Vibrations when accelerating (Fixed)

[zetoast]

Hello.

I had some issues with my E46 this spring that I finally resolved.
I checked a lot of forum posts while trying to figure it out, but didn't find anyone that had the exact same issues.
Figured I'd make a forum post about it in case anyone else gets the issue I had. Always good to have several possible explanations when you have a problem.

I've had my manual gearbox 330 Diesel E46 coupe since 2013. mileage is now at 140 000 km
About a year ago I started to notice something was a bit off but couldn't quite say what it was. A few months later the problem became so pronounced I could tell what it was: The car would vibrate (more than usual) when I accelerated hard. The problem quickly got worse, and the vibrations changed to an awful studdering shake every time I gave even a tiny bit of gas in 1st and 2nd gear. In 3rd gear or above, I mostly didn't feel it, unless I really hit the gas hard, or if I was going uphill. If I disengaged the clutch and just revved the engine, there was no unusual vibrations from the engine.
If I hit the brakes hard at cruising speed, the whole car would shake just the same as if I was accelerating hard.
Typically, the car would shake when taking off in 1st, unless gas was being applied veeery carefully, then it would shake in 2nd unless gas was being applied (again) very very slowly. Once it got up to mid 3rd or 4th, the shaking would susbide. I could drive at 60-70 kmh without noticing much. Trying to take off in 1st uphill would guarantee hard vibrations.

It was obvious that the magnitude of the shaking was proportional to the torque and rpm going through whatever part was causing the problem.

MY main suspect was that the springs in the dual-mass flywheel had gone bad, causing the dual masses to start bouncing too much in high torque situations, and slowly wrecking my clutch. A friend of mine (with a different car) had the exact same symptoms as me, and for him, it was the flywheel that had gone bad. His issues cleared up when he changed the flywheel.
The whole car was shaking so violently at high acceleration in low gear that it almost felt like the clutch was engaging and disengaging several times per second, making the acceleration feel like it was caused my a mechanism similar to the rotary hammer in an impact wrench, instead of a smooth increase in rpms.

Several forum posts suggested that it might be worn engine mounts, but I knew fairly early on that those weren't the issue, as it didn't seem like engine vibrations had anything to do with this at all.
I knew the issue had to be somewhere in the drivetrain as it did not have anything to do with the engine or wheels/suspension.

A lot of people with automatic transmissions apparently had similar symptoms as mine due to worn out torque converters.

In the end it turned out that the flex disc had worn out, which is a rubber disc that takes up vibrations between the transmission and the rear shaft. When changing the flex disc we discovered that the rear shaft bearing was borked, so that had to be changed . When the new rear shaft bearing arrived, it turned out that the rear shaft itself had a small bend, so the rear shaft also had to be replaced . After changing those 3 components, my issue disappeared completely.
I don't know where the problem appeared first that caused the other 2 components to break, but if I was to bet I'd say the flex disc probably wore out first. I'd love to hear other peoples opinion on that matter though.

[MIKYZZ4]

So for those of us in the States,
Guibo-Center support bearing-Drive shaft to the rear of center support bearing,
NOT the forward one between the guibo and center bearing.