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Thread: Using Chevette Springs to Re-gain Original Ride Height

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    Registered User Hardway's Avatar
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    Default Using Chevette Springs to Re-gain Original Ride Height

    So after putting the front suspension back together on my '72 the King lowering springs are not going to cut it for me. They do work but the car sits too low and less than an inch off the bump stop. I want to get back to something a little more stock looking. On Zcar.com several members reported back in the late 90's and mid 2000's about using some front Chevette springs for the front and rear of a Z. They are not a bolt in affair as they have to be cut to produce the ride height that is desired but they are the correct diameter. The years to get look to be '77-85, auto. trans, and air conditioning. Moog #6558 comes up for this and seems to be what everyone else used as well. Are there any members here that have used them and have any results to report back on?
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    Hey Hardway, I'm not sure if we have exactly the same problem, but it's similar. My 240Z came with lowering springs, but they are too low and way too hard. To correct the problem, I spoke to Motorsport (and others) and everyone suggested the progressive Eibach springs, which should bring it back up to near-stock height (1" less) and provide a gentler ride. I like good handling, but my spine needs something softer for railroad tracks. I have not installed them yet, so I can't report on whether or not they did the trick, but I thought I'd offer my $.02 anyway. Good luck!
    Current Z: 1971 Datsun 240Z, 3.1 Stroker (F54 block, P90 head, 490-290 cam, triple Webers); 95% complete
    First Z: 1972 240Z, destroyed in a shipping accident. Ack!

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    Hey Z Boy, yeah I have read that using Eibach springs would be better but owners have reported some of the same issues that I am having already. So far from what I have read about the Chevette springs that in un-cut form they are almost 100% stock ride height and then can be cut to suit the owners taste. Plus they are supposed to be a little stiffer than the stock springs so that seems like a plus to me. For $88 for all 4 I think they are worth at least picking up a set and trying them out. My local O'Reilly Auto Parts store can get them but they will take a week to arrive as no one carries them in stock. I figure if they are not what I want I can always return them and go another direction.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    The real question here is do you really believe that a $88 bandaid is a good deal when you can cure the problem and improve your cars performance for a little more than twice that...

    It is your car do what makes you happy, but I think there are better answers than the one you are considering-if money is that tight, put a suitable collar spacer under the offending springs to bring the ride height up... A band aid should be a small percentage of correct answer, not nearly half of it.

    As and example, The oil filled sub-frame bushings on my Z32 'vert started leaking a while back-the only way to get them is in a new $700 subframe assembly(or buy after-market Urethane replacement that ruin the ride and provide a direct and highly efficient path for noise into the cockpit by most accounts)-as I bandaid I spent $27 for a set of ebay sub-frame spacers...not quite 4% of the cost of the correct answer...

    I won't even get into the ramifications of even thinking of putting chevette parts on a Z...but as you are out of my jurisdiction as a founding member of the Zpolice, I can tell you that is a Z forfieture transgression for sure-don't get caught pulling that stuff here in Georgia! Texas is a bit of a walk home...

    Again-it is your Z, it is your money, If you can live with it will being your fault, do what makes sense to you in your situation.
    Last edited by hls30.com; 01-04-2013 at 02:17 PM.
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    The Chevette springs work well and give more rate then the stock springs. I've installed them (cut) on my own and customer cars. Check over on HybridZ.

    EDIT: I'll post the info here:

    Rate: 197 lb. in.
    Stack height: 9.75" @ 800lb. corner weight
    Free height: 14"
    ID: 3.5"
    OD: 4"

    You will need to cut them to get back to a stock ride height.
    Last edited by John Coffey; 01-04-2013 at 03:12 PM.

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    Nothing wrong with using non-Z specific parts, I'll second JC. A spring is a spring, sounds like the Chevette ones might do the trick for you.

    EDIT: Wow, those springs are stiffer than I expected! Looks like a nice solution for those looking for a stock-ish ride height, but stiffer springs.
    Last edited by LeonV; 01-04-2013 at 03:16 PM.
    2/74 260Z

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    Same rate as the Tokico 5022R (280Z rear springs).

