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I have recently noticed a clicking noise from the front differential on my 2000 Chevrolet Silverado when traveling at low speeds (under 10 MPH, but I'm sure it's always there, but it's too fast/too much road noise which makes it impossible to hear at faster speeds).

I know it's coming from the front, and I even removed the tire and the driver's axleshaft and rotated the shaft coming out of the front differential directly and I still heard/felt the clicking noise from the front differential.

So here's what I have eliminated/things I have tried

  1. It's not the wheel bearing since it wasn't turning once I disconnected the axleshaft
  2. It's not the inner or outer CV joints for the same reason as above (and I replaced it for good measure since I had it out... and it looked original)
  3. It's not the U-Joint coming from the transfer case because the 4 wheel drive was disengaged when I was spinning the axleshaft by hand which would not have turned the transfer case
  4. Partially locked 4 wheel drive/bad vacuum solenoid. I eliminated this by driving the car and putting it into 4 wheel drive. There was a definite shift in power but the clicking was still there. I only attempted this because I have heard that the solenoid can get partially engaged constantly, which might have explained the clicking.

Things I have yet to do

  1. Replace front differential fluid. I know this is an obvious one, but I didn't have what I needed to do it yesterday because I had originally suspected the wheel bearing. Also, on the advice of my wife's uncle, when I change the fluid I will check the old fluid for any signs of issues. I know to look for metal shavings, but is there anything else I should look for in the old fluid?
  2. Take it to my mechanic to check it out. I definitely trust my mechanic but I'm trying to find out is there anything else I can try changing/troubleshooting before taking it to my mechanic?
  • What is bothering me here is the fact this is happening in or out of 4wd. The front diff should be completely disconnected from the drive axles and not rotating when in 2wd mode. You shouldn't hear anything from it. It sounds as though one (or both) of the drive axles are stuck in the engaged mode, yet the power is still not applied until the transfer case is engaged. I'm thinking you could be looking at multiple issues, but all residing in the differential itself. – Pᴀᴜʟsᴛᴇʀ2 Jul 20 '15 at 13:32
  • Well, the half shafts both turn with the wheels when 4WD isn't engaged, and I turned them by hand when jacked up and heard the same noise. So it seems it must be something about where the half shaft connects to the differential... – StephenH Jul 20 '15 at 13:35
  • It is my understanding they should be "engaged" or "not-engaged". I thought that occurred at the differential, not the hubs. It's the difference between 2wd and auto-4wd, the shafts are engaged to the diff at that point. When you have it in straight 4wd, both the shafts and transfer are locked in. This is all predicated on you having the push-button 4wd and not the manual setup (assuming the push button due to you having the vacuum solenoid). – Pᴀᴜʟsᴛᴇʀ2 Jul 20 '15 at 14:00
  • Right, but in any mode the half shafts will spin because they are always engaged to the wheel hubs. So they will always be spinning inside the differential even when the driveline from the differential isn't engaged. And I did test it in straight 4WD, so it all should have been engaged and I still heard the noise... – StephenH Jul 20 '15 at 14:06
  • No, what I'm saying is the shafts will be disengaged from the differential if in 2wd mode. This is an "auto hub". When you push the auto-4wd button, the hubs engage. It's why you get worse gas mileage in auto-4wd than you do in 2wd because you are pushing the diff gears around. – Pᴀᴜʟsᴛᴇʀ2 Jul 20 '15 at 14:15
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Ultimately, I replaced the half shaft and found out that wasn't it (although, for reference, the half shaft ended up being really easy to change. Was able to do it without even removing the wheel bearing). Even though it seemed full, I just added some differential fluid and the noise seemed to subside. I will be changing the fluid entirely in the future and looking for any metal shavings to decide if there is any damage.

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My problem was when i heard clicking noises coming from my diff, it ended up being the pinion gearing. It was a tooth chipped off. So you should check that out when ya get a chance.

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