2006 Nissan PF SE Transmission Thunk when shifting

[rannunziato]

2006 Nissan PF SE, 4WD, Auto, V6, 4.0L. What is the thunk I hear during 1st drive of the day. Only happens once, then not again until trans is cold. Sounds like dull metal thunk similar to the sound of driving over a man hole cover. Is this the Trans?, Transfer Case? Rear Diff? Front Diff? Drive Shaft? Yolks? Doesn't seem to affect the performance at all and after it occurs, doesn't happen again until the truck sits for a while. Also, the noise occurs when coasting in neutral while going down my street in the AM.

[NVSteve]

Do you hear it when the speedo hits 15mph? It's normal. I can't remember if it is the VDC or the ABLS that does it, but every time I start the car & it hits 15mph, I get the same noise. I thought they all did it, but there are some on this forum who claim they can't hear it. Mine is loud enough to wake the dead. I know I always startle people walking in a parking lot as I drive by them and hit 15mph, such as when leaving a store.

[rannunziato]

Yes it does. I find it hard to believe that this is normal. VDC and ABLS huh? What part is bad? Can it be fixed? Sounds like someone is hitting my transmission case with a hammer....

[slavabon]

This is ABS check. Perfectly normal. It happens every time you start you car and start moving and reach 15MPH. It will not happen until you shut it off and start driving again. Don't worry about it and let the truck do its thing.

[rannunziato]

Okay, so this noise is "normal". If this is true, then why didn't it occur until after the odometer hit 107K? Can anyone please tell me what exactly is happening? What is the noise? Does it have anything to do with the E Brake because that is not engaging also. I haven't had the time to take a look at it yet and was wondering if they are connected. Cable engages and tension is applied but rear brakes don't lock. Could the two be connected. I would love to fix, that's what I do, I fix broken stuff....Thanks for all of your valuable input.

[mar1]

actually the ABS check is not a "thunk" sound, but more of a spring being pulled and released sound. could be something else making that sound. have u checked ur tranny fluid recently?

[rannunziato]

Had the tranny flushed and replaced with matic s fluid, then had the transfer case main seal replaced (leaking), rear drive shaft seal replaced (pro-active), also replaced front and rear drive shaft u joints (rusted, which caused the fr. seal to leak). Also had the transfer case and rear fluids replaced. So all in all, basically a soup to nuts tune up from the tranny all the way back to the rear.... The ABS spring thing sounds close...Wonder why all of a sudden it's making noise...

[NVSteve]

Have you owned the vehicle for all 107k of mileage? Just to go along with what mar1 said, mine also sounds more like a cross between a spring slamming shut in a cylinder and some sort of hydraulic brake actuating. As I mentioned, some people on this forum swear they don't hear this, which might partially/fully explain why you never heard it before. Hard to say since I've only ever heard it.

[rannunziato]

No I haven't, bought it with 98k. Didn't hear the thunk until 105K. Is the ABS activated with a spring or hydraulics?

[CPLTECH]

Mine does what I refer to as a “diagnostic check” of the anti-lock brake system also at about 15 MPH.
Are you aware that when in 4 wheel drive, it uses the ABS if wheel slip detected? From experience, it works nicely since the diff is not the locking type. There is also a control button called VDC (Vehicle Direction Control???) designed to keep you safe in a turn (skid). Be glad it does its check first thing. Just how loud is too loud I can not say.