Poor ride quality

[davidr]

My V12 has a distinct vibration at 65-75mph even though I've had the wheels balanced, changed shock absorbers etc and the suspension bushes, steering gear etc all appear to be fine (passed MOT with no worries)
Has anyone else had this and how did you fix it?

[scotty]

Cant give you the definite answer but on one of my Triumph TR's I had a similar problem . I eventually got each wheel on the balance machine and found that although they had been balanced one of the wheels had a slight buckle . That one is now in the boot and the spare is on the car - no vibration . Unfortunately the staff in half of the tyre shops are uninterested and do not look a the wheel as it spins - its obvious when one is not straight . Might be worth checking , at least it shouldn't cost anything.
Let us know how you get on

[henry]

david r
i dont have the problem with my XJS, but i've had this problem on an off with several jaguars over the years and generally it comes down to bad balancing
the wheels are quite big and wide and unless they are properly balanced on both rims then you will get a wobble type of imbalance at higher speeds

most tyre fitters will try and tell you that putting the weights on the inside only is just the same well thats just not true make sure that the wheels are balanced on both rims, use stick on weights on the outside if yor rims cant have clip on weights and watch them balance the wheels make sure that the last thing they do is get a zero reading for both rims
if everything else is fine that should help your problem, the only other cause of higher speed vibration is a badly balanced propshaft, but i would check the tyre balancing first

Henry

[poprivet]

I had the wheels 'back balanced' by Solent Wheels of Romsey, this places all weights inside so that none show. It is more time consuming to get right, and needs to be done by a skilled operative but worth it. I wouldn't ever use a normal tyre outfit for the Jaguar.
Try swapping the spare as Scotty suggested with each of the wheels in turn to see if you can identify the rogue wheel.

[henry]

pop
unless the wheels are balanced by putting weights either side of the centre line of the wheel it is technically not possible to balance them correctly you can get a reasonable level of balance, its what is called static balance or single plane balancing, ( even if it is done on a rotating balancing machine) ie if you put the wheel on a freely rotating set of bearings it would stop in any position, there would be no heavy point which would fall to the bottom, but that only takes out the if you like up and down vibration that is caused by imbalance, but for good vibration free rotation at speed the the wheels need to be two plane balanced this also takes out all of the wobble type of imbalance, ie the imbalance caused by the weights not being on the rotation plane of the wheel, you could for example add a big weight on the inside rim and the same big weight 180 dergees round on the outside rim and it would pass a single plane balance but would cause significant wobble vibration when running at speed

It is possible to add the weights to the inside of wide alloys using stick on weights on the inner diameter of the wheel but with weights either side of the centre line on the inner edge of the inside surface and out near the outer edge of the inner diameter of the wheel as close to the spokes as possible that way you do not show the weights but the weights are applied either side of the centre line to allow you to get a good two plane balance but it depends on the type of wheels that you have fitted, I have lattice alloys on my XJS and it is not possible to use the technique identified above, it has stick on weights on the flat inner diameter on the outer edge of the wheel and on the inside rim, but on my S Type with wide BBS alloys the weights are all on the inside diameter of the wheel as there is plenty of surface either side of the centre line to add the weights

[davidr]

Thankyou all for your suggestions. My car is currently in a thousand pieces as I got carried away changing the cam cover gaskets and had stripped out most of the engine bay before I came to my senses!!
Once everything is cleaned up and refitted I'll try your suggestions and keep you posted.

[Norman]

Hi David R
Apart from checking the wheel balance also check the prop shaft as this can cause vibration problems if not secured correctly i.e. check all the fixing nuts and bolts for tightness.

Norman (JEC XJS Forum Co-ordinator)

[davidr]

I'm now starting to suspect the front-subframe mounts as the problem is not consistent - it can be improved by gentle throttle.
She who must be obeyed has me on a building project at the moment but when I can sneak back into the workshop i'll change the subframe mounts and see what that does.
I've already changed suspension bushes, ball joints, springs etc.

[davidr]

Well I've now changed the front subframe mounts and all is sweetness and light again!
It's taken me over 2 years to get on top of this one - just shows that the obvious can be just that and a big distraction from the real problem!