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23:56:07 - 04/25/2024
Off Road
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jmal
Dodge Dakota
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10/18/2002
20:55:25
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 Subject: '89 4wd problem
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Message:
My '89 Sport's 4 wheel drive is not working again. 3 years ago I had to replace the Shift Motor Assembly attached to the front axle and it worked fine for a while. Now it won’t engage into 4wd at all! I think something is wrong with the vacuum system. I tried replacing the vacuum switch on the transfer case, but that didn’t fix it. Anyone have any thoughts?
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Brent88
Dodge Dakota
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10/23/2002
00:02:22
|  RE: '89 4wd problem
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i think mine has a vacuum problem. it sometimes takes a sec to disengage from 4wd. all i can think of is that it might be the vacume lines. sorry i cant help more
Brent
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Walt Felix
Dodge Dakota
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10/23/2002
10:00:05
|  RE: '89 4wd problem
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This is a common question with early Dakota 4x4s that pops up every couple of months on the various Dakota message boards. It sounds like you already know what the components are, but I’m going to go through them again for those who don’t.
The front axle has a Central Axle Disconnect or CAD. The CAD works sort of like an automatic hub and on early Dakotas works completely by vacuum. There are two vacuum lines that connect to a small round canister on the passengers side of the front axle that looks kind of like two small pie tins pressed together. The other end of the vacuum lines run to a switch on the transfer case. If you look under the truck, you'll find it to the rear of the transfer case on the driver's side of the truck. It will have 4 vacuum lines connected to it. Two lines for the front axle, one from the engine and one to a ball canister connected to the underside of the bed.
1, Check to see if you are getting vacuum to the switch on the transfer case. Unplug the connector with the four vacuum lines and with the engine running, you should have vacuum to one of those four lines. If not, you’ll need to trace the line going to the TB/Carb for a break or leak. If you do have vacuum, continue to the next step.
2, Reconnect the lines to the transfer case switch and disconnect the two vacuum lines from the front axle. With the truck running and in two-wheel drive you should have vacuum to only ONE of these two lines. Make a note of which line has the vacuum, shift the truck into 4Hi and recheck the lines. The vacuum should change to the OTHER line. If it does not, the switch on the transfer case is bad and should be replaced. If I recall correctly, it will cost around $30-$40 at the dealer. It's kind of like an oil pressure-sending unit and will screw into the transfer case. It has a small metal ball on the threaded end and when the transfer case is shifted into 4WD, something inside the transfer case pushes in the metal ball and changes the valve inside the switch unit. If at any point during this step, you don’t have vacuum to either line, check the two lines, from the transfer case to the front axle, for breaks. If the vacuum does change from one line to the other, the actuator on the axle is stuck. Like I said earlier, this is very common. You can try to loosen it up by spraying some WD40 into each vacuum tube the lines connect to. Don't be shy, really try to flush the crud out of it with the spray. Reconnect the lines and drive the truck forward shifting in and out of 4WD. Repeat the process rolling backwards. If it doesn't come loose, you will have to replace the actuator. Once it is working, repeat the flushing process about once every six months to prevent it from happening again.
Also, sometimes when in 4WD, if you shift back into 2WD, the front actuator will stick. Usually happens in cold weather. The transfer case will be in 2WD but the CAD is still locked and the 4WD light will stay on. Shift the truck into reverse and back up about 15-20 feet. That will usually pop it loose when stuck locked.
Walt Felix
Walt@Walt-n-Ingrid.COM
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President – Mopars in Motion Ltd.
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