Single dull knock sound when accelerating during driving.

[D.J.]

Yeah, the rear diff is probably toast.

Toast, or in need of a slightly different shim to correct the backlash

#5 here

http://www.kstinger.com/rear_differential_carrier-547.html

 

[oddball]

Toast, or in need of a slightly different shim to correct the backlash

#5 here

http://www.kstinger.com/rear_differential_carrier-547.html

A diff improperly set up by the factory and run like that for >60k miles? Still toast.
Worse yet, someone poked around inside the diff and clearly had no idea WTF they were doing? Burnt toast.

 

[Matheuszh]

Update.
They replaced rear diff, at first I thought the knocking disappeared. But it didn't.
Any suggestions what else it could it be? I'm kinda done at this point and I won't go to KIA with this problem anymore because they clearly have no clue what could it be.

They said everything in the driveshaft is sturdy, nothing wiggling etc.
I cant say how accurately they checked that or if they missed anything. Any other suggestions? I'm worried that it might be some transmission related problem but I am not sure how it is working inside accurately. When rolling without pressing gas, what happens after I accelerate? Is there some operation happening inside transmission that could potentially give me this fkin knocking sound?

It happens sometime when I'm changing gears but rarely, 95% of the time when just pressing gas slightly when allready moving or sometimes when slowing down in slow traffic right after it reduces gears.

 

[MerlintheMad]

It happens sometime when I'm changing gears but rarely, 95% of the time when just pressing gas slightly when allready moving or sometimes when slowing down in slow traffic right after it reduces gears.

Is it exactly the same thumping sound in your video? Did all the engine mounts get checked, etc.?

 

[Matheuszh]

Is it exactly the same thumping sound in your video? Did all the engine mounts get checked, etc.?

Pretty much the same, at first I thought it got quieter but sometimes it bangs the same as before.
I also thought about mounts but I cannot tell they've checked that. I've found another workshop and I will ask them to check everything trough. Also I will call KIA tomorrow and ask if they have any report of checking it exactly during my visits.

It doesn't happen when revving on neutral, so I think it may be more like transmission mount (if that makes any sense) if thats the case.

 

[Matheuszh]

Also for clarification, it happens 95% IF it happens. It doesn't always knock when accelerating. Sometimes it is subtle and sometimes loud. It is the loudest when the RPMS are low and it needs more force to accelerate, for example driving on 5th or 6th gear with about 2k rpms and pressing gas will knock louder more often.

And most importantly, it occurs when I let it roll for a while when rpms lower down (possibly reduce gears) and then accelerate. When I press it constantly back and forth it doesn't hit. It needs time to "settle down" - about 2 seconds or so

 

[MerlintheMad]

So, when you "hoon" about a little bit, you get nothing?

 

[Matheuszh]

So, when you "hoon" about a little bit, you get nothing?

Haha can you be more specific?

When pressing gas back and forth constantly while driving it doesn't happen. Only when I accelerate, wait 2 seconds and then accelerate again. On the video you can hear that I am waiting for rpms to lower a bit after acceleration and then i press it again.

 

[nhcowboy28]

It’s a 10mm socket on the floorboard.

 

[Rodtheviking]

It’s a 10mm socket on the floorboard.

Check under your seats.

But it's most likely the transmission.

 

[Matheuszh]

But it's most likely the transmission.

It is loudest in the backseats / trunk area, wouldn't transmission bang on the driver's area? I really hope it is not the case.

 

[Rodtheviking]

Center support bearing or the silly rear flex coupling( I hate those things) could cause some weird noises especially under load.

 

[AtomicGTL]

It is loudest in the backseats / trunk area, wouldn't transmission bang on the driver's area? I really hope it is not the case.

Do you get any codes?

 

[Matheuszh]

Nope, they've checked that. Would transmission show any codes?

 

[MerlintheMad]

So, when you "hoon" about a little bit, you get nothing?

Haha can you be more specific?

When pressing gas back and forth constantly while driving it doesn't happen. Only when I accelerate, wait 2 seconds and then accelerate again. On the video you can hear that I am waiting for rpms to lower a bit after acceleration and then i press it again.

No, I can't tell anything about RPMs, up or down, in your video: only the rhythmic thudding.

When you accelerate "spiritedly", pass fast and/or take the twisty bits with enough Gs to start to hear the tires a bit, do you get any thudding then?

 

[Matheuszh]

No, I can't tell anything about RPMs, up or down, in your video: only the rhythmic thudding.

When you accelerate "spiritedly", pass fast and/or take the twisty bits with enough Gs to start to hear the tires a bit, do you get any thudding then?

Nope, it only happens right before car starts accelerating, one single thud. In sport mode it happens nearly at the same time. Pressing gas - knock - gaining speed. On the video im pressing and releasing after each knock

Only happens happens after leaving it to roll without pressing gas for couple of seconds.

Also Im not really "hooning" kind of driver haha

 

[MerlintheMad]

Nope, it only happens right before car starts accelerating, one single thud. In sport mode it happens nearly at the same time. Pressing gas - knock - gaining speed. On the video im pressing and releasing after each knock

Only happens happens after leaving it to roll without pressing gas for couple of seconds.

Also Im not really "hooning" kind of driver haha

This is helpful. A single knock/thud with each incident, means that something is moving and then binding, as if there is play where there ought not to be. That does not sound like a transmission generated issue. A similar single click or thunk happens on some cars with aftermarket brake pads: the aftermarket pads can be a tad loose (not quite filling the caliper, and requiring a shim to fit snuggly), and when the car in reverse is stopped there is a single thunk as the pad shifts. It can happen again the first time the brakes are applied moving forward: the noise won't occur again until the car is reversed. But your noise is drivetrain related: so, under power, whatever is sloppy is bound in the "drive" direction. But upon releasing the gas the drivetrain is freewheeling. Then you get on the gas again and the slack is taken up again with a *thud*. Is it possible that the new differential was installed carelessly? I hope that your next inspection at that shop reveals the source. You know, a soft *thud* when accelerating or decelerating wouldn't bother me, as long as I knew that it didn't mean something is going to fail: that would take a thorough explanation from a mechanic that I trust.

 

[Matheuszh]

But upon releasing the gas the drivetrain is freewheeling. Then you get on the gas again and the slack is taken up again with a *thud*.

That is exactly how it feels like, thats why I was wondering if this could be transmission related, like changing some gears after rolling for a while. They said at KIA that everything is fine with the drivetrain but im not feally sure about that

Is it possible that the new differential was installed carelessly?

I don't think so but, you can never be sure.

You know, a soft *thud* when accelerating or decelerating wouldn't bother me, as long as I knew that it didn't mean something is going to fail: that would take a thorough explanation from a mechanic that I trust.

I hope so too. A subtle knock also wouldn't bother me but sometimes when it bangs loud and when I still dont know if this is something serious, im getting really anxious.

 

[vipeboy2000]

You'd think they checked... but differential mounts? they could look fine and feel fine by hand... but with the torque , it's enough to thud/clunk after it settles in to a neutral position ? which is why you wouldn't hear it if they were already in the "stressed" position and once there you could accelerate hard and not clunk since it's not moving more... i've read they are pretty soft bushings... I had a similar on first accel/ decel thunk in our e39 wagon which was the rear diff bushings..

 

[n8hegr8]

something loose rolling around under the seat or trunk? its usually my sons roblox figurines or a water bottle.