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Unread 07-25-2010, 09:59 AM   #1
RikRotorhead
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~ True Neutral Plate ~

There is a common misconception that when you put your YJ transfer case into the neutral position it is in neutral from the engine and axles. Not so.
The front and rear drive shafts are still connected together in neutral, 4 high, and 4 low. The only time the two drive shafts are independent of each other is when the t-case is in 2 wheel drive.
Not a problem at all if you are flat towing and do not have a locker in the front axle.
But lunchbox lockers like the Aussie etc... are engaged by the input from the driveshaft spinning and the torque from it. So flat towing with a lunchbox locker and solid axles is difficult if not impossible.
You either have to disconnect the drive shaft or put it on a trailer.
But there is a solution...

When you pull the 4wd lever in your Jeep it moves a rod that is connected to a shaft that goes into the t-case. That shaft is welded to a plate that selects the mode of the t-case by moving the mode selector forks to different positions along the main output shaft.
In the YJ when you put the t-case in neutral, it does not move the large mode fork to a true neutral position. It moves the front mode fork enough to put the front drive gear between the front planetary gears and disconnects the transmission from the t-case only.
It does not disconnect the front drive shaft from the rear drive shaft. They are still directly connected by the main gear cluster which turns the chain to the front output shaft when you turn the rear drive shaft by flat towing.
The rear drive shaft forcing the chain to turn the front drive shaft causes torque to engage the Aussie locker.
If you were to disconnect the front drive shaft while flat towing the Aussie would never engage because it receives it's input to engage from the front driveshaft input.
So the 'true neutral plate' is a mode plate from a TJ transfer case. It is basically identical to the YJ plate with the exception of a very large dip in the middle that still allows the front gears to find neutral in the planetary gears to disconnect the transmission from the t-case. The dip in the plate allows the main gear shift fork to move to a position where it disengages the chain from the gear cluster and thus the chain does not move the front drive shaft. The front and rear drive shafts become independent of each other in the t-case neutral position.
I have made several of these plates from YJ plates. I purchased one and made a pattern from it. I tested it extensively on my t-case while I had it on my work bench.
You can buy one from Tri-County Gear in Pomona California for $65 plus tax ($72+/-) plus shipping if you are not local. Or, talk to me and save some $$.

This is extra important to know if you have an automatic transmission.

UPDATE/EDIT: The true neutral plate/TJ plate is now available at Summit Racing for $24.95 plus shipping.

Info:
Brand Omix-Ada
Manufacturer's Part Number 18676.32
Part Type
Product Line
Summit Racing Part Number OMX-1867632
UPC 804314030582


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Unread 07-25-2010, 10:30 AM   #2
cubewhiz
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Well put Rik.

Here you can see the difference between the two plates. The one that is rounded is the YJ plate and the one with the dip in it is the TJ plate.

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Unread 07-25-2010, 10:41 AM   #3
UltimatE
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What about 242 transfer cases? Do they have true neutral?
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Unread 07-25-2010, 11:39 AM   #4
Area.3.Fiftyone
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Could one of you guys trace that out and send it to me or upload a scan so I can make my own template?

I've seen this before and want to be able to mod my TC's as well.
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Unread 07-25-2010, 11:57 AM   #5
RatherBeJeeping
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Or do the 2 LO conversion and get the Neutral setting too. I love 2 LO
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Unread 07-25-2010, 02:05 PM   #6
RikRotorhead
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Quote:
Originally Posted by cubewhiz View Post
Well put Rik.

Here you can see the difference between the two plates. The one that is rounded is the YJ plate and the one with the dip in it is the TJ plate.

