spring rates for 240z

[240zchevyv8]

Hi guys right spring is in the air, nights are getting light and its warmer in the garage, time now to sort out my dreaded oversteer problem, ill start at the begining and go through all the changes made, firstly its a 1970 240z left hooker imported last year, fitted with a 5.4 litre chevy v8 in the scarab position, problem was it scared me to drive it with any kind of agresiveness not down to the horsepower but the lack of handling (road holding) car had, first thing i replaced all bushes on the car with superflex no real change in handling fuck me what next, changed the suspension fitted some coilovers that came with the car, spring rates were 8kg im sure i read somewhere that it equates to 400lb springs way to stiff but thought id fit and see, very little change, bloody hell this is a nightmare right ill lower the car and lower the centre of gravity, lowered car 1" using the newly fitted coilovers no change, erm erm what next i know ill move the engine back further, removed the engine made some setback plates, sent drive shaft away for shortening fitted a stronger R200 dif and re-fitted engine 3/4 inch from bulkhead this gives near stock weight distrubution, a bit better but not to my liking, bloody car well it has a 1" front anti sway bar and 3/4 inch rear dont think this is the problem but it will be making the car stiffer which i think is the problem, im going to swop the front and rear coil over springs but not sure to what rates i thought 250lb, any suggestions, but to get the correct size do i jack up the car and measure the spring lengths while not under load and order new ones this size and adjust the height of the car with the colar on the coil over, also car is lowered how important are bump steer spacers, i ask because even before i lowered the car it felt like it wandered so will it make much difference fitting them, now onto tyres it has 225-50-15 futura GLS super sport tyres all round i know these are not a very good sports car tyre but car came with 4 brand new ones fitted, they themselves may be contributing to my over steer problem but not to the overall poor feeling of how the car handles, the body shell is good has nothing that makes me think this is any way to blame, i suspect that over all the car is to stiff so rather than riding bumps and road unevenness it skips and feels loose instead, can any budding fomula 1 drivers confirm this, the car has improved in handling since i got it, but still feels unpredictable, also if any one thinks im expecting to much from the car, this is my second 240z and my last one had standard springs standard bushes 195-70-14 tyres and it handled better than this oneany suggestions would be helpfull just want to get the car right without robbing fort knox,

 

[tel240z]

sounds like you need some softer rubber and springs on the back what pressure are you running in the rear tyres

 

[240zchevyv8]

running 32lb all round ???

 

[moggy240]

what spec shocks are you using

 

[240zchevyv8]

when you say specs in what way do you mean, they were 8kg coilovers with a helper spring not sure of the make only cheapies i think as they came with the car, but quality wise they look fine although im sure they are to stiff. just been on net type in 8kg spring and it appears they are 447lb springs its 8kg mm2

 

[moggy240]

i mean what shocker insert do you ........tokico hp/5way adjustable etc

 

[240zchevyv8]

using KYB 240z rear insert in the front strut, and i think a vw one in the rear but cannot remember which one, at the time it was one which everyone said worked best when sectioning the struts, i forgot to mention that when i fitted coil overs i sectioned the strut towers by removing 1.5" from each strut to lower the car before fitting the threaded colar.

 

[zbloke]

If you haven't done this already, I'd take your car and have the wheel alignment checked, front and rear, caster, cambers and toe settings, if one or more of these are incorrect your car will not handle great

 

[240zchevyv8]

i took the car in to have them checked and they said they could only check the tracking, isnt that toe in and out, which when altered made little difference???

 

[zbloke]

On a standard 240 you can only alter the front toe angle, tracking, but the other angles can still be measured and if found to be wildly out need, IMO, to be corrected but the only way to do this is with aftermarket suspension arms.

I just think its important to know where your wheels are pointing, if the caster and camber are pretty much even side to side and not too OTT then move onto another part of the suspension to look for the problem

 

[zeeman1972]

From memory, when I was looking at using iron block chevy's, unless your 327 has ali heads/inlet manifold/water pump/exhaust manifolds etc and your battery is still under the bonnet you will still be 60-70lbs heavier on the front than the rear, even with the engine in the set back JTR position. However I wouldn't have though that this was the cause of your problems but perhaps exacerbating it?

All I can suggest, as Zbloke says above, is when I bought my coilovers over from the US I also purchased adjustable lower arms and camber plates to enable the adjustment of the camber/caster back to something resembling normal when the ride height altered. As you have mentioned there isn't exactly much in the way of adjustment of these things with stock 240Z suspension.

 

[Rob Gaskin]

First of all a 240 is a great handling car and shouldn't give you any scary moments unless you are a maniac driver. I've only had the one car but can tell from other peoples cars on track that they are the same. A lot of power and torque will make it harder to drive if you're not smooth with the right foot.

