I have a 70 Mach 1, FMX auto transmission and there is a violent jolt when I go from Park into drive or reverse, it's worse when the car is warm, ie it doesn't happen when i'm reversing the car out of my garage, apart from that the gears shift great when driving, there is no knocking or delays when going through the gears, i've currently got the car booked in with a Mustang specialist as I had to have the carb rebuilt, but any ideas what the problem could be, do you think the transmission could need rebuilding? I sure hope not, we've got a new modulator valve on order as that is the cheapest option at the moment, thanks for any help

 

The first thing I'd do is check the fluid level. Do this when the fluid is hot and add as needed.

 

could be several things for sure. As stated above fluid level. Time for a fluid and filter change. Tq coverter going south. Maybe drive shaft ujoints?<----that was my first thought