Clonk from rear right wheel area

[maximus]

If driving slowly in traffic and I take my foot off the accelerator there is a distinctive knock from the back and that happens again when you press the accelerator and take up the drive. This only happens at real slow speeds. Local Jag specialist reckon it is the fact that the car is fitted with 20'' wheels. There is no whine or problems otherwise only when you take your foot off and back on the gas.

Any help would be appreciated as it is driving mad.

[J44EAG]

To my mind a rather odd diagnosis. Quite what wheel size has to do with it seems somewhat strange to me.

Differential or prop shaft wear can give such symptoms. I would be checking basics first. Are the wheel nuts tight?

Mike K

[Montana5]

Have to agree with Mike for a first look at the wheelnuts. It has happened to me, power off and on the driveshaft caused a clonking sound due to the slack wheelnuts, only heard it when slowing down and taking off, reason for it was one of my newly Powdercoated Wheels had to be repainted to my satisfaction, this meant one wheel had a thicker coating than the others and after a couple of hundred miles, due to the compression of the new paint, it had been losing its grip against the Hub, thus slackening the nuts.

Doug.

[J44EAG]

It is also worth checking that the correct nuts have been fitted for your wheels.

I believe there are two types. Taper seat and flat seat. Wheels may also be machined with similar reverse tapers or flats. The use of the wrong nut on what ever type of wheel you have could well lead to loosening and thus cause the wheel to move around on the hub. In other words, check to see the wheels are not about to fall off!

Loose or worn prop shaft to differential drive pinion flange bolts will also cause a clonking sound. Flange holes should be checked for ovality if bolts are found loose.

Mike K

[mike020150]

Another common issue with Jaguars, not mentioned so far, is the end float of the bearings associated with the differential output shafts. Since these bearings have to cope with suspension loads as well as power transmission, they can lead a hard life and occasionally, wear can generate clunks. Usually, the shaft oil seals begin to leak as wear becomes excessive and oil under the differential gives the game away if there are no other symptoms.

Try jacking the rear of the car and pushing/pulling the drive shafts in and out. There will be some end float (0 to 0.15mm is acceptable). Beyond 0.15mm indicates that the bearing requires replacement. Mike.

[maximus]

Thanks everybody for the advice. I shall be looking at it at the weekend and post a reply when I find out what the problem is

[maximus]

It looks like it is the diff. The question is do I live with it as by adapting my driving style it is not noticeable or do I change the diff? Any reconditioned diffs around and how much do they cost?

[J44EAG]

Here are a couple of second hand units on eBay for 4.0 litre cars.

I would certainly contact Eurojag who have an excellent reputation within the JEC for good quality parts supplied with a reasonable length warranty. Most units supplied come from accident damaged written off cars. Don`t let that put you off. The car that a diff is removed from may well have had a front end shunt and the diff will be unaffected by such an impact. It`s the economical way out of a problem.

The second unit below seems a little expensive but may be worth investigation.

Bristol Transmissions besides reconditioning gearboxes also have ready to go reconditioned differentials. Costs will however be considerably higher than buying a good second hand unit. MD, Simon Park is the man to speak to.

http://www.ebay.co.uk/itm/Jaguar-XK8-Fi ... 1e65e7b2a9

http://www.ebay.co.uk/itm/JAGUAR-XK8-4- ... 23130679be

[maximus]

Thanks for taking the time to reply and info. I will keep you guys informed

[aaj]

I had odd noises under very light aceleration. (my XK8 has done approx 102k miles)

It ended up to be the diff. It went from an iritating noise to something more serious in about 200 miles. There was no excessive play in drive shafts etc nor oil leakage 2 weeks before it was replaced.

The sh diff cost me £350 + fitting but it looked in a lot better condition than the 2 on e-bay (for that matter so did the u/s one)

Allan Jones

[maximus]

AS I am going to replace it anyway I have replaced some of the oil with 140 which is thicker and it has made a differance. Watch this space

[SilverXKR]

I asked my local Indy to investigate a similar problem:

Remove rear pro-shaft flange for access.
Found differential companion flange nut loose.
Tightened nut as best as possible and refit prop-shaft flange.

This improved the situation for a while but clonk is back. I find that driving style certainly helps to mitigate this irritation however it will be sorted next winter. This will probably mean a replacement diff and while that's down a rear sub frame refurbishment would make sense. Gonna be expensive.

[mike020150]

Good luck with the costs! Mike.