Diagnosing a Bearing-like Whir/Rumble at 1800rpm, 25 mph

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Jun 11, 2016
Hi All,

As with many cars of increasing age, it is once again time to play "Find That Sound!" (In my head the game title is read in the same manner of "Don't Get Eliminated!" from MXC, but it probably doesn't translate to text well.) But in all seriousness, thank you for taking the time to read my post. Here are the major points:

- Stock 1997 TLC, 192K on the clock, been in the family for 12+ years.
- Noise started about 3 months ago when I took the car onto some light trails near Fordyce (small rocks, a few puddles). This was the first time the car was taken wheeling. Until then, it had been used only on pavement and packed dirt roads.
- Noise came on the commute home after the trail.

- The car makes a Whirring/Rumbling noise under light/moderate throttle input.
- Noise is most common around 1600-1800 rpm around 20-30 mph.
- It happens at lower and higher speeds, but less frequently.

Treatment So far:
- Greasing all U-joints and slip yokes. No major effect on noise noted.
- Replacement of AC drive belt, Fan belt, AC idler pulley, Fan belt idler pulley. No major effect on noise noted.
- Changing of front differential, rear differential, and transfer case fluids.
Diffs were 80W90 Lucas, T case was 75W90 Lucas. Front diff fluid was dark and looked as if it hadn't been changed in a long while. T case and rear diff looked recently changed. All drain plugs accumulated normal fine particulate. However, the rear diff drain plug had a large amount of particulates (~4 q-tip heads' worth). This is especially surprising since the fluid looked relatively new. No large chips were found. The build up was completely composed of fine particles. Sound frequency seems to have increased.
- Front wheel bearings adjusted. Took place same time as fluid change.

Most recent and alarming incident:
- Driving on back roads home. The car starts to make noise during the acceleration uphill. When I finally park the car there is a warm smell similar to... hot brakes? from the front of the car. This is particularly odd as I didn't use the brakes much between the hill and home.

I cannot seem to find a thread on MUD or elsewhere that has similar symptoms or find a cause. My Search-Fu grows weak and I reach out to for help. Any thoughts on additional diagnoses to pinpoint the noise or suggestions for likely suspects would be tremendously appreciated.

Thank you for your time,

Bad U-joint symptom. Even though they were greased doesn't mean they are operating properly. Remove each drive shaft and rotate each joint both ways on its axis. The one that has a rough spot on its rotation needs to be replaced. Here's my similar experience:
94 growling from rear end easily fixed.
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You MUST completely insure the u-joints are good. You will waste a bunch of time if you causally pass them by during your trouble shooting. Also, hopefully you read about in all your searching that it is very easy to over grease the slip joints on the drive shaft. After pumping some grease in them, you really need to remove the grease nipple and allow any extra grease to flow out.

And Welcome! :flipoff2:
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Wheel bearings also make that kind of noise. Did you check them before adjusting them?
Thank you everyone for the reply! I apologize for the late response, as I was out of town for a few days.

I will have to check the U joints more thoroughly. The only treatment I did was to grease them. Over greasing the slip yokes definitely was a concern, but the only caution I encountered was to apply grease sparingly. I didn't know that you could relieve the excess grease by removing the zerk fitting.

I checked the one adjusted on the driver side and it showed no obvious signs of wear. The passenger side was done by Georg at Cruiser Brothers and Valley Hybrids in Stockton as he was kind enough to show me how to adjust the bearings.

Thank's for the advice. I'll keep trouble shooting and let you all know what shakes out!

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