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Old 08-10-2012, 06:25 AM   #1
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What is the vacuum tube for?

I noticed this yesterday and was wondering what it's for and if it should be plugged into. It normally hangs down near the firewall
but I propped it against the heater hose for the pic
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1993 YJ "ZORV-1122"
4.0 AX15 4in Rough Country Lift 1.25in Perf. Acc. Shackles, few other things here and there.
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Old 08-10-2012, 06:30 AM   #2
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Quote:
Originally Posted by raycer View Post
I noticed this yesterday and was wondering what it's for and if it should be plugged into. It normally hangs down near the firewall
but I propped it against the heater hose for the pic
Attachment 148922

IF IM NOT WRONG THOSE GO TO YOUR 4X4 AND CARB IF YOU HAVE CARB. MINE WERE ALL REMOVED ONCE I WENT WITH THE POSI LOCK AND WEBBER CARB. I HATE THE VACCUME SYSTEM ON THE YJ'S

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Old 08-10-2012, 06:36 AM   #3
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relief tube

That is the relief tube for the vaccuum shift on the front axle CAD (Central Axle Disconnect). When the vaccuum is switched to engage, or disengage the other side needs to have a relief so it can compress. That is what provides the relief. That is all switched on the side of the transfer case. 4 vaccuum lines into the switch, 1 for vaccuum, 2 to go to the CAD (1 for each side of the diaphram) and one for relief when it switches.
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Old 08-10-2012, 09:18 AM   #4
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That is the vent line for the CAD switch. It is exactly where it's supposed to be, dangling by the battery.
Edit: ballistx, you beat me to it, my phone app is being dumb this morning
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Old 08-10-2012, 09:19 AM   #5
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OK cool. Thanks guys
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1993 YJ "ZORV-1122"
4.0 AX15 4in Rough Country Lift 1.25in Perf. Acc. Shackles, few other things here and there.
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Old 08-10-2012, 09:20 AM   #6
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In my opinion I would get a posi lock. Those lines crack soon and leak. Then your 4x4 won't engage.
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Old 08-10-2012, 10:13 AM   #7
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Hah, I've gotta go and look in my engine bay for that line. I found one of those cut off and under the drivers seat.

Would 4x4 work if that line was cut off?
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Old 08-10-2012, 12:20 PM   #8
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In my opinion I would get a posi lock. Those lines crack soon and leak. Then your 4x4 won't engage.
Well, I already did the CAD bypass mod
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Old 08-10-2012, 01:59 PM   #9
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Well, I already did the CAD bypass mod
Den why you gots useless chit still hangin around under da hood??
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Old 08-10-2012, 03:10 PM   #10
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Gut it out maaan
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Old 02-21-2013, 01:28 PM   #11
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  1. Raise and support the vehicle safely.
  2. Disconnect the vacuum harness and connect a hand vacuum pump to the front port. Apply 15 in. Hg (381mm Hg) of vacuum to the front port and rotate the right front wheel to fully disengage axle shafts.
  3. The shift motor should maintain the vacuum applied to the front port for a minimum of 30 seconds. If the motor does not maintain the vacuum, replace it. If the motor does maintain vacuum go to Step 4.
  4. Connect the vacuum pump to the rear port. Cap the port for the indicator lamp switch and apply 15 in. Hg (381mm Hg).
  5. The shift motor should maintain the vacuum applied to the rear port for a minimum of 30 seconds. If the motor does not maintain the vacuum, replace it. If the motor does maintain vacuum go to Step 6.
  6. Remove the cap from the port for the indicator lamp switch and determine if vacuum is present. If present, the shift motor is functioning properly. If not, proceed to Step 7.
  7. Apply 15 in. Hg (381mm Hg) of vacuum to the shift motor rear port. Rotate the right front wheel to engage the axle shafts. The axles must be completely engaged!
  1. Determine if vacuum is present at the port for the indicator lamp switch. If present, the shift motor is functioning properly. If not, replace the shift motor.
  2. Fig. 1: Command-Trac® vacuum control system
  1. Fig. 2: Command-Trac® vacuum axle shift motor

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