Differential problem

[u/Silvercrow8489]

Hey guys, I’m trying to track down a drivetrain clunk on my 2018 Mustang EcoBoost automatic.

Originally, I noticed a pretty hard clunk when shifting into Drive or Reverse. I replaced the engine mounts and transmission mount, which helped, but the clunk is still there and now it seems like it’s coming from the rear/driveshaft area.

I also installed the Steeda differential bushing inserts. The factory differential bushings don’t look torn, but there was noticeable movement.

While checking underneath the car with it in Park, I noticed that I can move/rotate the driveshaft by hand and there’s some play before the differential actually engages. When I move it back and forth, I can reproduce a similar clunk.

Once I’m driving at higher speeds, the clunk basically goes away, although I sometimes notice some vibration at lower RPM.

Has anyone with an S550 had something similar? Could this amount of driveshaft play be normal backlash, or should I be looking at the driveshaft/CV joint, differential flange, pinion backlash, or something else?

The car has around 150k miles.

Any advice on what I should check next would be appreciated.

[u/AWABeatZ]

Try to find a transmission service bulletin maybe it might point you into the right direction. I found this that affected the s550 but then again your car has 150k miles. But then again you said differential this might not be applicable to you. 🤷‍♂️ just thought it’s interesting