Car Repair: Mechanic Can't Find the Problem?

Hello everyone.

I drive an Insignia 2.0 CDTi MK:DTE, manufactured in 12/2013, with 104,000 km on the odometer. The problem started around 100,000 km with a slight swaying (from side to side) of the front of the car when accelerating fully in 4th gear between 80-100 km/h (1800-2000 RPM). It only really starts when the engine is warm (after about 15-20 km) and when the car is fully loaded.
After driving another 4,000 km, the issue now occurs in 3rd gear during 90% of acceleration attempts, and the vibrations are increasing. It feels like the car is shaking back and forth, and there's also a slight vibration in the steering wheel at high speeds.
It also seems to me that the road noise is getting louder, with the loudest noise occurring between 70 and 110 km/h, almost like a rumbling sound.
I've been to the Opel dealer twice now. They've balanced the wheels multiple times, swapped them from front to back, checked the control arm bushings/suspension, and, on the advice of Opel, rotated the drive shafts 180 degrees at the splines.
"I then went to a friend who runs a small workshop, but he's also hesitant to take on the job because it would likely involve a lot of parts replacements. It could be anything from the drive shafts and wheel bearings, all the way to the transmission. He suspects the problem might be related to the transmission/differential, possibly due to a transmission repair that was done 1.5 years ago, approximately 40,000 km ago, at the official dealer."
They replaced the second gear and the synchronizer rings back then because the gear would frequently pop out.

How would you proceed now?

Best regards,
Thomas

I would search for a solution based on the principle of exclusion, without resorting to excessive swapping.
Perhaps start with the suspension. Have the wheel suspension checked at the TÜV (German technical inspection agency) for both the front and rear.
The vehicle is resting on plates that are moved back and forth by compressed air.
Is the problem still present when using completely different wheels (winter tires)?
hg
Herbert.

I had a similar problem with an A4 B5. In that case, the cause was a worn-out tripod joint, and the issue only appeared after driving for 30-50 kilometers.

Golf 4, at 120,000 km: slight shaking and vibration. By 150,000 km, the shaking and vibration became progressively worse.

Then I disassembled the internal constant velocity joints. A picture is worth a thousand words.

Hi!

A close relative has the same or a very similar car.

So, it's basically a permanent construction site, and a lot of things were already broken.
I also know that he had to replace both drive shafts.

Sometimes, when I have no idea what to do, I call my parts supplier.

He can tell me whether he sells part Y for car X once a year, or 20 times a day.
That gives you a starting point.

@herbert @rüdi @Bertil @SteffenG

Thank you for your responses; they actually confirm my initial suspicions. I had mentioned the tripod joints to the dealer, but they said it was practically impossible given the mileage.
I have to say that 90% of the kilometers driven are always with 4 people and luggage. I can imagine that my driving style, always utilizing the full torque, and the total weight of approximately 2 tons are not beneficial for the bearings. I suspect that the bearings, like in the photo above, always engage at the same point, then become misaligned under load, and cause an out-of-round condition in the shaft?

I realized today that it gets significantly worse when the passenger is inside. Is that then the right side? Logically, shouldn't both sides have a way out?

Best regards, Thomas.

It's also possible that the tread separated from the tire.

It's not always noticeable on the tire balancing machine.
Have you ever tried using a different brand of tires?

Best regards, Frank.

Hi,
I wanted to add a follow-up to my post, and thank you all again!!!!!
As I suspected from the beginning, it was the drive shafts, likely the one on the driver's side.
Da mein FOH nach mehreren Werkstattbesuchen nicht sagen konnte was denn nun als erstes gewechselt werden soll, habe ich zwei Antriebswellen von LÖBRO für 135 Euro das Stück im Internet bestellt und bin zu ihm hingefahren. Der Werkstattmeister fand das gar nicht so schlecht dass ich ihm die Entscheidung abgenommen habe und wir kamen überein dass die Wellen für 130 Euro getauscht werden. Ich habe den Werkstattmeister mal gefragt, ob er Opel in Bezug der Aussage "die Antriebswellen bei mir um 180 Grad in der Verzahnung zu drehen" falsch verstanden habe und Opel vielleicht meinte die Wellen von rechts nach links zu tauschen. Da sagte er, er hat zweimal telefonisch nachgefragt und diese Antwort bekommen. Er denkt aber auch jetzt dass wahrscheinlich das Tauschen gemeint und richtig gewesen wäre. Aber egal ich hab zwei neue Wellen drin und die Werkstatt ist mir nochmal entgegen gekommen und brauchte auch den Reparaturversuch nicht bezahlen. Am Ende waren es insgesamt 170 Euro für 3 Werkstattbesuche und etliche Probefahrten + 270.- für die Wellen. EHe checked again how much the wave generator costs for him: 1200.- for a refurbished one, without installation.
I once opened the suspicious hose clamp, but besides the coolant, I didn't see anything else and I didn't want to take it apart any further. What was noticeable was that only a cheap, loose hose clamp was attached to the flange; perhaps someone in the workshop also took a look.

@Herbert @Rüdi @Bertil @Steffen_G