Dropdownlist no se actualiza

[chemicalboy]

tengo 2 dropdownlist que cargan datos de una base, al escoger el primero se llena el segundo dropdown con los datos relacionados, yo quiero que al escoger un valor del segundo dropdown se me actualize un txtbox pero no lo hace, los dos estan con autopotback true aqui esta el codigo



----Aqui relleno el primer dropdown-----
Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
GetCars()
End Sub

Private Sub GetCars()
Dim objCarCollection As New CarCollection(CarCollection.FilterType.ByBrand, Settings.DefaultBrand)
ddlCars.DataSource = objCarCollection
ddlCars.DataTextField = "Name"
ddlCars.DataValueField = "Id"
ddlCars.DataBind()
End Sub
-----------

Dropdown 1
--- aqui si cambia el dopdown 2 -----
Private Sub ddlCars_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlCars.SelectedIndexChanged
ddlModels.Items.Clear()
Dim objModelCollection As New ModelCollection(ModelCollection.FilterType.ByCar, ddlCars.SelectedValue)
ddlModels.DataSource = objModelCollection
ddlModels.DataTextField = "Name"
ddlModels.DataValueField = "Id"
ddlModels.DataBind()

End Sub

--------------------

Dropdown 2
------aqui deberia cambiar el txtbox-----
Private Sub ddlModels_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlModels.SelectedIndexChanged
Dim objModel As New Model(ddlModels.SelectedValue)
txtPrice.Text = objModel.Price1.ToString("##,##")
txtPrice.ReadOnly = True
txtcuotas.Text = String.Empty
End Sub
-----------------------
Bueno espero que me ayuden si no me explico bien me avisan gracias!