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

Competition Orange

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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]
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MSMStannyl

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Welcome to the Ford Mustang and the MT-82.

Could also be that Torsen diff. Haven't some people been talking about it thunking?
 
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Welcome to the Ford Mustang and the MT-82.
This is not the same "thunk" that plagues these cars/transmissions when selecting gears (I also have that).

This also isn't the normal driveline slop that these cars have.

It's a distinct metallic pop/thunk type noise when transitioning at slow speeds from forward to reverse and vice versa.
 

MSMStannyl

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Does it only happen when turning? If so, it could be the diff potentially.

Mine is a non-PP with the 3.55 limited slip so I haven't dealt with it. However, I've definitely read about others with the PP diff having some thunking issues.

Before the Mustang, I had a WRX. One day, as I was pulling out of a parking spot, turning the wheel sharply, I started hearing this loud thunking. It turned out the rear diff went bad. It was basically locking up and not letting the rear wheels spin at different speeds during a turn. The thunking in that case was the tires breaking free while being "locked" at the same rotation speed. In this case, it wasn't just 1 thunk but it would thunk, thunk, thunk as you were turning, speed dependent.

Does that sound like what you're experiencing? I take it from your first response that this is definitely a new sound and not something you've heard before? A dealership visit may be in order regardless.
 

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Does that sound like what you're experiencing? I take it from your first response that this is definitely a new sound and not something you've heard before? A dealership visit may be in order regardless.
It is independent of steering angle. It seems related to the forward/backward forces, not turning.

No, car will turn just fine, no noises while driving that I can hear. The car does seem to chirp the tires when turning very easily, but it's always done that... Yep, new noise, nothing "normal."

Dealership will be last resort.
 

whatsup62

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Yeah...I have the same noise. Mine was much more apparent when I went to a aluminum one piece driveshaft and the DSS halfshafts. I have changed fluid twice, re-torqued axles three times and still does it. It also handles DR's with hard launches with more than stock hp/tq...which the original MT82 did not (on second trans). So with all that being said I guess I have decided to live with it.
 

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Are any of your diff bolts loose or broken?
Is your exhaust perhaps tapping the sway bar?
What IRS modifications do you have, if any?
If you jack the car up level in neutral, can you replicate any play in the driveshaft itself (the joints, not the diff/trans slop BS we all have)?
 

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When you drained the axle lube, was the oil relatively clean, with just metallic paste on the magnet, or were there larger bits of debris? Its clearly a backlash issue at load reversal; some amount is normal, but what you have likely isn't. I'd start by, as suggested above, getting the car off of the ground and trying to rotate stuff in the drivetrain and see if anything jumps out. The tricky part is that noises travel up and down shafts readily, and tracing their source while driving is near impossible. You should put the car on a chassis lift and and see what you find when you turn the driveshaft and wheels, etc.
 

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Are any of your diff bolts loose or broken?
Is your exhaust perhaps tapping the sway bar?
What IRS modifications do you have, if any?
If you jack the car up level in neutral, can you replicate any play in the driveshaft itself (the joints, not the diff/trans slop BS we all have)?
Haven't checked yet. No IRS mods.

I'll be looking tonight/this weekend.

When you drained the axle lube, was the oil relatively clean, with just metallic paste on the magnet, or were there larger bits of debris? Its clearly a backlash issue at load reversal; some amount is normal, but what you have likely isn't. I'd start by, as suggested above, getting the car off of the ground and trying to rotate stuff in the drivetrain and see if anything jumps out. The tricky part is that noises travel up and down shafts readily, and tracing their source while driving is near impossible. You should put the car on a chassis lift and and see what you find when you turn the driveshaft and wheels, etc.
Fluid was very dirty, and had some paste on the magnet plug.

I didn't notice any large chunks no.

Thanks for the info. I'll see what I can do, with the space I have, and access to a 4 post lift this weekend and go from there.
 
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I managed to put a socket on the rear axle shaft nuts with an 18" breaker bar. Got them to move about 1/4 turn, and seems better...

I need to source a deep socket to get full seating, and try again, but this might have cured it...
 

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I managed to put a socket on the rear axle shaft nuts with an 18" breaker bar. Got them to move about 1/4 turn, and seems better...

I need to source a deep socket to get full seating, and try again, but this might have cured it...
The spec is 98ft lbs + 45 degree turn.
 

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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:
My car is now making the exact same noise. What ended up being the issue with yours?

Thanks!
John
 

jgedde

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I fixed it!!! Clues were the fact that snugging up the axle nut made the sound change.

After reading some threads from an internet search it appears the 370Z has the same issue and they cured it. The fix is really simple... Lubricate the axle to hub flange and the axle splines... This may sound difficult, but you don't have to remove the axle shaft from the hub! It took me about 20 minutes in total.

Here's what I did. Remove the wheel. Remove the axle nut. Now give the axle shaft a few good raps with a brass headed hammer. If you don't have one, I suggest the following alternates: a large hammer and a piece of brass to protect the axle shaft. An aluminum block will also work. Wood may work but it doesn't transfer as much shock.

The axle shaft will move back into the hub about 3/4" then go no further. But this is enough to apply the lube. If you look behind the hub you'll see the flange on the CV joint has about a 3/8" gap.

Wrap the threads on the axle shaft with masking tape to avoid getting grease on the threads - you'll see why later. Get a spray can of SuperLube. Put some towels on the ground to protect the surface. Spray a liberal amount into the gap. Now, spray some into the exposed surfaces inside the hub splines from the nut side.

Remove the masking tape from the threads and make sure they're clean. Put some red Loctite inside the nut threads and reinstall the nut. Tighten to 98 ft-lbs followed by another 45 degrees. Put the wheel back on and be noise free!

Cheers,
John
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