coil spring sizes? help please!

ok so i am planning on putting four-link suspension under my 75 cj5 and i dont know what size coils i will need because it is being converted from a leaf-spring setup. i wanted enough room to fit 35-38 inch tires on with some flex left i also plan on extending the wheel-base. btw this is a wyotech school project and i just need a bump in the right direction so any help will be greatly appreciated!!

 

You may find it's a little tough finding room for coils on the stock width axles. Look into coil-over shocks. They are a lot smaller in diameter and are somewhat adjustable for height. Better have a bag of $ for this type of conversion though.

 

ha ha ya anybody know a ballpark range i would need to do this conversion?

 

I have a friend who installed ZJ coil springs and Nissan patrol axles on his jeep commando. Now he has better road manner and great flex. If you are interested I can say my friend that send you pics. of instalation and a little explanation.

 

Not sure if your planning on four linking the front or not, but heres some numbers to budget...16 heims or johnny joints--40 each, bolts/nuts/washers--4 each, tube adapters--15 each, jam nuts--2 each, tubing--8/foot, coilovers--600 each by the time you get springs, 4 link brackets--200. Some of these prices maybe a little low or a little high but there not far from what you'll be paying unless you can find some deals on some used parts. So thats $3032 bucks for the parts and dosnt include any time, coilover mounts, welding cutting grinding supplies, or steering stuff for the front. Im assuming your not going full hydro, so you'll need a track bar and the mounts for it. If I were you I would budget around 4500 bucks to do this project correctly. Im sure it can be cheaper using tractor heims or using square link tubing, or going with reg. TJ coils, but the parts I listed above you will have an excellent offroad vehicle that you can drive on the road without any ill effects.

 

Alright most all of this info is out of the "jeep performance handbook" by Jim Allen. (highly suggest buying this book, some of it is a little cheesy but there is def. some real good info in it)

If you need to know any Jeep spring rates they are in the book also, or ask here and I'll look it up, just tell me the year and vehicle.

To figure the amount of lift that you will aquire you need to know your spring rate of the springs and the sprung weight on the front axle/rear axle. Once you have those numbers, subtract the weight of everything bolted below the springs, axles, wheels, tires from the front/rear weight totals. Sample frotn weight is 2000#, axles,wheels,tires weigh 400# so your sprung weight would be 1600#. Divide that number by two since half the weigh will be on each spring, 800#s per spring. Once you have that divide the sprung weight by the spring rate. So a stock 55-65 CJ5 spring rate in the front is 240, this sample would give you 800/240 3.33" of spring deflection. Now once you have this number you can subtract it from the arch of the spring and that will show how much lift you will actually have with the weight of the vehicle on it. So if with stock springs you were at 1" of deflection these springs here would give you aproximatley 2"-2.5" of lift over the existing springs.

I used these calculations to figure out my stuff on goldmemeber and they all came out exactly how I wanted. I ended up with right at 4.5" of spring deflection, which with stock XJ/YJ springs makes them almoist flat but they have a little arch still left to them. Which in turn keeps the center of gravity down low and allows the springs to have more down travel offroad rather than alot of upward travel, or making the vehicle sit taller than desired.

 

wow thanks for all the help guys! i cant wait to get started on this jeep!

 

Just post some pics when you get started

 

ya i will if i can get wyotech to allow me to take a camera in