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    Quote Originally Posted by John Coffey View Post
    Same rate as the Tokico 5022R (280Z rear springs).
    Except considerably cheaper!

    Buy Chevette springs, paint them red, and they are now Tokicos. No more problems with the Z-police.
    2/74 260Z

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    Hmm, cheaper, just as effective, and I have two Z cars with old springs.
    This is something I'll have to remember.
    73 240Z
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    How much effect will there be having the same rate front and back, compared to the lighter rate front springs in the stock setup?
    1976 280Z, with some minor modifications

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    The ride may be a bit more "pitchy" for lack of a better term. In passenger cars, spring rates are typically chosen for ride quality. A stiffer rear spring makes the rear end settle quicker than the front, after a road disturbance. This decreases pitching motion felt by passengers and makes the ride more comfortable. With that said, I think you'll notice the added stiffness much more than you do the differences in front and rear rate, as the Z has a relatively short wheelbase.

    Handling-wise, if you notice anything at all, stiffer front springs (all else constant) will make it tend to understeer more. This can be easily alleviated though.
    2/74 260Z

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    As I recall from the days when I was futzing with the repro Nissan Euro springs, the stock spring rates were somewhere around 110 lbs. or so. The rates weren't all that different front and rear, but one end was longer than the other. So at close to 200 lbs, you should be in the same ballpark as many other performance oriented springs. Seems like the Arizona Z springs were around 200, too.
    Last edited by Arne; 01-05-2013 at 12:53 PM. Reason: typo
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    Someone has to be on the side of Keeping a Z a Z...admittedly I was on the path to use VW shocks with performance springs to move the travel of the shock to more closely match the travel of the performance spring, but a Chevette? Come on guys, Good or bad that just seems detrimental to a Z...it is a Z after all- not some nondescript, dismissed, and forgotten GM econo-box with about as much performance heritage as a pair of third grade walmart rubber boots!

    I get the upgrade specs, and the DIY appeal but this is something to pass around on the QT with Moog Part numbers disguising what the springs were actually made for...This is like one of those things you simply can't un-see... Improve the specs of your car any way you want, but when it isn't actually an upgrade from at least something of a better car, at lease hide that in an open forum so we aren't so readily the butt of upgrade jokes!

    I can hear it now-Those Z guys are soo dumb they don't know the difference between a Chevette and a Corvette...
    If you had only given the Moog part numbers it doesn't work quite as well
    Those Z guys upgraded with Moog parts...


    I was just yanking chains in both of these posts-If you see Smiles in my posts that usually means I am kidding

    An upgrade in performance that works and is cost effective is always a good thing, it isnt often better, and cheaper go hand in hand, and you should grab it when you can! But did you really have to put Z and Chevette in the same sentence?
    Will

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    After a night out for some Tex-Mex and watching football I had no idea this thread had gained so much attention. I ordered the springs today from AutoZone on my way home from work. Ran me $95 with tax and they should be here one day next week. I usually always go with O'Reilly's for my OTC parts but they wanted $18 for freight shipping and AZ did not so they got my business on these.

    I truly appreciate everyone's info, comments, and passion around these cars, in fact I have loved reading them. The whole reason I posted this up was because I could not find anything about them here on CZC and the last posts about them on Zcar.com were from around 2006. I did not venture over to HybridZ but it makes sense there would be more info there. I still need to do the rear suspension rebuild on my '72 so the results won't be seen for awhile with springs. Based on the experiences of other owners these should make a great option for those wanting stock height springs for their Z.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    hls30.com...................Click image for larger version. 

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    A spring is a spring. A bit of wound tempered spring steel rod.
    If it fits and does the job for you,then it is the right one.

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    Quote Originally Posted by 72 OJ View Post
    hls30.com...................Click image for larger version. 

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    As if stating the name was not bad enough...he had to go and post a picture...


    Will
    A Z is beautiful from any angle, I just happen to prefer to view from the drivers' seat!

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    Quote Originally Posted by John Coffey View Post
    EDIT: I'll post the info here:

    Rate: 197 lb. in.
    Stack height: 9.75" @ 800lb. corner weight
    Free height: 14"
    ID: 3.5"
    OD: 4"
    800 lb corner weight? On a 240Z it is around 635 lbs per corner.. So the 240Z is "about" 2540 lbs.. and that would make the Chevette ... what? 3200 lbs... I was thinking that the Chevette was a pretty cheap and light weight car - yes/no?

