TomaszGoc

gentlemen, I need help. I have been feeling vibrations in the cabin for some time. the mechanic claims that they come from the gearbox. the wheels were checked and balanced. brakes too. vibrations are felt most at the speed of 70-90mph under load. vibrations are transmitted throughout the car and you can feel them under the driver's seat, not on the steering wheel. Anyone had a similar problem? the gearbox is a 7g tronic, 4 matic drive.
the problem becomes more acute when I put on 20 inch wheels. currently, on winter tires and 18-inch rims, vibrations are less noticeable but still at the same speeds, or in the range of 2300-2600 rpm

Idklol69

Try this:
Not sure if it'll help, but worth a shot. How many KM are you at? Has it had a transmission service yet?

chassis

You need more diagnostic information.

Only at one speed?

Only at constant speed? What about accelerating, decelerating or braking?

Vibration in steering wheel?

Vibration in brakes?

Vibration increases or decreases when swerving left or right at highway speeds?

Vibration increases or decreases when braking?

Vibration increases or decreases when steering sharp corners (parking lot)?

Vibration coming from front or rear of car?

Vibration coming from left or right side of car?

TomaszGoc

Chassis thank you for your interest.
Vibration occurs from a speed of 120-140 km / h. They occur when the car is under load, if it turns on the cruise control at a speed of 130 km / h, the vibrations stop significantly, but they occur cyclically, e.g. 2 seconds vibrates, 2 seconds pause, 2 seconds vibrates, 2 seconds pause, etc.
Vibrations do not affect the brakes on the steering wheel
Vibration increases when swerving left or right at highway speeds.
They do not occur at low speeds and in the parking lot.
The vibrations come from the center of the car.

ss3964spd

Determine if the vibration is speed dependent or RPM dependent. If it is speed dependent try running the car at 70-90 but manually shift the trans into 6th or 5th. If it is RPM dependent it should do it between 2300-2600 regardless of vehicle speed.

Do your winter and 20" tires have the same diameter as the "stock" tires? Do your winter and 20" wheels have the same offset's as the stock wheels?

TomaszGoc

summer wheels have a greater offset. while the tires are selected according to the calculator.
Front 8 inch tire 245/30 (et30)
rear 10 inch tire 295/25 (et32)
The circumference of the wheel is the same (error within 1% tolerance)
However, vibration also occurs on summer and winter tires on original amg rims: (I did tests because I have 3 sets of wheels)
Front 8.5 inch tire 255/40 r18 (et37)
rear 9.5 opoina 285/35 r18 (et47)
Winter tires all 8.5 inch 255/40 R18 (et37)
On the other hand, on 18 inch rims (summer and winter tires), the vibrations are softer.
vibrations depend on the revolutions in the range of 2300-2600 as you write, but the higher the speed, the more it is felt.

ss3964spd

Try some additional tests.

Place the transmission in M. From a dead stop accelerate gently and see if the vibration presents between 2300 and 2600. Manually shift into 2nd gear around 2700. Accelerate gently through 2300 and 2600 again to see if the vibration presents, then shift into 3rd and repeat. If you have enough room do the same in 4th, 5th, etc. Repeat tests under moderate acceleration, and again under heavy acceleration.

If you can get the vibration to present itself always between 2300 and 2600, regardless of speed, it suggests the problem isn't the wheels and tires, especially since you've tried 3 different sets.

TomaszGoc

the wheels and tires are definitely not the problem, we've already checked it. during ecu tuning the first power measurement showed over 410 horsepower but we had to reduce the power as the vibrations were even more noticeable. so the problem is either the engine or the gearbox. My tuning specialist claims it is a gearbox.

chassis

Brakes, wheels, tires and steering are ruled out.

No noise while steering means front halfshafts are ruled out.

It's either propshaft joints or support, halfshafts or wheel bearings. Wheel bearings are a somewhat common failure item.

Is there vibration when swerving left and right at highway speed with your foot off the accelerator pedal (no cruise control)?

Beer_Bandit

After what you have eliminated, i would also check all the front end bushes.
Upper/lower control arms, end links and even the swaybar bushes.

blaise

Road force balance your best set of tires. Check your motor mounts and tranny mount. These trans are very stout, hardly any issues even with double torque limitations.The fact that you say it occurs cycling seems like a bent rim.

blaise

Most tire shops throw the wheel on balance machine and either add weights or subtract. They usually miss the bent rim because they are so easily fooled by the balancer. There is no need to put 1.5 oz or similar to correct a balance... yes it will zero out but a seasoned tech would notice a problem and realize the rim is in fact bent. This would explain the smooth ride certain speed but under acceleration it will manifest more depending on the harmonics of the bent wheel... Just saying, before you rule out wheel / tire. Im not saying this is your issue for sure but is something worth looking at.