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Driveline Thunk before takeoff.. GONE after install

Wolvee

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Since I bought my '16 GT I have had a Driveline thunk from the rear of the car. Every time I'd stop at a Red light and realign the gears to take off again, I'd hear and feel a "THUNK". (Almost like what we heard back in the old days with the Dog Leg lose under the SN95's.)


Since it's done it ever since it was new I didn't give it much thought other than doing quick Forum searches only to find out nobody really knew what it was. I figured it had something to do with the Torsion rear end loading up as I slide the shifter through the gears. I could make this happen only once every time I drove the car through the gears and coming to a stop but I couldn't stop it from happening.


Last week I installed Steeda's black Adjustable IRS Diff bushings. (All 4 black) Immediately I noticed the THUNK was almost completely gone.



Now it only does it after it's really Hot from Racing or long Trips. Even then the THUNK has diminished 50-75% of its previous feel and sound.


Does anyone know this sound? Can you explain why it happens and why the Steeda Bushings helped get rid of it?



#steeda
Diffbushings.jpg
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Lionorion

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'16 PP GT



Since I bought my '16 GT I have had a Driveline thunk from the rear of the car. Every time I'd stop at a Red light and realign the gears to take off again, I'd hear and feel a "THUNK". (Almost like what we heard back in the old days with the Dog Leg lose under the SN95's.)


Since it's done it ever since it was new I didn't give it much thought other than doing quick Forum searches only to find out nobody really knew what it was. I figured it had something to do with the Torsion rear end loading up as I slide the shifter through the gears. I could make this happen only once every time I drove the car through the gears and coming to a stop but I couldn't stop it from happening.


Last week I installed Steeda's black Adjustable IRS Diff bushings. (All 4 black) Immediately I noticed the THUNK was almost completely gone.



Now it only does it after it's really Hot from Racing or long Trips. Even then the THUNK has diminished 50-75% of its previous feel and sound.


Does anyone know this sound? Can you explain why it happens and why the Steeda Bushings helped get rid of it?



#steeda
The first sentence of the third paragraph explains:

https://www.steeda.com/steeda-s550-...insert-system-urethane-2015-all-555-4439.html
 
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Wolvee

Wolvee

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Learn something new everyday i guess. I did not thing that would cause an audible thunk just by lining up the gears in the trans.
 
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Wolvee

Wolvee

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Which one of those things causes the Clunk? I can't imagine Ford would design a car and let that noise get a pass.
 

JohnD

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I put those black bushings in as well, I have a LMR RSD which is just a hunk of carpeting with zero sound insulation. I have a ton of gear whine now and the thud is more of a clunk. Don't really like the clunk but I kinda like the gear whine. I also have their black bushings in the motor mounts and trans mount, that's probably adding to the NVH as well. I hardly ever drive it on the street now anyway so it's no biggie, but for sure the black ones do increase NVH substantially.
 

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Lionorion

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I put those black bushings in as well, I have a LMR RSD which is just a hunk of carpeting with zero sound insulation. I have a ton of gear whine now and the thud is more of a clunk. Don't really like the clunk but I kinda like the gear whine. I also have their black bushings in the motor mounts and trans mount, that's probably adding to the NVH as well. I hardly ever drive it on the street now anyway so it's no biggie, but for sure the black ones do increase NVH substantially.
GTK

When I eventually do this, I’ll try the red bushings first. Thank you
 
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Wolvee

Wolvee

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I put those black bushings in as well, I have a LMR RSD which is just a hunk of carpeting with zero sound insulation. I have a ton of gear whine now and the thud is more of a clunk. Don't really like the clunk but I kinda like the gear whine. I also have their black bushings in the motor mounts and trans mount, that's probably adding to the NVH as well. I hardly ever drive it on the street now anyway so it's no biggie, but for sure the black ones do increase NVH substantially.



That's funny because I have none of that from the diff bushing. LOL I have no idea why people keep saying this. :crazy:
 

ronemca

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What's the ideal way to install the front set of replacement bushings? I got the rears in alright, but the fronts are somewhat more involved. I got as far as removing the 2 black stamped steel brackets, but as I was getting set to remove the first enormous blue bolt I realized that obviously the exhaust needs to drop (or come out) And it never occurred to me before I started that I should be on a 2-post hoist so the axle can drop down; I was on a 4-post. :( But is the CBE drop/removal the only non subframe-related prep step? I'm pretty sure the rear blue bolts must be fully secured to maintain the alignment...but did you guys remove only one front blue bolt at a time or both at once? It seems like the diff wouldn't drop at the front end unless both blue bolts were removed(?)
 

JohnD

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That's funny because I have none of that from the diff bushing. LOL I have no idea why people keep saying this. :crazy:
I say it because that's exactly what happened. It only makes sense, Ford puts all that rubber in there to soak up the sound and then we lock out their bushings with virtually uncompressible delrin or aluminum. If there was no noise problem Ford wouldn't put so much rubber in there. You may have a different experience, wonderful for you, I'm just telling people what I found when I did this. Even Steeda told me there will be increased NVH with black bushings and motor mounts, so it's hardly unexpected. ;)
 

TheLion

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Word of caution, buy their upgraded grade 12 bolts. I just had a rear driver side 10.9 bolt shear off on my NA GT. I have my entire IRS now completely off the car as I'm going to have to pull the entire diff out, swap diff covers because the rest of the bolt is now stuck in the differential cover and the red poly insert is somewhere out on the highway. I've never drag raced or used drag radials, my car is NA with a Ford Performance Power Pack 2, so nothing super wild power wise.

Grade 10.9 should be plenty strong, but apparently their quality is not so great. This is NOT cool at all. Everything was torqued to spec. with a calibrated Tekton torque wrench as well, so there is NO reason it should have given out and that's using the softer 80 durometer red bushings. Do yourself a favor and get the grade 12 bolts and avoid this miserable issue.
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