One problem related to rear suspension springs has been reported for the 2006 Ford E-450. The most recently reported issues are listed below.
Startrans bus made by supreme. 24 passenger Ford e:450 shuttle bus. We have two- 2006 shuttles. On both buses with less than 50k miles the rear spring moreride through bolts break! this is very dangerous! both rear spring bolts break leaving the rear springs in dangerous! when I brought it up to my dealer, they said no recall. No accident happened but this in not something easily seen by a visual inspection and can go unnoticed. I have never had this happen with any other supplier.