Jaguar Repair/1985 XJ6 rear end noise
I have had my XJ6 for nearly 3 years, but only clocked about 4k miles. Since early on, I have heard a rhythmic, proportional to speed, knocking from my rear driver side as a coast through right hand turns. I only hear this when coasting, not when in thrust, or applying throttle. Over the years, I have replaced rear wheel bearings, shocks, radius arm bushings, calipers and pads, etc. I kick myself for not investigating this on previous opportunities as things are taken apart, but I can't help but imagine it is due to worn u-joints. Would you agree that is plausible, or is there something else I should consider as a cause?
Most common is one of the "U" joints or it can be a wheel bearing. Jack the Left rear wheel off the ground at the lower "A" frame. (it is actually an "I" beam) Then grab the tire at the top and the bottom and wiggle to see if there is any free play. You should not feel any free play at all. Don't skip this just because you had replaced the wheel bearings. Then rotate the wheel to see if you hear any noise. With this wheel off of the ground this duplicates the suspension compressed in a right hand turn and puts the "U" joints in the position they would be in a right hand turn. But keep in mind that it does not apply the same outward load on the "U" joints.
Remove the wheel and check that the dust covers on the outer and inner "U" joints are tight and in position. Now place a block of wood on a jack stand and set it under the edge of the sub-frame so as to support the differential so the drivers side springs extend downward. This forces the "U" joints into an angle of operation. With a pry bar rotate the wheel hub and watch the "U" joint cover to see that neither is bent or out of place.
If you can't find anything up to this point you will need to loosen the clamps on the "U" joint covers and slid them away from their joints to look at the joints to see if you can see any signs of rust at the bearings of each joint. Often when a joint is bad it is dry and you can see rust in the area of one or more of the joint bearings. Use a large screw driver as a pry bar to see if you can find any movement in either joint.
Another possible is the bearing in the short shaft in the side of the differential can be going bad.