    On a street driven 240Z - lowered - it would seen that 197 lbs. in. would yield a very stiff and harsh ride, even with properly matched shocks. {stiff and harsh being pretty subjective terms}

    Stock Springs on the 280Z are 103 lbs. in Front and 127 lbs. in. Rear

    FWIW,
    Carl B.

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    Wikipedia lists the curb weight around 1800 to 2000 lbs for the 85 model.
    73 240Z
    74 260Z

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    The Chevette front suspension is SLA, not coil over. The spring rate may be high but the wheel rate is very soft. The Chevette also has a 55F/45R weight distribution. The 800lb. number above is just an example, not a real number.

    Springs rate does not contribute to ride harshness. My racing 240Z with Penske triple shocks and 375/350 springs was more supple in ride them my street 240Z using Tokico HP shocks and the Eibach progressive springs. Ride harshness is more a function of shock compression damping, suspension longitudinal compliance, bushing material and compliance, tire construction, and tire pressures.

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    Quote Originally Posted by John Coffey View Post
    Springs rate does not contribute to ride harshness. My racing 240Z with Penske triple shocks and 375/350 springs was more supple in ride them my street 240Z using Tokico HP shocks and the Eibach progressive springs. Ride harshness is more a function of shock compression damping, suspension longitudinal compliance, bushing material and compliance, tire construction, and tire pressures.
    John,
    I find this intriguing. My suspension is a bit firmer than I expected. So all things being equal, (stock suspension components, rubber bushings), eibach spings and tokico blues, it sounds like perhaps a "softer" shock would improve ride quality?

    I like the stance with the eibachs, but suspect my bride would prefer it were more supple... Any thoughts?
    Julio
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    Quote Originally Posted by Oiluj View Post
    John,
    I find this intriguing. My suspension is a bit firmer than I expected. So all things being equal, (stock suspension components, rubber bushings), eibach spings and tokico blues, it sounds like perhaps a "softer" shock would improve ride quality?

    I like the stance with the eibachs, but suspect my bride would prefer it were more supple... Any thoughts?
    Most definitely, Julio! Ride quality depends on how the damper matches the spring. If you think back to your mechanical vibrations class (I know, I know ), the important bit here is the damping ratio (critical damping constant / damping coefficient). Generally, as the damping ratio approaches critical, you get better handling because of quicker response times, but ride quality goes down the drain since transmissibility goes up.

    There's a small sweet spot where handling and ride quality can co-exist, and that's where properly-matched dampers put you. Multi-adjustable, multi-circuit dampers make it easier and/or possible to get there.
    Last edited by LeonV; 01-06-2013 at 08:58 AM.
    2/74 260Z

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    Last edited by Blue; 01-06-2013 at 12:32 PM.
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    Leon,

    Your explaination is correct. What I was really hoping to get back was what "softer" shocks are available... I have a contact who develops custom shocks. They haven't worked on any for our old S30's, (market is too small), and they are a bit too expensive for a weekend street car.
    Julio
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    Off the shelf KYB GR2s or Monroe's are probably the best best for a softer ride. Rubber TC rod and CLA bushings help, tires with a taller side wall (55 or 60 series) and lower tires pressures.

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    Quote Originally Posted by Oiluj View Post
    Leon,

    Your explaination is correct. What I was really hoping to get back was what "softer" shocks are available... I have a contact who develops custom shocks. They haven't worked on any for our old S30's, (market is too small), and they are a bit too expensive for a weekend street car.
    I've been looking forward to getting some Bilsteins or Konis, as their valving seems to be "better" than Tokico's. However, I haven't done enough research as to which ones work for Zs and what's out there. I know John C. is involved in getting some Bilstein's that could be used for Zs but not a lot of news on that front.
    2/74 260Z

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    The P30-0032 Bilsteins are available, the issue is getting the correct gland nut. Its really hit or miss on whether you can get the gland nuts. There are two part numbers to choose from and I just received three of one and one of the other on an order. I'll have to cut the one down with a lathe to get it to work.

