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Doug
Doug, Australia Car Mechanic
Category: Australia Car
Satisfied Customers: 8538
Experience:  ASE Certified Factory trained technician
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2000 Pajero NM 3.5V6 Auto has a low frequency oscillating

Customer Question

2000 Pajero NM 3.5V6 Auto has a low frequency oscillating noise from the front of the vehicle at 40km/h on 3rd. The noise is pronounced during free-wheeling, but exists even when driven. The noise does not exist below and above 40km/h.
The vehicle has 133000km on the clock. In addition to engine oil change, the front and rear diff, plus transfer box fluids were all drained and changed at 131500km with exception of the Auto Transmission Fluid, which was flushed and topped up by 3 liters at 131500km due to the existence of 'rumble strips' noise, which disappeared within 100km of the flush.
The undercarriage is clean, no oil leaks, all grease nipples are regularly checked, greased (every 5000km to 7500 km) and the vehicle has not been subject to harsh off-road conditions. It has traversed light gravel road conditions (100km every month) and on occasion towed 2.5 ton loads (once in six months for 200km). Any idea what could be causing the noise at 40km/h please?
Submitted: 1 year ago.
Category: Australia Car
Expert:  Doug replied 1 year ago.

Hi,

If you are hearing this noise from the front of the vehicle your most likely suspects are going to be the tires first, followed by the front wheel bearings. These are both very common failure points and common complaints.

What I would be doing at this point would be to get the truck in the air with a helper "driving" it to ~40kmh in 4H and listening underneath with a stethoscope. This will confirm the location without fail.
If there is no noise while doing this, then you know the tires are going to be at fault, as the lack of contact on the road results in silence.
If the wheel bearings are at fault, listening at the back side of the spindle(s) right near where the axle shaft goes through should produce a very noticeable rumble.

Of course if nothing is heard there, then the rest of the vehicle can be probed with the stethoscope to help isolate the origin (front diff, for example). Given the narrow range of speed that the noise occurs it is of course possible that there is a wear issue on the planetary set inside the transmission.... however this will usually be heard either central or all over rather than just in the front end; likewise if you are free wheeling in neutral the noise would silence if this were the case. Never the less, the stethoscope again would help identify this if you found that the noise seemed to originate roughly in the middle of the transmission.

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