Cant do it with the current version. In the next version you should (I havent actually done it yet) be able to adjust any of the parameters on a joint and then that kind of braking would be possible.
At the moment suspension is no longer the biggest problem. few issues with the wheels. convex hulls not cylinders so there bumpy and the warthog ive downloaded doesnt have the wheels centred so that needs fixing
You can hook it up to use SketchUp's native walk, look, and collide. If you modeled a building, you can walk around in it with the gamepad. A lot easier than the mouse! It's almost like playing game...
Gears can be very finicky. Make sure you are clicking on the joint and not the object+joint group.
Wheel and door work fine for me. Make sure you have a floor or some other object when you are trying to create something. They need an object to connect to.
If that isn't the problem post a model and I will take a look.