I'm looking for any advice or insight on this. It's an 04 F350 6.8L This past winter when it was cold I would start it up and it would rock forward and bounce back as is you shifted in to park while rolling. Now that it's warmed up it won't jerk forward but the whole body shakes only at start up. As much as I like the idea of of the raw torque being so powerful the truck twists with power I don't think that's the case.

 

The park mechanisim will not last if you shift it into park while moving. I don't know what its like on the truck trans but on a car trans I took apart it was a notched ring and when you put it in park a small piece of aluminum rotating on a small pin engaged the notch in the ring.


Are you saying it has a rough idle? If you shift into gear before the startup idle comes down it going to lurch when it engages

 

The truck trans has a parking pawl, pretty heavy duty piece of steel shaped like a J that locks into the reverse drum that has notches cut into it, If you put it into park at high speed 10mph or so it will ratchet out till it slows enough to catch. That is not the problem, If the truck is shaking like a muscle car with a 3/4 cam in it, there is something going on. When was it tuned last? What are the miles, some times the COP, coil on plug, the boots carbon track and condensation from the temp. drop over night will cause a miss-fire till it dries off then hits on all 10. Any CEL light or does it flash? Did you scan it and see is there are any soft or hard codes. that's were I would start. Get access to a scan tool check for trouble codes and if none, go into test's and see what the miss-fire counter reads, see if 1 or 2 cylinders are miss firing, they will store in memory and tell you which one it is.

 

Check your engine and transmission mounts.

 

It has 197000 miles on it. I have scanned it and it has no codes. It doesn't idle hard or sputter or anything like that. It has been probably 30000 since it had a tube up. It just shakes once on start up and if it's really cold it jerks forward. I'm going to take a look at the mounts today.

 

it was the motor mounts worn out and when its started the motor twists until the other motor bottoms out on the passenger side mount causing the body to shake. what causes this to turn to forward movement when cold i have no idea. ill have to revisit the problem next winter.