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Clanking? Updated 6/06

thescreensavers

thescreensavers

Diamond Member
http://www.youtube.com/watch?v=HD3djYnuNVQ skip to 1:05, thats when you can start hearing it.

From what I can tell its coming from the rear of the car. Its not axle ticking its a clanking sound.


Any ideas? car has 47k on it.

Update 6/06: Driver side Diff mount bolt was extremely loose, 5 turns and it fell right out. Re-tightened both of them and now the sounds gone!
 
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What kind of car? Could be a number of things. U joints, drive shaft, shocks, shock mounts, differential mounts, bushings. It only does it on transition from drive to coast, not coast to drive, so think about how things are relaxing under those conditions.

Examples:

Gear lash is loose on both ends and knocks on both drive and coast transitions as it goes one way then the other, so you can rule those kinds of things out. But front diff mounts would allow the pinion to pick up on accel without making much noise (if there is nothing above it to hit) then clunking as it sets back down on the mounts on decel only.

See how I'm assuming it's RWD (G35?)? No clue what kind of car it is 😛 If it's FWD with a dead rear suspension it gets simple real quick.

Something is moving that isn't supposed to. Best way to find it will be to elevate it on ramps or drive on lift, and carefully repeatedly try to accelerate against the brakes to bind it up then let off suddenly, while someone is under the car watching.
 
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exdeath said:
What kind of car? Could me a number of things. U joints, drive shaft, shocks, shock mounts, differential mounts, bushings. It only does it on transition from drive to coast, not coast to drive, so think about how things are relaxing under those conditions.

Something is moving that isn't supposed to. Best way to find it will be to elevate it on ramps or drive on lift, and carefully try to accelerate against the brakes to bind it up then let suddenly, while someone is under the car watching.
Click to expand...


Its the car in my sig, Actually If you listen carefully, when I get on the gas there is another knock sound like bending metal? Like when you dent a can and you pop out the dent. When when I get off there is that louder clanking sound. Something is not right.

hmm
 
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Sheet metal poping sounds = shock and subframe mounts where the rear suspension is tied into the unibody sheet metal.

Also if the differential mounts are shot you'll get U joint noise as the pinion angle changes, then the clunk when it sets back down.

Probably just some rotted out rubber somewhere.

Compressed youtube + crappy laptop speakers so I can't really hear much.

If you can go down up down up down up on the pedal and make it jack hammer,(ie: just the drive train) without drastically unsettling the car's suspension, my bet is differential mounts or u joints, as everything else is tied to the movement of the car and the motion of the wheels.

Don't expect anything drastic when you go looking for it, you'd be surprised just how little movement and tolerance in parts can make the loudest noises.

Been driving it hard? :awe:

Just listened to it again, hear the accel noise, more of a clack than sheet metal. Could be inside the differential as well, but highly unlikey unless it's always been there and you're just now hearing it. And no other adverse noises like going over bumps or rough pavement at low speed, so yeah, u joints or differential mounts. Broken diff mounts are quite common on sports oriented IRS RWD cars, including Cobras (only ones with IRS), BMW Ms, G35s, etc. Alot of torque going through a piece of rubber.
 
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^ Last time I drove it hard was may 6th and that was one 1/4 run. I just started hearing this noise recently and the first noise thump/clack upon accel cannot be heard in the cabin only the louder clank upon getting off the gas.

In the video I go over 4 bumps/humps.
 
http://www.youtube.com/watch?v=GzLZkJPJsbs

Drag racing is hard on diff mounts. The side that will be the worst is the one the side where the driveshaft is rotating upward. Or depending on how the mounts are designed, whichever direction is twisting the diff mount away from it's mounting point.
 
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exdeath said:
http://www.youtube.com/watch?v=GzLZkJPJsbs

Drag racing is hard on diff mounts. The side that will be the worst is the one the side where the driveshaft is rotating upward.
Click to expand...

Thanks for the tip, Ill look into it, and get it check out. I never thought about that part at all.

There are ton of Aftermarket Diff mounts available for my car so I can prevent that from happening again with some stronger mounts, if that is the issue.
 
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Hmm, I just looked at the back of the diff while a friend held the brake and gave it a little gas in Drive, that taping sound is there but the diff looks solid, no movement. But I cannot see the mounts. It defiantly sounds like something in the area.

oh also it gets worse with heat It seems.


tomorrow I should be able to get it up on some jack stands and look from underneath.
 
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It will be the front of the diff that moves the most; the rear moves little, if at all. Look really close at all the mounts and bushings when you get under it. It takes very little for it to make a sound, don't be afraid to rev it up good and wind it up nice and hard. If you don't see anything there and are convinced that's not the cause, grab the drive shaft ( in neutral with the car off obviously) and rotate by hand and see if it's clunking inside the diff or at the yoke and u joints, etc. Give it some good lateral shoves and check front to rear end play also. You might also look around for interference signs like rub spots on the exhaust, etc. You got the noise with it parked, that means you have all day to look for it 🙂

Same with the inner CVs. Hold them still while you rotate the driveshaft back and forth and feel for excessive play in between the driveshaft and axle. If there is excessive play anywhere in between, the driveshaft will accelerate, and bang to a stop, and of course the second bang is when it overruns on coast and hits on the other side.

Another item I just thought of; loose pinion flange nut, you'll feel that with the driveshaft test, esp. end play.
 
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My little bro has a G35 and he had a very similar sounding clanking sound that got worse with heat. They ended up replacing his differential. It was a good excuse to mod his car, lol.
 
^ Ouch I dont know if my CPO warranty covers that, I need to find out. Though I still need to find out if its coming from there or what. My friend was busy today again, so hopefully tomorrow I can get it looked at.

I do have a Solid Diff bushing attached to my Sub frame when the OEM plastic one broke from when I got rear ended. But I dont think that can cause the diff to have problems? I am also using Amsoil SVG fluid.

Hmm all speculation I need to get it looked at lol
 
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Final Drive Housing is the Diff right?

On the drivetrain my warranty covers only Drive shafts, The FD Housing and all internal parts, Propeller shafts, Universal joints, Bearings, seals and Gaskets.
 
All this talk about diffs... What was the maintenance like on it? is the fluid original or have you changed the gear oil? Does it take 75-90 like the trans? Could try a drain and replace of the fluid see if it helps. Something like Redline.
 
thescreensavers said:
Final Drive Housing is the Diff right?

On the drivetrain my warranty covers only Drive shafts, The FD Housing and all internal parts, Propeller shafts, Universal joints, Bearings, seals and Gaskets.
Click to expand...

Final drive housing and all internal parts: includes ring and pinion gears and the differential itself. You're good 🙂
 
Well Exdeath you were spot on. though a diff mount was not broken it was very related 🙂


1 min after the the car was up, we found that the Driver side Diff mount bolt was loose, 5 turns and it fell out!. Re-Tightened both of them and the sound is gone now!

I am glad nothing was broken and it was just a simple tightening 🙂
 
Good to hear 🙂 Like I said, it's amazing how the slightest bit of imperceptible play can cause the loudest noises.
 
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