Auto hubs?

Frogstar7055

Frogstar7055

Wheeling
Location
Jacksonville FL
After changing broken CV (had both hubs off) I had a sticky hub.
Took it completely apart,plastic piece looked fine. Put it back together and now it's working fine.

Now to my question........

I've been a mechanic,gas turbine tech and lastly a machinist for the last 25 years but for the life of me I don't understand how these things work.
Not a dummy but I just don't see it. Don't see how rotational torque from the CV shaft makes it engage.

Anybody care to explain? (TJ hoping you'll chime in)
 
robcarync

robcarync

Sliders
Location
Raleigh, NC
I myself have wondered the same thing...It didn't quite make sense to me. Obviously there are some cam/ramped surfaces on the fixed cam assembly and in the outer hub, but I couldn't quite put it all together in my head.

Google didn't help a whole lot either.
 
Roadwarrior

Roadwarrior

Titan Swapped / SAS'd
Founding Member
Location
Probably in class..
See, I think you are thinking almost outside the box here.. (The X is a box, and you are almost outside of it thinking about the actual hub, versus the diff in the middle)

From what I have understood, these are always engaged, it is your differential that won't be engaged until you shift into 4wd.

Reason being is in order to make manual locking hubs 'go' you much climb out of the rig and then physically engage the hub yourself, where auto hubs are already engaged.

When you have manual hubs, you can have them locked, but not be engaged in 4wd and it doesn't make a difference. Granted I have been told not to run manual hubs locked if you aren't using them as they start to cause premature wear and tear on the gearing on the inside.



Well there are my two pennies rolling around, I'll let others chime in.
 
Prime

Prime

Shut up Baby, I know it!
Admin
Location
Denver Adjacent
Okay. So.

The wheel is driven by the hub cover which has the splines and is bolted to the brake disc.

There is a ring on the inside of the hub that has I think 4 large teeth on it. When the diff starts to turn the end of the hub where the splines are that disc rotates and locks the back part of the hub with the cover transferring the motion to the brake disc and by extension the wheel. This is sort of a loaded operation as you'll notice that sometimes you have to roll backwards to get them to unlock and freewheel.

If everything is in good condition and properly lubed, you shouldn't have any issues.

The difference with manual hubs is that the cover is always unlocked on the axle shaft until you go and turn the knob to push the splined end of the hub onto the shaft. There are no moving pieces at that point which tends to make manual hubs more reliable and stronger.
 
robcarync

robcarync

Sliders
Location
Raleigh, NC
When I swapped out and put manual hubs on, it was very easy to figure out how they worked. The twisty knob has a spring on a threaded screw type thing, so as you turn the knob, it pushes an outer splined collar down, which locks it. When you unlock the hubs, the spring backs up, and the outer collar is out of the way. Super easy.

I guess the thing that always tripped me up was how specifically they lock with torque from the CV, but not with torque from the wheel rolling on the ground.
 
robcarync

robcarync

Sliders
Location
Raleigh, NC
Muadeeb said:
Because the axel isn't moving?
Click to expand...

Let me clarify: What about it allows the CV axle to drive the wheel forward and reverse, but the wheel turning in forward or reverse from the ground pushing the tire to not drive the axle?

I no longer have the stock hubs so I don't remember how all the cams and teeth worked. I'm not looking at it to really think about it any deeper. That was just the part that was tricky for me to fully understand from the last time I looked at them.
 
Roadwarrior

Roadwarrior

Titan Swapped / SAS'd
Founding Member
Location
Probably in class..
i-have-no-idea-what-im-doing-dog.jpg
 
T

TJTJ

Skid Plates
Founding Member
Location
NJ
robcarync said:
Let me clarify: What about it allows the CV axle to drive the wheel forward and reverse, but the wheel turning in forward or reverse from the ground pushing the tire to not drive the axle?
Click to expand...


I don't actually know what you are asking?

If this helps...


In 2wd, the wheels just spin freely.

In 4wd, the half shafts are rotated, and, if the hubs are not locked, the rims don't care about that, because they are not connected to it yet.

You have to roll forward enough to allow the ratcheting to engage.

If the hubs are locked, they stay locked if you go forward and reverse as long as you're in 4wd.

If the hubs are locked, but you shift in 2wd...they only stay locked going forward, and, reversing ratchets them back out of engagement...if you reverse far enough for them to disengage.


If you hold a socket on a ratcheting wrench...you can freely spin the wrench around the socket in either direction when not engaged.

If you set the ratchet to say tighten, and rotate it, it gives torque in that direction, but can ratchet back for the return stroke.

If you are applying torque, and try to disengage the ratchet, you won't be able to, you'd need to back up enough to let it disengage.


Its like that.
 
robcarync

robcarync

Sliders
Location
Raleigh, NC
Well, I didn't think my question was unclear, but let me clarify the clarification (LOL)

If torque from the CV drives the wheels in 4WD, how does torque from the wheels not drive the CV when in 2WD (...meaning the ground is "driving" the tire, driving the system backwards and free spinning at the T-Case)? I haven't really tried to figure it out...I haven't thought about it again until this thread came up.

Of course this doesn't happen, so somehow in the kinematics of the teeth and fixed cam assembly, it allows the CV to "catch" the wheel but not the other way around.

