1992 XJS 4.0 knocking help!
 

Hi all!

I purchased a '92 4.0 XJS about a year ago as a drive able classic. It has covered 107000 miles about 3000 of those with me in the past year.

Just yesterday I took it out for the weekend and there is a rhythmic knocking sound coming from what appears to be the rear left of the car, but it is difficult to tell.

The sound starts at around 40 mph and gets louder and peaks at about 70mph. I am rather new to the whole classic car thing so please keep the answers as simple as possible! I am trying to learn!

Any advice very much appreciated.

Colin.

You can tell where the "knocking" might be from if you are able to tell the frequency of it. What I mean is, envision the tire rolling with a bump on it. The speed of the tire going round and round will be a tell tale sign of related noise or knock with the size of the tire. If the knock is of a high frequency, slightly faster time between knocks, then it is something smaller than the size of the tire. The next smaller size area is the brakes or rotors, calipers, handbrake etc. The sound might change or disappear if you apply the brakes if you suspect any part of the braking system. You can also slowly apply the handbrake to see if that is the issue. If the noise goes away, then you know it is brake related. Even faster frequency might be the universal joints of the axles going round and round. There are two inner UJ and outer, closer to the hub. I think you kmow where I'm going with this.

Hope that helps.