Skool me on the vacuum CAD system - Page 2 - JeepForum.com
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post #16 of 22 Old 10-16-2020, 12:03 PM
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So then why do you need those two tees and the check valve at all?
That's a good point. Without the check valve the vacuum might dissipate slowly, and the check valve lets it backflow quickly. If that's what you meant by dump the vacuum, then I agree with you. But I think the primary purpose of the check valve is to prevent the lamp from illuminating until the CAD shift has actually happened.


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post #17 of 22 Old 10-16-2020, 12:52 PM Thread Starter
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So today I observed what at first glance seems odd behavior. I was testing the vacuum motor and connections.

I disconnected the vacuum harness from the vacuum actuator, ran manifold vacuum directly to the center (yellow or apply) fitting on the vacuum motor, and jacked up the right front (passenger) wheel off the ground. I started the engine, put the transmission and transfer cases into neutral, and tried to turn the right front by hand.

I expected to see the front driveshaft turn. Instead, I could not turn the wheel in either direction.

With both front wheels off the ground, the driver's side wheel rotated backwards with the passenger's side wheel being spun forwards, with the driveshaft stationary, as one would expect.

Why couldn't I spin the passenger front wheel with only it off the ground? Was my transfer case somehow not in neutral (it must have been, because with the engine running I could shift the transmission into gear without anything engaging). Could this front axle have a locker (I've never looked inside but nothing has ever made me think there was - and if there was, both fronts would have turned in the same direction along with the driveshaft)?

Can anyone help explain?
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post #18 of 22 Old 10-16-2020, 01:19 PM
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...ran manifold vacuum directly to the center (yellow or apply) fitting on the vacuum motor, and jacked up the right front (passenger) wheel off the ground. I started the engine, put the transmission and transfer cases into neutral, and tried to turn the right front by hand.
I think this is because neutral in the stock TC does not disconnect the front and rear outputs. Unless you have installed a true neutral plate. True neutral did not start until the TJ came out.

Also, the fact that the opposite wheel turned in the opposite direction means you do not have a front locker.

Bill

1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #19 of 22 Old 10-16-2020, 01:29 PM Thread Starter
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I think this is because neutral in the stock TC does not disconnect the front and rear outputs. Unless you have installed a true neutral plate. True neutral did not start until the TJ came out.
You are correct; I forgot about that!

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Also, the fact that the opposite wheel turned in the opposite direction means you do not have a front locker.
Yes, agreed. But was hoping there for a moment.
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post #20 of 22 Old 10-16-2020, 01:46 PM
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I make this vid a few years ago. Mostly for my own future reference. It's a little different than the way you are testing, but I think it still demonstrates what you are seeing. If you consider that as far as the TC goes, being in neutral is the same as being in 4WD, when the TC has the stock mode plate.


I've added the true neutral mode plate to mine now, but at the time of that video I did not yet have it.

Bill

1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #21 of 22 Old 10-16-2020, 05:00 PM Thread Starter
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Originally Posted by bpounds View Post
I make this vid a few years ago. Mostly for my own future reference. It's a little different than the way you are testing, but I think it still demonstrates what you are seeing. If you consider that as far as the TC goes, being in neutral is the same as being in 4WD, when the TC has the stock mode plate.

https://www.youtube.com/watch?v=5V4Fzb_fKck&t=3s

I've added the true neutral mode plate to mine now, but at the time of that video I did not yet have it.
Very good video, thanks.

What are the two switches / doohickeys on the dash?
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post #22 of 22 Old 10-16-2020, 07:03 PM
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Proclip mounts for phone and GPS.

Bill

1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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