4WD not working. Why?

[Thomas DeBusk]

My front axle won't come in for 4WD. It's an '83 Wag with the underdash 2WD-4WD switch.

Is this a common malady? If so, what's the usual problem? I might get under the vehicle over the weekend.

If it's the vacuum switch on the axle, is it possible to rebuild it? Is there such thing as a kit, or do I just have to get the whole assembly? Is it worthwhile to use a used one?

Thomas

[El Gordo]

This is SelecTrac, correct? The first thing I would check would be the three small vacuum lines that come from the switch through the firewall. There should be a red one, a green one, and a yellow one. They can often become brittle and break spontaneousley. If not that, I don't know. It could be a mechanical problem.

[arter]

The vacuum motor shaft was frozen when I got the 87 GW, prolly lack of use. Dealer only, about $150. Might check the lines and put some vacuum to the vac motor and see if it works.

[Millerluck]

What kind of shape are your vac lines under the hood? Did a Previous Owner (PO) hack things up and go a bit to far and undo the lines to the 4wd?

I had a line simply fall off the cofee can vacuum canister before that kept it from shifting into 4wd.

Start with the cheap stuff first. Vac. lines.

You should be able to see if the transfer case is shifting by crawling under and see if shaft moves in and out when the switch is moved. Try and work it in and out and spray it with solvant if its froze up.

Some times I need to rev the engine up and take my foot off the gas real fast to boost the vacuum when the throttle plates snap shut.

Later

Larry Miller

[Crazy_Jeepman]

Test the front axle, to see if it is a bad shifter motor or a Vacuum line. Jack front drivers wheel off ground, and block, start engine, leave in park, put selector to 4 wheel drive try to rotate the tire by hand if it rotates it is not engaged at the axle, if it does not rotate it is engaged and the problem will be the transfer-case not being in 4 wheel drive. If it does rotate unplug lines off Vacuum motor, connect Vacuum pump to shift motor, pump it up, rotate wheel to see if it engages the diff, I forget what connection you hook too to get it to engage, try them all. After pumping the Vacuum pump up, and the wheel does not rotate then the front axle is engaged, this would indicate a bad Vacuum supply, look for a broken line, if after trying all the connections on the Vacuum motor with the Vacuum pump and the axle never engages then the Vacuum motor is bad. ;)

[andy d]

check the steel lines under the right exhaust manifold. the ones on my 83 parted a decade ago. 5$ worth of vacuum hose replaced it perfectly.

[FrankenJeep]

You can also rebuild the vac switch in the cab. Its held together with a pin, and you will need to put a little Vaseline on the wear surfaces. I just fixed the same problem on my 83. It went from holding no vacuum, to holding 15" Hg for over 1 minute.

If you don't already have one, a small vacuum pump (i.e. Mighty Vac) is real helpful for troubleshooting a Selec Trac system.

I jacked my unit up at all four corners and used the Might Vac to engage the axle vacuum motor. Once I verified that worked, I used the Mighty Vac to measure vacuum with the motor running. That showed me the the interior switch wasn't holding vacuum. Once I started digging into that, I realized that all of the vacuum lines had deteriorated. So I went ahead and replaced all the vacuum lines.

After doing all of that, I still wasn't sure the unit was working. I tried the infamous 'mud hole" test, but my face didn't get muddy. I finally verified that everthing was working by holding my rear in the air with a floor jack and engaging 4wd. I could then pull the vehicle foward by the front wheels alone.

Hope this helps ...

Frank

[FrankenJeep]

<blockquote>quote:</font><hr>Originally posted by arter:
The vacuum motor shaft was frozen when I got the 87 GW, prolly lack of use. Dealer only, about $150<hr></blockquote>

Sorry for the second post ... but didn't Dodge use a vac disconnect on the Dana 44 in the early 80's also? Might be a cheaper source. I've also read online that you can replace the vacuum motor with a cable replacement for the Dodge for about the same price. There were also earlier threads that stated that the vacuum motors become stuck with disuse, and can be "exercised" back to working conditions.

Frank

[Panoscopic]

When I got mine, same thing. The fix was as simple as you could imagine - the cotter pin holding the actuation bar from the vacuum motor had fallen of. A .02 fix! The Jeep gods were smiling that day.