Thanks for posting that Bob. Saved me the trouble of snapping a pic.
So in the pic you can see the slot in the plate.
That slot controls the front smaller mode fork that engages/disengages the t-case main output shaft to the transmission by a set of two gears in the planetary just behind the t-case input gear. The t-case imput gear drives the planetary gears and when engaged, the planetary drives the main t-case shaft.
The neutral position puts the drive gear on the main t-case shaft between the two drive gears inside the planetary that is driven by the input gear/shaft from the transmission. Between the gears is neutral, either forward or to the rear of the neutral position is the t-case engaged position.
So the slot just engages/disengages the transfer case from the transmission by how it places the smaller gear in the planetary with the smaller forward mode fork.
The chain is still connected to the main ouput shaft, and that output shaft is directly connected to the rear drive shaft, so the front drive shaft will spin because the rear shaft is pushing it.
When you put it in two wheel drive, the rear mode fork lands the sleeve on a single gear that disconnects the front driveshaft. In the picture that is the smallest bump on the lower left corner next to the big dip in the middle.
On the stock plate you can see that the arc is long. Right in the middle of that arc is neutral, but it only moves the front mode fork because of the slot. You can see how the slot does not follow the outer edge.
In the modified plate, the dip allows the large mode fork to move to a position where the sleeve lands between the 2wd and 4 high in a place where the gears spin independently of each other. Now the front yoke is no longer driven by the main shaft at all.
I know it sounds confusing, but when you have it sitting on the work bench and see it in action it all becomes clear as mud.

I don't know what other t-cases it works in. It works in all the 231's. What does the TJ use? The plate is a copy of the TJ one.
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Unread 07-25-2010, 02:09 PM   #7
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The four bumps on the left side are just detents for you to know when you have the t-case in what position and it kinda holds it there. The little metal thing with the spring on it is what travels between the bumps. It's what is behind that large nut that looks like a drain plug on the bottom of the t-case.
The bump on the top right is what tells the vacuum switch that you are in 4wd to illuminate the light on the dash.
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Unread 07-25-2010, 03:01 PM   #8
cubewhiz
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Quote:
Originally Posted by RikRotorhead View Post
The bump on the top right is what tells the vacuum switch that you are in 4wd to illuminate the light on the dash.
I didn't know that. Interesting.
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Unread 07-25-2010, 04:25 PM   #9
Area.3.Fiftyone
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I'll take it that it's a negative on the template then......
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Unread 07-25-2010, 04:32 PM   #10
cubewhiz
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Quote:
Originally Posted by IronMaiden View Post
I'll take it that it's a negative on the template then......
Er, I already have it installed in the Jeep.

If you wanted to come here, take my t-case down, pull it out, trace it, put it back, and reinstall the case, I'd let you.

But I think that is more work than anybody is willing to take on.
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[URL="http://www.jeepforum.com/forum/f12/bobs-build-thread-1081112/"]My Build Thread[/URL]
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Unread 07-25-2010, 04:36 PM   #11
Area.3.Fiftyone
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I was hoping that RikRotorhead would hook me up....

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Unread 07-25-2010, 04:44 PM   #12
RikRotorhead
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Quote:
Originally Posted by IronMaiden View Post
I was hoping that RikRotorhead would hook me up....

I make them and test them in a t-case I have here to make sure they are cut correctly.
If you want I could make you one and test it before shipping. Mine are cheaper than the ones they sell at tri-county gear or the stealership.
I'm not a vendor here, so I can't list them for sale, but iffn' ya' want to PM me we can work something out.
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Unread 07-25-2010, 05:00 PM   #13
Area.3.Fiftyone
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I would rather just make my own.

Time and equipment I have, money I don't. (Divorced, 10 year old daughter, child support, a couple Jeeps, etc.)

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Unread 07-25-2010, 06:18 PM   #14
plym49
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Thank you for posting this. We needed a thread with a single, concise explanation of True Neutral, and now we have it!

Perhaps this thread should be linked in the tech FAQ.
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Unread 07-25-2010, 06:47 PM   #15
YJames90
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Thanks, as I was just reading the flat towing thread this morning. too bad I already did the SYE. If I had only known earlier
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