1998 XK8 knocking from rear..
 

Hi Guys,
My XK8 has an seemingly untraceable 'knock' that usually occurs as l slow from 20-10mph (2nd to 1st gear?). It seems to come from the raer. its a loud n sounding thud that jolts the car.
Recently l had all the suspension bushes upgraded to polybushes which dramatically firms up the car although they are so tight that the whole car creaks... Also l had new shockers n springs fitted to the rear (20mm lower so a more sporty stance).
The gearbox was out and the infamous drum clutch replaced-but no other work done on it. No movement can be found in any of the U joints. So is this likely to be the diff, the gearbox or a UJ or something else and how can l trace this fault pls?

Welcome to the forums Grimalkin,

I've moved your question from X350 to X100 forum. This is the place to post technical questions about your XK8.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some information about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

2-1 down shift to stop is usually due to bad transmission fluid
 

Welcome to the Forum,

Sorry to hear about your problem. A few more details on your XK8 is needed MoYear, Engine, km etc. Plus what exactly has been done esp. with the suspension and gearbox. In what situations does your fault occur? Is it getting progressively worst?

I had similar symptoms and for my 1999 XK8, the “jolt” was on long hot freeway drives, down shifting to stop. As forum members know, my first Gen XK8 has the ZF5HP24 gearbox so I changed out the transmission fluid and put in the upgraded Transgo Pressure Relief Valve.

Do you have exact details of the gearbox work done on your car? Did you do it, or was it done at a reputable garage. There’s a very precise routine to get the right amount of fluid in. Too much is just as bad as too little. And generally you’ll need to check level again after a week. Also If you have the wrong ATF fluid installed in a ZF5HP24 gearbox, that could be a source of trouble.

Other Forum members, with more suspension experience, can chip in on the other potential source.