I have an 83 Caprice Classic with a 305 and 3 speed auto with electrionic overdrive. In park the car idles fine but in drive the car shakes quite a bit esp when u let off the brake to roll forward slightly. Anyone have any ideas as to why it is doing this? It is quite annoying while sitting in traffic.

I think your mistaken. The overdrive is the fourth gear in your automatic. It has to do with the gear ratios. First and second higher gear ratio for more output torque and your third is a 1:1 ratio. Your fourth or overdrive gear is a reduction for more output speed.

I really wasn't positive if it was considered a 3 or a 4 speed I guess now I know.

Does the transmission slip in any gears (engine revs higher than it should)?

The transmission doesn't slip in any gears, however sometimes it takes a little longer to make up its mind to shift.

The transmission doesn't slip in any gears, however sometimes it takes a little longer to make up its mind to shift.

You have a TH700R4 - pull the pan and remove the 1-2 accumulator cover and inspect the spring. These like to break and when they do, the 1-2 shift slips real bad. The 1-2 accumulator cover is just to the rear of the valve body - it has three bolts attaching it.

If the spring is broken, replace it with a WHITE spring. This will firm up the 1-2 shift a bit (it's a heavier spring). This will also prevent future breakage.

The reason I was asking if the transmission slips is because when the clutch packs wear completely (all paper wears off the friction plates causing metal to metal contact), it can cause the "rough idle" in gear syndrome that you are having.

How much would it cost me to have the clutch packs replaced, or is it easy enough that I can do it myself if I have the factory service manual?

How much would it cost me to have the clutch packs replaced, or is it easy enough that I can do it myself if I have the factory service manual?

It's a pretty involved job, it's a rebuild of the transmission. It involves replacing the steel and friction plates in the clutch packs as well as all seals and gaskets. If you've not done it before and don't have an excellent grasp on the way that automatic transmissions function, then it's best left to a pro.