    These shocks will work well for all street and most light duty track and autocross cars. Non-adjustable but the valving is good to 250/275 lb. in. and they are digressive. I'm still waiting for the 36mm Bilstein Motorsports shocks.

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    Quote Originally Posted by John Coffey View Post
    The P30-0032 Bilsteins are available, the issue is getting the correct gland nut. Its really hit or miss on whether you can get the gland nuts. There are two part numbers to choose from and I just received three of one and one of the other on an order. I'll have to cut the one down with a lathe to get it to work.

    These shocks will work well for all street and most light duty track and autocross cars. Non-adjustable but the valving is good to 250/275 lb. in. and they are digressive. I'm still waiting for the 36mm Bilstein Motorsports shocks.
    Cool, thanks John! Great info.

    Sounds like the P30-0032 works with sectioned struts. Digressive valving is something that the Tokicos are sorely lacking. If the Tokicos actually do have digressive valving, then their compression damping is just way too damn stiff.

    The P30 Bilsteins are sounding like the ones to get for me, as I'm looking for the car to ride better but not be severely underdamped for autoX and the track.
    2/74 260Z

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    My P30-0032 valving is linear. I've got a dyno plot somewhere around here for my revalved struts. The valving was changed, but the pistons were not. It graphs out almost straight on bump and rebound.
    Jon

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    Quote Originally Posted by jmortensen View Post
    My P30-0032 valving is linear. I've got a dyno plot somewhere around here for my revalved struts. The valving was changed, but the pistons were not. It graphs out almost straight on bump and rebound.
    Are you familiar enough with Tokicos (HP or Illumina) to compare them (ride and road-holding) to the P30?
    2/74 260Z

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    Not familiar enough with the P30. Haven't run it yet, and mine are valved funky (valved approx 60% critical damping of the UNsprung weight) so I don't know that I'd be the best person to ask. Mine won't ride well, that's a guarantee. I don't like the Tokicos much though, I can tell you that. Ran Illuminas for years and have friends with Blues. I think they're overly damped on compression so that they work well with the common but too soft lowering springs. It would be interesting to see a dyno graph from an Illumina to compare to a Bilstein, but just based on my previous experience with Bilsteins in other applications, I'd guess that the Bilsteins are better.
    Jon

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    I was mistaken with my post about the digressive valving on the P30s. That's the 36mm shocks.

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    JC, do you know what spring rates the 36mm shocks are valved for, or are they custom valved on an individual basis?

    JM, regarding the funky valving on your shocks, I believe compression damping is usually valved taking UNsprung mass into account and rebound damping is valved for the sprung mass. Are yours valved differently?

    I'm hoping the Bilsteins are better too, the Tokicos are definitely too stiff in compression.
    2/74 260Z

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    Interesting and useful discussion. Thanks John & Jon for the info!
    Julio
    1972 240Z (in-progress, 95% complete)
    CZC# 15388

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    You have that right. Mine were valved for the unsprung weight on both sides, the idea being that the wheel will stay in contact with the ground over rough surfaces because the rebound damping isn't preventing the tire from coming down and following the contours of the road. I had a mountain bike set up like this, and it tracked great on some really rough downhill single track stuff, but it was very uncomfortable to ride, especially when jumped. It was actually painful on the hands. I increased the rebound and it's more comfortable but doesn't track as well. On the car I talked to a shock guy and he suggested this setup. My car being a dedicated racer and all, I decided to give it a shot. I already have second thoughts about it because I actually started autoxing a Miata in the meantime, and one of the local autoxes where most of the SCCA events take place is VERY bumpy. I think once you hit some critical amount of bumpiness it not only gets uncomfortable, but the sprung weight starts to move so much that you lose whatever traction you would have gained otherwise. I do think this idea works on relatively smooth road courses, and I've found examples of older BMW touring cars in Germany valved the same way (it worked out to 90/90 instead of my 100/100 once you took the motion ratio into account).
    Last edited by jmortensen; 01-08-2013 at 07:52 AM.
    Jon

