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Discussion Starter #1
Hey guys, another clunk/dump/chump/spunk thread but anyways. I let the gas in and out and it feels like gears engaging/clunk and it only happens at 80mph and above. I’ve checked the 1 piece and it solid, mound is solid, no movement in the back, gears look good, fluid is good. Do I just put efforts towards a rebuild or is there something specific I can look at?
 

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Discussion Starter #3
speed dependent, never feel it any other time only at 80mph+ Usually 6th gear cuz that’s what I’m in. I can try 5th in the way home today
 

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Discussion Starter #5
Stock rear, just tried in 5th. I would say only 6th gear bc there’s a difference in gas/off at 5th vs 6th at 80mph. Dss axle tubes and 1 piece dss other than that it’s stock. I bought it with mods done
 

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Discussion Starter #6
Ok also, when I’m going 80plus I push the clutch in and it’s constant. I got it in video if anyone wants me to send it to them. It only does it 80, I tried in other speeds letting the clutch out and it’s quiet
 

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it really does seem load dependant. he only thing i can think of at this point is axles. maybe your CV joints are incredibly worn or one of the axle shafts isn't balanced.
 

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Discussion Starter #9
Well when I disengage the clutch and let the driveline free it makes the sound. When on gas or off gas WITH clutch engaged it does not make the noise consitantly just a clunk.
 

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Performance Addict
2005 PBM, 6 Speed, corner carver
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Did you drain the fluid from the trans when you checked it? If it is clean then I agree with the driveline.

it is possible some rear cradle or control arm bushings are going?

Is there any visible signs of the driveshaft hitting the exhaust or tunnel?

Is it possible the clutch is hanging up?

I am curious to hear the video as well.
 

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2005 PBM, 6 Speed, corner carver
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It was hard to make out the noise vs. the normal road noise but I definitely hear a rattling sound. Have you ever checked the temp of the rear wheels right after driving? I wonder if you have a rear wheel bearing bad that gets worse with speed. Touch all four wheels after a drive and see if any of them seem hotter.

Check the rear calipers and make sure they are tight yet still able to float on the rotors. If this is the case you should feel heat from one of the wheels as well.

Have you check the rear diff oil? Are there any tell tale signs of contamination in the oil?

Has the diff oil been changed lately? If so how much of the Type F friction modifier was added?
 

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2005 PBM, 6 Speed, corner carver
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The more I think about this I am curious about the friction modifier in the diff. I did an oil change on mine last year and didn't put enough modifier in it. It would make lots of noise when coming down from highway speeds. I added a few ounces and problem went away.

506539
 

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2006 Pontiac GTO
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do you feel any vibration above 80 in addition to the sound? Plus remember that the 1 piece shaft does not have the rubber flex discs to absorb drivetrain slop and I would think it might just be that as well.
 

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do you feel any vibration above 80 in addition to the sound? Plus remember that the 1 piece shaft does not have the rubber flex discs to absorb drivetrain slop and I would think it might just be that as well.
it shouldnt clunk though. a lot more people would be complaining if it was driveshaft related.

either gears in the rear end/rear end bushings/trans&motor mounts would be my check
 

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Discussion Starter #16
It was hard to make out the noise vs. the normal road noise but I definitely hear a rattling sound. Have you ever checked the temp of the rear wheels right after driving? I wonder if you have a rear wheel bearing bad that gets worse with speed. Touch all four wheels after a drive and see if any of them seem hotter.

Check the rear calipers and make sure they are tight yet still able to float on the rotors. If this is the case you should feel heat from one of the wheels as well.

Have you check the rear diff oil? Are there any tell tale signs of contamination in the oil?

Has the diff oil been changed lately? If so how much of the Type F friction modifier was added?
Fluid is good I used royal purple 85-140 no extra fm. I had the torco in it but it did have a whine. The old rear fluid in it came out black but I didn’t have a whine, went to RP and the whine went away. I clean in there now with fresh gear oil
 

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Discussion Starter #17
do you feel any vibration above 80 in addition to the sound? Plus remember that the 1 piece shaft does not have the rubber flex discs to absorb drivetrain slop and I would think it might just be that as well.
no vibes, it’s only a clunk when I let off/on the gas. Full on vibes when I disengage the clutch and coast freely.
 
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