If you have the optional front brake kit for your VMX450 or MM450, eventually you will need to replace the brake pads. Once the soft brake material wears off, the metal brake plates will grind on the metal disk. Not good. Long term solution is to replace the metal plates and with some made of fiberglass sheet material. You will need 2 of them and they will work directly with the metal disk brake. This is just how the 1/5 on road bikes are setup and should last a long time.
If you have a spare fiberglass (or carbon fiber) shock tower you can use that or buy a fiberglass part from another rc. Another source is locating a thin fiberglass sheet from maybe an electrics store used for circuit boards. The photos below show both an old shock tower being used as well as a Team Associated fiberglass part that is .063″ which is 1.6mm. The fiberglass will be thicker than the original metal brake plates so it is likely you will need to also replace the bolts that hold the brake pads together.
Once material is located, just trace outline of the original metal brake plates onto the material (two are needed) and mark hole locations, then cut and drill out holes where needed. When working with cf or fiberglass, you need to be careful and use safety gear from the dust generated, such as mask and containment of dust particles. In this case, the less dust you create the better, so working with a hacksaw instead of a dremel tool would be my suggestion. Consider a 3M Dust Mask rated for fine particles (the type that has the valve at the front), and a vacuum cleaner with a fine particle filter/bag to collect the most dust possible while cutting the material.
Below are some photos from Chris Haertel showing the brake pads he created from an old fiberglass shock tower. He had to replace the original bolts holding the pads together with longer ones. He cut these pads using a hacksaw with minimal dust in the air:
Below are some photos from David (RCGroup.com user Davehour) who located a nice Team Associated fiberglass part to make four pads from. He used a dremel tool to cut them out and wore a mask and vacuum to collect dust at the source as he was cutting.
Thank You to Chris Haertel and David (Davehour) for all the information and photos in this article. This is the link to original post by David on the subject. Both of you have been a huge help in keeping these bikes going!