That Annoying Mild Buzz On The Steering - Monitoring

While I have closed the entry on vibration, I did mark that while the issue has reduced, it wasn't gone.

Rhino drives great now, the springs have also settled down after the initial 3 weeks break-in period. It will need the wheel works soon with the new springs installed, only the alignment, castor, and camber alignment. 

I took the car in to get the road force balancing done and with the exception of 5g off a wheel, all other wheels needed no rectification.

A quick look under the car again saw no visible issues.

I am rationalizing the mild buzz that I am getting:

• Buzz starts from 65kmh (40mph)
• Buzz is felt on steering and seats
• Buzz is not felt on the dash, pillar trims, door trims, sun visor
• At 65kmh, the buzz is felt, at 70 buzz is at its peak, at 75 buzzes reduces back to what it felt at 65kmh
• Buzz is felt when the car is in motion and engine speed of 1800rpm onwards
• Buzz is felt on and off-gas, accelerating and decelerating
• When speed goes below 65kmh, buzz disappears again

Some thoughts around it

• The issue is not caused by a worn-out coupling / universal joint. It was inspected and also there is no 'clunk' when the gear is engaged
• The shaft has been sent for balancing, but the machine shop only rotated up to 100rpm. I also think the shafts were balanced one at a time instead of having both shafts balanced as one
• The shop also stretched the shaft to correct the imbalance but did not adjust and weld balancing weights
• The machine shop I went to says they are not able to guarantee 100% straight shafts after the work. While the repair improved the vibrations, it has not solved it

To correct this, I would have ideally replaced the pair with one that has not been detached from a donor car in Japan, but the shafts for E280 are difficult to come by in good condition.

The other option would be to continue scouting for machine shops that would balance at about 2000 rpm and uses welded weights to correct the balance and balance both shafts together.

Update #2:

After a long hiatus from updating, there have been some updates with this battle and hunt that started from vibration to milder vibration and then to the improved mild buzz that was observed on the steering.

The car was sent to an independent specialist for a check with the hope that the source can be narrowed down.

The initial check was to swap the wheels, but that did not yield any improvement.

The next order of the day was to hoist the car up and isolate the buzzing issue. After troubleshooting, the issue was determined to not be the prop shaft, the axle shafts were okay as well, but the vibration seemed to be originating from the axle.

They brought in an axle to be swapped and tested. The buzz is finally gone, the recently replaced axle was unfortunately faulty, while the issue improved, it did not resolve.

Update #3:

Rhino is ready to be brought home. Initial observations, the vibration that came up from 65kmh is not there anymore.

I drove it a good 30km on normal road speed, which is between 60-80kmh and it was all good.

I then drove it on the expressway and a new observation came up, which is vibration is felt at 120kmh and also a humming noise came up from 110kmh onwards.

To ensure the issue is consistent, I drove it through different speeds and yes, the issue was recreate-able.

The following day, a fellow old Merc enthusiast came over for a chat that resulted in us going for a drive where he shared similar feedback.

The car was sent back to the garage for further checks.

Update #4:

Got an update from the service advisor, he updated that the first order of diagnosis was to check if the driveshafts are the issue. They ran the car without driveshafts to eliminate that.

Confirming that the driveshafts are not the issue, they then swapped a prop shaft that I provided which has been balanced. The foreman updated that the vibration felt is no longer there at 60-80kmh range, the vibration from 110kmh is also not there and they tested it to 140kmh.

They mentioned that they added a 5g washer to the bolts in the input flange of the axle and had 2 inserted which reduced the vibration. 

I was asked to come for a test drive to confirm the fixes.

Update #5:

Rhino is ready for collection and the guys who worked on the car surrendered they are only able to best reduce but not remove the vibration.

From my observation, the mild but noticeably vibration starts at about 70kmh, at about 100kmh, it almost disappears due to the feedback from the road, the giveaway is the vibration that is felt on the armrest when it is pulled horizontally.

I also notice that the vibration was reduced on a slight slope on acceleration, this seems to be a symptom that points to the prop shaft universal joint.

The issue is almost coming down to only a few things left, but I am not able to get someone to thoroughly check the symptom.

• Prop shaft - needs to be completely straightened where the balance and alignment is perfect
• Axle - to be opened up and gears and bearings checked if they are worn out

And the issue continues to live another day...

Update #6:

I took Rhino for a drive and man, it vibrates pretty badly from 130kmh onwards. I did some thinking and below are some facts:

1. the axle shafts have been disconnected and tested, but it vibrates, this would isolate the wheel, brakes, knuckle, and assembly out
2. the vibration is revolving around the prop shaft and axle
3. front of the engine has been isolated out - not causing vibration
4. the recently removed prop shaft has got a damaged center bearing despite it has barely been installed a couple of months ago
5. Spare prop shafts (2 sets) has been sent to a machine engineering shop in for balancing, bearing replacement, and center bush installation
6. Springs were replaced recently in September, but ever since, the wheel works (alignment, castor, camber adjustment) has not been done
7. If the above are good and the vibration is still observed, the next course of action is to replace or check the rear wheel knuckles, rear-wheel hubs, and parking brake

Update #7:

I have received a call from the machine shop, they have assessed both sets of the prop shafts and as a result, they will now go-ahead to fix one set. The work to be carried out are:

1. Replacing the coupling (CV joint)
2. The front and rear centering bush will be replaced with new ones and pressed in place
3. Center mount bearing to be replaced
4. Prop shaft to be balanced once all work completes

Having had a few bad experiences and outcomes from other machine shops, hoping for a successful repair this time.

Update #8:

The prop shaft was scheduled to be installed, along with a new replacement for the rear right side wheel hub and knuckle. There was a slight play on the wheel that could have caused the vibration.

Upon installation of the balanced prop shaft, it was still no good. It is disappointing that despite a number of iterations of the prop shaft, the issue is still there. Despite repairing and balancing the prop shaft in different engineering shops, the prop shaft is still not true.

Taking Rhino to another garage for an opinion confirmed that the vibration is originating from the newly repaired and balanced prop shaft. The mechanic here mentioned that they have never had success with the prop shaft being balanced and highly recommended an undetached replacement to be sourced and fitted. They got a used unit but unfortunately, it wasn't the correct one. They then further scouted until they found an identical one with the correct dimensions.

They swapped and tested and the vibration has tremendously reduced and asked me to take Rhino out for a test drive. A mechanic who followed me for the test drive with me told me that there is a mild vibration that comes up at 60kmh and is suspected to be caused by a bad prop shaft mount that came with the replacement one.

The mech updated that to sort this, they will check my existing mount if it is still good, since it is relatively new and swap it along with replacing the prop shaft bearing to reduce rework since the prop shaft will be worked on.

I am now monitoring this issue and I hope it is the light at the end of the tunnel that I am seeing.

I will provide more updates when I have them.

Pictures:

Prop shaft center bearing, this is the high-temperature stable ones.