Technical Vibrations / bouncing Ducato Maxi - desperate owner

[campercan]

Hello!

I have a vibration problem with my Fiat Ducato motorhome and I’m starting to run out of ideas.

It’s a Fiat Ducato Maxi, 2020 model, 2.3 litre, 178 hp, 9-speed automatic, 3.3 tonnes.

The problem seems to be speed-related:

• At around 60–65 km/h, the vehicle/body starts to bounce.
• At around 80–85 km/h, the bouncing comes back clearly.
• At around 100 km/h, the steering wheel also starts to shake.

The bouncing is still there when the van is rolling in neutral. It also does not change much when accelerating, lifting off the throttle, engine braking, or braking normally. So it does not feel engine-rpm related, but more like something linked to road speed.

So far, this has been checked or done:

Wheels and tyres have been changed, but the problem remains.
Brake discs and wheel hubs have been checked with a dial gauge, with no clear runout found.
No visible play has been found in the suspension.
The old driveshafts had play and were replaced with newer used ones. It improved slightly, but the vibration is still there.

The van also had an engine replacement before. At that time, some engine/gearbox mounting parts were replaced as well, including the “Link Rod” 1396532080.

I no longer suspect tyres, wheels, brakes or the engine. My current thoughts are more towards:

• right intermediate shaft / support bearing
• inner CV joints
• engine or gearbox sitting slightly wrong or under tension after the engine replacement
• gearbox outputs, differential or bearings
• possibly something at the rear, such as shock absorbers, leaf spring bushes or mounts making a resonance worse

Has anyone had a similar issue on a Fiat Ducato, Citroën Jumper or Peugeot Boxer?

Can an intermediate shaft/support bearing or inner CV joints cause vibration even when rolling in neutral?

Can the engine/gearbox position be wrong after an engine replacement and cause bad driveshaft angles?

Or should I be looking more at the rear suspension, leaf springs, bushes or rear axle?

I really want to avoid replacing more parts just by guessing. I’d be grateful for any ideas or experience.

I'm close to give up...

 

[Mike1alike]

I'm thinking maybe the wheels bearings...

 

[bugsymike]

If it is coming through the steering , then front end.
All the usual favourites you have tried.
Misaligned gearbox/engine maybe, diff bearings?
What I would do if still working would be to safely support it on a garage ramp with front wheels off the ground and gradually build up speed whilst checking from underneath to see where shaking starts.
Note suspension would need to be supported so wheels and driveshafts in the same position as if on the road, not hanging down.
Another thing when on the road and it is just starting to happen, see if it goes away when on a left or right hand bend.
Has it been in an accident, is chassis or axles out of true, are you getting strange tyre wear?
Finally is anything to do with the Motorhome side creating strange wind turbulance.

 

[campercan]

@bugsymike thanks, no accidents as far as I know, no strange tyre wear.
No impact of steering when it's bouncing.
Lifting the van, supporting suspension and increasing speed is something I've mentioned for the workshop as well, but so far they didn't want to go for that. But I'll mention it again!

Front axle was also the thought, until I started wondering if it could be worn out shocks in the back, leading to bouncing and at 100 km/h it's enough shaking at a certain frequency that it interferes with the front axle as well. What do you think of that?

 

[bugsymike]

@bugsymike thanks, no accidents as far as I know, no strange tyre wear.
No impact of steering when it's bouncing.
Lifting the van, supporting suspension and increasing speed is something I've mentioned for the workshop as well, but so far they didn't want to go for that. But I'll mention it again!

Front axle was also the thought, until I started wondering if it could be worn out shocks in the back, leading to bouncing and at 100 km/h it's enough shaking at a certain frequency that it interferes with the front axle as well. What do you think of that?

Running a vehicle on the ramp can work , but it also can be dangerous, so great care needs to be taken to support it well and no moving the steering.
I have done it many times in the past though, with no accidents.
Safest is an MOT pit with a ramp jack with it's arms out on the lower suspension arms almost to the wheels. Modern "wheel free ramps" are useless for this.
If shock absorbers that bad then I would have thought giving vehicle a good rock would show it, also would it still happen on a really smooth road?
What about the turbulence, do you have any odd top boxes or anything to catch the wind?

 

[campercan]

@bugsymike true it sounds a bit scary but I hope the workshop is able to solve it.
Regarding turbulence, I only have a roof carrier made of 30x30 profiles from front to back holding solar panels, one MaxxFan in the front, one in the back - that's all. The fans are higher than the carrier with the panels. So nothing that should cause any trouble.

The shocks are still the Fiat ones, so they could be worn out (113 000km) or too weak for constant 3.3 tonnes? But nothing I can see or hear.

 

[bugsymike]

@bugsymike true it sounds a bit scary but I hope the workshop is able to solve it.
Regarding turbulence, I only have a roof carrier made of 30x30 profiles from front to back holding solar panels, one MaxxFan in the front, one in the back - that's all. The fans are higher than the carrier with the panels. So nothing that should cause any trouble.

The shocks are still the Fiat ones, so they could be worn out (113 000km) or too weak for constant 3.3 tonnes? But nothing I can see or hear.

Heavy loads high up can make vehicles unstable.
Have to tried someone driving alongside when it is doing it to see if any thing strange is happening?
I have seen large roof racks with sheets of board nearly bent double, but when the vehicle slowed down it all fell back into place and looked normal.
Even any rear windows open can upset some vehicles at speed.

 

[campercan]

There are 3 panels on the roof, framed with aluminum profiles on all sides, so I guess you could lift the van on that carrier.
But no, didn't have someone looking from outside yet, good idea!