2010 V6 4.0L Vibration Issue, 1,400 & 2,800rpm

[TerryZak]

I purchased a 2010 V6 Mustang for our younger son. Got a deal because I was pretty sure the rear end was shot.

After installing the rear end after we did a full rebuild, I noticed some other mild vibrations. I've replaced both engine motor mounts (were leaking) and the rear transmission mount. I've also had the upper link and bushing replaced.

The remaining issue is that when cruising around town there's a slight vibration at 1,400 rpm. Vibration is present when the car is in park, but only at a very narrow rpm of 1,400 and 2,800 rpm. Since 2,800 is a multiple or harmonic of 1,400 rpm I inspected the harmonic balancer carefully and didn't find any issues.

I've read that some of these had issues with cracks in the flex-plate, so I removed the starter and made an inspection. There wasn't anything obvious. I did find some hair-lines that looked like they could have been a crack, but used a metal seal-pick to scratch across the marks to see if I could "catch" a crack and was not able to.

The care could use the rear main seal replacement, but I don't want to go further on that until I have a better idea if I need replace the transmission or not.

Has anyone out there come across vibration at these rpms? If you vary by more than +/- 20 rpm from 1,400 and 2,800, the vibration will go away. Any ideas?

Thanks in advance,

Terry

 

[SVT Rider]

How's the pinion angle and drive shaft? Was the vehicle lowered to your knowledge?

 

[TerryZak]

Thanks SVT, the vehicle was not lowered. The vibration exists in park and in-gear.

I fully rebuilt the rear end and inspected the driveshaft as well.

I know this is a real head-scratcher, but I'm hoping someone has an insight.

Thanks!

 

[SVT Rider]

Thanks SVT, the vehicle was not lowered. The vibration exists in park and in-gear.
Thanks!

Well that would disprove the driveline. I am not an expert on the V6 of this generation, but it does sounds like a harmonic and something is out of balance. Hopefully someone else can chime in on V6 know-how.
Is this an automatic or manual?

 

[TerryZak]

Ah, good question SVT! This 2010 V6 has an automatic transmission.

 

[SVT Rider]

I don't see anyone giving advice, so I will throw another thought your way.
Any chance this is a drone vibration from the exhaust system? Can you tell if the exhaust/muffler is original or aftermarket?

 

[TerryZak]

Thanks for hanging with me SVT. The exhaust is bone stock and is not rubbing on anything. I'd also think that since there's no torque transmission in park, that the drivetrain would not be moving then. But when in drive when there is torque transmission I'd expect to hear more of an issue if it were the exhaust.

I've been working on cars as a hobby for 10-years, and this one has me baffled. I did tell my son that sometimes you have to wait for an issue to get bad enough to determine what it is. But I'm trying to get any/all issues sorted out so that this car will get him through college and perhaps a few years after that.

I have thought of dropping the auto trans out to change the rear main seal. If I do that, then I'll start the engine with the transmission out and see if the noise (1,400rpm and 2,800rm) goes away. At least that will tell me if the issue is on the engine or transmission side.

But thinking about that now I think I'll give my automotive stethoscope a try. It's just so hard to hit that narrow rpm band at 1,400rpm. I wish there was an idle adjustment screw like in the old days, which would make it easy to park the speed at that rpm.

I'll be sure to post what I find, if I ever find anything!

Thanks again,

Terry T.
St Augustine, FL

 

[Flapjack]

My 05 started out as a 4.0L V6. I believe there were exhaust balancers hung in a few places off the exhaust. Might want to check if those came off.

Check out this post on the mustangforums:
https://mustangforums.com/forum/4-0l-v6-technical-discussions/682201-exhaust-resonance-vibration-wieghts.html

Different RPM ranges, but might be the issue.

 

[TerryZak]

Thanks Flapjack!!

I've been under this car a few times inspecting the expansion accordion on the driveshaft and took some pictures of it, and never saw a weight in that location. No way I would have missed that.

Leaves me wondering if the exhaust hasn't been replaced?

Does anyone know the outside diameter of the stock exhaust pipes, so that I can measure them?

Thanks in advance,

Terry T.