[6thgenB]

I've had my 2018 SS M6 going on two years now. About a year ago going to work, I looked at my shift knob and saw it vibrating slightly. Ok, no big deal, it's probably just road vibration. As time went on, that vibration slowly got worse and worse to the point where I could feel it in the seat, and eventually see it vibrating my sun visors and anything loose in my passenger seat. All of this was happening at highway speeds between 55mph-85mph with its peak being around 70mph. It happens in any gear and is most noticeable while cruising at said speeds or coasting. It is very faint while accelerating.

I changed to new rims and tires back in May of 2023. That is when I started feeling the vibration in my seats. I had the tires road-force checked and rebalanced many times for reasons unrelated to the vibration (TPMS issues) and it did not fix the problem. In early December, it has gotten so bad that the shift knob is vibrating a good 3/8".

Stupid of me wait so long to take a look, I decided to finally lift the car up and feel around at some things. The transmission mounts feel and look great. The drive shaft feels nice and tight. The driveshaft to differential feels good as well. The axles however could be moved up and down significantly, forward and back significantly, and twisted a bit with a little clunk.

I know the axles are a problem, but is it the cause of the vibration felt through the entire car? Would the axles make the shift knob vibrate violently even when the differential is solid mount to the frame? Could the differential casing be an issue? What could be some other causes of the vibration?

[arpad_m]

The primary suspects behind speed related vibrations are still wheels and/or tires. Any chance you can put the originals back for a test? Or maybe borrow a set from someone for a test drive?

[6thgenB]

When getting my current wheels fixed with the TPMS issue, I was on my stock wheels. Before going to my current wheels, I first noticed the vibration on the stocks

[NiickySaz]

Alignment? Maybe the weights are not balanced properly?

[6thgenB]

I did get an alignment after getting the new wheels put on. It's very unlikely that both the stock wheels and the new wheels and not balanced properly, especially with the vibrations being the same between the wheels.

Just a little background on my new wheels (unrelated to the post except for the balance of the wheels), I ordered my rims online. I ordered the tires and TPMS through a local shop. The shop installed everything and then put in on the car. 1st time balancing. Everything was fine other than the vibration which was still the same with my stock wheels. I go 10 minutes down the road and the right front TPMS disconnects. I go back to the shop where they relearn it and send me off. Again, 10 minutes down the road and the same one disconnects. They ask me to leave the wheels with them until they get a ew sensor to put in. I put my old wheels back on for a little over a week. They call me back and put the new tires with the new sensor back on. 2nd time balancing. This time, after 10 minutes of driving, the left rear TPMS disconnects. They do the same thing again. after ordering a new sensor. 3rd time balancing. Now its both front right and rear left. They tell me they're going to order a completely different type of sensors. At this point I'm frustrated and say go for it. Luckily its not out my pocket. 4th time rebalancing. None of the sensors connect. I get my money back and take it to a new shop where they put the correct sensors in and rebalance.5th time rebalancing. No problems after. That's where I am now.

Even with the stock wheels, I felt the vibration. It is not the wheels.

[arpad_m]

Okay, thanks for the extra info. I'm not an expert, but if this is not gear dependent either, the next thing I would get checked out is the diff.

[NiickySaz]

Could be a misfire but I'd imagine you would get a CEL, could always check the plugs though. Can you put it in neutral and try to steadily rev it and noticing it?

[6thgenB]

Definitely not a misfire. Car runs and drives smooth up until 55mph-85mph. Even in that speed range, the engine runs smooth. A flashing CEL will show if there’s a misfire.

I will definitely try to lift it up again and take a proper look at the axles taken out of the differential at some point in the future. I’ll look at the differential too.

[CalgaryZL1]

Originally Posted by 6thgenB

Definitely not a misfire. Car runs and drives smooth up until 55mph-85mph. Even in that speed range, the engine runs smooth. A flashing CEL will show if there’s a misfire.

I will definitely try to lift it up again and take a proper look at the axles taken out of the differential at some point in the future. I’ll look at the differential too.

You mentioned “The axles however could be moved up and down significantly, forward and back significantly, and twisted a bit with a little clunk.” I would definitely start there.

[Spaceme1117]

It could be the center support bearing of the drive shaft. There is a TSB for 2016-2019 cars. Just a guess.

I get a little bit of driveline vibration in my car at about 75mph. I had brand new tires installed in December and just had a rebalance done about a week ago and still have it. I am considering changing the support bearing just in case. My car (2017 2SS, 8-spd auto) is at nearly 57K miles.