Answers can take from a few minutes to a day or more depending on who sees your post and when, and whether someone knows the answer. Some of us will research with our noses in the service manual for an hour or more before we post what we think will be a worthwhile reply. In this case there is no such thing as a "common problem". If there was, we wouldn't need mechanics to diagnose these things.
Not sure what you mean by "pull forward". It doesn't move forward when you accelerate? It doesn't creep ahead when you release the brakes? When does it vibrate, whenever the engine is running? Just when you raise engine speed? Only in reverse? Do you feel it in the seat, steering wheel, whole van? Is it a low thumping-type of vibration or a high-frequency one? A shudder? Have you checked the fluid level? Checked for leaks? Checked for diagnostic fault codes? Is the Check Engine light on? These are all things a mechanic will ask you or they will observe on their own to start the diagnosis process. You're expecting us to guess.
You didn't even bother to list the engine size or transmission model. The transmission might be something you don't know, but we can figure it out if you at least give the engine size. Without that information a lot of people are going to skip over your question and move on to one they can help with without dragging the information from you.
Wednesday, October 17th, 2012 AT 8:09 PM