Engine Mount Step 2 - When an engine mount fails it can cause a heavy clunk when accelerating which indicates the engine moving around in the engine compartment. Other times the engine vibration may become more pronounced due to the mount collapsing, this will transfer the vibrations of the engine to the frame. In front wheel drive vehicles, a broken mount can cause the axle to fail or pop out of the transmission, causing the vehicle to stop moving. Oil contamination, hard shifting (manual transmission), excessive high idle, or the combination of age and engine compartment heat can cause engine mount failure. To inspect engine mounts use a flashlight and check for deterioration or tears from the weight of the engine.