At 60mph or 100kmh I get a bit of drumming from the rear end seems to move up and down in pitch. Any ideas on what this could be? And how often should diff oil be changed? Mick. P.s. the mighty xj40 12/91 kingfisher blue 4.0 is on the road and swallowing up the miles!!!

 

Hi Mick,

Checking the differential for any signs of fluid leaks is not difficult. Check for wetness at one of the output shafts or pinion shaft. Replacing the pinion seal is a differential-out job, but the output shaft seals can be done without removing the diff, and a failed seal is typically a sign that the bearing is failing, which could possibly be the source of your noise. I don't know if Jag-Lovers has their photo albums back up and running, but if they do I have some photos in my albums - try the link in my signature.

A wheel bearing will typically make noise over a wider range of speeds and may change sound when turning.

A bad tire can cause speed-related noise.

Another possibility is failed subframe bushings, which allow metal-to-metal contact between the subframe and body and transmit differential gear noise into the passenger compartment.

Please keep us informed!

Cheers,

Don

 

Thanks Don. My car has done a lot of km, so failed sub frame bushes or even hardened and compressed subframe bushes is a possibility. Ill check for leaks round bearings, inspect the jurid coupling (which would be pretty hard anyway so may need to go) also you never know about uni joints on the half shafts, sometimes they sieze or become rough rather than get sloppy and clunk. Ill also check for movement in bearings. I wonder if the centre bearing at the front of the prop shaft and the uni there are worth looking at. Yes the whole rear and is next on the list. I hope jag lovers has all your photos up, they are a veritable treaure trove!!!

p.s the tyres are new, but have been sitting round for a couple of years, and even though ive moved the car to share the load round you never know how they have held up

 

Yes, the U-joints are worth inspecting. The most common problem with the propshaft centre bearing seems to be failure of the rubber surround, which allows too much movement of the propshaft and noticeable low-frequency vibration from under the car. If you can read the propshaft between the exhaust pipes you may be able to test for excessive side-to-side movement.

They could be flat-spotted, but typically you would notice the "thump-thump-thump" sound over a wider range of speeds.

Please keep us informed!

Cheers,

Don