Hello. New member but I've been reading through the forums for quite a while now.

I'll get right to it: My 93 4Runner's rear is sagging, and I'm looking for inexpensive ways to replace the coil springs.
I have a pair of 98 Jeep ZJ (Grand Cherokee) FRONT coils that my buddy and I got from the boneyard for his XJ, but he ended up not using them.
Has anybody tried frankensteining a pair of front ZJs into a 2nd Gen's Rear?

Thanks!

 

I doubt anybody has tried it here, but try it and see if it works. You might start a new trend.

 

I'll give it a shot.
Is there anything out in the knowledge base (or just something I should inherently know) which makes it a bad idea to use front springs in the back?

 

I think spring rate and fitment are the bigger issues. 3rd gens use the front springs out of a fj80 to get a big lift while the 2nd gens use the rear coils. Before you tear it apart, I would at least measure the width of the coils to make sure that they are going to fit.
Also aren't the grand cherokees pretty low with stock coils? It will be interesting to see how it turns out. keep us posted!

 

Look at the ZJ springs.

Look at your stock springs.

Is the inner diameter close?

Is the wire diameter close?

Do they have the same number of wraps?

I am going to guess if they fit, they are lower than stock.

 

They won't fit.
Even eyeballing them, the coils are very different. The Jeep coils have about 3 turns more, are 4 inches taller, and an inch or two smaller in diameter than the stock 4Runner coils. So... no go.
In case anyone is wondering why the ZJ coils are so much taller, it's because they were taken from the front, not the rear.

 

I wouldn't let the height stop you from trying, but the difference in diameter is a deal killer. FJ80 coils are much taller than stock 4runner springs, but they work. Keep trying, you might find something that'll work.

 

FWIW, putting ZJ front springs on the rear of a ZJ gives it 3.5-4" of lift. this is due to the slightly heavier spring rate and the fact that they are taller as well.

 

Any coil would/could work simply by repositioning the coil itself or adjusting the coil length(cutting & bending). Coil rates are available from the manufacturers specs but front coils will have a substantially stiffer(less flex) ride on the rear in just about any vehicle. You might check out some of the Coilover shock coils for just about any coil rate(very cheap from Summit or Jegs) and a smaller footprint. Coils are not a cureall but they can be the answer.....I like to play with the width to get the flex and ride I want, we are replacing the rear axle on an FJC tommorrow with an FJ80 rear and going to use QA1 2 1/2" ID coilover springs(~225-250lb), should be fun.....