2011 128i SULEV 6MT Vibration at Load

[rivesalex21]

TLDR: My baby beemer vibrates at certain RPM ranges and I've done tests to see if I can nail down why.

Hi All,

So far this group has helped me sort out some previous problems and I really appreciate it. I am now trying to sort out one final quirk that my car has.

Between 1500 - 3000 RPMs I'd say that there is noticeable vibration that that car goes through. It's usually felt during acceleration, but its also felt during deceleration through engine braking, this has been the case since I've owned the car and I've put approximately 7k miles. I also put in a new differential with a higher gearing alongside poly differential bushings so it's felt a bit more.

Couple notes below that I hope help troubleshoot this issue:

- It is felt under LOAD. I've put car on jackstands and have done accelerations up to 4k RPMs, decelerations with only engine braking and decelerations with actual braking and the car does not vibrate the same way.

- It occurs when the engine is connected to the drivetrain: If I am in neutral and rev the engine past 1500 RPMs there isn't any concerning vibrations. If I am coasting in neutral and begin braking.. the car does not vibrate the same way. BUT if I am coasting in neutral and put the car in gear.. then the car will vibrate as the clutch/transmission catches up to speed - proportional to the gear chosen.

- The vibrations are proportional to the chosen gear. It vibrates the most in gear 1 through the rev range, and least in gear 6.

- I've changed the guibo. I also looked at the center shaft bearing and it looked fine.

- I've also changed out most of the rear suspension components of the car except the springs.

- Previous owner changed out the motor and transmission mounts.

- Intuitively, I want to say that this is an engine related problem. I've seen people mention that changing the ignition coils would solve the problem, I'm not really sure that is still the right solution in my case since the car has been driving the way it has for over a year. I'm sure a code would've been thrown. I also notice a slight tick coming from the the passenger rear when I removed the insulation. It sounds like a puff of air or a purge coming out of a vacuum hose. This happens in 4th gear and when I blip the accelerator. It is not the axle. I don't know much about the N51 but could it be possible that a vacuum leak could cause issues when balancing the engine performance for current loads?

Again any help is appreciated.

[mkeiser]

Originally Posted by rivesalex21

- I've changed the guibo. I also looked at the center shaft bearing and it looked fine.

The CSB might look fine but unless you get eyes on it while the driveshaft is spinning you shouldn't count it out.

On my E46 I was chasing a vibration issue that only happened under load around 50-60mph. I eventually rigged up a GoPro pointed at the CSB and was able to see it flop around at that speed. It looked fine on a visual inspection.

[rivesalex21]

Originally Posted by mkeiser

The CSB might look fine but unless you get eyes on it while the driveshaft is spinning you shouldn't count it out.

On my E46 I was chasing a vibration issue that only happened under load around 50-60mph. I eventually rigged up a GoPro pointed at the CSB and was able to see it flop around at that speed. It looked fine on a visual inspection.

I hope that the solution is something simple. I've put a camera to look at the driveshaft before while the car was in the air. And the CSB didn't move.. but since the car was on jackstands then the load my car would've normally felt wasn't there.

I'll put a camera underneath and drive around with it to try to diagnose the issue. Do you have a picture of how you set up the gopro/can you tell me the attachment you used?

[mkeiser]

Originally Posted by rivesalex21

I hope that the solution is something simple. I've put a camera to look at the driveshaft before while the car was in the air. And the CSB didn't move.. but since the car was on jackstands then the load my car would've normally felt wasn't there.

I'll put a camera underneath and drive around with it to try to diagnose the issue. Do you have a picture of how you set up the gopro/can you tell me the attachment you used?

I rigged up the gopro on something like this with a bunch of zip ties securing it wherever I could. Then I used the mobile app to make sure the camera was pointed where I wanted it. I did this so many times pointing at different things until I saw the vibration under load.

[AKA]

My e46 intuition also says CSB. If not that, then PO misaligned things slightly when replacing mounts. Loosen mounts, raise engine a bit, wiggle it, tighten mounts.

[Olgeezer1]

I assume you've eliminated Tire / wheel balance or a slightly bent rim. I avoided poly diff. bushings specifically because of vibration, but sounds like this problem was pre-existing . If there's a local shop with a chassis dyno it might be worth the expense to get a good look underneath while under load.