Hi, I was driving on the freeway and all the sudden my brakes got lockdown; the car was going at 60 mph to 20 mph and eventually stop even if I stepped on the acceleration. I took it to a shop and replaced all 4 disc brakes (pads). Now it still gets lock down after I drive it for about 6-7 miles. I brought it back to the shop and they told me they were not sure what caused this. Any advice is greatly appreciate. Thanks.