replacing struts

Is it possible to replace struts on the back of a car and use coil springs instead, rather than struts?

I dont think your grasping the concept, struts are used in conjuntion with springs.

Struts are a shock, spring, and one control arm of the suspension all in one. In order to not use a strut you would have to redesign the suspension to accept all three of these parts separately. So, unless you are a master of calculus and welding and have access to all the formulas, I might recommend against it. :)

So what should I look for if i am wanting to lower my vehicle? Another set of struts?

Nope; replacing the springs that are part of your struts. It requires disassembly of the strut unit (requiring special spring compressors) and replacing the springs with different ones.

So is it at all possible to put coil springs on a strut or is that whats already on the strut?

Take a look at this photo from howstuffworks.com

http://static.howstuffworks.com/gif/car-suspension-11.gif

The strut is the green part. Notice how it does three things. It contains the shock, the spring, and is the rigid locating mechanism for the top of the suspension. What you have to do is remove the strut, compress the spring, remove the upper plate mount, swap springs with aftermarket lowering springs, and reassemble. As you can see, there is no way to just replace the strut with a coil spring since it wouldn't do two of the three requirements.

So, yes, the strut already has coil springs on it, and yes you have to put different coils on in place of the old ones.

Let us know what kind of car you have so we can narrow it down more.

I have a corolla. See, I was looking at this site and it has a set of lowering coil springs kit, but the picture really doens't look anything like a spring.
http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Product.CATENTRY_ID:2005845/showCustom-0/p-2005845/N-111+10201+600003440/c-10101

That bunch of jumble should go to the site but basically the thing looks like a bar with two nuts, one on each end and then two snake-like pieces on it. Its a pain to describe but like i said, that should take you to the site. But I honestly, don't believe those are springs.

They aren't springs. They are spring compressors. You attach those little U-things to the coils and tighten down the bolts to draw the spring shorter. The problem is that they are unpredictable. Springs provide a predictable rate based on their wire diameter, number of free coils, and overall diameter of the coil. Simply placing a restrictor on the coils doesn't do things right. What you are basically doing is removing a random number of active coils from the vehicle's suspension. The result is unpredictable handling, rough ride, and a possibly dangerous condition.

Just pay the proper money for proper lowering springs. You'll be happy you did.

Now I'm sure with it would work with these then.
http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Product.CATENTRY_ID:2005865/showCustom-0/p-2005865/N-111+600003419+1991+200729273/c-10101.

I just need them for both front of rear.

Word of advice- stay away from products that dont list a manufacuture name, how much its dropped, or the spring rate.

Got any other websites with lowering kits? And why do you say that?

Because companies like that are just out to make a quick buck selling drop springs...they put no thought into engineering the springs to improve the handling of the car, or to make it ride well. They just sell shorter springs...nothing like drop springs from companies who do testing on their vehicles to ensure that spring rates are good for the design of the chassis, etc. Plus, you normally can't get progressive spring rate springs from those cheapo knock off manufacturers, something nice for a street ride.

If you told us what you were putting them on we might help you, were not fucking mind readers (well.. one of us is.. but he's asleep).

they are going on a 91 corolla, darn... and i expected every last one of you to be mind readers.

Ground Control makes coilovers for that car, they are adjustable 0-4" drop and are progressive rate springs made by elbach. They are about the only sleeved coilovers on the market that I would recomend, I would pick those up along with some shortend struts, and a camber kit.