93Toyota PU

A strange noise started coming from my front driveline. I have a 93 Toyota pickup, 115k miles, 22RE, 5 spd, 4x4, manual lockout hubs. If I have the hubs locked, but leave it in 2WD, a strange nosie starts when I am on the highway. It starts about 50 or 60 MPH. It is a very low frequency resonance...almost sounds like the faint whirl of a helicopter or something. It does not occur if the hubs are locked and the transfer case is in 4 hi or 4 lo, or if the hubs are unlocked in 2 wd. Just occurs when the hubs are locked and I run in 2 hi. The last time it happened I pulled over on the highway to unlock my hubs...I had only driven 3 or 4 miles. I could smell a burning odor. Don't know if it was from my truck but it sure appeared to be coming from the driveline somewhere. I have changed all the differential, transfer case and transmission fluids. The noise is still there.
It doesn't sound like a wheel bearing to me...are there other bearings or shafts that could be casusing this noise? I've searched the forum but can not find anything close to my problem...

mt_goat

That's interesting because I've always wondered if it was safe to run in 2wd with the hubs locked. If it is, why did Toyota design the ADD system? You might just check if the transfer case gets abnormally hot when it happens. It could be there is a bearing in the transfer case that gets oil when in 4wd and doesn't when in 2wd but is turning because of the hubs being locked.

93Toyota PU

Mt Goat: thanks...will check out the transfer case bearing theory...the dealer told me it was OK to have hubs locked and run in 2WD...then just shift into 4wd when needed. It sounded good to me because there are occassions where it's slippery and then you hit drive pavement. I don't like to run 4WD on dry pavement, so I would just shift transfer case out of 4WD to 2WD.

mt_goat

I had heard of others doing that too, and no problems. I am kind of surprised the dealer told you it was ok.

Another possibility is the gears in the front diff are in some sort of trouble. I know you said it doesn’t do it in 4wd, but in 4wd the gears would be running more on the drive side of the gears. In 2wd they would be making contact on the coast side. Might also see if the front diff is getting abnormally hot. Something must be getting too hot if you smell something burning, feel around to try and find it.