HELP! Front end grinding noise in 4H/L

[timjw83]

Hi all,
Hoping someone can help me out with diagnosing the cause of a noise from the front of the vehicle-particulars below:
- D40, 4x4, 4L V6 petrol
- only happens when in 4H/L
- it's in time with the wheel rotating
- squeeling/grinding noise
- comes on stronger when/after hard right/left
- has front LOKKA installed, but have had this pulled out and checked already (at HUGE cost!)
- pads/discs just replaced
- wheels spin ok when in 2wd and jacked up
- have been told CVs ok-but not by necessarily a reliable source
- no obvious rubbing on any moving parts

Any ideas? Thanks in advance....Tim

 

[Old.Tony]

Given that the noise happens when the steering is used I'd either look at CVs or the wheel bearings (because wheel bearings get loaded up as you turn).

Wheel bearings are fairly easy to spot. Find a smooth corner somewhere and take the corner at the advised speed. As the weight starts to shift towards the outside of the corner, it adds a load to the bearings on that side of the car. It might sound like tyre noise or just road noise that isn't there when travelling straight. Mine did - developed a whiny sound on left hand turns - turned out to be the front right wheel bearing.

I had another sign of the problem appear - my ABS and 4WD lights came on intermittently, and even when braking on a sealed road and gently applying the brakes, my ABS was coming on. ABS sensor is close to the wheel bearing on the front axle - as the bearing is destroyed, it interfers with the sensor.

 

[timjw83]

Thanks Tony,
But if it were wheel bearings, wouldn't it be making the noise in both 2wd and 4wd? This noise only comes to life in 4wd.
Does that point it more toward a CV?
This was my first thought, but my local mechanic said diff.
I think he might have misdiagnosed....

 

[Old.Tony]

It's a question of load. In 2WD there's zero loading on the drive shaft, the front wheels are turning the CVs over and the axles, diff and prop shaft oblige by turning too. But there's no load on it - so it's unlikely to make a major noise.

It could be the diff - if the bearings on the main axles are a little suspect, propelling the car and giving it a side load by turning the car could make noise.

It's easy enough to diagnose a bad CV. Put the front of the car on a hoist or jack stands, get underneath with someone sitting in the cabin, key to accessories only. Turn the wheels over by hand - you'll be able to track where the noise comes from easily.

Come to think of it, several members here have had problems with the front prop shaft. Again, it's only loaded in 4HI/4LO but it turns regardless. Loading it up will make the noise louder - but with the engine off and you right there underneath you should be able to spot the source of the noise. A mechanic's stethoscope is often helpful. The front prop shaft shouldn't slop around in its bearings either - it should be so tight that a nun would be proud of it.