'18 3.73 PP Diff whine

[HourlyB]

I have no idea if they did the job properly or not. I was just putting out the correct procedure.

Sometimes crap happens.

True, I'm jut worried since this is my daily, and on top of this if the mistake is on their end, I don't want to be the one literally paying for it to be fixed, y'know?

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[K4fxd]

True, I'm jut worried since this is my daily, and on top of this if the mistake is on their end, I don't want to be the one literally paying for it to be fixed, y'know?

If it didn't whine before the pinion swap, it's on them.
Can you contact the previous owner?

 

[HourlyB]

If it didn't whine before the pinion swap, it's on them.
Can you contact the previous owner?

Yes, he said there wasn't any noise.

 

[HourlyB]

Al

It's probably just not torqued correctly.

Actually just came to me; where did you find these instructions?

 

[Brian@BMVK]

Al

Actually just came to me; where did you find these instructions?

I have a digital copy of the service manual.

 

[HourlyB]

So, something odd I've noticed is that when the whine starts happening, as soon as I put the car out of gear the whining stops. I've even accelerated and let the car decelerate through where the noise is the loudest, and it doesn't seem to be there. Not sure if that indicates anything.

 

[Cobra Jet]

So, something odd I've noticed is that when the whine starts happening, as soon as I put the car out of gear the whining stops. I've even accelerated and let the car decelerate through where the noise is the loudest, and it doesn't seem to be there. Not sure if that indicates anything.

So few questions:

Why did the Seller remove and sell that rear differential? Was it from a salvage facility, re-sale shop or private seller?

The reason I ask the above is - more than likely that diff was replaced because it had the noise issue you're now dealing with. It's cheaper for a shop (Ford or other) to replace the entire rear pumpkin, than to "gut it" when talking labor rates. Even for a DIYer, it's easier to swap than gut. My guess is, that rear you now have was problematic and that is why it ended up for sale.... Anyone can say after the fact that "it had no whine", because how can you test a pulled pumpkin without it being on a vehicle?

As for your above response that when you take the car out of gear, the noise subsides.

That's typical of a bad rear (one where there is excessive audible whine), and the reason the noise subsides is because now the rear and driveline is no longer under load. The moment you either accelerate OR put the car back into gear, the driveline is under load again, which is pressure against the gears/pinion bearing.

In a normal environment such as the S550, even with 3.73s OR jumping to 4.09's, there really shouldn't be that much of an audible whine or noise coming from the rear diff IF there's no issues with the pinion bearing or heard themselves. Even when under load, you shouldn't hear any audible difference from your old pumpkin to this "new to you" one.... If you're hearing a very loud whine, like one that is very audible, it's not normal.

I've had plenty of Mustangs and upgraded rear gears, some extreme some just the normal gear jump. By normal I mean going from say 3.08's to 3.55 or 3.73's. In my prior 96 Cobra I jumped extreme and went from 3.08's to 4.30's. In every instance, there was no audible whine or NVH AFTER the swap or upgrades. If the rear pinion bearing is good (or new), the pinion nut or flange is torqued properly, and the gear set was set up correctly - you really shouldn't hear anything.

Now also with my prior 96 Cobra, I blew the 3.08's coming back from TX to NJ. You want whine, it was not only a screaming whine - but extremely harsh grinding (like mashing sand against the sides of a bowl with a spoon) and it was so loud in the car at speed (70+) that you couldn't even hear the stereo at all at top volume. The car literally sounded like a Mack truck from the inside - that's how loud and bad it was...

My suspicion with your differential is - you were sold one that was done, that needed repairs and was being dumped - whether purposefully or unknowingly, it was bad.

The only way to remedy it would be to gut it and replace with new (pinion bearing, gears etc). Set it up correctly and use new hardware for pinion depth/torque etc.

---
As for the speedometer/odometer - yes as was stated above a few posts back, the PCM is hard coded for the As Built gear ratio. You can't "disconnect the battery" and it magically fixes things... LMAO. You have to get Forscan and go into the logic and change the hard coded ratio to the direct ratio, which will remedy the Speedo/odo and power issues. There's many threads on how to do it on this site.

 

[HourlyB]

So few questions:

Why did the Seller remove and sell that rear differential? Was it from a salvage facility, re-sale shop or private seller?

The reason I ask the above is - more than likely that diff was replaced because it had the noise issue you're now dealing with. It's cheaper for a shop (Ford or other) to replace the entire rear pumpkin, than to "gut it" when talking labor rates. Even for a DIYer, it's easier to swap than gut. My guess is, that rear you now have was problematic and that is why it ended up for sale.... Anyone can say after the fact that "it had no whine", because how can you test a pulled pumpkin without it being on a vehicle?

As for your above response that when you take the car out of gear, the noise subsides.

That's typical of a bad rear (one where there is excessive audible whine), and the reason the noise subsides is because now the rear and driveline is no longer under load. The moment you either accelerate OR put the car back into gear, the driveline is under load again, which is pressure against the gears/pinion bearing.

In a normal environment such as the S550, even with 3.73s OR jumping to 4.09's, there really shouldn't be that much of an audible whine or noise coming from the rear diff IF there's no issues with the pinion bearing or heard themselves. Even when under load, you shouldn't hear any audible difference from your old pumpkin to this "new to you" one.... If you're hearing a very loud whine, like one that is very audible, it's not normal.

