Hi everyone. I'm new here and new to JKs. I recently sold my TJ and bought a 2015 TJ so I'm not completely new to Jeeps. I've read and searched until I can't see straight so sorry if this has been covered. Here's my issue:

Bought a 2015 TJU sport auto transmission with 90,000 miles from a pre-owned lot of a local new car dealer (not Jeep). Looked it over. drove it. Did my best to inspect it. It came with a 30 day/ 1000 mile warranty.

After about two weeks and a 6 hour round trip drive, I noticed a vibration after I had driven it for about 20-30 minutes. Happens at about 600-1000 rpms. It's the worst at idle or at slow turns or in reverse. It can get bad enough to vibrate the plastic in the interior. It is not violent. More like a harmonic vibration. I can feel it trigger if I stop abruptly. It feels like it kicks in. It happens with the AC on or off though it seems to happen sooner with AC on. When if first get in the Jeep it runs very smoothly which is annoying because I get a taste of how it should run. The vibration does not feel normal to me at all. My hands and feet feel like I've been pushing a lawn mower after I've been driving it for a while. This issue feels like engine vibration is being transmitted through the steering wheel, pedals and seat. Basically anything connected to the engine/ chassis.

So, I took it back to the dealer. They looked it over, replaced an oil cooler and cleaned the throttle body and said the vibration was normal and there was nothing else wrong with it. They said they checked engine mounts and transmission mounts. Sent me on my way.

It happened again so I called the dealer took it in and the tech stood there with me and said it was totally normal.

Looking for a second opinion, I took it to a Jeep dealer service dept. and paid them to look it over and they said I had a broken transmission mount...(and leaky axle seals and had a coolant leak but that's not this discussion). Soooo....I take it back to the original dealer and they still say nothing is wrong with it. They said the Jeep dealer is wrong and they want me to come in and take a look under the Jeep with them.

I know the basic anatomy of a Jeep and other vehicles but I'm not a mechanic.I looked at the transmission mount before I took it in the first time and it looked OK I have no clue what to do at this point.

Here are a couple of more things I've noticed. Maybe red herrings? There seems to be a delayed shifting around 40 mph. Maybe 4th gear? Also, after that shift the engine feels like its vibrating and growling a bit. I read about a TSB that requires a PCM flash. Could that affect the vibration at idle? Or is that issue something else entirely.

This leaves me with a bad taste in my mouth about the car.

 

My 2 cents, the vibration you describe is not normal. I assume your old transmission went out, you replaced the transmission and had no problems for a couple of weeks and then the problems started. I am guessing there is no vibration or issues when idling? Does the vibration change with engine speed or is it always the same? A broken mount can cerate vibration so I would make sure they are good. You may not see a broken mount by just looking at it. You may need to stress it and look closely for failure. Did you put in a new torque converter? I had a car with similar problems that was due the converter. It was a new (Rebuilt) but it had problems and I had to swap it out to remove the vibration. I am sure there are more knowledgeable people here that can help. Good luck!

 

Well one thing is for certain, it is NOT normal, and anyone who suggests that it is normal is a complete imbecile. I think I'd be angling for them to take the jeep back and just walk away from it if there is any possible way to do that. Too many other jeeps out there with no issues.

 

Does it make an audible noise when doing this? My 15 JKUR does something similar when idling with the ac on but not when driving. I think I remember reading somewhere about issues with the ac compressors, and I have been meaning to have someone check it out but honestly don't use the ac much and tend to forget about it.

Also you didn't mention if your JK was lifted and if so how much? There is always a chance that your exhaust is binding somewhere up front causing the feedback you get, and running with ac on drops your idle some so if that were the case it would definitely amplify the vidration.

 

@Ryan0260 it doesn’t make an audible noise unless it starts vibrating the plastic. There is no lift. It’s completely stock except for wheels and tires but it started before I changed those out.

I went back to the original service dept. and looked under the Jeep while it was on the lift. The service manager pointed out that the transmission mount looks good. Rubber is springy and not cracked. He used a pry bar to put pressure on it and it looked good. There is some rust on the metal of the mount where it mounts to the crossmember but it looks superficial.

 

Does the engine run rough or idle lower than it should?

 

The engine doesn’t seem to run rough. Idles at about 600rpms.

the only time is seems like it runs tough is after a gear change. Maybe 4th? I feels like it growls a bit and vibrates.

 

photo smith - wondering if you have checked out the fan, could that be the source of your vibrations ? fan motor bearings? could be that the vibrations don't occur until the fan motor is totally warmed up and bearings heated up ?

 

This makes a lot of sense. When I have described the issue previously, I have compared it to a vibrating room fan. One that might be slightly loose or something. Also, driving at highway speed, there is a vibration that comes in long 2-3 second cycles which really fits a fan noise.

So, what’s the easiest way to troubleshoot this?

At this point, I think it’s too late to walk away from it. But, I do think the dealer would address it if we could figure it out.

 

This is a weird situation so all ideas are good while trying to think things through IMO, but I have a hard time seeing how that electric fan sitting behind the raditator could be sending vibes all the way back to the seat/peddle/steering wheel which is where I think vibes have to eventually end for the OP to feel like described in the original post. We're also talking about a '15 with 90k miles on it -

If this were my Jeep I think I would seriously be questioning those tranny mounts regardless of visual inspection and even the torque converter as Ronandjanet suggested above. You say you changed out wheels and tires, but did you stay with factory sizing or are you running larger tires? If they are larger tires the delayed shifting could just be more related to that regardless of the new tire size being programmed or not. It wouldn't shock me at all if this is precisely why the PO moved on from it.