Differential morning "clunk"

[SanDiegoTexan]

I have a 2012 2SS, manual 6, just broke 2100 miles on her. I have not dropped the clutch or done anything rough with the car. Parked over night, first thing in the morning I have a distinct "clunk" as the car just starts to roll. Comes from the back end. Doesn't happen parked at work, it has to rest longer. I've parked on flat surfaces, the angle on the driveway, left it in first, reverse, neutral, all the same clunk, so I assume it's the diff.

Has anyone else seen this issue, and/or did I miss a thread with this discussed? I want to have some info before I take her into the dealership.

Thanks!

[PQ]

Nothing I recall. Don't rule out drive shaft. Hanger bearing can do similar after sitting.

[My 5th]

You're noticing the driveline "clunk" or slack inherent in the M6 drivetrain. Most dealers will tell you the noise is "normal". IMHO the primary culprit is too much backlash in the ring and pinion. I also think it is possible the noise won't go away completely even if I have the backlash set on the tight side of the spec, because other components could be contributing to the slack. It's possible there's some tolerance in the clutch disk, as well as in the transmission AND also in the driveshaft.

I'm considering starting with the rear differential and upgrading to a JRE posi unit and having the backlash tightened while doing that. I may have to wait to do this project because while I'm in the diff I might as well replace the axles with some 1400 HP units--and they aren't cheap. If the noise still persists after that, I'd replace the 2-piece driveshaft with a one-piece unit. If the noise is still there a ZR1 twin disk clutch will go in. If the noise is still there after that then rebuild the tranny with carbon syncros. If the noise is still there after that I'm buying a Mustang. Err wait... that's too extreme...I'll just get a bigger amp and subwoofer and drown out the noise.

[SanDiegoTexan]

This is a pretty substantial noise, and you feel it in the car easily. My driveway has a slight incline to it, enough that I can put it in nuetral and slowly coast into the street. The mornings that get this noise (which is most of them) I actually have to put the car into gear to move it. Can this driveline slack really give that much resistance?

[PQ]

Originally Posted by SanDiegoTexan

This is a pretty substantial noise, and you feel it in the car easily. My driveway has a slight incline to it, enough that I can put it in nuetral and slowly coast into the street. The mornings that get this noise (which is most of them) I actually have to put the car into gear to move it. Can this driveline slack really give that much resistance?

NO. There should be no resistance at all. If you have resistance then take it in. Are you possitive that it's not the brakes sticking with overnight rust or something?

I've had my brake pads stick before overnight and it felt and sounded very much like you describe. Happened mostly overnight. Would definitely explain why it does it forward and reverse.

[Swytch]

Originally Posted by PQ

NO. There should be no resistance at all. If you have resistance then take it in. Are you positive that it's not the brakes sticking with overnight rust or something?

I've had my brake pads stick before overnight and it felt and sounded very much like you describe. Happened mostly overnight. Would definitely explain why it does it forward and reverse.

+1

This happened the first time i went 24 hours without driving the car (few weeks after owning). I freaked, took it to the dealer and they could find nothing. It has happened a few times since, always when i set the parking brake and leave it over night. Almost always there is some moisture too. I am about 99% sure its the rear brakes sticking.

[PQ]

Originally Posted by Swytch

+1

This happened the first time i went 24 hours without driving the car (few weeks after owning). I freaked, took it to the dealer and they could find nothing. It has happened a few times since, always when i set the parking brake and leave it over night. Almost always there is some moisture too. I am about 99% sure its the rear brakes sticking.

[PQ]

In fact if your parking brake is set I'm willing to bet that's what it is.

Next time it happens, brake immediately and go back and look at your rotors. I'll bet you'll be able to see the outline of the pad on them.

[Swytch]

Small side-jack... I assume you intentionally distorted the rims in your sig PQ? Savini's?

[PQ]

Originally Posted by Swytch

Small side-jack... I assume you intentionally distorted the rims in your sig PQ? Savini's?

Yup. The distortion is from the early problems and the flat tires are because they just won't seal air. Never really did.

[Big Daddy Kane]

I also think its the brakes sticking since you say it happens only in the morning, after sitting all night. I've noticed it with other cars too.

[Squintz Palladoris]

Originally Posted by PQ

In fact if your parking brake is set I'm willing to bet that's what it is.

Next time it happens, brake immediately and go back and look at your rotors. I'll bet you'll be able to see the outline of the pad on them.

More than likely it is the Parking brake sticking. I have had it happen as well. Not a big deal.

PQ there will be no evidence of this on the rotors. The parking brake is a drum style brake, the "Drum" is the hat of the rotor. Seeing the outline of the pad on the rotor is from a bit of surface rust that forms when the car sits.

[PQ]

Originally Posted by Squintz Palladoris

More than likely it is the Parking brake sticking. I have had it happen as well. Not a big deal.

PQ there will be no evidence of this on the rotors. The parking brake is a drum style brake, the "Drum" is the hat of the rotor. Seeing the outline of the pad on the rotor is from a bit of surface rust that forms when the car sits.

Oh. Damn. I didn't know that. I thought the parking break was the full rear calipers.

[hypurone]

Originally Posted by PQ

Oh. Damn. I didn't know that. I thought the parking break was the full rear calipers.

Silly PQ!! You must still be shell shocked from getting your finger jammed in where it didn't belong, to have noticed this....