Auto Hubs, where's the magic?

[bajawind]

(95 mazda b4000 4x4 autohubs) I have been having a thumping noise from the front axle, but only when i switch from 4wd back to 2wd. It seems that the noise is likely coming from a bad u-joint.

But it seems to me that the auto hub must also be locked in order for the wheel to be turning the front axle in 2wd. I removed both hubs (they look to be in good shape) with plenty of grease but there doesn't seem to be anything that engages/disengages.

THE QUESTION: So apparently the engage/disengage mechanism is further inward on the axle? Any ideas on locating/checking this?

There are splines for the axle (on the inside) and splines on the outside that mate to an outer ring with tabs. the outer ring moves in/out an 1/8 inch or so but not much else.

The auto hubs do reset when i stop and fiddle with the 4wd--then i am good to go again in 2wd. Sometimes a bump will bring back the thumping though replacing a ball joint and u-joint on the driver's side has helped to prevent this.

 

[Will]

I had auto hubs and found that they would work well if you kept them clean and very thinly greased. I used the grey moly grease and just barely coated them. Other grease gets too stiff when it's cold--and when it's cold is when you need your 4x4 to work. The grease turns into wax and plays merry hell with the works.

When they are working they unlock when you change directions and relock the other way if the axle is turning them. It's extremely likely they arent unlocking and you are hearing a bad axle. Take them apart and try them dry or with WD40 to verify they are working, then lube them lightly and frequently clean them. Or bang them into the Dipsey Dumpster and put on some manual hubs. They are convienient, but it gets old having them turn on you when you need them most.

 

[jasonl]

If I remember correctly you have to back up like 7-10 feet to disengage the auto hubs.

 

[bajawind]

There was vast amounts of grease in the hub and around the axle.
I cleaned up the hubs and as i was putting them back on i noticed that on the passenger side, around the axle there is a ring with (what used to be) three tabs protruding. these tabs seem to put pressure on the outer ring in the hub.
On the drivers side (where the tabs are present) there was a slight spring-like resistance to the hub seating that was missing from the hub on the passenger side. Damn, i missed that before. simple is better...i will put manual hubs on my wish list.
thanks for your notes...

 

[AllanD]

"The Magic" on a factory auto hub truck with an electric T-case
is that there is an electro-magnetic clutch INSIDE the transfer case
that "spins up" the front driveshaft before the electric shift motor
will move the front drive into engagement.

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[dennis461]

"The Magic" on a factory auto hub truck with an electric T-case
is that there is an electro-magnetic clutch INSIDE the transfer case
that "spins up" the front driveshaft before the electric shift motor
will move the front drive into engagement.

AD

Are you sure about this?
I have a 1996 and never heard of this spinup, although it does makes sense.
.
As far as noise and such, when my wheel bearings wore out, the hub would tilt and seem to engage. Looking at the inside of the auto hub showed wear when cleaned up of the grease.
I would check the side with the missing three tabs for missing wheel bearings ( mine got that bad before I realized what was going on.)