If your car is scary then something is wrong. As suggested you need to be sure that all 4 wheels are pointing in the right direction.Things like bump-steer spacers, different dampers etc, will make a difference but this is tuning really.

Have you changed the rack mounting bushes as well as the suspension bushes. My car was dangerous until I made sure the rack stayed in position when I steered. Look at the rack whilst a mate turns the steering wheel. My rack moved from side to side and the wheels stayed still!!!

Are the rear arms located properly? The inner bolts (the big ones that thread into the ends) come loose on my car. Check all the mountings and bushes for tightness.

400lb springs and stiff anti-roll bars will make the car 'twitchy', you really need to try it with softer springs (200 - 250) and perhaps the ARB disconnected/removed.

I had a problem with a worn front crossmember on an Avenger once. The inner TCA bolt holes were worn into a slot and halfway through a corner the TCA would move with a resulting steering angle change - nasty.

Tyres - they make a huge difference - can you try someone else's wheels/tyres on your car. Also don't go too wide until you have got the suspension geometry sorted. When I got my car it had 225 Kelly tyres on the rear and it was undrivable in the wet even at slow speeds. Changing the rack bushes and rear tyres transformed it.

 

[twoforty]

I had a few issues with mine over the last few years, First off change the steering bush for a nylon type and change the rack mount bushes. The front tie rod bushes and lower arms bushes need to be changed for nylon too. As for spring rates I have 200 front and 185 rear right now with uprated anti roll bars...I wouldn't go stiffer than that for road use. I think the main problem, well at least on my car is the change of wheel and offset....this changes the Scrub radius and SAI and makes a bit twitchy, If you have adjustable ride height you also need to have the car setup on corner scales or it will feel very strange!

 

[240zchevyv8]

Well guys i can see that ill get sorted from the suggestions made, firstly yes zeeman 1972 the 327 is slightly heavier and it could be slightly adding to a balance issue but car has a R200 fitted this is around 15 kilos heavier?? so would have thought that balances things out, car has new steering bushes fitted and lower ball joints and wheel bearings, ive been swapping all suspect parts, ill recheck for movement on the steering parts but dont suspect that, first job is sort out the spring rates would 200 all round surfice or should i do as two forty and have different front to rear or go with robs advice and go 225 all round, as i mentioned earlier how do i measure for spring length, is it jack up car and measure the complete length of the existing set up and buy springs that length, ill recheck for rear arm locations to make sure nothing has moved, how does one set up the car on corner scales, what is the process? i suspect that camber and caster are out, should i fit bump steer spacers due to lowering the car or are they a waste of money,

 

[amocrace]

i would say straight away that your rear springs are way too stiff.
to have a car with independant rear suspension handle properly you need to allow the suspension to actually work, most people seem to go too stiff on springs.
the other major problem can be rear wheel alignment, if the rears are toe-ing out you will get rear wheel steer which can be really scary!!
4 wheel alignment needn't be rocket science, we still, at times, do it with string at a race track.
simply put an axle stand at each corner, go round with string parrallel to car both sides and measure with a tape. if front edge of rear tyre is closer to string than rear edge thats your problem. hope this helps
cheers
brian

 

[240zchevyv8]

Cheers brian will check tommorow, i know springs are WAY to stiff i just need someone to comfirm if i measure them the way ive suggested then i can order new ones and scrub another suspect of my list, just been looking at new tyres what tyre do people recomend obviously goodyear dunlop are the obvious choices but it does not mean they make a good sports tyre,

 

[Rob Gaskin]

go 225 all round, jack the car up and measure the complete length of the existing set up and buy springs that length, fit bump steer spacers

Yes!

 

[240zchevyv8]

cheeers for that rob will measure springs tommorrow and order bump steer spacer from black dragon

 

[twoforty]

Don't forget dampers change the ride a huge amount, adjustable oil type give the best ride.....some of the gas shocks around make the cars feel like they have no suspension.

 

[240zchevyv8]

Hi guys finally getting some where, tried to get 225 lb springs but 2.5 inch more rare than 2.25, so ended up settling for 2.5"id 200lb simply because they were on ebay buy it now £164 delivered, fitted them all 4 corners and cleaned wheels in and out 4 hours (not bad going now wheres the application form for F1 pit crew) still awaiting bump steer spacers to arrive hopefully next week, but been out in car and it is driving a lot better now not stiff like it was, i havent gave it a damn good thrashing yet to test how it handles but it does feel better, still adjusting levels to get the right stance just about there now i think lower the front 5mm and raise the back 5mm and that should be spot on, engine running a lot better now easily leaves 50 ft tyre marks on the road frigin unbelievable have to ease of the throttle for that as well otherwise id have no tread left will keep you informed how the bump steer spacers affect handling.