FWD Car, Accelaration vibration (at cabin and a bit steerings)... sometimes also braking vibrations

Maintenance/Repairs
1

I have my car (Alfaromeo / Fiat 500x) which has An strange issue (another topic been opened but not so clear till now). Dual clutch gearbox.

Wheel speed sensitive

I’ve have some strange shuddering vibration (not exactly shimmy) at acceleration (sometimes) between 130-160km/h (germany)
When the car is driven for a while also under braking it starts shaking. Also during normal coasting without gear in.

I’ve been on a garage (after multiple visits on different). We checked the car for all the following:
CV play (no probs)
Wheel bearing,
LCA bushing, nothings obvious
Engine mounts nothing! they even removed the rear engine mount to check it visually…

The more you drive the more it becomes obvious as a vibration. Can felt on steering wheel as a hand massage. can also be felt on gear lever and foot rest. If put it on neutral. it stops

After today 300kms of driving just before home i tried to brake (on highway) and it start a shuddering and shimmy on steering wheel too! then the car had a constant smaller shimmy when not braking!
After a bit this stopped or been reduced.

260km out of 300 where highway driving!
Car is having the acceleration issue for almost a year and the braking started 3 months ago! but even with new rotors/pads still does it (new brake lines etc…). Wheels not seem to be hot or disk rotors sticky! but you never know

I suspect wheel bearing… or CV Axle (can this cause also the braking/ coasting vibration?

When the car stays for some days parked the problem becomes less obvious. the more I use it the more it grows, even with overnight breaks

2

Something wrong with the transmission or clutch I would guess.

3

And the shaking while braking on neutral later?

The symptoms are classic cv joint. But the braking makes it confusing (which happens during long rides)

4

Even if a wheel bearing has no play it doesn’t mean it is good.They need to listen to it with a stetoscope to confirm that. Its very rare that both wheel bearings go bad at the same time.
CV joint gets noisy when you turn…they make the usual click,click sound.Try driving on a different road to see if the shaking stops.Maybe the road surface where you drive has a problem.

5

Inner CV joint or bent axle/hub is my guess.

6

I didn’t know a Fiat 500X would do 100 mph. Is the X model all wheel drive?

7

it is FWD, it does up to 120 mph with the engine i have
the problem is ok under load I suspect CV axle but after LONG rides why the brakes shake? even if new?
and when they start shake if you press them more and abuse them they stop!

It is something mechanical…

Can a CV joint do also give symptoms unde braking (some times?)