What causes motor mount problems in Pontiac Bonneville 1992 to break?

The motor mounts are made of rubber and have to handle the stress of holding the engine and transaxle weight and forces of turning the wheels during acceleration. Over time, the rubber weakens and will eventually break. Some things that can shorten the life of motor mounts are:

1) exposure to oils or brake fluid

2) high idle

3) misfire

4) aggressive driving style

5) hard-shifting tranny

6) putting the gear select in P or switching between D and R without coming to a complete stop

Use of the parking brake can extend the life of motor mounts. To use the parking brake in this manner when parking the car:

1) Come to a complete stop and hold the brake pedal down.

2) Shift into N

3) Set the parking brake firmly (but not excessively)

4) Momentarily release the brake pedal, then reapply.

5) Shift into P

After you start the engine again, follow this procedure:

1) Apply the brake.

2) Release the parking brake if it is not auto-releasing type.

3) Move the gear select out of P.