U-joints

I just put new plugs and wires in my 96 3.8 this weekend, it took me a total of 7hrs to do.  Next weekend I'm replacing u-joints.  I've looked through my Haynes manual just to get an idea of how to change them (I know the book will probably make a better table stabilizer then a manual but...) but the manual used terms I had no clue as to what it was talking about.  Well heres the deal, whenever I put my car from park into reverse or drive the car jerks quite a bit (and yes I have my foot fully on the brake when I do it).  I originally thought it was my transmission mount so I replaced that and now it is still doing it.  I should have tried to spin the driveshaft by hand when I had it up in the air before replacing my tranny mount, just to see if it would spin.  From what I hear if you can spin the driveshaft by hand when the car is in park (and off the ground) then that means the u-joints need to be replaced.  But what I have found out reading the manual was that the 6cyl models have a two piece driveshaft (I never really looked at mine) and I was just wondering if it's not the u-joints then could it be where the two shafts connect that is causing the car to move when putting it in gear? 

most likely your U-joints and they are also the cheapest and easiest option

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ORIGINAL: purpl96
From what I hear if you can spin the driveshaft by hand when the car is in park (and off the ground) then that means the u-joints need to be replaced.  But what I have found out reading the manual was that the 6cyl models have a two piece driveshaft (I never really looked at mine) and I was just wondering if it's not the u-joints then could it be where the two shafts connect that is causing the car to move when putting it in gear?

If you were able to spin the driveshaft while in park, then you would have either a snapped u-joint, and the car won't drive at all, or the parking pawl inside the trans is broken. When the trans is in park, the driveshaft, (and therefore the rear wheels) are prevented from turning so the car won't roll. From your description, neither of these is what you have going on. What do you mean by the car moving when putting in gear? All cars move when put in gear. Need to clarify that. Are you getting a clunk sound like from having excessive rear differential slop, or do you feel something moving around under the car like the driveshaft flopping like a fish?

It moves as though someone has set a 50lb weight on the trunk lid of your car and then quickly picked it up.  It isn't making any noise, but when I'm on the highway or just anywhere cruising and I hit the brake to slow down (when I'm still moving) when I go to put my foot back on the gas to accelerate it seems as though the driveshaft spins a quarter of a of a turn before it actually starts putting more power to the wheels.  I can't hear that making a noise either but I also have Magnaflow so I might not hear it.  I just talked to my dad and he just thinks it's how the car is.  He also said that all cars move when you put them into gear, but I've drove trucks and SUV's with V8's and I've never driven one that did this when I put it into gear.  It could just be that I'm a perfectionist, but the car does have 160k on it so I guess I can't expect it to operate like it did when it was new.