I understand everything on the conceptual level, but when I was looking at my old auto hubs and the fixed cam assembly and trying to figure out how all the teeth interlocked and actually engaged, I couldn't see it.
 
Frogstar7055

Frogstar7055

Wheeling
Location
Jacksonville FL
The wheels don't drive the CV in 2wd because the hubs are unlocked.
When you engage 4wd the CV's rotational force causes the hubs to lock thus engaging the wheel.

I got that, it's how this happens mechanically in the hub that I'm not seeing.
Just don't see how that rotational force is causing the engagement.
 
robcarync

robcarync

Sliders
Location
Raleigh, NC
Frogstar7055 said:
The wheels don't drive the CV in 2wd because the hubs are unlocked.
When you engage 4wd the CV's rotational force causes the hubs to lock thus engaging the wheel.

I got that, it's how this happens mechanically in the hub that I'm not seeing.
Just don't see how that rotational force is causing the engagement.
Click to expand...

Exactly what I am trying to say here...I understand they are unlocked, allowing them to free wheel. I understand the function. I understand how to cycle through them and unlock them when in 4wd vs. 2wd. I don't understand how the hub distinguishes between torque from the CV vs. torque from the road pushing the wheel. From the tooth-to-tooth engagement, I could not figure it out to that level of detail.

The high level explanations are like saying "the hub locks with CV torque and not the wheel torque because...the hubs only lock from the CV axle and not the wheel"

For the ratchet comparison, that is easy to understand a one way ratchet...it is directional as far as the rotation direction, but not directional as far as the wrench driving the bolt, or the bolt driving the wrench. Say you have a bolt in your hand, and a socket wrench in the other hand. You can turn the wrench and it catches on the bolt, however, if you hold the wrench still, and turn the bolt in the same direction, the bolt catches on the wrench...IE the wrench drives the bolt, or the bolt drives the wrench (assuming they are both being turned the right direction...the wrench slips based on direction of rotation, not which one is driven/driving).

What the auto hubs seem to do is allow catching the wrench on the bolt, but not the bolt on the wrench.

It really is a clever device.
 
Bklyn.X

Bklyn.X

Skid Plates
Moderator
Supporting Member
Founding Member
Location
Brooklyn, NY
Let me try...

AX-8.jpg


There is a spring within the internals of the hubs that keeps the engagement teeth of the hub separated allowing the wheel to "Freewheel" when it is not under power from the differential.
The "fixed cam assembly" is "fixed" to the knuckle spindle. It does not turn with the wheel or half-shaft so it is the anchor within the hub enabling the hub to distinguish the half-shaft moving.
When you put the transfer case in 4wd the rotational power, transferred out to the hubs via the half-shaft, causes the "fixed cam assembly" mechanism within the hub assembly (transforming the rotary motion of the half-shaft into linear motion) to push (overpower) the spring, allowing the teeth of the locking the hub to engage.
The "fixed cam assembly" can not tell if the wheel is turning (torque from the road pushing the wheel) before this happens because the teeth locking the hub are not engaged until it does (refer to 1st sentence).
They stay engaged until you go from forward to reverse and the "fixed cam assembly" (transforming the rotary motion of the half-shaft into linear motion) releases the spring that then pushes the teeth of the locking the hub to the unlocked position. In 2WD (receiving no rotational power) the spring will cause the teeth to stay disengaged. In 4WD the hub assembly (receiving rotational power) will disengage and re-engage very quickly.
Rocking your auto hub equipped truck back and forth is what usually blows a hub (disengaging and re-engaging while receiving rotational power).
This is why folks change to a Manual Hub; it does not depend on rotational power from the half-shaft, it is always locked or unlocked.
 
Last edited:
Bklyn.X

Bklyn.X

Skid Plates
Moderator
Supporting Member
Founding Member
Location
Brooklyn, NY
Okay, I’m just posting the following info in this thread rather than in each of the many threads asking about our auto hubs. I wanted to update you folks as soon as I found out this information I got from a friend of mine.

He needed to replace his Auto Hub and was able to order the “Fixed Cam Assembly” from his local dealer for $83!

This is apparently a new thing. The “Fixed Cam Assembly” is now called a “Thrust Washer”;

Nissan Lookup code 40256D
Nissan part number 40218-8B400

This part will not be around long because, as you know, the Auto Hub (40260-9Z500) has been discontinued. So if ya need one and can still find it act fast.

My friend also bought a new Auto Hub Assembly! It a bit different than the old one in that the “Fixed Cam Assembly“ is built in and therefore not serviceable and a PITA to line up correctly so it fits flush. It uses the same hex screws as our old one, works in the same way and according to my friend “works perfect”.

New%20Auto%20Hub_zps0lcwbb47.jpg


The part number for this new Auto Hub Assembly is 40260-1S700 and will come up in a Google search. I’ve seen it discontinued, in stock online for $323.39 (YIKES!), on Amazon for $173.63 and for $160.46 on ebay where my friend got his;

http://www.ebay.com/itm/252039017682?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I’d act fast if I wanted any of this, no telling when these links will be no good and the parts, like our old Auto Hubs, will disappear.
 
Joey

Joey

First Fill-Up (of many)
Location
Indianapolis
I have two or three extra's of these auto lockers. I like the idea that they are the weak link. Heck of alot easier to change that a cv half shaft or a drive shaft. How they work....Magic
 
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