Hi guys, I recently (last month) put three new tyres, two front and right rear on my XJ6. The left rear was replaced twelve months earlier. All tyres are Pirelli P Zero All Season Plus.


When I move off from a start I can feel a gentle waddle from the rear end.


At 60kph a thrumming vibration sets in which can be felt through the seat. The steering does not shake at any time. This thrumming vibration stays present all the way up to 100kph.


Any ideas as to what this might be and how to overcome would be greatly received.


Thanks all.

 

The prime suspect is the rear wheel with the new tyre - I would go back to the workshop to double check on the installation, in particular the use of appropriate and all identical wheel nuts.

 

hi guys, I realise I have been a little economical with the facts.

This problem started a while back. I changed the left rear tyre first, no change.

Then I replaced the right rear with the spare, no change.

Then I put a new tyre on the right rear along with the two fronts, no change.

So the right rear has been through three tyres. The original, the spare and now the new one and two wheels. The original and now the spare wheel, no change.

I am thinking I can discount the tyres, balancing etc.

Unless you guys know different.

 

Have you looked at the driveshaft coupler to see no nuts are missing? If the coupler is damaged or any mounting nuts missing the drive shaft may cause vibration.

 

Thanks Qvhk, I will have a look at that.
Cheers.

 

The vibration may be your engine or transmission mounts. The rear waddle might be worn out sway bar bushings, endlinks, or any of the other rear suspension components to be honest.

 

Also, check your wheels for bends

Many tire shops don't check, or ignore if they note bends

My XJR waddled just like this at first: bent LH inner rim

 

You could also check rear hub run-out.

 

Thanks hisport.
Back in tyre shop on Friday to check for bent rims.

 

Took the XJ back to the tyre shop and had all five rims checked for buckling, tyres for out of round and rebalanced by Road Force. Moved the worst rim to the spare. No change in the thrumming sound at 80kph.


Unless....


I noticed that the tarmac road outside my house has ripples in it than run diagonally across the street. As I moved away slowly from home it occurred to me that one wheel would be at the top of one ripple while the opposite wheel would be in the trough of another ripple. Is the Jag suspension so sensitive that at slow speed this might be the waddle I am feeling when leaving home? This is the first air suspension car I've had so I could just be super sensitive. I'm doubting my self now.


Anyway the thrumming at 80 I can still detect but again I am wondering if the suspension is so sensitive that it is picking up stuff you don't normally feel in inferior motors.


Anyway, taking it to an indy on Friday and he is going to drive it and give me his opinion.


Stay posted for more indecision and paranoia.

 

I had something similar plus the car felt like it was riding in jello. Pretty loose in the back. I checked the rear suspension and all the bushes were shot. After replacing the parts, it rides really.

Before the fix, I almost sold the car becuase I didn't like the ride.

 

So after two years and many trips to main dealers and indies, a new development.
Just to recap
My car has a thrumming sensation through the drivers seat at 80kph.
Four new Pirelli All season tyres.
Road Force Balanced.
Four wheel alignment
Wheels rotated several times.
Prop shaft balanced.
Main dealer check for anything loose or wearing out, nothing to report there.
My indy drove it and said "it is there, but not as bad as some"
Another indy advised changing out the prop shaft.
Took in for service last week and the tyres where rotated front to back.
Now my thrumming has moved up to 90kph.
Thrumming is more prevalent in colder temperatures as it seems to dissipate after a long run.
Maybe these all season tyres need to warm up.
if anyone as anything to throw into the mix please feel free but before I spend a ton of cash on replacing the prop I am confused as to why the tyre rotation would move the thrumming unless the tyres are still the culprit.

 

Assuming that all four tyre treads are identical, the thrumming sensation is now prevalent at the driver's seat according to your description. Does this mean that the problem has now shifted over to the front due to the tire rotation? If so, what would happen if you simply shifted the front tyres over to the rear again, and vice versa? Would the thrumming sensation transfer over to the rear afterwards?

 

And what size wheels ? Very low profile tyres are very unforgiving when it comes to ride quality.

 

Hi Fraser, wheels are standard at 18" with 235x50 Pirelli tyres so pretty much stock there.

 

Hey Rickkk, the thrumming in still in the seat and has always been there. The only difference since the rotation is that it now starts at 90kph instead of 80 kph before.

 

So you've got what I had on my last X350, incl the Pirellis. That car was pretty good with none of your symptoms, so more investigation needed !!

 

Have you checked the brake rear discs?, I had a similar vibration, tracked it to the left hand rear brake caliper which was dragging with a sticky piston, changed the caliper Discs and pads and all is good now.

 

Did you ever check the transmission mount?