Wheel Bearing Or Diff

[200tdistu]

Hi all got a small maintenance problem I can't work out, so I'm after a little advice.

The car is a 02 ls400 and it has a humming noise from the rear around 40mph, sounds like its coming from the centre of the car when you get it the back seats and move around. Replaced both rear tyres with new as 1looked worn, still no change.

I'm use to working on land rovers and if a wheel bearing is on its way out you get play in the wheel when you jack the landy up. I used this method to test the Lexus bearings and I can not feel any play in any wheel all wheel rotate smoothly

Took the car to main dealer for advice and they have said that its a wheel bearing but the cant say what side and it will be £350 to do a bearing.

I think it's the diff, as I can't feel any play, so I'm going to order some new crush washers and take a look at the oil in the diff at the weekend and see how it looks (or if it has any lol)

Any help or advice from members would be good

Thank you

[steve2006]

Hello and welcome to the LOC.

Diff whine usually increases in pitch the faster you drive, years ago I had a Morris Marina van that sounded like a 737 on take off!

Changing the diff oil makes good sense to see if there is any change in the symptoms and also see if there are metallic particles in the old oil.

As you mention diagnosis could be difficult, I don't know how fast you can drive on an MOT brake tester but it would be useful to be able to lock up each wheel in turn to see if the noise goes on one side indicating a bearing fault or the diff if it remains.

Does gentle braking above 40 MPH make any difference to the noise as this would tend to take up any bearing play?

Other things to consider are the diff mounts and the propshaft rubber joint, also check the transmission mount.

[JZS147]

Very often a diff bearing noise will change between under load (foot down accelerating) and coasting, try getting up to speed so you can hear the noise and dip the clutch and knock it into neutral (assuming it's a manual) if the noise changes it's USUALLY the diff if not it's USUALLY the wheel bearing. This isn't definative but is a good pointer.

HTH