant.

So only three factors determine "ride height" as far as the springs are concerned(ruling out wheel/tires) ... once the spring is installed on the car. The Installed height of the spring is determined by its Free Length, Spring Rate and Typical Load.

If the Free Length of the Stock and Euro.Spec. Springs were the same to begin with..and the only difference between them was their spring rate - then yes - the stronger spring would result in an increased ride height.

But that isn't the case.. the Stock Front Springs have a Free Length of 14.7 LF and 15.2 RF with a spring rate of 83 in/lb. and an Installed Height of 7.9 inches. Typical load is 604lbs on the Right and 562 lbs on the Left.

The Euro Spec. Stage I Springs have a Free Length of 13 inch, a spring rate of 102 lb/in and an installed height of 7 inch.

So if everything is to spec. - The Euro Spec. Springs "should" lower the front of the car 0.7 inch.

The Stock Rear Springs are 15 inch in Free Length, are rated at 103.6 lb/in and carry a typical load of 635lbs. So their installed height comes out to 8.86 inch.

The Euro Spec. Stage I springs have a Free Length of 14.2 inch and are rated at 112 lb/in.. with a typical load of 635lbs. - - - so their Installed Height is supposed to be 8.86 inch as well.

For a rough aproximation of the installed height - you can take the Free Length and apply the Load to a given Spring Rate... The spring rate isn't as constant at it's free length - but you'll be close to the real world..

Stock Rear:

15 inch free length minus (635lbs divided by a 103.6 lb/in rate) =6.13 inch of compression) = 8.87 inch installed height

Euro Spec Rear:

14.2 inch free length minus (635lbs divided by 112 lb/in rate)= 5.67 inch of compression) = 8.53 inch installed height.

Of couse all this is based somewhat on the Factor Spec.'s being correctly rounded, converted and reported...

FWIW,

Carl B.