My friend car shakes when he switches from park to drive, what is the problem?

Transmission problems. Go see some mechanics.

i figured as much, do you think you might know what with the transmission?

It could also be the engine mounts. Time for a mechanic.

It’s impossible to know without seeing it. Chances are, it’ll need to be rebuilt though.

well, thats gonna be bad news for him because this is his replacement car for the car they tried to rebuild the engine before, and messed it up.

I don’t know – but I wouldn’t drive it to the mechanic – I’d have it towed there. Pronto.

My wife’s old Mazda 626 did similar things; it had the (defective) Ford CD4A transmission, which has a bad reputation. Our Saturn did this too… after it cracked the diff pin and shot it through the bell housing in such a way that it would not hold transmission fluid.

I’ll wager that the transmission went. My experience is that it’s often cheaper to replace an automatic transmission than to repair it if it’s that far gone. In fact, repair may not even be possible.

@Zen_Again At this point, I think it makes little difference. If it is the transmission then the worst that could happen is that it will finally let go en route.

It could be a numerous amount of things, like Captain Fantasy said, it’s impossible to know without seeing it.
It could be the alternator, the timing belt or the entire car itself.

could be a bad universal joint. not hard to do if you’ve ever worked on your car before.

http://autorepair.about.com/cs/doityourself/a/aa102602a.htm

Unfortunately, I had a 2004 Ford Explorer. That thing had the nations worst transmission at the time. It literally was made out of aluminum. Dealing with this hunk of metal taught me alot about transmissions. Automatic transmissions have divots or little side wholes that are numbered (mostly) 1–6. There’s also P(ark) and D(rive). When you put the car in drive, the transmission pulls a pin from P to 1. A faulty transmission has varies types of problems with “shifting” (You don’t shift an Automatic transmission, it shifts itself). The pin could be getting stuck, so the Engine is reviving at 1st gear, but the pic is stuck in Park for the moment. When the pin finally moves to 1st gear, the car “jerks” because the engine is already spinning and the rest of the car has to catch up quickly. Normally, if the car jerks when shifting up, there might be a problem with the transmission holding gears. Those divots I mentioned early could be worn down, making it harder for the car to hold the pin in that spot. When the pin slips out of that divot, the car jerks because it was running at gear 4, but slipped down to 3rd gear. 4th gear is obviously faster than 3rd, so the engine has to do the opposite, instead of “catching up” it has to “hold up”, it’s going too fast for the transmission.

Basically, here’s a easy way to look at it:
the letter “c” is a divot. After years of dwonky driving, that “c” divot is worn down into a “r” divot. The pin looks like this “o”. c can hold o, r can’t hold o. So the “o” slips out of “r” into the next lower “c” divot. Comprende?