Help Whit Adding New Parts To Car

When I Add Parts To Cars Parts Just Doesn't Stick.
Some Times Every Part In The Car Doesn't Stick.

So How I Fix This Problem

 

To clarify, you are creating a mod that adds a new component to a vehicle. When you select the new part in the parts selector, it spawns but falls to the ground. Is that correct?

 

sorry for the late answer but No the part is attached to car but doesnt stay in one place when turning or part spawn to the ground and does the same thing
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and sometimes this happens

 

Make sure to apply the location, rotation and scale of the objects before exporting them.

If you are using blender: select the objects, and press CTRL + A

 

apply the location in blender?

 

Yes

 

Thank You So Much