2003 Rear thump at 15 MPH

[Adelina Brann]

2003 T-bird with 44000 miles. Every time we slow down, coming to a stop, there is a thump in the rear at EXACTLY 15 mph. 4 mechanics have tried to diagnose it and cannot without a tear down of the rear end or transmission. What are your thoughts of a thump in the rear at EXACTLY 15 mph, with no other issues?

 

[edward301]

Next time manually shift the transmission and see if it happens, could be when transmission
automatically down shifts, slop in the gears, u joints, or even worn bushings on rear differential,
or suspension components is the cause.

 

[biddle]

Put the 4'digir model year in the subject as prompted on future posts. Added for you.

 

[Frankie the Fink]

Next time manually shift the transmission and see if it happens, could be when transmission
automatically down shifts, slop in the gears, u joints, or even worn bushings on rear differential,
or suspension components is the cause.

That would be my suggestion as well as putting the car in neutral and letting it coast down to 15 mph withOUT using the brake, then putting it in the highest manual gear with the select shift 4th ? and doing the same thing agaon, with foot OFF the brake. and see what happens. One or other of these checks should tell if its transmisson related or not. I would do these checks with EVERYTHING out of the trunk except the battery - just to eliminate variables.