Rear gears and whining... question - Forums at Modded Mustangs
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post #1 of 7 Old December 10th, 2018, 10:55 PM Thread Starter
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Rear gears and whining... question

So I had my rear end rebuilt with FRPP 4.10 gears, new Trac lock, ext. Put an aluminum drive shaft in and there is a loud hum. Put the stocker back in and gone. Annoying.

Today cruising I notice the car shake at speeds above 55mph. Great. Now I never drive the car so this stuff I never notice until months later. All this rebuild and install stuff was done in October.

Google says frpp gears are motive made. Fantastic. I'm using royal purple 75w140 with a bottle of friction modifier. Some say red line is better.

I'm thinking of putting the aluminum back in and seeing what happens. If the shake is gone I know the reason is the drive shaft and then the humming is back.

Shop says aluminum drive shaft acts as a noise amplifier as its hollow so that's why I hear it.

Questions

Do I line up the dot on the tranny with the dot on the drive shaft then turn the wheels to line up that dot on the pinion? I have an aftermarket pinion on the rear since the stock leaked and the shop that did it made a tiny purple dot which I'm assuming is the dot I'm supposed to line up with.

This weekend I'm thinking of switching the ds and see what happens?

I know my tires are balanced and alignment is good. The shake is more of a mid car shake then steering shake.

Damned if I do. Damned if I don't. Ugh. Ideas?

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post #2 of 7 Old December 11th, 2018, 03:15 PM
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How reputable is the shop that did the gears? In my experience, all 4.10s whine a little around 40 mph lol, something about resonance frequency at certain speeds. But a really loud whine, on or off the throttle, usually means the gears weren't shimmed correctly. I have an aluminum ds and mine got louder with the install, which is slightly annoying, but with the NHV I have from coilovers it's the least of my worries

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post #3 of 7 Old December 11th, 2018, 03:17 PM
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Also, what type of motor/trans mounts do you have? And how low is the car?

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post #4 of 7 Old April 17th, 2019, 09:31 PM Thread Starter
6 Cylinduh, Really Bruh?
 
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I'm bringing this back to life because the whining turned into a grinding and I joined the local mustang club and got a recommendation on a shop most people use.

I decided to get the rear rebuilt again. This time with 3.73s as I'm going centrifugal and went with a 31 spline conversion from the factory 28.

The new guy showed me what was going on. Not only was the backlash pretty bad but one of the axles had some pretty bad pitting in it. Apparently when the old shop rebuilt my rear, they ignored the pitting and it slowly ate away at the new bearings first causing a whine then a grinding noise.

Long story short, I got a cobra Trac loc, Moser 31 spline axles, 3.73 gears, put my aluminum drive shaft back in, changed the rear finned cover for a Ford racing girdle with morroso reinforced studs and it's quiet as a mouse now. All rebuilt with Ford racing bearings and axle bearings and seals. New royal purple 75w140 put in.

Lesson learned. Go with a shop people vouch for when getting work done.

I actually enjoy the 3.73s over the 4.10s NA. Makes for a more enjoyable driving experience instead of always in your face torque. Now I went 3.73s because of boost reasons but just saying.

Couldn't believe it

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---------- Post added at 09:31 PM ---------- Previous post was at 09:31 PM ----------

Quote:
Originally Posted by poweredpony69 View Post
How reputable is the shop that did the gears? In my experience, all 4.10s whine a little around 40 mph lol, something about resonance frequency at certain speeds. But a really loud whine, on or off the throttle, usually means the gears weren't shimmed correctly. I have an aluminum ds and mine got louder with the install, which is slightly annoying, but with the NHV I have from coilovers it's the least of my worries
This guy was right on the money. I learned my lesson...the expensive way

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post #5 of 7 Old April 18th, 2019, 09:31 AM
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That's sucks about your first experience but at least you found the issue and are getting it resolved.
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post #6 of 7 Old April 24th, 2019, 09:41 AM Thread Starter
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Quote:
Originally Posted by ZEN357 View Post
That's sucks about your first experience but at least you found the issue and are getting it resolved.
A very costly mistake. That's twice rebuilding it - but I guess the light at the end of the tunnel is I found a reliable mechanic now and have a 31 spline rear now. Just got there in a costly way.

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post #7 of 7 Old April 29th, 2019, 09:03 AM
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I've had very costly mistakes over the years, but we all live and learn and use our experiences to try and not make costly mistakes in the future.
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