Vehicles

I'm using the SCNVehicle test as a template to add a vehicle to my game. The problem is that the vehicle bounces uncontrolably as soon as it's added to the scene:

    func loadCar()->SCNNode {
        let carScene = SCNScene(named: "art.scnassets/MyVan.scn");
        let chassisNode = carScene?.rootNode.childNodeWithName("Toyota_Van", recursively: true)
       
        /
        chassisNode!.position = SCNVector3Make(0, 0, 0);
        chassisNode!.rotation = SCNVector4Make(0, 1, 0, 0);
        scene.rootNode.addChildNode(chassisNode!)
        let body = SCNPhysicsBody.dynamicBody()
        chassisNode!.physicsBody = body;
        body.allowsResting = true;
        body.affectedByGravity = true
        body.mass = 80;
        body.restitution = 0;
        body.friction = 0.5;
        body.rollingFriction = 0;
        /
        let wheel0Node = chassisNode?.childNodeWithName("fDWheel", recursively: true)
        let wheel1Node = chassisNode?.childNodeWithName("fPWheel", recursively: true)
        let wheel2Node = chassisNode?.childNodeWithName("rDWheel", recursively: true)
        let wheel3Node = chassisNode?.childNodeWithName("rPWheel", recursively: true)
       
        let wheel0 = SCNPhysicsVehicleWheel(node: wheel0Node!)
        let wheel1 = SCNPhysicsVehicleWheel(node: wheel1Node!)
        let wheel2 = SCNPhysicsVehicleWheel(node: wheel2Node!)
        let wheel3 = SCNPhysicsVehicleWheel(node: wheel0Node!)
       
        var min : SCNVector3 = SCNVector3Zero
        var max : SCNVector3 = SCNVector3Zero
        /
        wheel0Node?.getBoundingBoxMin(&min, max: &max)
        let wheelHalfWidth = 0.5 * (max.x - min.x)
        var ve : vector_float3 = [0.0,0.0,0.0]
        ve.x = wheelHalfWidth
        ve.y = 0.0
        ve.z = 0.0
        wheel0.connectionPosition = SCNVector3FromFloat3(SCNVector3ToFloat3((wheel0Node?.convertPosition(SCNVector3Zero, toNode: chassisNode))!) + ve);
        wheel1.connectionPosition = SCNVector3FromFloat3(SCNVector3ToFloat3((wheel1Node?.convertPosition(SCNVector3Zero, toNode: chassisNode))!) + ve);
        wheel2.connectionPosition = SCNVector3FromFloat3(SCNVector3ToFloat3((wheel2Node?.convertPosition(SCNVector3Zero, toNode: chassisNode))!) + ve);
        wheel3.connectionPosition = SCNVector3FromFloat3(SCNVector3ToFloat3((wheel3Node?.convertPosition(SCNVector3Zero, toNode: chassisNode))!) + ve);
       
        /
       
        let vehicle = SCNPhysicsVehicle(chassisBody: (chassisNode?.physicsBody)!, wheels: [wheel0,wheel1,wheel2,wheel3])
        scene.physicsWorld.addBehavior(vehicle)
        _vehicle = vehicle;
       
        return chassisNode!