what sandpaper should i use to remove bad primer job and smooth out the old pant below so new primer can be applied?

It all depends on how much material you plan to remove, or need to remove. Just remember the new paint will only be as good as what's under it. If there are any adhesion problems, cracking, shrinking etc. then I would recomend stripping the car. If you just want to remove some of the buildup then I'd try 180 grit moving to 220 or 320 before application of any primer. You may want to chemically strip and take it all off and start fresh. Any idea what kind of paint is on the car-laquer? enamel? urethane? You could remove some material then straighten it out with a good urethane primer surfacer but the lifespan of the new paint will be cut short if the undercoats are old laquer or enamel. If this car is a keeper I'd definately recomend stripping ind starting fresh. JMO smile.gif