XK8 Stability Control/Grinding Noise

[jonywishbone]

I have been living with an intermittent grinding noise on my 97 XK8 which I was convinced was a gearbox issue, the noise occurs rythmically in 5th at low revs and when maintaining constant speed on an incline (40-50MPH). If I floor it from rest I don't get the noise at all. The car has been throughly checked including with full diagnostics kit and nothing is amiss in the gearbox plus all the drive shafts /wheel bearings etc have been checked and nothing was noted except it was noticed that the vehicle has a new factory replacement gearbox. Given that the car has done 63K then it also seems unlikely to me that the car will have gone through 2 gearboxes. Having eliminated over 6 weeks all the above I am back driving again with the problem unresolved.

What I have noticed is the revs dip when the grinding occurs its very rhythmic) and I recorded a drive where I deliberately induced the noise and both engine revs dipped and the ignition timing advanced changed at the same time when vibration occurred. I am wandering if the Electronic Stability Control ECU is faulty and is switching on the Rear ABS and also retarding the engine fuelling which would explain the grinding noise and the revs dipping. Short of getting into the CAN bus and finding out what messages are being sent out I can't think of any other tests. Is it possible to switch the ABS off without causing any issues with resetting system etc. Has any other XK8 owner had a similar problem???

[Trooper2]

Hi again Jonywishbone, your symptoms remind me of a 2004 XJ I repaired a few months back, it ended up being the torque converter clutch. When climbing as you have described these ZF transmissions are put into "gradient mode" by the TCM as it senses increased engine load. This allows the Torque Converter Clutch to engage all the way down to 2nd gear to save fuel and keep the transmission from gear "hunting".

Are you getting a sensation like the boot is half full of water and it is sloshing about when you get the RPM drop and the grinding?

Your RPM drop could very well be the TCC engaging, it will always drop the RPMs 300 to 400.

I'm wondering if the lining on your TCC has failed or the Torque Converter has some other issue. I know the TCC lining is an issue with the ZF 6 HP 26 transmissions in some S-Types....

Putting a new torque converter in the 2004 XJ did the trick.

[jonywishbone]

Hey Derric thanks for another comment I can certainly mention this to the garage, the revs do dip around the 3-400 rpm mark when this noise arrives. The grinding appears to be coming from only one of the rear wheels but this might be a bit of an audible illusion. Will keep you informed what the solution is when I get it.
Thanks Jon