Someone on another forum said that if you want to isolate a noise from the rear end and determine whether it's the differential or axle related like a wheel bearing, then shift into neutral while at a speed that produces the noise and if the noise remains it's axle related (hub/wheel bearing), if it goes away it's likely the differential.

So, if the shifter is selected to neutral, do the driveshaft and differential stop turning because the differential thru some clutching means responds and disconnects from the axles, or do they keep turning because they then become driven by the wheels/axles? If they keep turning, I don't see how this proves anything.

I've got a rear end roar that starts at 55mph and gets much louder from 60-80mph then suddenly goes completely away. When I shifted into neutral at 65mph it remained. But it seems to me that bearing or tire roar would be more linear, appear at a slower speed, and not vanish suddenly.

 

The driveshaft and differential still turn ... *but* the loading on the gears and bearings is different. That is why it is useful as a diagnostic.

 

isnt putting the car in neutral at speed the same as towing it?

 

Towing and being in neutral while running differ in that the pump is operational in the second case. Therefore, there is no risk of damage due to lack of lubrication.

 

Which pump is that?

 

The ATF hydraulic pump that runs the whole show. It's in the transmission.

 

So if the diagnostic is correct, where is the 60-80mph roar I'm hearing likely coming from?

 

so if my engine is running is it ok to tow the car?

 

I would be very uncomfortable having my car towed in neutral with the engine running. I can't say it would hurt anything because I don't know but it just seems wrong. I'd just have it put on a flat bed.

Mark

 

Does the noise change when you are cornering?

 

"So if the diagnostic is correct, where is the 60-80mph roar I'm hearing likely coming from?

First off is the roar followed by or does a vibration/shake occur during the 60-80- mph Roar???

Second because we can't hear the sound,,, does it sound like something winding out??? Does it have a definate mechanical tone to it,,, or could it be wind resistance? Maybe something... like the plastic air dam(under the car flips up or down? or something else?) again we cannot hear the sound so I am just fishing hear...

3rd can you pin point the area of the sound somewhat???

Ohhhh Flatbeds ONLY,,,, IMHO,,, Most companies are upgrading their fleets to flatbeds, (cheaper to Insure the business,,, Less vehicle damage,,, AND OWNERS ARE REQUESTING THEM MORE) The old Hooks are going the way of the Buggy Whip...

 

I do feel a vibration from the floor when the roar gets going. I wonder if the drive shaft has gotten out of balance and caused the ring and pinion diff to get unstable and get noisy.

 

It only occurs at highway speed, so the most cornering I'd be doing is taking an off ramp, so I haven't noticed anything like that.

 

There was a TSB regarding the S-Type for a rear-end whine several years ago. The whine manifested itself at around 55 to 65 mph and was not evident at speeds significantly lower or higher than that range. If I remember correctly, the fix was a redesigned and improved differential. Several forum members who own S-Types with this annoying whine obtained this repair from Jaguar under warranty, and it indeed resolved their issue....

Is there a similar TSB for an XK8 rear-end whine?

 

"I do feel a vibration from the floor when the roar gets going. I wonder if the drive shaft has gotten out of balance and caused the ring and pinion diff to get unstable and get noisy."

Something is out of balance,,, All rotating parts need to be considered in this eval.... Wheels,,, Drive shaft,,, ETC,,, Also any mounting Bushings,,,

Now for the ROAR,,, Again is it a mechanical tone??? A wind Roar,,, Or from the VIBRATION???

HHMMmmm I wonder if the vibration can be SEEN??? Assuming based on what you say there is a Vibration,,, Driveshaft maybe,,, Do you have a laptop,,, webcam,,, and Velcro??? Reason being I was all set up to record our fishing trip today with mine but we never went (lost steering) so could you mount the cam under the car and see if you can record a vibration??? Even if you can't still be interesting to see the footage

 

It doesn't have to be severe cornering, just a shifting of weight from one side to the other to determine if it might be a hub bearing. Also, while driving and hearing the noise ease on and off the accelerator to determine if drive loaded/unloaded/coast loaded causes audible change.

 

I agree..its the same as putting your can into neutral at 55..70 miles per hour the only differance is is how the car got its motion..what would happen if you put your car into neutral at seventy then put it back into drive?..DENS NOT TRYING IT ON HIS XK

 

I don't think there are any serious consequences of doing this. I haven't done it yet with my Jaguar but I have had a number of cars where I was on some very long downhill run on the freeway and, out of curiosity, shifted in to neutral (rpms would of course go way down to idle) and then shift back into drive. Sometimes I would first goose up the rpms but sometimes not. Never had any bad consequences from doing this.


Doug

 

It's louder when accellerating, then diminishes slightly when speed is constant.
It's mechanical.

 

Don't think so, but it would be helpful to know what the exact issue was with the S-type.