Excessive intermittent vibration

emtor · Post by **emtor** » 20 Oct 2021, 01:09

Volvo V70, 2008, 2.4d front wheel drive.

On my way to town the whole car suddenly started vibrating excessively making a loud BRRRRR-sound.
The vibration was not at all like an unbalanced wheel.
It seemed like coming from the front on the passenger side.
I engaged the clutchpedal and the vibration/noise stopped.
Happened again while accelerating and then after a short distance yet again while cruising at constant speed.
After this it has never happened again.
I haven't been under the car yet to check motormounts/driveshafts etc.
What could cause such an intermittent and excessive vibration?
Dual mass flywheel? -Wouldn't this cause symptoms more or less constantly?
Driveshaft? -Usually shows symptoms every time when accelerating and especially when turning.
Motormounts? -Usually shows symptoms when turning off the engine or when accelerating.
The driveshaft on the passengerside has a support bearing in the middle of the shaft, Could the bearing have worked itself loose from the bracket and slid out causing vibration, and then sliding back in causing the vibration to stop?
Any suggestions?

Post by **RickHaleParker** » 20 Oct 2021, 01:26

Did you check the tires for broken / shifting steel belts?
Harmonic Balancer condition?
Was the A/C engaged?
Timing belt and auxiliary belts tight?
Water pump have any play?
Alternator have any play?

emtor · Post by **emtor** » 20 Oct 2021, 03:17

I have recently replaced the timing and aux belt plus rollers and tensioners.
Doing this I had to take off the harmonic balancer and the four smaller bolts and the center nut were torqued to spec when putting it back on.
I reused the four smaller bolts but later I ordered new ones, so I guess I should replace them when inspecting the harmonic balancer.

Yes, the AC was engaged.

All the things you mention sits on the passenger side of the engine and could cause vibration that would be felt/heard coming from that side..

Post by **RickHaleParker** » 20 Oct 2021, 03:40

emtor wrote: ↑20 Oct 2021, 03:17 Yes, the AC was engaged.

Take a good look at the clutch / pulley. I had one where the hub broke away from the outer rim. It would catch and shudder before I discover what was going on.

emtor · Post by **emtor** » 20 Oct 2021, 04:03

Will do.

bobjet · Post by **bobjet** » 14 Nov 2021, 10:18

I would guess it is the right motor mount. I had a very loud intermittent noise when mine went bad on my 2008 XC70 at around 120K miles and replacing that motor mount solved it.