If it is is park and still rolls, your Pawl is bad. Neutral and Park are actually the same thing, the only difference is, that when you put it in Park, the gear selector moves a rod that enhances the parking Pawl. Pretty much a large wheel in the back that looks like it has gear teeth and the Pawl is a stub of metal that fits into one of the groves and locks the shaft from turning. They can brake. Always use your E brake on hills. I rebuild transmissions.
Your probably letting your transmission roll forward or backwards after you put it into park. This puts pressure on the transmission where it stops and it "pops" out of park for this reason, making the loud noise. Apply the E-Brake after putting it into park but before you let off the regular break, it wontcontinue to roll.
You need a transmission or gear shifter repair. The only reason for it to roll is that it is not actually engaged in the park position.
I asked a service writer at a Ford dealership , and he said that was normal when the transmission is warm and you take your foot off the brake , even though it is in drive , it will roll backwards on a slope
the transmission
No, No car equipped with an automatic transmission should, unless the linkage is out of adjustment and it is not going into park.
I think you might be talking about a backwards roll which is basically a roll from crouching where you lean backwards onto your shoulder and your arms are straightened, and you end up standing.
the problem is u have to take it to a transmission repair guy
the car will probably roll backwards or forwards if it is on a hill. If the car is on a flat area of the ground, nothing.
Either your brakes are 'ground' or something is wrong with the connection between the stick and the wheels. Go see a mechanic or car professional.
If you more specifically meant "why does it roll even after you put it into park?" its because the parking gears are sliding into spot. When you throw the car into park the gears attempt to push into their proper place, then when you let off the brake they slide into their spot, and theres room to work with so your car may roll back and forth. That's why if you have a large truck with huge parking gears like the Allison transmissions do the gears will produce a loud click as they literally fall into their designated spot and clang against the transmission's teeth.
I have read that the piece in the transmission that holds a car in park can break. I would just use the parking brake each time.
I will bet that you are parked on a hill. If the car drifts backwards, it can bind the park pin in the transmission and make it difficult to take it out of park. Before you have it hauled off to the transmission shop, see if you can convince some friends to push the car uphill an inch or 2 while you try to drop it out of park.