[palm sander spins too fast]

All 3 are makitas 5 inch palm sanders.

[palm sander spins too fast]

On the job site we have 3 orbital hand sanders.  All three of them have been spinning uncontrolably, so fast that you cant lift it and put it back down without leaving spin marks. Does anyone know what causes this and how to fix.  We replaced the bering and bering housing on one with no effect.  Thanks for any help.