The differential in my 133K mile 2001 XK8 is starting to act a bit worn and loose. When I change directions, I get this loud "clack" out of it. So I have some questions:

1) Hard to know but about how long do I have before differential failure?
2) Where I can find a good re-manufactured unit?
3) Are there other differentials which will fit?
3) How hard are they to swap?
4) What other questions should I be asking?

Thanks,

 

When you say changing directions, do you mean going between forwards and reverse? If so it's worth checking that the diff input pinion nut hasn't come loose and the prop and drive shaft universal joints have no free play in them. It's also worth checking the oil level (not easy!) as due to being "sealed for life", often gets neglected.

I have the same problems as you, with the diff clunking and whining. A recon diff and labour will not be cheap. I believe if you're brave enough to tackle this yourself, the problem is getting the car high enough on axle stands to drop and remove the rear suspension. Also do you take a chance and go for a 2nd hand diff or pay more for a recon unit?

As long as you have oil in it, your diff will likely go on for miles and miles. the ones of a XJ look similar except for the input flange ( 3 bolts instead of 4) and possibly different ratios.