1998 Dodge Ram 1500 5.9 Vacuum Diagram
1998 Dodge Ram 1500 5.9L 4WD Vacuum Lines
11-22-2013, 08:48 PM
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1998 Dodge Ram 1500 5.9L 4WD Vacuum Lines
Help. My 4WD is not working. The front drive shaft turns when the 4WD is engaged but the hubs are not locking. I have replaced the actuator. That didn't fix it so I started checking (rechecking) vacuum lines. I discovered that part of the line going from the engine to the transfer case was missing. In fact the vacuum tube for the 4WD from the port off the engine was also unplugged. Earlier I had a shop change my spark plugs and wiring harness; my guess is that they unplugged the vacuum hose and may have cut the smaller line leading down to the transfer case. So I bought the wiring harness from the dealer and replaced it. And still nothing. I am not sure what to check next. Any help would be greatly appreciated.
11-22-2013, 11:40 PM
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Well, I have been looking at other post. I have not changed the transfer case switch. I will change that and hopefully that was the problem, among others. Basically I will have switched everything out after that. I will let everyone knows how it goes. But if that doesn't work I think I am going to install the posi-lock system. The vacuum system seems to have way too many points of failure.
11-23-2013, 06:13 AM
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11-23-2013, 09:07 AM
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have a look at the steel lines that go from the trans cross member, down to the axle. those tend to rot out and leak. a quick and easy fix is to buy a roll or brake line, and put new lines in. takes about 10 minutes.
11-23-2013, 11:20 AM
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treat the vacuum lines like water. if the result is not correct at the end point (cad), then either start at the source and follow it forward step by step, or start and the end (cad) and follow it backwards.
prove you have vac at the engine.
prove you have vac at the t-case.
remove the vac switch from the t-case and test it. note the 4 ports and the keyed connector. it can only go one way. one line is input, one is vent. one is 2wd output (inside button not depressed). other is 4wd (button pressed). bench test it. reinstall switch and move to the cad.
as said the steel vac lines along the transmission cross member get torn up. you can replace with anything. brake line, fuel line, copper line, aluminum, rubber hose.
11-23-2013, 01:01 PM
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Thanks. Great advice. I don't think I am getting vacuum to the transfer case switch. I will replace it and I am also cleaning the port off the engine. Thanks again.. great advice. I just got back from the auto store with the switch. Hopefully I will have this figured out and fixed in the next few hours.
11-23-2013, 01:23 PM
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don't just replace it. test for incoming vac and then test that the switch properly switches the vac from 1 output to another.
11-23-2013, 01:47 PM
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Originally Posted by dhvaughan 
don't just replace it. test for incoming vac and then test that the switch properly switches the vac from 1 output to another.
x2
It's a lot cheaper to verify what is missing/not working than to just keep throwing parts at it
Good Luck
11-23-2013, 04:26 PM
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4WD fixed
Thanks all for your help. 4WD is working. There were a few breaks in the vacuum lines and I cleaned the port from the engine. It has some carbon built up inside of it.
11-23-2013, 07:16 PM
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good deal.
Posted by: garden-goodies.blogspot.com
Source: http://dodgeforum.com/forum/2nd-gen-ram-tech/366469-1998-dodge-ram-1500-5-9l-4wd-vacuum-lines.html