I've had plenty of Mustangs and upgraded rear gears, some extreme some just the normal gear jump. By normal I mean going from say 3.08's to 3.55 or 3.73's. In my prior 96 Cobra I jumped extreme and went from 3.08's to 4.30's. In every instance, there was no audible whine or NVH AFTER the swap or upgrades. If the rear pinion bearing is good (or new), the pinion nut or flange is torqued properly, and the gear set was set up correctly - you really shouldn't hear anything.

Now also with my prior 96 Cobra, I blew the 3.08's coming back from TX to NJ. You want whine, it was not only a screaming whine - but extremely harsh grinding (like mashing sand against the sides of a bowl with a spoon) and it was so loud in the car at speed (70+) that you couldn't even hear the stereo at all at top volume. The car literally sounded like a Mack truck from the inside - that's how loud and bad it was...

My suspicion with your differential is - you were sold one that was done, that needed repairs and was being dumped - whether purposefully or unknowingly, it was bad.

The only way to remedy it would be to gut it and replace with new (pinion bearing, gears etc). Set it up correctly and use new hardware for pinion depth/torque etc.

---
As for the speedometer/odometer - yes as was stated above a few posts back, the PCM is hard coded for the As Built gear ratio. You can't "disconnect the battery" and it magically fixes things... LMAO. You have to get Forscan and go into the logic and change the hard coded ratio to the direct ratio, which will remedy the Speedo/odo and power issues. There's many threads on how to do it on this site.

It was from a private owner, and unless he had a second PP Mustang GT, the Mustang looked fine. He said that he swapped out the rear end for a 4.09 setup. The input flange was swapped for the one on my 2016, and that is where the noise might've started, since the input flange nut also controls the alignment on the pinion gear. If it was from that, then the shop is at fault for not checking when the swap was done. And I can possibly hold their feet to the fire on that. If it's from a bad bearing set that needs to go, then I'll just eat that cost, PP diffs are pretty hard to find around here and I'll still probably be paying less than the cost of a brand new PP diff, esp given that any new diff I have to put in will still have to have their flanges swapped and then pinion gear adjusted to fit on the 2016. I'm in a win or deal scenario it would seem, and I'm in the mood for either lol, just not a noise.

 

[HourlyB]

Took it back to the shop, they replaced both the bearings and the diff fluid. (I believe they replaced it with Spectro 75W-140, but I'll confirm the grade. They also said that they did not add a LS additive)
They solved the first noise, but now there is either a new or still a noise. And it is distinctly gear sounding.

I recorded it any made it into a video. Anyone have any idea what's going on now?

 

[andrewtac]

Took it back to the shop, they replaced both the bearings and the diff fluid. (I believe they replaced it with Spectro 75W-140, but I'll confirm the grade. They also said that they did not add a LS additive)
They solved the first noise, but now there is either a new or still a noise. And it is distinctly gear sounding.

I recorded it any made it into a video. Anyone have any idea what's going on now?

Mine makes a very similar sound much louder. Pulling the diff today and taking it to a shop to put new gears/rebuild. Hopefully it fixes it.

 

[HourlyB]

Brought it to the shop and drove it with the mechanic, and he agreed that there was a definite gear noise coming from the rear end. He said that it really should not be making any gear noise, since he used the factory shim set, verified the backlash spec, pinion depth spec, etc, etc.

The only thing substantially different outside of the bearings is they took out the BG Ultra Guard oil and replaced it with Spectro 85w-140 oil without a LS modifier. I'm guessing it's this oil, given that's the only 85w-140 that Spectro makes. (Unless he meant the 75w-140 diff fluid Spectro also makes) Haven't heard of Spectro before, seems like it's a company mostly catering to Harleys and other motorcycles.

Any idea if that's going to cause a noise issue, specifically the lack of a LS modifier? If not, I'm still probably going to replace it with the BG fluid as soon as it stops making the noise. I'm not enthusiastic about having a non-synth heavier weight oil in. Unless it pans out to be the 75w-140 synth diff fluid.

 

[shogun32]

it's not the oil.

 

[K4fxd]

it's not the oil.

Nope not the oil.

Once a gear set starts making noise it is almost impossible to get them quiet again. If the noise bothers you you will have to put new gears in the car. Hopefully the shop will take care of you.

Back in the day, probably still happening, shops would add saw dust to the gear oil. This would stop the noise for a few months.

 

[HourlyB]

it's not the oil.

I assumed, but I'd be remiss if I didn't mention it.

Nope not the oil.

Once a gear set starts making noise it is almost impossible to get them quiet again. If the noise bothers you you will have to put new gears in the car. Hopefully the shop will take care of you.

Back in the day, probably still happening, shops would add saw dust to the gear oil. This would stop the noise for a few months.

So you think the gears are done and it isn't/wasn't bearing noise? Maybe the pinion depth was off and that did them in?

Any way to prove it, or do wrecked gears look the same as good gears?

 

[K4fxd]

Any way to prove it,

Just by the noise. They will look fine if taken out and inspected.

Maybe the pinion depth was off and that did them in?

This is most likely what happened, assuming they were quiet before the pinion swap.

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