Mystery knocking sound only while accelerating
08-12-2010, 10:06 AM
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Mystery knocking sound only while accelerating I spent about an hour under the car last night trying to figure out where this sound is coming from and haven't found a damn thing.
The sound started while I was at the racetrack last week and once I noticed it, I stopped racing the car, took it home, and parked it. Haven't moved it since last night. It sounds like a metal on metal knocking that varies with how fast the cars moving, its fairly loud, and seems to sound like its coming from under the car-- possibly towards the rear. When I get above 50mph it turns into to like a really fast scuff sound. It only happens when the drivetrains under a load, so when I got the rear of the car up in the air with jackstands under the axeltubes, it didn't make a damn sound.
At first I thought maybe my exhaust came loose and it was hitting the driveshaft but that wasnt the case, plenty of clearance there (I've got one of those big, fat LS1 aluminum driveshafts from a '99 Z28). Same with the clearance between the torque arm and driveshaft. There's no evidence of scraping or any damage anywhere. I took the driveshaft out and checked the u-joints and yokes on both ends and all was well there, too. I know when yokes go bad they mainly just vibrate but I was running out of ideas.
Anyone have any guesses?? Maybe I'm missing something obvious.
My next guess was gonna be to take the rear plate off the differential and make sure the gears look ok, but I don't think that'll be the problem either. I've blown my diff before and when you break teeth off gears its a big ugly mess and the cars not drivable, but I'm just out of ideas.
The sound started while I was at the racetrack last week and once I noticed it, I stopped racing the car, took it home, and parked it. Haven't moved it since last night. It sounds like a metal on metal knocking that varies with how fast the cars moving, its fairly loud, and seems to sound like its coming from under the car-- possibly towards the rear. When I get above 50mph it turns into to like a really fast scuff sound. It only happens when the drivetrains under a load, so when I got the rear of the car up in the air with jackstands under the axeltubes, it didn't make a damn sound.
At first I thought maybe my exhaust came loose and it was hitting the driveshaft but that wasnt the case, plenty of clearance there (I've got one of those big, fat LS1 aluminum driveshafts from a '99 Z28). Same with the clearance between the torque arm and driveshaft. There's no evidence of scraping or any damage anywhere. I took the driveshaft out and checked the u-joints and yokes on both ends and all was well there, too. I know when yokes go bad they mainly just vibrate but I was running out of ideas.
Anyone have any guesses?? Maybe I'm missing something obvious.
My next guess was gonna be to take the rear plate off the differential and make sure the gears look ok, but I don't think that'll be the problem either. I've blown my diff before and when you break teeth off gears its a big ugly mess and the cars not drivable, but I'm just out of ideas.
08-12-2010, 09:38 PM
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I took a good look at the torque arm when I was unbolting the driveshaft Wednesday night and it looked fine. Wasn't bent or cracked anywhere.
To me, this knocking sound honestly sounds like a yoke on my driveshaft is rubbing on my exhaust or the torque arm or something, but there's tons of clearance between all 3 and no evidence of scraping at all.
All I know is that its coming from under the car somewhere, sounds like from the back half of the car but I could be wrong.
Next thing my guts telling me to do before I bring this car to a mechanic is to open up the differential and see whats going on inside. Maybe I somehow managed to damage one of the teeth or something..
To me, this knocking sound honestly sounds like a yoke on my driveshaft is rubbing on my exhaust or the torque arm or something, but there's tons of clearance between all 3 and no evidence of scraping at all.
All I know is that its coming from under the car somewhere, sounds like from the back half of the car but I could be wrong.
Next thing my guts telling me to do before I bring this car to a mechanic is to open up the differential and see whats going on inside. Maybe I somehow managed to damage one of the teeth or something..
08-13-2010, 02:50 PM
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Never checked the tranny mount, though I was always under the impression that they make more of a 'thunk' when you accelerate when they go bad. This is more like a rapid repetitive knock.
But who knows, I'll check it out next chance I have to get under the car, most likely Sunday.
Thanks for the input.
But who knows, I'll check it out next chance I have to get under the car, most likely Sunday.
Thanks for the input.
08-16-2010, 02:44 PM
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Found the problem! I took the rear end cover off and found two teeth sitting in the bottom of the pumpkin, they broke clean off the ring gear.
Strange thing is last time I blew my differential racing, there was all kinds of carnage. I had to get the car flat-bedded home because if I tried driving it was like riding a horse during an earthquake, and there were all kinds of teeth and chunks of metal everywhere when I opened it up. This time around the car drove butter smooth like it always does with just a slightly obnoxious knocking sound.
Soooo now I know the wise thing to do would be to take the car off the road for the season and save up for a Moser 12-bolt over the winter since I've managed to nuke 2 sets of gears in the 4 years I've had the car. Butttttt then again its only August, what's another set? I destroyed a set of Richmonds pretty quick, and now my Stranges that have lasted much longer and have been much quieter are gone, so that leaves Motive... maybe I'll give them a try and I could say I've had all the major name brands.
Strange thing is last time I blew my differential racing, there was all kinds of carnage. I had to get the car flat-bedded home because if I tried driving it was like riding a horse during an earthquake, and there were all kinds of teeth and chunks of metal everywhere when I opened it up. This time around the car drove butter smooth like it always does with just a slightly obnoxious knocking sound.
Soooo now I know the wise thing to do would be to take the car off the road for the season and save up for a Moser 12-bolt over the winter since I've managed to nuke 2 sets of gears in the 4 years I've had the car. Butttttt then again its only August, what's another set? I destroyed a set of Richmonds pretty quick, and now my Stranges that have lasted much longer and have been much quieter are gone, so that leaves Motive... maybe I'll give them a try and I could say I've had all the major name brands.
08-16-2010, 02:51 PM
#7
Found the problem! I took the rear end cover off and found two teeth sitting in the bottom of the pumpkin, they broke clean off the ring gear.
Strange thing is last time I blew my differential racing, there was all kinds of carnage. I had to get the car flat-bedded home because if I tried driving it was like riding a horse during an earthquake, and there were all kinds of teeth and chunks of metal everywhere when I opened it up. This time around the car drove butter smooth like it always does with just a slightly obnoxious knocking sound.
Soooo now I know the wise thing to do would be to take the car off the road for the season and save up for a Moser 12-bolt over the winter since I've managed to nuke 2 sets of gears in the 4 years I've had the car. Butttttt then again its only August, what's another set? I destroyed a set of Richmonds pretty quick, and now my Stranges that have lasted much longer and have been much quieter are gone, so that leaves Motive... maybe I'll give them a try and I could say I've had all the major name brands.
Strange thing is last time I blew my differential racing, there was all kinds of carnage. I had to get the car flat-bedded home because if I tried driving it was like riding a horse during an earthquake, and there were all kinds of teeth and chunks of metal everywhere when I opened it up. This time around the car drove butter smooth like it always does with just a slightly obnoxious knocking sound.
Soooo now I know the wise thing to do would be to take the car off the road for the season and save up for a Moser 12-bolt over the winter since I've managed to nuke 2 sets of gears in the 4 years I've had the car. Butttttt then again its only August, what's another set? I destroyed a set of Richmonds pretty quick, and now my Stranges that have lasted much longer and have been much quieter are gone, so that leaves Motive... maybe I'll give them a try and I could say I've had all the major name brands.
Take my word for it.
