one of the mounts on my transmission busted the other day. my question is, can i replace it with the transmission in the car, or do i have to take it out?

 

You can replace it while the transmission is under the car. Here are some steps to follow:
1. Raise vehicle until you are able to slide under the vehicle. Best to have all wheels off the ground and use a reliable jack stand.
2. Use a jack and place it under the rear of the tranny. Raise jack until snug with tranny.
3. Unbolt all bolts holding the cross member to the chassis.
3. Proceed to remove worn out tranny mount. I suggest using a ploy urethane mount.

 

should i loosen the engine mounts before i jack it up?

 

I hope you are referring to the tranny mount and if so, you could losen the tranny mount prior to raising the jack until it meets with the tranny. Just to make it clear, all your doing with the jack is to support the tranny when you remove the cross member. You shouldn't have to raise the tranny at all.

 

Where can I get on of these Poly mounts you guys are always talking about?