Spring lengths

[SteveK]

Just about to do a spring change on a Stock 240Z (European car) in favour of new shortened, firmer springs and am checking the lengths, the ones I have been supplied are different lengths front to back, 11 inch long back, 9.5 inch long front but the Haynes manual says they should be pretty much the same length ???
Is the Haynes book up to its usual tricks again? Any one happen to have some dimensions as a guide line as I am just about to start dismantling and don’t want to get all the way there and find something is wrong.

[g260]

Steve,

I have a 74 260 and as an example in the FSM it shows the std length of the coil springs as 15.98 inches (406mm) 9.5 coils. It does not specify different lengths for front and rear. At the same time my car is lowered and it is a bit lower at the front than the rear.


Cheers,


geoff

[Bruce Woolmore]

as many of us have learned, its very easy to get this wrong, as a shorter spring can end up riding HIGHER if it is very stiff

for a Zwith stock 100mm diameter springs, the formula in Puhn's book "How to make your car handle" can be simplified to: "W^4 * 23438 / N" where W^4 is the wire gauge in mm to the fourth power, and N is the number of active coils (= free coils + .5)

e.g. for 11.3mm wire springs, poundage is 918 lb/coil.

this will give you the poundage of the spring, so you can work out what the compressed length will be from the cars weight at each corner.

[SteveK]

Thanks very much for the info guys

Spent a little while measuring up and things look hopeful, whilst the spring length looks a little short they are measurably stiffer so won’t compress as much

Rears are longer but the pitch of the coils greater than the fronts which are shorter.

I think I will offer them up and see how the car sits first, as they were made by a very reputable manufacturer that has made them for a number of Z's in the UK and they have infinitely more experience than me.


I am about to enter the operating theatre to commence surgery ---wish me luck --Once more unto the breach, dear friends, once more; and all that.

If it’s all-ok I shall emerge and post triumphantly, if not I shall be conspicuous by my silence

[SteveK]

Its looking good nurse,

Got the rear ones replaced and guess what, on a UK 240Z the stock springs are shorter than the Haynes manual states (made a phone call or two)

Haynes manual says 15 inch
My old ones = 12 inches
My new ones 11 inches

Now I will admit that they could have weakened and compressed a little but not 3 inches and besides that would have made the ride height so ridiculously high

Now for the fronts --- tally hoe