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    Quote Originally Posted by jmortensen View Post
    You have that right. Mine were valved for the unsprung weight on both sides, the idea being that the wheel will stay in contact with the ground over rough surfaces because the rebound damping isn't preventing the tire from coming down and following the contours of the road. I had a mountain bike set up like this, and it tracked great on some really rough downhill single track stuff, but it was very uncomfortable to ride, especially when jumped. It was actually painful on the hands. I increased the rebound and it's more comfortable but doesn't track as well. On the car I talked to a shock guy and he suggested this setup. My car being a dedicated racer and all, I decided to give it a shot. I already have second thoughts about it because I actually started autoxing a Miata in the meantime, and one of the local autoxes where most of the SCCA events take place is VERY bumpy. I think once you hit some critical amount of bumpiness it not only gets uncomfortable, but the sprung weight starts to move so much that you lose whatever traction you would have gained otherwise. I do think this idea works on relatively smooth road courses, and I've found examples of older BMW touring cars in Germany valved the same way (it worked out to 90/90 instead of my 100/100 once you took the motion ratio into account).
    Interesting, I'm curious as to how it's going to work out for you.
    2/74 260Z

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    The Bilstien Motorsports 36mm shocks will come with 5 different tarmac valvings and 2 different gravel valvings. That will cover most of what people will run on a S30. Revalving is $60 per unit (estimated) with a two week turn around.

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    Quote Originally Posted by John Coffey View Post
    The Bilstien Motorsports 36mm shocks will come with 5 different tarmac valvings and 2 different gravel valvings. That will cover most of what people will run on a S30. Revalving is $60 per unit (estimated) with a two week turn around.
    Excellent, thanks!
    2/74 260Z

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    I have the Bilstien shocks for the 240Z, that they sold in the 70's - on my Blue 72. As I recall I put them on in 74.. they are STILL the best shock I've ever had on a 240Z. Wish Bilstien would offer them again..
    FWIW,
    Carl B.

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    So I finally got around to messing with the Chevette springs this evening and apologize for the delay in getting back on this topic. I have had my rear suspension apart for a rebuild and figured this was the time to look closer in to them. Below is a picture of the Chevette spring on the left with the King lowering spring on the right. As you can see there is a big difference between the two. The coil diameter on the Chevette spring is 12.56mm and on the King spring it is 11.90mm. The height of of the Chevette spring is 14 2/8 inches and the King is 12 1/4 inches. I installed them as-is, got the lower control arm connected and the half shaft, all temorarily so I could do a mock up with the wheel on. Once it was on I jacked up the hub assembly to see how far it would compress before it lifted the car off the jack stand. As soon as the jack started pushing up it lifted the car off the stand, the spring just barely compressed if any at all. Granted, the gas tank is almost empty and there is no one sitting in the car but I was hoping it would compress a little. Based on the other info I could find I need to cut atleast one coil. Do any guys that remember using the springs cut off more? If so how many and what was the result? I want to regain a factory ride height or just slightly lower.

    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    Search John Coffey and Chevette spring on Google. I recall him writing about them in a positive way.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Thank you John. From the looks of it I need to cut off 1 coil and possibly 1.5. I will start with 1 and go from there.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    I thought I would post an update on this topic. I cut 1.5 coils off of all 4 springs and installed them thus resulting in the picture below.



    I like where the rear is at but as you can see it is sitting nose high. So earlier this week I took the front driver side spring off and cut off another coil giving the spring an uninstalled height of 10.25" I was hoping to see a .5 - .75 inch drop once it was installed but only saw about .25 inch drop. It still looks a little nose high so I am going to do the other side this evening or tomorrow and see if that helps. If not I may pull them off again and cut off half a coil and see where that gets me.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    You can't just cut one corner and expect a major change on an end of a car. What's happening is the right rear is helping to hold the right front up (sounds crazy but its true - diagonal corner weights and all that).

