Harmonic vibration with center diff locked?

[Frontline]

Was on a 1000 mile weekend overland trip and ended up encountering first snow storm of the year. Temps were warm enough for the roads not to freeze but slop was building up so I locked in the center diff. I instantly started getting a waxing and waning vibration that you could hear and feel in the pedal. I unlocked the center diff and the vibration instantly went away. I was traveling at about 70mph. I used the center diff locked the second day for 300 miles on two tracks and muddy, sloppy water submerged roads with out vibration. However, the speeds were never more than 45 mph. Any thought? Could it be a bearing in the center or front diff failing?


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[Door Ding]

Sounds like we might have the same thing going on. Maybe the front diff input bearing on its way out? Is it constant?

Mine has a similar noise but it's almost always there whenever I'm on the highway where I'm usually going 60-65. I've got an 05 v8 so I'm awd.

My noise is only present when I'm on the throttle and it's definitely coming from the front. Does yours happen constantly or only when on the throttle? My first thought was a wheel bearing but that wouldn't make sense given the on throttle thing...


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[Frontline]

I have a 2004 v8. It has all new half shafts and wheel bearing up front and a completely new rear end and all the bearings as well. At highway speeds it is constant with the center diff locked and not there without it locked. However, it may just be below a noticeable threshold without the center locked. This is why I was wondering if the front or center diffs need new bearings? This is my ski truck truck so the worse the conditions the more likely we are to chase the powder. So in the winter I use the center diff lock multiple times everyday. Most weeks in the summer it is engaged as well.


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[RonJR]

I have a 2004 v8. It has all new half shafts and wheel bearing up front and a completely new rear end and all the bearings as well. At highway speeds it is constant with the center diff locked and not there without it locked. However, it may just be below a noticeable threshold without the center locked. This is why I was wondering if the front or center diffs need new bearings? This is my ski truck truck so the worse the conditions the more likely we are to chase the powder. So in the winter I use the center diff lock multiple times everyday. Most weeks in the summer it is engaged as well.


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Why in the world are you locking the center diff at 70 mph? A locked center diff (and for that matter any locked differential) is not your friend at highway speeds - it forces wheel slippage on corners and increases your risk of losing control. If conditions are such that you need the center diff locked to make progress you should be limiting your speed to below 30 mph or less.

 

[Civiceg94]

Why in the world are you locking the center diff at 70 mph? A locked center diff (and for that matter any locked differential) is not your friend at highway speeds - it forces wheel slippage on corners and increases your risk of losing control. If conditions are such that you need the center diff locked to make progress you should be limiting your speed to below 30 mph or less.

Same here. You should really read the manual. Having the diff lock is not ment to be drive. Highway speeds the wheels are basically fighting each other sooner or later your going to blow things up

 

[m85476585]

The harmonic vibration sounds like the front differential damper issue. Mine does it very slightly with it unlocked between 60-65mph, and I haven't tried driving with it locked at that speed since there's no need to. There was another thread about it, and Lexus has a fix for the 470, but I don't know if anyone has tried that part on a 4runner. IIRC most people say the vibration is subtle, but if yours is very strong then there might be another problem.

Slightly off topic, but I can confirm that having the center unlocked is much better for handling on slippery roads. It's easy to test yourself, and you should find that understeer in hard corners is worse with it unlocked. I have a friend who has a Tacoma, which doesn't have a center diff so it's locked all the time when it's in 4WD. He has snow tires and I have all season tires. I've driven with him on snowy and muddy roads, and he couldn't keep up with me in the turns because his truck would understeer. He had to go slower to make it through the same turns, or if he was going the same speed he would have slid off the road.

The center diff is limited slip, so you shouldn't need to lock it unless you're in a situation where you might get stuck. For highway driving if you encounter unexpected ice or something like that the traction control and stability control will help, though they are not perfect. You definitely want VSC on if you're driving on slippery roads as long as there's no significant risk of getting stuck, and locking the center disables that.

 

[DoorDing]

Could you elaborate on the Lexus front differential damper issue you mentioned? Thai sounds like what is going on with my truck.

Edit: after a little reading, this Lexus issue is EXACTLY what I am experiencing around 60-65 mph. I plan to look into obtaining and installing the part to see if it helps the anointing vibrations I'm feeling as I do about 150 miles a day on the highway...

 

[m85476585]

If it's louder than normal, maybe the front diff pinion gear might not be properly adjusted. I think that could be the source of the noise, then the damper is what makes it periodic, increasing and decreasing in intensity. But I'm just speculating. Let us know how the revised differential damper works out.