1986 Toyota 4X4 pickup

I have a problem with my truck for over four years now,the problem is a noise from the front end that occurs when hubs are in Locked position a loud humming that comes and goes,I can hit the brakes hard and it goes away for a few seconds ,I can hit a bump and it goes away for a few seconds,I can take a sharp turn and it goes away for a few seconds.This woowoowoo or hum only happens when the hubs are locked not when they are in the free position,I can shift inot 4wd and make it go away for a few seconds,the noise gets worse the faster I go,it also gets worse the colder the weather is.I have replaced the axles twice and the front diff once and still has a noise ,I have checked the wheel bearings for play and they are fine,I have repacked the hubs with fresh grease,the sound ,sounds like metal to metal friction,this noise drives me crazy and every mechanic friend and rock crawler enthusiasts are all stumped–can somone please help?Everytime I call car talk I am told it is not available,please someone help me.

Are you using 4WD on dry pavement?? Many of the old 4WD systems used front and rear axles of slightly different ratios. 4:11 in the back, 4:10 in the front. This helps the vehicle track better when off-roading…But on dry pavement, it puts the drive-train in a bind and you can hear the complaint…

“every mechanic friend and rock crawler enthusiasts are all stumped”

Are you rock crawling with this? On “slickrock”? What size wheels and tires do you have on it? Is the suspension elevated?

I ask because oversize wheels and tires place a lot of additional strain on drivetrain parts. And lifted suspension places a lot of addidtional strain on U-joints and carrier bearings. The higher articulation angles can be brutal. Compound all that with rock crawling, including slickrock (which is as bad as driving paved streets in 4WD), and that changes the suspect areas to the U-joints, transfer case, and perhaps the front differential.

When the hubs are disengaged, you’re freewheeling the front wheels when you drive (not turning the front axle or driveshaft), and no noise, correct? If you engage the hubs and leave the truck in 2wd, the front differential is turning and you’re getting the woo woo noise, correct? If that’s the case, I would think it narrows this down to the front differential gears. What do you mean when you say you replaced the front axles twice? Do you mean the whole axle or the axle shafts? When you replaced the differential, did you replace the pinion gear as well?

My Jeep doesn’t come with hub locks–the front diff spins all the time whether i’m in 2wd or 4wd. Is driving in 2wd with the hubs engaged considered acceptable? I imagine that this is done in part for gas mileage, but is there a mechanical reason not to do this?

My axle knowledge isn’t comprehensive by any means, and I know that finding a oldschool mechanic who understands differentials well is essential–there’s more to it than just slapping all the gears into the pumpkin and bolting it up.

One more possibility is that someone at some point has had the front driveshaft out and gotten the u-joints out of phase, also a possibility the front driveshaft is bent. Just a few more items to check. Good luck.

Whoa wait…before you go suspecting the expensive front diff… Check into this…

Sounds to me like your locking hubs aren’t…locking…that is…(fully locking as they should). This is a very common sound on Ford Explorers with Auto lock hubs…and its a royal PIA… The final cure is to switch to manual lockers… I’d pull one or both of your hubs and have a looksie, sounds like textbook…semi-locking hub syndrome to me… There is a ring in your hubs that sort of slides over the axle shaft and hub body splines…it moves into position and locks the two together giving you 4wd…and when they slip or one or the other has damage to the splines (axle) or spline cutouts (lock ring)…this is the sound they make. Its a common thing actually…surprised your crawler doods didn’t say the same…it’ll drive you nutz…if you never heard this before. I’ve been dealing with this for a long while… Planning on new manual hubs this season.

The reason the sound is deceptive is bec when you are in 4wd the axle is spinning at the proper rpm as the wheel is turning…and only at certain times will they get out of phase will you hear the sound. Usually worse on deceleration.

If you pull the hubs on either side…you will be looking at the splined ring in the hub that gets moved into position to do the locking between the axle and hub body…Savvy? They get stripped out sometimes…and you wont see it till you are looking for this particular issue with the hub in your hand. Its the small ring that gets moved by the rotation of the “lock switch on the hub” You may need to tear into the hub a bit to see the health of the splined cutouts in the ring…also look at the axle splines in that area as well bec it could be one or the other…either the splined cutouts are “cutout or erroded” (MOST COMMON) or the axle splines are damaged in the area of where the ring locks the axle shaft (LESS common)… It’d be better if it was your hubs/hub lock ring and not your axles…my money is on the hub mechanism…see it much more often as the hub mechanism is the weakest link here. It’s either the hubs ability to LOCK…or they dont UNLOCK as they should…each can be caused by the hub lock mechanism…look into your hubs thoroughly…maybe borrow a known working set off a buddy for a weekend project? Hope this helps you… Let us know what you find.