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Discussion Starter · #1 ·
Hi all, last week I posted about my car making a loud clunk when I go over bumps. I'm 99% sure it was a bad trans mount. So I ordered a new GM trans mount and got a review shift insert for it. Got everything g put together, backed it off my ramps and had a horrendous scraping noise. I've read it could be the seat bolts hitting the drive shaft, so I crawled back under it and couldn't find anywhere where it would be hitting.... Then I found this....as you can see, who ever put the exhaust on before I purchased the car cut an old hanger off and let the stub sit there. So I took off the "axle back" and ground cut the stub off. Took it for a test drive and it seemed okay until decel, and turning. Other than hitting it with a ball peen, do you think I can bring the exhaust down a bit where the cats mount? Also, could a bad diff bushings be causing the diff to move just enough to where it rubs the driveshaft? I do have a peddlers insert I could throw in there. Just trying to get the car to not sound like a shit box coming to a light lol
 

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I would add the diff bushing regardless.
Also look into getting diff bracket. Gforce makes one.
If I were you, I would put the car on all 4 Jack stands. Take the wheels off, spin the axles(or driveshaft) and see what's touching.

Try to take a peek above the driveshaft. A shop noticed a metal nub(I dont remember exactly where) towards the rear scraping up against my driveshaft. He cut it off and my driving noise considerably went down.

Still show us a video if you can I hope I helped. If you were in so cal I would pull up and we'll solve it together....
 

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Here's are pics
Consider looking into cutting the bolts I'm pointing at.
You can also see that one of mine is cut already.
 

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Discussion Starter · #6 ·
Ina half hour or so I'm gonna put it back up on stands. Weird thing is that I have had it on Jack stands a few times today trying to chase down the noise. But it wouldn't make any noise on the stands. Only when I dropped it on the ground. Then I found the old exhaust hanger was hitting the rear of the driveshaft. It's still hitting in that spot for sure. To me... It seems like the exhaust is ran too tight to the bottom of the car and maybe is off just a little in the rear. But the only adjustment I think I could make is at the trans where the cats bolt
 

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Are those rear seat belts bolts?. I pulled my rear seats, added 2 or 3 washers then but bolts back in now bolts underneath are flush and don't rub on my 1 piece CF driveshaft. I knew to do this before I installed it few summers back. I also has one exhaust hanger bar that was so close I cut 3 inches off it to make sure I had clearance.
 

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Discussion Starter · #8 ·
Are those rear seat belts bolts?. I pulled my rear seats, added 2 or 3 washers then but bolts back in now bolts underneath are flush and don't rub on my 1 piece CF driveshaft. I knew to do this before I installed it few summers back. I also has one exhaust hanger bar that was so close I cut 3 inches off it to make sure I had clearance.
I'm 99.5% sure it's not the rear seat bolts. I should have mentioned I have an SLP loudmouth cat back (installed by previous owner) where it's hitting is at the rear of the resonator on the passengers side. It's like the exhaust is twisted or something. I just pryed it away from the driveshaft (it also squared up my exhaust tips) and the noise went away until I horses on it.

I'm trying to post a video I took of the noise but the page isn't letting me.
 

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Ina half hour or so I'm gonna put it back up on stands. Weird thing is that I have had it on Jack stands a few times today trying to chase down the noise. But it wouldn't make any noise on the stands. Only when I dropped it on the ground. Then I found the old exhaust hanger was hitting the rear of the driveshaft. It's still hitting in that spot for sure. To me... It seems like the exhaust is ran too tight to the bottom of the car and maybe is off just a little in the rear. But the only adjustment I think I could make is at the trans where the cats bolt
Ok let me know if you need any photos off of my car to better help you.
 

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I'm 99.5% sure it's not the rear seat bolts. I should have mentioned I have an SLP loudmouth cat back (installed by previous owner) where it's hitting is at the rear of the resonator on the passengers side. It's like the exhaust is twisted or something. I just pryed it away from the driveshaft (it also squared up my exhaust tips) and the noise went away until I horses on it.

I'm trying to post a video I took of the noise but the page isn't letting me.
Throw it on YouTube and give us the link.
 

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You can purchase stiffer hangers for the exhaust. Walker makes a few sizes, 3", 3.5", and 4" that will fit on the stock hangar locations. They will move a lot less than the stock silicone hangars.

This is what I use on my exhaust to maintain clearance with my CF driveshaft, as well as having threaded the hangars welded to the mufflers and using bolts to tighten them to help secure them from moving.

I'll link you to the walker rubber hangers in a minute.
 

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Discussion Starter · #15 ·

Here's a link to the video I made. After looking at it (5 or more times today) I marked the driveshaft with a marker in the area I think is rubbing. In my original post, you can see the rear of the resonator. That's where it's hitting. It rubbed the marker right off. But again, it's only after I romp on it or slam on the brakes. It's literally rubbing on the weld of the one piece driveshaft.
 

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Discussion Starter · #16 ·
You can purchase stiffer hangers for the exhaust. Walker makes a few sizes, 3", 3.5", and 4" that will fit on the stock hangar locations. They will move a lot less than the stock silicone hangars.

This is what I use on my exhaust to maintain clearance with my CF driveshaft, as well as having threaded the hangars welded to the mufflers and using bolts to tighten them to help secure them from moving.

I'll link you to the walker rubber hangers in a minute.
I'll definitely take that link when you get a second. I thought about looking for something like that today. The rear exhaust hangers really are almost too long and really do nothing, and the one in front of the axle could use to be a little longer/ stiffer as well. It would help push the exhaust down a smidge right where it's hitting.
 

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Here's a link to the video I made. After looking at it (5 or more times today) I marked the driveshaft with a marker in the area I think is rubbing. In my original post, you can see the rear of the resonator. That's where it's hitting. It rubbed the marker right off. But again, it's only after I romp on it or slam on the brakes. It's literally rubbing on the weld of the one piece driveshaft.
Yea something is flexing/stretching(slightly moving when you weight is being transferred from front to back and back to front. Have you changed any bushings as of yet?

The 3 main points that keeps coming to my mind is your motor mounts, trans mount(always double check cross member bolts), and your differential mount.

I recommend either of these two when it comes to the differential mount over just the bushing.
509867
509868
 

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Discussion Starter · #18 ·
Yea something is flexing/stretching(slightly moving when you weight is being transferred from front to back and back to front. Have you changed any bushings as of yet?

The 3 main points that keeps coming to my mind is your motor mounts, trans mount(always double check cross member bolts), and your differential mount.

I recommend either of these two when it comes to the differential mount over just the bushing.
View attachment 509867 View attachment 509868
I checked the motor mounts when I did my first oil change, they seemed okay, and looked to be in really good shape, possibly new.
The trans mount I bought an OE GM mount with Rev shift insert (just installed today and then heard the grinding noise).
I have the peddlers poly diff mount in my garage waiting to go in. I looked at the other style diff mounts buuuuutt, the girlfriend and I are expecting a baby in december. That's the main reason I went with the peddlers mount. The price was more my speed for right now. Can't fit a car seat in my Silverado, so I've been searching for a "family car" lol.

For 127k the car is really clean and deserves all of the bushings replaced, just trying to get some of the cheaper simple stuff out of the way so I can drop the rear subframe this winter.
 

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I'll definitely take that link when you get a second. I thought about looking for something like that today. The rear exhaust hangers really are almost too long and really do nothing, and the one in front of the axle could use to be a little longer/ stiffer as well. It would help push the exhaust down a smidge right where it's hitting.
There is also a mounting point attached to the rear subframe that I felt came too close for comfort to the driveshaft. I chopped it off.
 
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