XC60 D5 Resonant Vibration

[stiggles]

Hi

I've recently purchased an XC60 D5. It's a 2013 Model year (pre face-lift) D5 Geartronic AWD, with the 230BHP Polestar upgrade. The car generally drives very smoothly with no weird clunks (perfect shifts on the gearbox etc). It's done 95k.

One thing I've noticed however is that occasionally there's some sort of deep resonant sound somewhere in the drive-train. At speeds of 30-40mph you can provoke by maintaining a light throttle on a slight incline. A deep bassy rumble can be heard through the car. Knock it into sports mode, and it doesn't tend to happen as much.

At speeds exceeding 60-70mph again with light acceleration it feels more like a going over a rumble-strip and can be physically felt & heard through the vehicle. At these speeds sports mode doesn't seem to eliminate it. Lifting off or really accelerating hard does seem to cancel it out.

I've been advised my vehicle is current with all of it's software updates. The only other thing to mention is the tyres do not match front to back with Michelin Pilot Sport 4 SUV's on the front & Continental Sport Contact SUV 5's on the rear. The rears have 4mm of tread - the fronts are brand new).

Am I chasing down a normal characteristic of these cars or should I be looking to get the drive-train checked over? I'm considering putting 4 cross-climates on it so that I've got a full matching set of tyres, but obviously it's a large expensive particularly if they all drive like this!

Thanks

David

[Whyman]

Swop the fronts to the rear.

Two reasons.

1 it will tell you if it is a tyre problem.

2 All the tyre and vehicle manufactures advise that you should always have the best tyres on the rear.

[maweu]

I have the same car which has hit 71K and when it hits 80KM/H it makes a lot of noise. At slow speed it has some noise as if something is shifting inside the car. No mechanic seems to understand what is the issue.

[AndyB06]

It’s the dynamics of a 5-cylinder engine - She’s a big rumbly beast, and with time the mounts don’t do their job as well. At low rpm you will naturally get more vibration, the older D5 engines had hydraulic mounts which became active from around 1500rpm, smoothing out the movement. I’m not exactly sure how the mounts work on the euro 5, I’ll do some digging. With the new software determined to optimise economy, you will find yourself in, say 5th gear, when you wouldn’t necessarily choose so if driving a manual. Hence you describe observing the ‘resonance’ around 30-40mph, where the software will initiate 5th gear with the resultant rpm around 1300. Perhaps more economical, but dynamically unfavourable.

[koppernob]

I have a similar problem, manifests itself at low speed over less than perfect road surfaces, sounds to be coming from front left hand side.

It's been present for the lat 3 MOT's and nothing has been picked up during the test, so wheel bearing, shockers, springs, track rods etc must be OK. Only other thing I can think is maybe failed engine mount which is a lot of hassle to get to and I don't really have access to facilities any more.

Guy doing the test took it out for a run and couldn't find anything obvious, his advice was let it get worse then bring it back!

[Aus2012XC60]

My 2012 D5 has a similar issue. From other searches, I'm going to check the torque rod tonight but I'd be surprised if that is the problem.

I'll be following this thread closely and will report back if I find anything.

[stiggles]

Thanks everyone for the replies. I've decided to start out by swapping the tyres (I wanted Crossclimates on the vehicle anyway so just bringing that forward a bit). I'll report back once I've tried that.

[stiggles]

Well I had the crossclimates fitted today and unfortunately the resonant vibration is still there at 70mph on inclines.

Weirdly initially it looked like it had gone. I had a couple of goes at trying to provoke it lifting off and on the throttle but eventually it came back after I rounded a roundabout and headed back the opposite way on the dual carriageway.

I might try a Haldex service next, or see if everything is up to date software wise.

[JJJ]

Pull the Haldex fuse and see if it still does it. Only the front wheels are driven then.

[stiggles]

Cheers, I'll take a look for the Haldex fuse.

As it turns out I may need to re-roadtest it before I try that anyway. I checked my tyre pressures cold this morning and they had inflated all of them correctly bar the offside rear...which they had inflated to 47PSI

Just goes to show you should never trust what they put on the job sheet!