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driveline noise - changing direction (reverse to drive, vice versa)

KillerStang

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Joined
May 17, 2021
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Location
Duluth, GA
First Name
Geoff
Vehicle(s)
2015 Mustang GT PP
My car started making a strange noise. I noticed this a few weeks ago when pulling into a parking lot, stopping, and putting into reverse and backing into the spot. It'll emit a small thunk, what feels like slop somewhere, and has a medium/high pitch metallic sound to it. It sounds and feels like its coming from the center/rear of the car.

Over the last week or so, it's been getting worse. It'll start doing it both directions from a stop (not every time) but can replicate pretty consistently.

I haven't looked at the car, or taken to the dealer. I am planning on inspecting it on a 4 post lift this weekend, and putting a wrench on everything with a few friends.

PS, car is a 2015 GT PP manual.

Any thoughts?

UPDATED WITH VIDEO: [ame]

Thanks for making this post Competition Orange. My 2015 GT PP manual with just over 42k miles on it started making the same thunk sound as in your video. The thunk would happen at the initial change in direction (forward or reverse) and would also do it when coming to a complete stop and then taking off again. Took it to my local mechanic and they said it might be the u-joints in the half-shafts, but that seemed strange because while driving at a steady speed it didn't make any noise.

So, decided to replace both rear end axle nuts before messing with the half-shafts. I read elsewhere that these nuts are ONE TIME USE only, so I decided to get new ones instead of simply re-tightening the factory installed nuts. The new nuts I ordered from CJPony are completely different than the factory installed nuts as you can see in the attached picture. The factory axle nuts came off fairly easy and that was my 1st indication that they were loose. Installed the new axle nuts and tightened to 98 ft-lbs followed by another 45 degrees. To make it easy for inspection in the future and to determine whether or not they have loosened, I drew a line with a sharpie on the nut and shaft threads once tightened to 98 ft-lbs torque position and then tightened the additional 45 degrees with a breaker bar and a pipe extension for leverage. Now, I'll know if they came loose again just by looking at the line on the nut to see if it's 45* past the line on the shaft threads.

I think the design of the factory nuts was flawed and is the main reason why they did loosen over time. Also the reason for the new design of the OEM axle nuts you can purchase now. Thanks again for this info, which made for an easy repair and noise free driving once again!!!

Axle Nuts.png
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