Transmission noise OK or imminent death?

[BennyM]

So, my already noisy 5 has begun making a new noise. It's more like a gear whine actually--the kind of whine our old John Deere lawn tractor makes when it's cruising across the yard at high speed (for a lawn tractor), or the kind of whine that any car makes when it's reversing at relatively high speed (for reversing). It's a gear noise.

It only occurs when the car is in gear and my foot is off the accelerator so that the car is gradually loosing speed. The noise is absent as soon as I add the slightest amount of gas or put the car in neutral and coast. The pitch of the whine is relative to vehicle speed, but not engine speed. It also doesn't seem to change pitch if I shift from one gear to the other. I suspected the transmission was low on fluid so I drained it and put new ATF in. The whine remains.

Any ideas? Is my 250k mi transmission about to explode? Could it be the diff?

[Ross]

If it is gear whine then the diff is more likely to be the problem. A howl on coasting is too much backlash between the ring and pinion. Correcting this requires disassembly of the diff. Check or better yet change the gear oil and see if it helps. It will likely go like this forever with the only consequence being the noise.

[BennyM]

In addition to what I described above, the car also makes a clunk when I release the clutch to engage a gear. I'm assuming these two things are caused by the same failing part of the drive train. Any other ideas besides Ross's? (I certainly will replace the diff fluid shortly).

Thanks.

BennyM

So, my already noisy 5 has begun making a new noise. It's more like a gear whine actually--the kind of whine our old John Deere lawn tractor makes when it's cruising across the yard at high speed (for a lawn tractor), or the kind of whine that any car makes when it's reversing at relatively high speed (for reversing). It's a gear noise.

It only occurs when the car is in gear and my foot is off the accelerator so that the car is gradually loosing speed. The noise is absent as soon as I add the slightest amount of gas or put the car in neutral and coast. The pitch of the whine is relative to vehicle speed, but not engine speed. It also doesn't seem to change pitch if I shift from one gear to the other. I suspected the transmission was low on fluid so I drained it and put new ATF in. The whine remains.

Any ideas? Is my 250k mi transmission about to explode? Could it be the diff?