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Old 01-31-2012, 08:29 PM   #1
69MustangCoupe393cid
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Default Horrible grinding noise from rear end... need some help

Ok so this is on my 2000GT, its a metal on metal grinding noise coming from somewhere in the rear. I had my buddy listen and he said it sounds like its coming from both sides of the car in the back.

It sounds very similar to what a brake caliper would sound like on a rotor with no pad left and seems to go with wheel rotation. It also seems to only happen when the car has been driven and is warm. Also only at low speeds while I'm slipping the clutch (clutch slipping is probably unrelated, it's just because it only happens at low speeds). Once I'm moving the sound goes away and my buddy also said it seems to sound louder in the car than outside it.

I have no idea what this can be. My universals on my driveshaft seem tight and I see no clean scrapes on the driveshaft or rotors from something maybe rubbing it. I pulled on the rear wheels left and right and top to bottom with the car in the air to test wheel bearings and they seem tight as well. Oh and I checked my brakes pads too, they're fine so it's not the pads. I also jacked the car up and tried to create the noise with the car in the air, but it will only do it while the car is on the ground at low speeds (under 5 mph). What can this be, it's driving me nuts and I don't want a wheel bearing to fail while I'm driving or something of the like.
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Old 01-31-2012, 10:31 PM   #2
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Could be something grinding in the rear diff? When is the last time you changed the fluid (I believe every 60k miles is recommended).
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Old 02-01-2012, 08:33 AM   #3
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Does the noise happen when travelling in a straight line or while turning, or both?

Regardless, I would pull the differential cover and have a look inside...
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Old 02-01-2012, 09:02 AM   #4
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Open the rear cover and inspect it, anything grinding should be noticable on the inside.
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Old 02-01-2012, 10:07 AM   #5
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Quote:
Originally Posted by Syracuse315 View Post
Could be something grinding in the rear diff? When is the last time you changed the fluid (I believe every 60k miles is recommended).
20k miles ago with Amsoil synthetic. It was changed at 60k on the nose, car now has 82k.

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Does the noise happen when travelling in a straight line or while turning, or both?



Regardless, I would pull the differential cover and have a look inside...
I think both, but possibly more while turning.

Booooo it's cold.

I bottomed my car out a while ago actually when this noise started now that I think about it, my K-member shifted back about 1/4 inch. Could that have jammed the entire drivetrain back into my rear end and messed something up?
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Old 02-01-2012, 10:22 AM   #6
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Quote:
Originally Posted by 69MustangCoupe393cid View Post
20k miles ago with Amsoil synthetic. It was changed at 60k on the nose, car now has 82k.



I think both, but possibly more while turning.

Booooo it's cold.

I bottomed my car out a while ago actually when this noise started now that I think about it, my K-member shifted back about 1/4 inch. Could that have jammed the entire drivetrain back into my rear end and messed something up?
Its possible, granted i dont think a 1/4 could jar anything in the rear because the slip yoke on the trans end of the driveshaft would just slide in another 1/4 inch. But its possible that the driveshaft angle can be off on top of any other vibrations with the driveline are being transferred to the driveshaft which i personally think is the issue here and not the rear.
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Old 02-01-2012, 11:48 AM   #7
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Enough of a jolt to push the K-member back 1/4" could have shoved the engine/transmission assembly back considerably farther as both motor and transmission mounts are flexible in all three planes. It could be the pinion bearings/crush sleeve took some of it and the pinion/ring backlash was affected--or that a bearing inner/outer race was dented...
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Old 02-01-2012, 08:17 PM   #8
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Originally Posted by cliffyk View Post
Enough of a jolt to push the K-member back 1/4" could have shoved the engine/transmission assembly back considerably farther as both motor and transmission mounts are flexible in all three planes. It could be the pinion bearings/crush sleeve took some of it and the pinion/ring backlash was affected--or that a bearing inner/outer race was dented...
Well as you remember it was a hard enough hit to set off my airbag module, so yeah it was a pretty nice hit. Caught the road for sure. But why would I only hear it at low speeds and only when warm? Fluid gets thin when warm maybe? But I still don't get why it's only heard at low speeds and than goes away.

EDI: Should I try to somehow move the K-member back to where it was? Or is it not a bag deal that it's further back since it's already there now?

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Old 02-01-2012, 08:25 PM   #9
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Quote:
Originally Posted by 69MustangCoupe393cid View Post
Well as you remember it was a hard enough hit to set off my airbag module, so yeah it was a pretty nice hit. Caught the road for sure. But why would I only hear it at low speeds and only when warm? Fluid gets thin when warm maybe? But I still don't get why it's only heard at low speeds and than goes away.

EDI: Should I try to somehow move the K-member back to where it was? Or is it not a bag deal that it's further back since it's already there now?
I don't have a clue, open up the back end and let us know...
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Old 02-02-2012, 09:37 AM   #10
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could you maybe post a video and/or sound clip??
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Old 02-02-2012, 09:37 AM
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