Rumbling Mystery

[thomas45]

Heres hoping someone will have an idea of what causes this rumble.
It became noticable as a constant slight rumble at all speeds. I tried selecting Neutral when going downhill but noise still the same.
Thinking that it might be wheel/ tyre related I decided to get the four wheels balanced and lazer alignment done.
( Oh! I forgot to mention that some weeks before I thought tyres may have been too hard and so I had reduced the pressure which quietend the rumble a bit) However, arriving now at tyre fitters the first thing they pointed out was underinflated rear tyres. Not only that but one was worn on inside edge and the other was wearing in the middle of the tread. ( they looked ok to me but I took their advice and had them replaced.) Alignment done, pressures correct, road tested and declared OK. So set off home and finding that the rumble is now more evident than before. Ok ! so its a 2.7 diesel but it did used to waft along reasonably quiet. I dont think its engine related but could it be transmission related ? I would appreciate any opinions.
Thomas

[J44EAG]

The propeller shaft has rubber Durite dough nut type couplings fitted at either end. The rear most one is secured to the prop shaft and differential by as I recall six bolts. It is the same at the front end where it joins to the gearbox output yoke.

These couplings are very similar to those found on IRS cars such as the Triumph Vitesse and TR range. The Hillman Imp also had them. The coupling is a circular rubber dough nut with six inbuilt steel tubes mounted at a PCD of 60 degrees between centres around the periphery. The six bolts pass through the tubes which are molded into the rubber when manufactured. Loads of reinforcement string type material also figures in the construction. Given age and mileage these couplings do break up. I know because I had a front coupling disintegrate on my V8 S-type at around 80k miles. It was ok but was finished about 100 miles after the rumbling first started. A shot coupling can be changed in about twenty minutes. My independent Jag man had a second hand one in his pile and fitted it for me for 40 quid. Bargain!

When the coupling gives up, it literally drops to bits. That is easy to see as the stringy stuff sticks out from the rubber like Worsal Gumages` whiskers.

So that is one idea. Differential wear is another possibility especially if it has never had an oil change.

Front wheel bearings are only really good to about 90k miles. They can make a terrible noise if worn. OE quality front bearings can be found for £80 or thereabouts on ebay. Fitting is difficult unless you have a bench press. See the suspension section on this BB for other related posts on S-type front suspension issues.

Rear wheel bearing noise and wear is rather less common than front bearing failure. Again a press is needed to remove the bearing from the hub carrier. Good bearing replacements are about £40 each.

I suggest you explore those ideas and see what you find. Come back to us again if you need more advice.

Mike K

[thomas45]

Thank you Mike, I will consult with my mechanic on those particular possibilities. I guess I had better not delay too long.
Many Thanks,
Thomas.

[J44EAG]

Sorry,
I forgot to mention there is an intermediate Plumber Block type central bearing and support in the middle of the two part prop shaft. That can also cause issues.

Mike

[thomas45]

Ok Mike I will have a chance to look at that too when it is up on the lift for a now more pressing problem which has since established. That is to say I have encountered a fuel leak from the bottom of the filter. It was that little plastic or nylon drain thing and on tightening it snapped off so awaiting new filter.
In the meantime I will not grumble about the rumble !
Thanks,
Thomas