A rear coil isn't near the kind of pressure a front coil is under... especially when you can unload the rear suspension and take all the pressure off the springs.
I NEVER trust the floor-jack method for front coils. At $35, a coil spring compressor is cheap compared to a trip to the ER.
Also, if the engine isn't in there, you'll just lift the truck. And sometimes, even with the engine in, you'll lift the truck.
KD Tools makes a great spring compressor--it uses real course Acme threads. I've got that one, and another with fine threads. I like the Acme threads better.
-Brad
