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Auto Hubs Explained;
https://www.nexterra.org/forums/viewtopic.php?f=39&t=8212		 Page 1 of 3
Author:  Bklyn.X [ Sun Feb 08, 2015 9:13 pm ]
Post subject:  Auto Hubs Explained;
Let me preface this by stating once again that I am not a mechanic or and engineer. I take my 2001 Xterra off-road and work on it now and then.

That said, someone asked about how the Auto Hub on a 1st Gen Xterra work on one of the other boards and I answered with;

Image

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.

…thought it might be useful to archive it here. Hope it helps someone…

Image
Author:  RomeoEJ [ Sun May 22, 2016 8:40 am ]
Post subject:  Re: Auto Hubs Explained;
I would like to add the following to Tom’s topic: I just recently broke the fixed cam assembly so when needing to order the product you will need the following information:

When needing to replace the “Fixed Cam Assembly” you will find the part is now called the “Thrust Washer”

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

In addition I have spoken with Brian from Cherry Hill Nissan and he has informed me if you buy a hub assembly the fixed cam now comes built into the hub assembly so the “Fixed Cam Assembly aka Thrust Washer” is now being discontinued. At some point it will all be discontinued and our only option will be aftermarket manual locking hubs by Warn or equal.
Author:  Bklyn.X [ Sun May 22, 2016 11:20 am ]
Post subject:  Auto Hubs Explained;
Wait, he has these parts? I thought they discontinued them all already....


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Author:  RomeoEJ [ Mon May 23, 2016 6:04 am ]
Post subject:  Re: Auto Hubs Explained;
I was able to order the Thrust Washer aka Fixed Cam Assembly at my local Nissan dealer for $83. Basically I ended up figuring out that the Thrust Washer was the Fixed Cam Assembly because i reviewed piece by piece the assembly diagram with the actual parts and then i just called my dealer here and they ordered it so i could 'look' and see if it was what i needed. Turned out it is the correct item, I believe the dealers do not know that somewhere down the line the part name changed.

Thrust Washer aka Fixed Cam Assembly:
Nissan Lookup code 40256D
Nissan part number 40218-8B400.


I also bought the full hub (with he cam built in) on Ebay and it works perfect. I installed one yesterday on the broken side. Link to type purchased:
http://www.ebay.com/itm/252039017682?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

PS the new hub with the cam built in is a pain in the ass to line up correctly so it fits flush before putting the hex screws into it to hold it together.
Author:  Bklyn.X [ Mon May 23, 2016 9:38 am ]
Post subject:  Re: Auto Hubs Explained;
Did you happen to take a picture of the part (40218-8B400)?


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Author:  RomeoEJ [ Mon May 23, 2016 3:00 pm ]
Post subject:  Re: Auto Hubs Explained;
Bklyn.X wrote:
Did you happen to take a picture of the part (40218-8B400)?


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No but i can take a picture of the old part that i am speaking of. Nissan ordered it and i went to look at it to confirm for my knowledge and it was the fixed cam assembly. I told them it was the wrong part so they could take it back and not charge me because at that time i already had the new hubs.
Author:  Bklyn.X [ Mon May 23, 2016 5:27 pm ]
Post subject:  Re: Auto Hubs Explained;
Sorry to keep asking but I want to be sure I understand. Is Thrust Washer aka Fixed Cam Assembly:
Nissan Lookup code 40256D
Nissan part number 40218-8B400.

This part;
Image

Exploded picture of the same part;
Image

Thanks
Author:  RCHeliman [ Mon May 23, 2016 5:35 pm ]
Post subject:  Re: Auto Hubs Explained;
Is it the plastic piece that keeps breaking? If yes, I wonder how hard it would be to make one. Wonder if a printed one would last...
Author:  Bklyn.X [ Mon May 23, 2016 5:39 pm ]
Post subject:  Re: Auto Hubs Explained;
MMDR Designs wrote:
Is it the plastic piece that keeps breaking? If yes, I wonder how hard it would be to make one. Wonder if a printed one would last...


:shock: Wow, that's very interesting. I bet it would and would make for a great item for you to sell (and make money on). I got a spare you could use if that would help.

Eric, do you have the Nissan part number for the newer hub assembly with the fixed cam now built into the hub assembly or is it the old part number; 40260-9Z500 (shown as discontinued from most dealers)? Is it 40260-8B400? Or is it the 40260-1S700 listed in your ebay link?
Author:  MtDewMike [ Tue May 24, 2016 7:55 am ]
Post subject:  Re: Auto Hubs Explained;
Bklyn.X wrote:
MMDR Designs wrote:
Is it the plastic piece that keeps breaking? If yes, I wonder how hard it would be to make one. Wonder if a printed one would last...


:shock: Wow, that's very interesting. I bet it would and would make for a great item for you to sell (and make money on). I got a spare you could use if that would help.

Tom, do you have a broken one to take apart to confirm it is the plastic piece that breaks?
Author:  Bklyn.X [ Tue May 24, 2016 8:35 am ]
Post subject:  Re: Auto Hubs Explained;
No, I don't keep broken ones...gotta be honest, I've never broken one, but that's the part that breaks.
I got a old, used spare I'll send to David for him to take apart and examine.


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Author:  MtDewMike [ Tue May 24, 2016 11:35 am ]
Post subject:  Re: Auto Hubs Explained;
Weird how they would have a piece of plastic in something like that.
Author:  Bklyn.X [ Tue May 24, 2016 1:27 pm ]
Post subject:  Re: Auto Hubs Explained;
The only other material I would think they could make that part out of would be stamped steel. I'm think they used plastic to keep the thing quiet. There's a bunch of stuff moving around in that assembly, plastic kind of helps deaden the noise.
Author:  MtDewMike [ Tue May 24, 2016 1:34 pm ]
Post subject:  Re: Auto Hubs Explained;
Yeah, the noise part makes sense, but wouldn't a little packed grease fix that if it were metal?
Author:  Bklyn.X [ Tue May 24, 2016 2:15 pm ]
Post subject:  Re: Auto Hubs Explained;
You can't put alot of grease in there because it would gum up the cam action it needs to go through to lock/unlock. There should be very little grease in there...synthetic lube w/ptfe works as a lubricant but doesn't help deaden any noise...

It might be over greasing that causes it to break...
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