One problem related to brake master cylinder has been reported for the 2004 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Ford Mustang based on all problems reported for the 2004 Mustang.
Casual driver. Noticed acceleration and coasting/rolling were sluggish. Mechanic noted brake area temp on front driver's side was over 400 degrees. The brakes on that wheel would not release completely and caused continuous friction producing overheating. (I noticed I am not the only one to submit this brake problem to this board. ) the mechanic replaced the total front brakes and master cylinder system. Cost over $1100 to do this back in 2013. It is now Jan 2021 and I still have less than 50,000 miles on my baby Mustang.