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I am hearing a pretty strong roaring from the rear end. FJ has 180k on it and the roaring stops when I turn left but returns as soon as I stop turning. Turning right it still roars....

Any thoughts on where to start?

Btw... it sounds like it is coming from the rear but....

Greg
 

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I am hearing a pretty strong roaring from the rear end. FJ has 180k on it and the roaring stops when I turn left but returns as soon as I stop turning. Turning right it still roars....

Any thoughts on where to start?

Btw... it sounds like it is coming from the rear but....

Greg
One slightly time consuming but pretty effective way to isolate elusive driveline, wheel bearing, and suspension noises is to run lengths of 1/4" diameter polyethylene tubing from the cab to the suspect noise sources. Tape one end of the tubing to the A-arm, axle housing, spindle, control arm bushing, etc., right at the possible noise source, and leave enough free length in the cab to reach your passenger's ear. Mark the ends of the tubing with masking tape, identifying where the other end of the tubing is taped. Secure the tubing to the undercarriage and bodywork with duct tape so it doesn't flop around.

You are essentially making an extended-length, multi-channel mechanic's stethoscope. Shop around, and you can find cheap 1/4" polyethylene tubing for only a few cents a foot. If the noise only appears at higher speeds, orient the "sensing" ends of the tubing so they point straight towards the rear of the vehicle to minimize wind noise.

Have a passenger along, listening to the ends of the tubing, while you make left or right turns, accelerate or decelerate, drive over speed bumps, or whatever driving conditions trigger the noise.

This technique should make it pretty easy to isolate the actual noise source.
 

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Check your oil if its very dirty and has metal in it its most likely the the diff, the bearings I believe are sealed but from what your describing it sounds like the outer axle bearing.
 

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What year fj? If it’s a 2007 it’s probably the rear diff. My rear diff bearings started making a lot of noise at 112k. It’s a common problem for that year fj, Tacoma, and 4Runner. My wheel bearing was going bad as well but wasn’t making noise. I replaced it but that was a nightmare. My bearings needed a special jig and a 40 ton press if I remember correctly. No regular automotive shop could do it, had to go to a machine shop who built a jig. It was a pain the rear. It’s actually much easier to replace the diff than the rear wheel bearings.


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You can hear the diff bearing dying if you jack up the rear axle or have the truck lifted on a 4-point lift and put mechanic's stetoscope to the 3rd member. Have someone run it on D or R and listen. In fact, you can also listen to the wheel bearings in the same fashion.

Also the diff bearing noise is somewhat "faster" than the wheel bearing noise.

By all means take any and all safety measures, if you choose to jack up the axle only!
 
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