3.73 Gear whine on acceleration - Mustang Evolution

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Old 01-18-2019, 11:18 AM   #1
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Question 3.73 Gear whine on acceleration

Hello All, my car is a 2008 GT auto. Originally had 3.31 rear gears. I got a set of Ford performance 3.73 gears as well as all new Ford performance pinion shims, carrier shims, ring gear bolts, carrier bearings, pinion seal, crush sleeve, pinion bearing, and new ford performance traction-LOK clutches installed in November. They were installed at a reputable shop and the tooth pattern was near perfect. Filled with 2 quarts of Mobil 1 full synthetic 75W-140 and a bottle of ford friction modifier. I followed the break in period instructions, 500 miles of light driving. After the 500 miles I replaced the diff fluid with new Mobil 1 full synthetic 75W-140 and the ford friction modifier.



My problem is that whenever I am on the accelerator I can hear a whine or howling from the rear end, it the worst when I am on the highway cruising at around 60-80mph. I can hear the gears over the engine and road noise. Once I let off the accelerator, even if I'm coasting at high speeds, the noise goes away. I took it back to the shop which did the work, their diagnoses was either the pinion bearing was bad or simply the 3.73 gears are naturally loud (I've read on plenty of posts this likely is the case). Well the shop replaced the pinion bearing for free and there was no noticeable difference in noise, basically told there was nothing I can do further.



Any suggestions or personal experiences? I'm thinking I'll need to buy a new set of 3.73 gears from ford or a taller gear set. So far I've put on about 1000 miles. Even with music on loud I can hear the whine.
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Old 01-18-2019, 04:54 PM   #2
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The shop telling you that “3.73 gears are naturally noisy” is B$))$%*T.....The spacing between the ring and pinion in Ford gear sets is critical and takes an expert, experienced mechanic to do the spacing correctly.
Particularly when you’ve done everything right to break in the gears, they should NOT be making any noise! 1,000 miles may or may not be enough to ruin them should they be reset — depends on how badly they’ve been scraped up by the wrong setting.....
Your choices are:
1.Change shops and try to get your current gears shimmed correctly. Ask how many Ford gear set changes they’ve done and if they know how to shim them.
2. If the gears are still whining after being reshimmed, then the gears are probably going to have to be replaced.....or:

3.Take your car back to the original shop — tell them if they cannot make your gears work silently, THEY are the ones who will be buying you new gears and paying a competent mechanic to install them.
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Old 01-18-2019, 06:11 PM   #3
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Originally Posted by Guard 5.0 View Post
The shop telling you that “3.73 gears are naturally noisy” is B$))$%*T.....The spacing between the ring and pinion in Ford gear sets is critical and takes an expert, experienced mechanic to do the spacing correctly.
Particularly when you’ve done everything right to break in the gears, they should NOT be making any noise! 1,000 miles may or may not be enough to ruin them should they be reset — depends on how badly they’ve been scraped up by the wrong setting.....
Your choices are:
1.Change shops and try to get your current gears shimmed correctly. Ask how many Ford gear set changes they’ve done and if they know how to shim them.
2. If the gears are still whining after being reshimmed, then the gears are probably going to have to be replaced.....or:

3.Take your car back to the original shop — tell them if they cannot make your gears work silently, THEY are the ones who will be buying you new gears and paying a competent mechanic to install them.
Thanks for the info. The shop I brought it to said they have a guy who was a ford tech for 15 years take a look at it (as far as I know only the tooth pattern). They’re also a semi performance shop and have done plenty of rear ends. I’ll likely find another shop to take a look at the shims and see what they can do about it, or I might even just buy new gears and have them install it, they’re cheap enough.
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Old 01-18-2019, 08:31 PM   #4
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Originally Posted by daviswarnerS197 View Post
Thanks for the info. The shop I brought it to said they have a guy who was a ford tech for 15 years take a look at it (as far as I know only the tooth pattern). They’re also a semi performance shop and have done plenty of rear ends. I’ll likely find another shop to take a look at the shims and see what they can do about it, or I might even just buy new gears and have them install it, they’re cheap enough.
Have another set of gears ready to go in when they take it apart.....if the experienced mechanic thinks he can fix your current gears (and does)...you can probably take the new gears back if they have not been opened.....but if the current gears are trashed, you have the new ones with you ready to be installed.....might save you a couple hundred in labor.
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Old 01-20-2019, 05:02 PM   #5
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Quote:
Originally Posted by daviswarnerS197 View Post
Thanks for the info. The shop I brought it to said they have a guy who was a ford tech for 15 years take a look at it (as far as I know only the tooth pattern). They’re also a semi performance shop and have done plenty of rear ends. I’ll likely find another shop to take a look at the shims and see what they can do about it, or I might even just buy new gears and have them install it, they’re cheap enough.
By your description of the noise intensity, a guess would be the gears are not likely "trashed" but indeed as Guard says are noisy due to incompetent set-up. Good tooth contact pattern is only part of the equation: with inadequate bearing preloading, especially of the pinion bearings, the gear teeth separate enough under load to lose their nice pattern; then they whine.

If the teeth are scored, galled, or marred in any way, forget about re-using them, unless the condition is such that adequate "good" contact area is still present; otherwise, they will howl forever, no matter what "fix" is applied. If the teeth have a nice, shiny appearance, AND no sharp knife-edge has been built up on the outside corners of the ring gear tooth surfaces, they will likely run quietly if set up correctly. Declaring the noise as inherent in the "ratio" is patent B.S.
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Old 01-20-2019, 06:13 PM   #6
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Good luck I’ve had my differential rebuilt like 5 times with 3.73 gears on my 08 gt. And they have whines every time. Mine is doing the same thing yours is doing but getting worse. I wish u luck. I’ve had mine built bye 2 reputable shops to.


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Old 01-23-2019, 03:06 AM   #7
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Classic installer gear **** up.
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2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.

Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.
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