One problem related to brake drum wheel cylinder has been reported for the 2007 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2007 Toyota Sienna based on all problems reported for the 2007 Sienna.
Noticed a vibration starting on a 2007 Toyota Sienna xle. Initially thought it to be tire related. Upon investigation noticed the left rear wheel was too hot to touch. Revealed that the brake assembly had siezed and was causing the brakes to overheat (blue dick and cylinder). Toyota claims they have seen this on many Sienna's and they regularily lube the slides that mount the wheel cyinder. Mine had not seen lube. Brake pads on the remainder of the car were ~ 50%. I believe had I not found this, there would have been a fire (it was that hot). Now I'm stuck on my $ to pay almost $1000 for new brakes (opted to overhaul the other three to eliminat the same problem elsewhere).