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1G Noise in rear of the car when decelerating

SasaniFab

Proven Member
2,471
786
Dec 1, 2013
Mexico, Connecticut
I have searched and it appears this has been a common issue. It doesnt appear however that the issue was ever remedied. The driveshaft was completely rebuilt, the rear end is all new with ingall control arms, jays rear toe elmimator etc. The rear end is a lsd 4 bolt with 90k on it. The noise only exists when im decelerating in any gear. When the clutch is depressed the noise goes away. Its sounds like a thud thud thud ....thud thud thud. Ive tried adjusting the driveshaft angle with no luck. The clutch is a act 2600 with a act flywheel. Bul fab mustache bar. On one hand people say drivetrain harmonics, others say backlash. Does this happen to everyone with these mods? Has anyone fixed the issue?
 

Paintballaa5

Proven Member
507
158
Jan 23, 2012
Houston, Texas
It's possible the solid mounts are causing the extra gear noise. Although you say "thud," and I would describe it as more of a "whimper" sound if that was the case.. My Cobra with IRS didn't make any noise until I added delrin and aluminum diff mounts. Then the gear noise was significantly louder on decelerate.
 
Last edited:

Car Cannibal

Proven Member
438
10
Jun 7, 2003
Chicago, Illinois
I have the same issue with similar recently done mods. Just did 3SX rear camber arms, Jay's toe kit, Boostx subframe and mustache bar bushings and Moog ball joints. Even after an incomplete alignment (going back) the deceleration whine is still there. It's almost like a wheel bearing but not as loud or tire noise but it's only on deceleration around 15-30mph when you're off the gas.

I do have sloppy driveshaft carrier bearings that the assignment shop showed me by literally moving the driveshaft massively up and down so that's the other variable to my issue. I'll post back if it gets resolved.
 

SasaniFab

Proven Member
2,471
786
Dec 1, 2013
Mexico, Connecticut
I have aftermarket mounts also, 75 durameter. Everything was replaced on the entire car, wheel bearings are all oem, all new bushing etc when decelerating the noise isnt continuous. its not a whine, i can only describe it as a thud....thud... thud.......or a banging, metal to metal its very dense or deep so to speak. this video describes it perfectly
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. ?
 

19gsx91

Proven Member
1,201
293
Apr 20, 2011
Walworth, New_York
Driveshaft harmonics causing an exhaust rattle? It may be a pain but remove your exhaust save for the downpipe (for me its 2 bolts and a bunch of rubber hangers) and go down the road (briefly, gonna be a loud trip) and see if it's still there. My rear carrier bearing is going on mine and it causes a noticeable vibration, but that sounds like metal on metal to me.
 

SasaniFab

Proven Member
2,471
786
Dec 1, 2013
Mexico, Connecticut
Watch the video closely.... Clutch in , noise goes away immediately. How would that constitute a exhaust rattle?
 

Lou98GSX

Proven Member
703
61
Mar 13, 2004
Carmel, New_York
the reason you don't hear it with the clutch in is because your taking the load off the engine or drivetrain like putting it in neutral. to me it sounds like something is rubbing against something under a load like metal to metal . could be your exhaust or driveshaft or something in the rear diff area .look for rubbing marks or if something is to close to something else .
 

SasaniFab

Proven Member
2,471
786
Dec 1, 2013
Mexico, Connecticut
So when I'm driving around , accelerating hard, turning hard. Exhaust is fine, not hitting anything. But when I'm decelerating it's hitting? Doesn't seem plausible, I'm gunna be changing the hangers anyway so I'll see if that theory stacks up with an open downpipe
 

19gsx91

Proven Member
1,201
293
Apr 20, 2011
Walworth, New_York
It's a suggestion, I'm trying to help you diagnose, not getting into a contest about whether or not you believe it is plausible. If you research it you'll find it is a very real thing that causes a LOT of issues for any AWD vehicle, especially one that's been modified, and even more so if it no longer has the stock flywheel to soak up some of the vibration.
 

dsmspick

Supporting Member
912
25
Apr 7, 2011
Overland Park, Kansas
My 2g did something similar, and mine ended up being the bushings for the rear end had fallen apart. But since you have replaced that it could be a carrier bearing or something along those lines. Hell maybe the clutch chatter although that more on acceleration.
 

SasaniFab

Proven Member
2,471
786
Dec 1, 2013
Mexico, Connecticut
I'm not trying to be an ass.l, I appreciate everyone's input... Just a debate. I've done a lot of research on all of the Dsm sites. It's a very common issue, I just can't fin anyone claiming they nailed a diagnose. More or less just that it's a Dsm issue deal with it r/t the stiffened drivetrain components. Like I said I tried the factory spacers, and tried different angles on the driveshaft with no change. Ive read that people have replaced everything trying to track down the problem with no luck.
 

19gsx91

Proven Member
1,201
293
Apr 20, 2011
Walworth, New_York
The only solution I ever heard of was someone put the car on a lift and put small counterweights on the driveshaft and it dramatically improved (not eliminated) the issue, combine that with a stock weight flywheel and it would no longer be an issue, what my car does I would consider liveable, but what you posted in your video I would find alarming and would stop driving it until I located the source.

I wish I could point you to the thread where they did the counterweight thing, If i remember rightly it was large washers bound to the driveshaft, and was a large trial and error process. I was investigating that before I decided to fill my carrier bearings with RTV, which helped me quite a bit. See if removing the exhaust helps, and I only say that because the sound that YOU are experiencing is not normal compared to what other people are experiencing.
 

Maes

Proven Member
504
56
Oct 20, 2014
Mishawaka, Indiana
It really does sound like the exhaust. I could see accelerating it not happening because of momentum everything's lifting or going back. And on decel everything is dragging forward and possibly way more vibrations will occur if that makes sense.
 

Stew Pidaso

Proven Member
163
6
Apr 25, 2012
Canton, Ohio
Its definitely a driveshaft problem. Although I cant watch the video right now I have the same issue of a loud metal to metal banging in the rear of the car, seems like right above where the back seats would be. Not an exhaust issue because I'm running side exit but under decel until the car comes to a "coast" or near idle rpms it goes away but under decel load I get the same noise. I have built my entire driveline and tested with different tcases and diffs so its not that. Only thing I havent done is replaced driveshafts. My theory is the last piece of the driveshaft is twisted from repeated abuse or launches etc. and causes an imbalance in rotation. Thats usually the piece of the shaft that breaks first anyways.
 

YanDsm

Proven Member
152
3
Jun 2, 2010
Thetford Mines, QC_Canada
My car only started doing this noise when I've filled my driveshaft support bushing with windshield urethane.
 

19gsx91

Proven Member
1,201
293
Apr 20, 2011
Walworth, New_York
The windshield urethane is too hard from everything I've read, that's why I opted for a type of RTV, It'll dry and remain somewhat malleable. whereas the urethane will act almost like solid mounts, even worse in some cases. My rear carrier bearing won't take it because there's too many rips in the bushing, so I just got one from Miller import. But bastarddsm is right, vibration and some noise is going to happen with any modded dsm, but what you're hearing I don't think is normal
 

luv2rallye

DSM Wiseman
8,025
881
Jun 7, 2003
Minneapolis, Minnesota
Have you jacked up the car and manually turned the driveshaft right where it enters the rear diff? My friends 95 made a similiar noise only on deceleration and it turned out to be a bad drive pinion front bearing inside the diff.
 
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