'08 GT500 rear axle whine

[Gabe]

Car has approx 62k miles on it.
Rear diff center section (new spider gears and all) was replaced with a new Ford Racing unit approx 2 years ago and fresh Amsoil fluid was put in then.
It had a moan from the rear diff during low-speed turns, so about 1-2 months ago I changed the fluid, put in fresh Amsoil 75-140 again, but with 2 bottles of friction modifier this time. A bottle of the Ford Racing stuff and a bottle of Lube Guard Limited Slip Supplement, bought at the local O'Reilly.
Moan is gone, but the gear whine is horrible at about 80 mph.
Car has a tubular non-adjustable Steeda UCA, billet aluminum Steeda LCA's, CHE relo brackets, and a BMR Watts Link.
The center section was installed by a master Ford tech friend of ours.
I never checked gear pattern when I recently had it apart, I wish I did.
Thoughts?

 

[o2sys]

Sorry not helpful but my car has the exact same whine. But I recently did a 3.73 swap myself and probably messed something up.

 

[travelers]

Gabe did you use synthetic or regular oil? Did it do that before you changed the oil or install the watts link? Petroleum based oil from what I've read lately is preferred for aftermarket gear sets.

 

[Gabe]

Gabe did you use synthetic or regular oil? Did it do that before you changed the oil or install the watts link? Petroleum based oil from what I've read lately is preferred for aftermarket gear sets.

It was noisy before, but at a different speed.
However, that was also with the CHE axle brace installed.
Removed the brace, the noise moved from 60-65 to 80
And I don't really remember if the noise was there before the brace was installed, which I think happened about 2 years ago.
Fluid used was Amsoil which is synthetic.
Pretty sure the gears installed are Ford.

Made this video when I was last changing the fluid, not sure if will tell anybody anything:

 

[Sky Render]

What differential do you have?

 

[Gabe]

Factory 8.8

 

[Candy10]

Hard (for me) to tell for sure in the vid, but its only under light acceleration? Not at constant 80, like with Cruise on?

 

[BruceH]

FYI Friction modifier is what allows the clutch packs to slip when you turn a corner. Putting too much in allows the clutches to slip more. It's not a good idea.

 

[Sky Render]

Factory 8.8

The factory TracLock? How many miles are on the clutches? Also, you might be using too much friction modifier. FWIW, I used only the Motorcraft oil and friction modifier.

 

[Gabe]

It's happening when cruising, constant on the gas, goes away when letting off the gas.
If there's any load put on, the noise shows up.
Ford has it in their manual somewhere that sometimes more than one bottle of friction modifier may be needed.
My buddy the Ford tech agreed, he's done it many times.

Factory track-lock, clutches are about 2 years old, maybe 10k miles on them, maybe closer to 15k?

 

[Candy10]

Hard to say since only the fluid was changed. Could just be different fluid, different properties. Double check the fill level maybe?

It honestly doesnt sound bad. First time I had my gears done it sounding like a wolf howling in my ear over 65mph. Mine was louder with no load (clutch in) though.

What's your friends opinion?

 

[AlbertD]

Was there a definitive point where it started whining? Was it right after the install? After installing suspension pieces?

Sounds like install issue to me exacerbated by the aftermarket suspension components.

When I had the 07 GT500 with all aftermarket BMR suspension out back it was still very quiet. Factory carrier setup and fluids. I drove that thing hard and it remained solid.

 

[Gabe]

My friend hasn't heard it yet.
Plan is to take him for a road test soon.
I kinda want to get the car on a lift, spin it to 80 and see where the noise is coming from.
I guess it could even be axle bearings but highly doubt it since they wouldn't be noisy only at 75-85

 

[o2sys]

Might be hard to replicate on a lift since there is no load.

 

[Candy10]

You'll know bearings. They grind!!!!! Its horrible.

Waiting for Ford Tech guy's diagnosis.

 

[travelers]

Might be hard to replicate on a lift since there is no load.

I agree with no load you probable won't tell much.

Just to clear something up, the noise is when your at 80 going straight?
IIRC rear clutches chatter in a turn only.

 

[BruceH]

I agree with no load you probable won't tell much.

Just to clear something up, the noise is when your at 80 going straight?
IIRC rear clutches chatter in a turn only.

Correct. If there is chattering during a 90 degree turn the clutches aren't slipping which usually means a problem with the friction modifier. Adding more friction modifier than needed will allow the clutches to slip when you don't want them too, like under straight line acceleration. Basically turning the limited slip into an open differential. Almost every brand of gear oil is blended with additives that act as friction modifiers, in most cases additional fm is not required.

For help diagnosing gear noise try reading these:

https://www.ringpinion.com/technicalhelp/TechHelp.aspx#14

https://www.ringpinion.com/Technica...to/generalinfo//diagnosing_noise_(part_1).inc

https://www.ringpinion.com/Technica...to/generalinfo//diagnosing_noise_(part_2).inc

 

[Sky Render]

^^^

And that's why I go with Motorcraft oil, because I know it doesn't have friction modifiers in it. Gabe, what oil are you using?

 

[Pentalab]

The oem differential is junk. This is where you need either version of the eaton tru-trac ( 31 / 33 spline)... or the torsen. And all 3 use dino oil, no synthetic, and no Friction modifier. Nothing to wear out.

 

[Sky Render]

The oem differential is junk. This is where you need either version of the eaton tru-trac ( 31 / 33 spline)... or the torsen. And all 3 use dino oil, no synthetic, and no Friction modifier. Nothing to wear out.

Yeah. I hate to say it, but the stock TracLock is insufficient for anything other than tooling around town. The clutches begin to wear immediately, and cornering (or launching) with sticky tires only speeds that process up.

Think about it this way: after one hard launch, autocross run, or hot lap, you've already worn the clutches an infinitesimal amount, meaning their bias ratio has already decreased.