75 Series, grinding noise from rear end when wheels slip?

[Vasimo]

Hi guys, having a problem with my 75 series that i have had no luck finding any info on so far.

While offroad, either turning or straight if the rear wheels slip or drop hard into a rut or dip there is a fairly loud grinding sound heard from what i think is the rear differential. It can easily be recreated by going up a slippery bumpy hillclimb, when the rear wheels start to bounce and slip the grinding noise appears.

I have changed the rear diff oil and this has not affected the grinding noise, and the grinding noise does not appear on road either when turning or going straight.

Im out of ideas as to what it would be, would greatly appreciate any thoughts as to what it would be

 

[CharlesHS]

If the noise does not occur in 2HI on the highway; then the problem is not in the rear differential.
I would guess the transfercase is where the noise is coming from.
The internal gears connecting the front and rear driveshafts may not be fully engaged or something is worn internally.
You can further verify this by placing the truck on jack stands and engaging 4HI to see where the noise is coming from.
Be careful if you decide to climb under the vehicle while suspended on jack stands while in gear.

 

[Vasimo]

Thanks for the reply, only just realised i forgot to mention one thing , it will grind offroad when it is in either 2 wheel drive, or 4 wheel.

 

[AirheadNut]

Is it possible that the truck has a limited slip diff or some sort of auto locker?

 

[Vasimo]

Yes, it does have an lsd, is filled correctley with lsd oil and the limited slip works

 

[CharlesHS]

It sounds as though you are confident the noise is coming from the rear differential.
When you drained and filled the differential gear lube; was there metal particles in the oil ?
I would disassemble the rear third member and do an inspection before something grenades itself.

 

[Vasimo]

There were small amounts of metal sticking to the drain plug, a concern was that the oil has started to intake some water and had become slightly milky, guessing previous owner went through some fairly deep water crossings, or the breather is mounted strange