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    Quote Originally Posted by John Coffey View Post
    You can't just cut one corner and expect a major change on an end of a car. What's happening is the right rear is helping to hold the right front up (sounds crazy but its true - diagonal corner weights and all that).
    You were spot on John. I got the passenger side spring cut down and everything reinstalled and the car did level out. Now I have a problem with too much positive camber. I posted pics of it all on my resto thread -> http://www.classiczcars.com/forums/o...tml#post432836 I am not sure what I need to do to go about correcting it.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    As I cruise through the threads I noticed Grannyknot's thread regarding his suspension and the numbers he posted. He is running a set of illumina's along with new Eibach springs. He posted the following numbers.

    driver front - 26.125"
    driver rear - 26"
    passenger front - 26.250"
    passenger rear - 25.5"

    On the Eibach's I know a lot of guys cut one of the front coils to help level their car out so Grannyknot may need to do the same. However, below are my numbers taken from the same point, in the middle from the ground to the edge of wheel opening. Now I am really lost.

    Driver front - 25 3/4"
    Driver rear - 25 7/8"
    Passenger front - 25 2/8"
    Passenger rear - 25 1/4"

    As of right now I am sitting lower than what Eibach's would give me but in my opinion the car is still sitting high. I have considered taking the front springs out and cutting another coil out but this would result in the spring being very loose in the upper spring pocket when not under load and possibly coming out completely when the car is jacked up. I am beginning to think the coils are just too thick and spaced too far apart to get the end result I want. Right now on the rears I have cut down 1.5 coils and on the fronts I have cut down 2.5 coils. Any ideas besides ditching these springs and buying a set of Eibach's and cutton one coil off the fronts?
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    If you take the car out for a quick drive the suspension will settle down a little compared to how it sits after jacking the car up in the air.

    I'm not sure how big of a difference it will make but it's worth a try to see if that front will come down.

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    Although few will care... never use the wheel well arches to measure ride height. Use the bottom horizontal surface of the rocker panels.

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    Jeff,

    I just made an xls spreadsheet for estimating your front spring compression. Here are the numbers and spring constant changes:

    Stock Chevette Spring Front
    Compressed Spring Height 11.27"
    Spring Constant 197.00 lbs/inch

    1.5 Coils Cut from Stock
    Compressed Spring Height 9.60"
    Spring Constant 237.48 lbs/inch

    2.5 Coils Cut from Stock
    Compressed Spring Height 8.29"
    Spring Constant 275.17 lbs/inch

    3.0 Coils Cut from Stock
    Compressed Spring Height 7.63"
    Spring Constant 298.90 lbs/inch

    3.5 Coils Cut from Stock
    Compressed Spring Height 6.97"
    Spring Constant 327.09 lbs/inch

    4.0 Coils Cut from Stock
    Compressed Spring Height 6.31"
    Spring Constant 361.17 lbs/inch

    I think you are at 2.5 coils cut from stock so the compressed height should be close to stock of ~8". I would only cut 0.5 coils at a time on the front until you get it where you want. The spring constants climb significantly.


    FYI: I used a car weight of 2,244lbs (estimated as car and one 150lb driver) and a 47/53 front/rear weight distribution. If anyone can give better weight and distribution I'll plug it in.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
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    1 month old 72 for reference




    here is a 71




    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Blue; 07-03-2013 at 06:57 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Thanks Blue for reminding us that shortening a spring has the (perhaps) undesirable effect of making it a stiffer spring as well.

    Since I've always had a hard time conceptually understanding why this is, so imagine others do as well, try thinking of it this way.

    Instead of a coil spring, think just of a long retanglar straight bar of steel. Perhaps you have a springy 36 inch ruler in your shop to try this with.

    Clamp one end to your bench with a c-clamp and let the other end extend off of the bench toward you. Press down on the end of the ruler. It takes a certain amount of force to push it an inch downward.
    Now press on the bar at a point half way along it's length instead of the very end. It is much harder to push down. You have in effect a shorter lever arm so you need more force to get the same deflection
    (at that position on the ruler, not at the end. Feel free to cut your ruler in half to confirm...).

    So we see that compressing a spring is just deforming the steel with a given force, and if you have more length of steel to push on, you have more leverage to do the deforming. Cut coils off and its harder to deform.

