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Front end harmonic vibration at 35 mph and at 45 mph

my 97 4runner makes a harmonic sound and vibration in the front diff, but only in 2wd at 35 mph and continues up to about 45 mph. The sound and vibration go away if 4wd is engaged. Is this a front diff problem or bearing or what? dealer thinks it might be from the diff but wants 1200 just to check if it is the problem. Any suggestions and why only in 2wd and not 4wd?

Check and see if there’s a bad CV-joint to one of the front hubs.


how does one check for a bad cv joint? put on lift and turn wheels?

First you crawl under the vehicle and see if any of the CV boots are opened up. Then you grab each halfshaft and try pushing it up and down to see if there’s any slop in the CV-joints.


all boots look good and intact. no significant movement on either shaft, but a slight difference on driver side. I bought used and only after purchase found repair work receipt for damage to driver side a few years ago and that cvj was replaced with tie rod, and rest of suspension parts due to a hit and run on the vehicle while parked. should cvj be replaced as a set instead of individually? since the quick cvj trouble shooting does not show anything obvious what is next?

I Hope The Vehicle Was Properly Repaired Following The Collision Damage.
Otherwise, replacing parts may be futile.

Is this harmonic sound something new?
How many miles have you put on the vehicle? How long have you had it?
Does the vehicle track straight or does it ever “pull”?
Have you ever had an alignment done on the front-end?

Should other diagnostic approaches fail, you may have to consider having a high quality Body/Collision Shop (one with “frame” straightening/alignment equipment) take a look.

If they suspect something isn’t right, they should have access to specifications for your specific vehicle that indicate precise measurements for frame and suspension components and they can check these.


I purchased 4 months ago with 175K. Upon purchase I had a full service inspection and prevenative work performed…, replace timing belt and water pump, and replaced a leaking seal on transmission and transfercase and checked alignment as I noticed the steering wheel did not line up with column.
The vehicle has always driven straight and has never pulled and the alignment check showed everything within spec.
Since I did not own but for a few days before I had preventative maintenance work performed I may not have noticed the low thumping vibration at the speeds mentioned, but I later suspected the issue may be related to the replacement seal on the transfercase as the vibration is more felt on the driver side floor board and very little if any on the steering column.
After a month both rear hub seals started leaking, so had them repaired, but the dealer also found that the transfer case seal they had replaced before was leaking again so they replaced without charge.
Tires needed replaced and so I purchased 4 new tires thinking that was a possible reason…but did not change a vibration.
Another item of interest is that the vehicle came with 17" toyota brand rims, and the original Limited would have come with 16" rims (as indicated by the 16" spare tire), and so have no idea as to when the increased rim and tires were added, could this be a potential issue?
In another web search I came across a very similar story where the owners mechanic said the front diff needed replacing, the master mechanic in the forum with 30+ experience advice was to look at the bearings and to find another mechanic. As the dealer said it was the front diff that needed replaced or repaired, I am also looking for another opinion.

Could this be a automatic disconnecting diff (ADD) system problem? Since, in 4x2, the right wheel shaft is always rotating with the wheel, the left wheel shaft is disconnected and the diff is not rotating. Could the vibration be caused by a partially disengaged ADD system? Would this indicate a driver side bearing or cv-joint problem?