I am new to this group, so if this issue has come up before, apologies. I am a 2 yr. owner of a beautiful 2004 XK8 convertible. Over the last year, I've been hearing a howling noise at about 40-50mph coming from the rear of the car. Only lasts for a few seconds, but it had not led to anything other than the noise itself. Recently, on 3 random occasions, I got a transmission fault code while driving. Pulled car over, re-started it and it was fine, and I was on my way. I want to discuss this with my mechanic but thought I would check with anyone here that has had a similar issue so I can talk more intelligently about it. Thanks everyone!

 

Have you done a rear end and transmission service yet ?


Especially if the age or level of the fluids is unknown, R&R’ing both fluids would be my first move .

Z

 

Thank you for the response. I have not done that yet, but will do so. Appreciate your time.

 

Have you noticed what your right foot is doing when the noise occurs? ie. Is car under power, coasting or decelerating, this info could give a clue as to cause.

 

Always happens when accelerating. Never coasting or decelerating. Greg

 

Hi weststargroup,

It sounds like you need to have the entire rear end and driveshaft carefully inspected. Your symptoms could be caused by failing differential output shaft (or less likely the pinion) bearings, a failing driveshaft center bearing, or possibly a wheel bearing, driveshaft flexible coupling, or half-shaft/axle inner CV joint. The differential or transmission could also be low on oil - see if any leaks are apparent.

Cheers,

Don

 

Thanks for the info, Don. Greg

 

The Transmission Fault codes may be the key. The other components should not cause a speed differential alert. Perhaps it is a wheel bearing and allowing the reluctor ring to give a false reading. This has been know to cause Tranny to go into a limp mode. The cause should not be too difficult to locate unless inside the dif. housing. Good Luck! Happy Turkey Day!

 

Yes, that is what it went into - limp mode. Thanks for your info. Getting so much good info from everyone. Wonderful site! Greg

 

leave it alone buy a used unit when the time comes

if it’s not coast/throttle related it’s not going to be your diff

 

Ignoring trouble today always ends up costing more tomorrow.


Z

 

Well the differential does not throw fault codes so apart from checking the oil level it looks like the problem is the the hubs/wheel bearings.

 

The age of the oil is a factor that also matters. Rear end oil is often left in place so long that it has lost all of its additive pack benefits.

on our cars the fill / drain hole is fairly difficult to access, making it likely that the lubricant changing schedule has been ignored far too long.


In my limited experience, replacing the old worn out fluid has always quieted down a noisy rear end.

For a rear that is already howling, going to a 75w-140 lubricant might extend the life of the gears. Since my XKR is a daily driver, with frequent cross country trips, I use the Mobil 1 75w-140 exclusively. The only drawback is the cost; it’s more expensive than the OEM spec 75w-90, but can handle the heat and pressure better.

However, if the wear is substantial, only a replacement set of gears or bearings will suffice. The main benefit to new and heavier rear endlube at this point would be to keep additional wear down to a minimum, before a permanent fix can be scheduled.

Z

 

140 EP ..forget the 75w/140