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CAD Vacuum

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Anyone know how to test the vaccuum for the CAD 4x4 axle. Specifically - not sure if I have a problem with the CAD itself - or vacuum isn't correct on the two lines (red and black). Is there an easy way to test a) There is vacummb) Its the correct vaccum pressure I suspect my main issue is the actuator/thing on top of the transfer case - as it was pretty dirty when I reinstalled my tranny - so I cleaned out as best I could. Just want to know what I could do to test each component - before I go out and buy a posilok. :thumbup2: thanks

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  • Owner

Well the best I can say is pull both lines at the CAD unit and test for vacuum on both lines in both position 2WD and 4WD. As for after that the only thing I can say is to jack up the front axle (and use jackstands) and lock it into 4WD. Don't put the main trans in gear! But you should be able to tell because either the front wheel will turn free or the front driveshaft will turn with the tires.

  • Author

Well the best I can say is pull both lines at the CAD unit and test for vacuum on both lines in both position 2WD and 4WD. As for after that the only thing I can say is to jack up the front axle (and use jackstands) and lock it into 4WD. Don't put the main trans in gear! But you should be able to tell because either the front wheel will turn free or the front driveshaft will turn with the tires.

thanks man - yeah I was wondering on details of the vacuum system here. eg At what point do the lines have a vacuum - as you engaged only ? all the time ?? both lines or just 1 ?? And how to test vacuum ? Just by feel or is there a guage for vacuum etc ? :shrug:

Have you followed your diagram down to the accuator on the transfer case? if so attach a vacuum hose and draw on it like a straw,if you have resistance on both ports diafram is ok.

  • Author

So couple questions here1) 4 vacuum lines, white, green, red and black.Red and Black used to the CAD.White and Green go to the back actuator on top of XFER case.What are the white and green vacuum lines for ??? 2) Green vacuum line looks like its capped off at the end ? Its not attached to the "T-LINE" that runs along the firewall. The white-one is however. Normal ? 3) Do all 4 lines have vacuum all the time ??? Or only when 4x4 engaged etc ??

One of the two lines on the cad will always have vacuum. One will pull it to 2wd and hold it there and the other will pull it to 4 wd and hold it there. On the t-case there will be the main vacuum line from the pump and 2 going to the cad and the 4th would be a vent if I remember right.

  • Author

Ok - good to knwo that there will always be vacuum in one of the red/black lines depending on which axles emgaged (2WD/4WD). Was reading the FSM page 24-12 - it talks about the vacuum diagram and wire colors - but I think this must be for HVAC only - as there is no white vacuum line - and I definately havea whte line connecting the vacuum at the firewall to the XFER case. Might have to buy a cheap vacuum gauge to play around and see if I have enough vacuum in each line. Damn hard to get to that sensor/actuator thing on top of the XFER case though.

if you had a vacuum brake bleeder, you could pull you own vacuum on the CAD shifter to see if it moves. i use mine for more than bleeding brakes! i filled my front pumpkin up with it the other day because someone gave me oil that was in a one gallon jug.

Save yourself the headache and just buy a posi-lok!

You can suck on the CAD unit to tell if it is working okay. As for the vacuum lines, I'm not sure which does what, but I'm sure if you started the truck up and got under it, you could tell if you are getting vac like you should.:thumbup2:What is it doing anyway?:shrug:

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