hum/whine from front end when 4WD Hi at higher speeds

Was turning the 4WD on and off on my ride home from work to lubricate things (had forgotten to do so over the fall months) and noticed an audible hum or whine from the front end. 4hi engages and locks and disengages as well and seems to be working but I was a bit put off by the sound. It's more pronounced under acceleration. Speed was about 70-80 kmh.

Any thoughts?

 

Do you notice it around 45km/h and up and especially when it's cold outside? (below -6 Celsius)

 

definitely at that speed and higher. it wasn't particularly cold today (-10 C/14 degree F) but colder than -6. Was it perhaps not lubed that well as after not been used for months?

 

Honestly, I wouldn't worry! I have a similar noise that begins right at 45km/h and it's louder during winter but barely audible in the warmer months. I took mine into the dealer last April and they inspected the drivetrain (even replaced the front driveshaft and front differential - because they assumed it was the common needle bearing issue) but the noise still remained.

I recently had a 2019 SR5 rental with less than 20,000km and it made the exact same noise at 45km/h and up.

I would only worry if 4x4 engagment becomes an issue or you actually hear grinding but I think it's a "Tacoma thing" I also noticed the noise gets louder when the drivetrain is under a load - going uphill in 4HI

75W gear oil is particularly thick, especially for our Canadian climate.

 

Hm, interesting. Well feels better to know I'm not the only one. It's weird because this is my second winter with the Tacoma and I don't recall hearing it before.

Only other thing I noticed was one buck when I was switching in and out. I changed it out of 4Hi maybe 6-7 times and it bucked slightly on engagement once, I assume it was just slippage on the somewhat icey roads.

 

Me too! But once you start hearing something, it's hard not to unhear it imho.

The bucking is normal - that's the tension being released. Since our trucks don't have a center differential, the transfer case essentially locks the front drive shaft and rear driveshaft together when in 4HI.

During a turn or driving on a curved road, the front axle and rear axle drive a different distance, but because they're locked together, they constantly "fight each other" - this is where that tension in the driveline comes from and this is why it's harder to steer when in 4HI and also why you feel a skipping sensation during a tight turn in 4HI.

But you would feel that bucking on disengagement and not on engagement unless I'm thinking of something else completely.

When it bucked on engagement, were the rear tires slipping while you were engaging 4HI?

 

hard to tell, it happened by quick on a straight line. wasn't like driveline binding on a tight turn on dry pavement but more of a hiccup and the system engaged or disengaged, honestly can't remember which now. Tried to reproduce it but couldn't, ended up focusing more on the humming noise.

i'll try turning it off and on again tomorrow morning and see if I notice anything else. One thing is for sure these trucks have a host of, let's say "characteristics" which Toyota regards as normal, this might just be another one.

 

Oh I agree. I had the noise last winter and then forgot about it during the summer because it got warmer and the noise went away. I was concerned again this winter when the temps got cold again but was instantly happy when my low mileage rental had the exact same noise.

The noise is hard to describe too. Some of the techs I drove with last year couldn't even hear it. I would say it has something to with cold gear oil and resonance. Nothing ever works right in the cold.

 

4WD always sounds different than 2WD. No worries.