Hello....my son has a 2006 Ford Mustang that intermittently "jumps" when put into reverse. Do you have any ideas regarding this problem??

The dirt shield might be bent and dragging on the rotor.

tow it to the dealer. you need to use the scan tool to reset the security module. requires 2 keys to complete the proccess

Since this trips to prevent fuel from pumping in a collision, it is made to be manually reset. The device on a son's Ford used to trip occasionally on our rough easement. On his car it was located behind a panel in the trunk.

when engaging into reverse, there are two actions coming into play, reverse band and high reverse clutch. so it seems really dramatic, but its not nearly as dramatic as say shifting into second. if you have a billet servo that is

Transmission needs repair and service.

Gonna give you a list of items that I've come accross with this vehicle same problem.
Hope it helps!
EGR stuck open
battery and cables ( weak and corrosion)
Fuel pressure regulator (stuck open)
PCV valve defective
Fuel pump defective check ball ( little to no residual pressure)

its most likey your altenator there =s no charge going to the batt

your Transmission is controlled by a cable on the mustang. it could have Came off of the transmission. it just snaps on to a lever on the transmission. or the cable broke. other wise it came unhooked from your shifter.

maybe you got a bad transmission??? did you check all the vacuums and lines and fluid level?

if its in park or neutral can you rev the motor or does it stumble on itself?