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4x4 vacuum lines

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Old 12-17-2010, 01:18 AM
junkyarddogfan junkyarddogfan is offline
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Default 4x4 vacuum lines

hya;

does anyone have a diagram that shows where the vacuum lines go between the cad, the transfer case, and wherever else they go on a '97 ram 1/2t 4x4...
i believe i have a small vacuum leak somewhere and while i can trace most of them underneath the vehicle, i have a feeling someplace on the firewall a vacuum line goes thru it to someplace under the dash...

thanks for the help and info.

have a great day!
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Old 12-17-2010, 10:25 AM
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Lines on for the front axle go to steel lines on the frame, over to the crossmember for the t-case. From there, they are soft lines again to the switch on the t-case. Two lines go up from there, one is just a vent line, the other is source vacuum, and goes to the bag of snakes on the passenger side rear of the motor. A selection of lines come together there. One does indeed go into the dash, for vent controls, another goes up under the cowl to the vacuum reservoir. There is yet another line that goes from the throtle body, over to the cruise module, at the front of the motor. (follows the cable from the cruise module) If you have cruise...

Steel lines like to rust out.
Source line likes to lean against the exhaust manifold, and burn itself.
Lots of hard plastic lines get brittle with age, and break easily.

There really aren't that many lines under there.... some of them are just rather fun to follow.
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Old 12-19-2010, 07:45 PM
junkyarddogfan junkyarddogfan is offline
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ok...here's an update with new questions...
first off, for understanding purposes, my test area is a commercially zoned lot about 3/4 mile long and gravel...and i have previously replaced the CAD ($119), the light sender on the CAD ($7), and the pressure switch on the transfer case ($12)...also purchased new(used) harness for the 4wd from CAD to pressure switch minus hard lines from a dodge truck only salvage yard...

as it was 50 today, and since the reply suggested looking at the cruise control vacuum lines, i did..of the 3' of plastic line that goes from the vacuum port to the cruise control pod, not even 1" of it was good...all was either cracked or had holes in it...i replaced with 3' of rubber line and tested vehicle...no 4wd but engine idled much better obviously.

replaced the harness from the CAD to the hard lines and tested truck...no 4wd.

changed out the pressure switch to the old one and tested vehicle. no 4wd.

replaced pressure switch...unhooked cruise control vacuum from port and tested vehicle...no 4wd.

removed all vacuum lines from said port minus the one for 4wd harness...
just below this port was another that was rubber capped off, un-capped it, and ran all rubber lines taken off 4wd harness port to that port and tested vehicle...success! tested vehicle in both 4hi and 4lo...dis-engaging, driving, then re-engaging..4wd engagement worked flawlessly.

now, that port was supplying vacuum to the 4wd harness, as well as the cruise control canister and (2) small plastic lines that go back thru the firewall...all on the pass side...

since i removed those lines from the 4wd harness port and the 4wd engagement works flawlessly...and since i replaced the plastic line from the cruise canister to the port with new rubber line...i must assume the problem is with the (2) smaller lines that go into the firewall...

my question is...what do those (2) small plastic lines operate?

now, last spring heat, defrost, etc..all controls on heater/vent worked great...when ac was in use, if i accelerated HARD, the ac would quit cooling until i quit accelerating hard, then it would again blow cold...i had ac system checked and freon was up to snuff, so i passed it off as a bad hi-pressure switch...is it possible (1) of those plastic lines runs to a vacuum canister for the ac under the dash?

something that went into that port was affecting the engagement/disengagement of the 4wd...any ideas?

thanks.
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Old 12-19-2010, 07:56 PM
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There should be a check valve hiding in there somewhere as well...... just a little round plastic feller. I think though, that if it was installed backwards, your vents wouldn't work either.

The vents switching is indicative of the that valve having failed though. Your A/C works just fine, its just in low vacuum situations, (hard acceleration) your vacuum controled vents, switch back to the default. Which is defrost.

One of the lines from the bag of snakes there goes into the vent controls. Another goes to a vacuum reservoir hidden under the cowl there somewhere. There is also the vacuum source line for the CAD. (which you have obviously found. )

Check if/where you have check valves in the vacuum system, make sure they work, and are installed in the correct orientation.
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Old 12-19-2010, 09:00 PM
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on my 01 there is a vacuum canister under the passenger side cowl. one of those firewall vac lines snakes up there to it. i think the others go into the interior to the heat/ac controls.

the vacuum canister, in partnership with the check valves, is supposed to hold a vac supply for the heat/ac controls
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Old 12-20-2010, 12:32 PM
junkyarddogfan junkyarddogfan is offline
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appreciate the replies guys...i know where the breather is as i still have that 1/2 of the harness i purchased...it ends up being in the distributor area...
i will check all vacuum pods under the dash but i havta believe its one of those or the lines going to them that is bad or has a hole or whatever in it..i remember the guy who sold me the (new)used harness saying something about if its a line going thru the firewall into the dash, that instead of trying to replace it, just drill a new hole and run a new line instead of fighting it...

hey, right now i'm just bouncing off the walls that the 4wd works, lol...
its like...i fixed it, but i dunno how or y what i did worked other than there hasta be another line that was associated originally with that port thats bad and i just placed that trouble spot someplace else.....lol.

again, thanks guys...

one last thing...this is a '96 and has that crazy long bent transfer case shifter on it...the newer ones, ie:2000 up have the nice short one like the older ('73-'82) chevys use to have...
will the 2000-up transfer case shifter assy's retrofit easily where mine is...not worried about hole in floor, just asking if i purchase a used shifter assy from a 2000-up will it go/mount/work where the '96 shifter goes/mounts/works.

thanks again.
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Old 12-20-2010, 01:07 PM
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Shift pattern changed in 98, so, not sure if the T-case changed... or just the linkage.
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Old 12-20-2010, 01:07 PM
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