Perplexed by whining noise ..... not spousal

[adm333]

Can someone please explain what is going on here....
Some time ago the P38 developed a fairly high pitched whining sound (no, SWMBO wasn't in the car), which I am sure was coming from the rear passenger side.
It is evident when the car is coasting, but is not noticable with a bit of throttle applied.
I thought it might have been a hub bearing but my mechanic said it was to do with the brakes, and filed down the leading edge of the brake pad which helped for a while.
Then about a month ago I bought 2 new tyres, put them on the front and put the two best remaining tyres on the back.
When I left the tyre place the whine was back with a vengence.
Its been there for the last few weeks until last weekend when i went off road and staked one of the brand new tyres (thats another story).
I put the spare on and on the way home I noticed the lack of the whining noise for the first time in ages. For some reason i thought that the traction control activity might have helped with the brakes and the whine had gone away.
Yesterday when I got the new tyre put back on (the front) guess what .... the whine is back.
I would still swear it is coming from the rear drive train somehow, but clearly there is a relationship to the front and to the new tyres.
Can any engineering types speculate on what is going on ?

I should add that it is definitely not road noise from the tyres, it is a distinctive medium to high pitched resonance.

Cheers
Dave

[Tank]

You haven't got Tony Abbott stuck under there have, he'd whinge if a snake bit him, seriously I would be jacking up the rear end with the tyres off and check for anything loose especially the rear wheel bearings or disc calipers. I don't know if your model has replaceable/adjustable wheel bearings, but if they are I would check for wear and play in the bearings.
Check clearance on exhaust pipe over and near diff housing, I once had a 4wd that when the exhaust pipes got hot and expanded touched the diff housing and setup a woeful din, was hard to pick because as soon as the pipe started to cool it moved away from contact with the diff housing, anyway check it all and get back and let us know what you find, Regards Frank.

[Dave109]

Could the Vicous coupling be seized and the different tyre sizes are causing windup putting a heavy load on the diffs causing the increase in noise?

[fraser130]

Could the Vicous coupling be seized and the different tyre sizes are causing windup putting a heavy load on the diffs causing the increase in noise?

This is where I'd put my money..

Try swapping one front wheel/tyre with one rear wheel/tyre, just to see if it helps....

Fraser

[tony66_au]

Could the Vicous coupling be seized and the different tyre sizes are causing windup putting a heavy load on the diffs causing the increase in noise?

Err yeah...

I was told years ago that with the constant 4WD systems you never mix old and new tyres no matter what.

I also rotate my tyres to keep the wear even and so i don't bugger the diffs.

Tony

[adm333]

Yes, I was thinking along these lines, but wasn't sure if the tyre size would be significant enough to cause the issue.

But it has to be since nothing else changed other than old for new tyre swapping.

Will go and get 2 more new tyres and a viscous coupling !

Thanks
Dave

[adm333]

I replaced the older tyres with new ones this morning and the whining has gone away.

Never would have thought it would be that sensitive.

I don't think the VCU is seized as its not showing the symptoms, but I will attempt to do the proper test on the weekend.

Dave

[tony66_au]

considering how many revolutions wheels do even on a short drive its not that implausible and its a common mistake.

I also rotate my tyres every 10 thou just in case as the front tyres seem to wear prematurely if i don't.

Glad to hear your issue is solved

Tony

[loanrangie]

Err yeah...

I was told years ago that with the constant 4WD systems you never mix old and new tyres no matter what.

I also rotate my tyres to keep the wear even and so i don't bugger the diffs.

Tony

On a viscous coupled vehicle maybe but an RRC/D1/Defender shifts power F to R individually and not at the same time unless center diff is locked, unless tyre size is way out you wont have any problems and windup is impossible unless locked.