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Old 09-08-2016, 07:02 AM   #1
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HELP: '12 GT Rear End GROAN

Help me out here guys, been searching all morning, can find anybody that reports the same conditions I am experiencing
2012 GT, 3.55s, 41k miles. I do have a set of Boss302R Lower Control Arms & GT500 Mufflers.
That's the only mods near the back of the car.

In any gear at low rpms when I lean into the throttle I get a very loud grinding/groaning sound from the rear end
This is not a clunk or a sqeak or a consistent high-pitched whining sound...
It does it on bumps or on a perfectly smooth surface.
It does it in a straight-line or a turn
It Immediately stops as soon as I lift off the throttle. ZERO noise while coasting
the only way to induce the sound is to apply torque forward to the drivetrain, throttle-on and you hear the noise.
Coasting in gear, holding speed, like with cruise control on, sounds fine, there has to be a heavy load like while accelerating.
And it appears to be getting worse.

Thanks for your inputs: Discuss
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Old 09-08-2016, 09:46 AM   #2
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Probably your lower control arms messing. They can throw everything off if not adjusted properly.

Also, are they tightened down?


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Old 09-08-2016, 09:52 AM   #3
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Quote:
Originally Posted by DiESeven View Post
Probably your lower control arms messing. They can throw everything off if not adjusted properly.

Also, are they tightened down?

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I'm gonna jack it up tonight and get underneath it.
See if I see anything obvious
I'll grease and torque the LCA's to be sure.

They are Ford Racing Boss302R LCA's, I thought those wouldn't throw off any of the rear end geometry???? and with the stock 2-pc driveshaft should the pinion angle not be as critical??
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Old 09-08-2016, 11:50 AM   #4
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I just took it for a lunch-time ride...
I don't think its a driveshaft/diff/gearing issue
its NOT speed related... SAME NOISE, pitch, volume at 1mph as at 35mph
and its VERY intermittent. Takes about 2-3 miles of driving minimum before it starts doing the noise.
I can launch hard and go through the gears and it sounds normal...
then it'll grind & moan around the best buy parking lot...
very strange. I'm gonna grease and re-torque my lower control arms after work.
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Old 09-08-2016, 12:18 PM   #5
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Heavy load or in turns? I'd look at your limited slip first. Easy thing is add another 2 oz of Ford Fish Oil and see if the noise dissipates or changes. The Fish Oil friction modifier does wear out with time.
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Old 09-08-2016, 12:21 PM   #6
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it does it going straight and in turns without a change.
it doesn't have to be a heavy load, it can be heavy or light
just a FORWARD load it seems, when weight is transferred rear-ward
decelerating or braking = NOTHING
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Old 09-08-2016, 01:37 PM   #7
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Could be a bad bearing in the diff, a gear that is chewing itself up, or a noise in the transmission (Had tail shaft bearing for example) resonating through the driveshaft. A resonating noise can cause a lot of headache chasing down, but it happens.
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Old 09-08-2016, 06:57 PM   #8
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I am going in tomorrow to go for a test drive with a ford technician tomorrow to have them diagnose this same (well it sounds the same) issue. I already dropped it off to them once and they were unable to hear it... k...
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Old 09-09-2016, 08:27 AM   #9
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WELL I'm a little embarrassed to admit, but glad to have troubleshooted & diagnosed on my own what was causing this...
I was driving home yesterday with the car still making this awful noise...
I was stopped at the last street light before my apartment, and this is where "the break-through" happened
SITTING STILL I rev'd the car a bit, just because... And heard the noise... I rev'd it again harder, there was the noise...
A noise, while sitting still, reving the engine, distinctly from the back passenger side...
I thought it cannot be anything rotating (driveshaft, u-joints, bearings, differential, etc.)
HAS TO BE the exhaust rubbing on something.
Which was hard to believe because the noise was AWFUL
I got it up in the air about 15 min later... crawled underneath and couldn't really identify anything obvious
I re-torqued the LCAs to 130ft/lbs to be sure that wasn't an issue. I readjusted the mufflers and went for a quick drive...
Still got the noise, but much quieter...SO Back to the garage, back on the ramps...
I'm looking up at the CLASS 1 trailer hitch I installed on the car, to tow my jet ski...
And how close it sits to the mufflers... dot...dot...dot...
So to eliminate that possibility I took 30min and completely removed the hitch (4 big sub-frame bolts)
AND NO MORE NOISE...
there is a scratched and worn area on the hitch where that passenger side muffler was rubbing on it...
Hasn't made the noise once AT ALL since I removed the hitch... ***sighhhh***
So now I need to address that issue, but what a small issue compared to what I thought it could have been
lesson learned, slow down, look at what you've done to the car, think it through, trouble shoot the problem
You might just surprise yourself with a the right solution.
My cousin is a welder and metal fabricator, I'm going to have him modify the hitch ever so slightly to fix that rubbing issue.
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Old 09-09-2016, 10:03 AM   #10
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There ya go. I teach auto shop and always tell the kids, what did you touch last? When looking for trouble that diagnostic step 1
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Old 09-09-2016, 01:59 PM   #11
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Great advise
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Old 09-09-2016, 05:55 PM   #12
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Too bad that wasn't included in the original post. Boss LCAs, mufflers and hitch. Put a hitch on my buddy's SUV and a week later says he's got a weird noise. The muffler hanger had enough play to allow the muffler to touch the hitch at certain times. A fabbed bushing on the post to take up the space solved it.
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Old 09-09-2016, 06:21 PM   #13
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One of the exhaust hangers was broken on mine and rubbing/rattling also. Small world
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Old 09-09-2016, 06:44 PM   #14
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Just me but why would you put a hitch on a performance car


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Old 09-09-2016, 08:47 PM   #15
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So he could tow his jet ski, he said that. I'd do it, if I needed to trailer my bike to the track...
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Old 09-10-2016, 05:25 AM   #16
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Just me but why would you put a hitch on a performance car


Sent from my IPhone at 120mph in 3rd@10psi
not just you, there's others that wouldn't do it either but to each his own.
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Old 09-11-2016, 12:28 PM   #17
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I would never put a hitch on my mustang, come to think of it I've never seen a hitch on any Mustang around here.
nononono:


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Old 09-11-2016, 01:28 PM   #18
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I saw an S550 the other day with bikes loaded on the hitch rack. Looked kind of out of place but if that is your thing it is not up to me to say you shouldn't do it.


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