As the Jaguar XK8 gets older it is expected that the front suspension parts will become worn and require replacement. Typically wheel bearings, top and bottom wishbone bushes, springs, shock absorbers ball joints etc will all eventually require replacement.
However, if your car’s front suspension is making a knocking noise do not necessarily assume it is caused by one of the above and fork out a heap of cash to replace one or more of these parts. A clonking sound from the front suspension can be a far more serious problem to resolve.
This could be due to the top wishbone bushes seizing to the steel fulcrum pin. The combined seized unit then wearing away at the all aluminium sub frame of the car and creating an oval shaped pin hole. When this happens the wheel and the suspension become unstable and tend to float around with the excess play. This will obviously then manifest itself with a deterioration in handling and increased road (clonking) noise.
It is not hard to understand how this can happen when you look at Jaguar’s poor design of the top wishbone, bushes, fulcrum pin assembly and area. At each pin hole end, this is hollowed out and allows water, dirt and salt etc to ingress into the hole and corrode the bush and pin. No protection is provided for the exposed area or in fact Jaguar maintenance advice to periodically clean and protect the area with grease or waxoyl.
The top front and rear bush parts are designed to self lubricate and rotate as required around the fulcrum pin. However, when these become corroded, the combined seized unit then wears way at the aluminium sub frame. To make things worse, an electrolytic reaction can take place caused by the steel pin passing through the aluminium sub frame and the steel inserts of the bushes.
If the sub frame wear is excessive, this may require complete replacement with either a new or good used sub frame. A new XK8 subframe part will be well over £1500 to replace!!. A much lower cost solution would be for an experience motor engineer to add new inserts into the sub frame and then replace the pin and two bushes. At the time of adding this article I don’t know how successful this latter approach has been.
I have checked my XK8 car for play and corrosion in this area and all seems to be working fine. I have fully protected the bushes, pin and general area with waxoyl. If I do hear a knocking sound from the front suspension, then this will be the first area that I will check.
Finally, if you having work done to remove the XK8 top wishbone assembly parts then maybe it’s more cost-effective to replace all the bushes and ball joints, even springs and shock absorbers at the same time as these will inevitably have to be replaced at some point in the future and the finished job will contribute to improved handling, piece of mind and enjoyment of your car.