    To further cement the understanding that is not just a function of the material that the spring is made of that determines the lb/in rating, but the leverage you are excerting to deform it, imagine putting your ruler on edge in the above experiment and pushing down on that.... Its a combination of the material stiffness and its manufactured length that gives a particular lb/in rating.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
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    Reference materials
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    jim we have the same geek gene Love your lesson... spot on.

    btw Pics of that series one please Hopefully I'll have the metal roof on the shed this weekend and pics to counter
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
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    Jeff,

    Revised with the following:

    Vehicle Weight: 2332 lbs (72z and two 150lb drivers per 72 FSM)
    Weight Ratio (F:R) 48.2:51.8 per 72 FSM

    This is for the front:
    Uncompressed
    Height (Inches)
    Compressed
    Height (inches)
    Spring Constant
    (ft-lbs)
    Stock 14.25 11.40 197.00
    1.0 cut 12.63 10.10 222.26
    1.5 cut 11.82 9.45 237.48
    2.0 cut 11.01 8.81 254.94
    2.5 cut 10.20 8.16 275.17
    3.0 cut 9.39 7.51 298.90
    3.5 cut 8.58 6.86 327.09
    4.0 cut 7.77 6.22 361.17


    This is for the rear:
    Uncompressed
    Height (Inches)
    Compressed
    Height (inches)
    Spring Constant
    (ft-lbs)
    Stock 14.25 11.18 197.00
    1.0 cut 12.63 9.91 222.26
    1.5 cut 11.82 9.28 237.48
    2.0 cut 11.01 8.64 254.94
    2.5 cut 10.20 8.01 275.17
    3.0 cut 9.39 7.37 298.90
    3.5 cut 8.58 6.74 327.09
    4.0 cut 7.77 6.10 361.17


    You may wish to cut 1/4 less coil off the rear to keep it higher than the front.


    3 coils cut from the front and 2.75 cut from the rear would be ~ .6" below stock.
    Last edited by Blue; 07-05-2013 at 09:35 AM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Thank you Blue! This definitely explains why I can barely push down on the front end as it is. If I cut another half coil off I will be looking at almost 300lbs of spring pressure. I would imagine the car would corner flat but the overall ride experience would be something reminiscent of an old heavy duty farm truck. I am thinking the Eibach's are looking better and better at this point.
    Last edited by Hardway; 07-05-2013 at 09:51 AM.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    It would be interesting to see how it works out if you complete the experiment. I am curious to see the ride height (compressed height of spring) vs number of cut coils and how it relates to the xls tool I made.


    I did some spring research yesterday and John Coffey mentioned in a post that shocks can have more of an effect on the perceived roughness than springs when driving. He knows suspension so it could be fun to see what happens.
    Last edited by Blue; 07-05-2013 at 11:26 AM.
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    The person who buys on price alone is this man's lawful prey.


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    hmmm looking at the FSM again and it is more precise than at first glace....it gives different corner weights for the front so a bit more care is needed. Nissan seems to address this by having a 1/2" longer spring on the passenger side 15.2" vs 14.7"
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    I took a new shot from the passenger side this weekend. I did not get around to working on the suspension but from this angle and compared to the pictures above it looks like it is sitting close to stock height. I think my short wall tires are making it look higher than it really is. It is odd, when it was parked in the drive way the positive camber looked like it was gone and even had a little negative camber. I am going to try and correct the toe on it using the string method and get my steering wheel centered. I think if I can get this correct and drive it more, the springs will settle a bit more and everything may correct itself. I don't think I will be able to dive in to springs anymore until it cools off in the fall.

    Last edited by Hardway; 07-07-2013 at 06:33 PM.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
    06/1973 VW Karmann Ghia - Black convertible, 4spd, 1600cc air-cooled engine.
    11/2013 Scion FR-S - Silver, 6spd, a car with the soul of a Z for the modern times.
    Restoration thread of my old '72 240z -> http://www.classiczcars.com/forums/o...1972-240z.html

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    Looks much better! I hear you on the heat.... good plan.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    ZCars in Eastern Canada seaport ready for shipment to Europe

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    Ride harshness has more to do with shock compression damping, tire sidewall height and air pressure (remember, a tire is a spring with a rate around 1,000 lb. in), and bushing compliance (especially the longitudinal compliance of the TC rod bushings). My racing 240Z with 375 to 400+ lb. in. springs and Penske triple shocks was described as "cat like" in how it rode and felt.

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