97 1500 4WD wont work.

Hi everybody. My name is Luke and I am new to the forum. I need help saving the first truck I have ever driven.

The 4WD wont engage I believe this is a vacuum issue, but am not sure. One of the vacuum lines got a hole burnt into it because it was touching the catalatic converter. My dad fixed that by putting a piece of vacuum hose on it, and that did the trick. But now it wont engage, and that was once promised to me maybe heading for the junkyard.

If I can fix it he will keep it. Please help. Thank you for reading this, and your response.

Of that vacuum hose is in good shape.

Did the 4WD work before?

A quick test is to put it in 4WD and try to turn the front driveshaft by hand. If it turns there is an issue in the transfer case. If not, and the front axle wont engage, you need to inspect the vacuum line coming from the differential all the way up to the intake manifold.

The plastic lines like to get brittle and crack over time.

Why would he get rid of it just because the 4WD doesn't work? Seems like a waste of a perfectly good 2WD truck to me. Thats all most cars are, its all my truck is and I get by just fine in Michigan.

dudeman2009 said:

Did the 4WD work before?

A quick test is to put it in 4WD and try to turn the front driveshaft by hand. If it turns there is an issue in the transfer case. If not, and the front axle wont engage, you need to inspect the vacuum line coming from the differential all the way up to the intake manifold.

The plastic lines like to get brittle and crack over time.

Why would he get rid of it just because the 4WD doesn't work? Seems like a waste of a perfectly good 2WD truck to me. Thats all most cars are, its all my truck is and I get by just fine in Michigan.

Click to expand...

Thanks for the info dudeman. I will give that a try in the morning, and will keep you posted.

He wants to get rid of it because he bought a 03 f150 that also has 4wd problems, but I'm not worried about that truck.

Good luck, fords have those stupid vacuum actuated hubs.

dudeman2009 said:

Did the 4WD work before?

A quick test is to put it in 4WD and try to turn the front driveshaft by hand. If it turns there is an issue in the transfer case. If not, and the front axle wont engage, you need to inspect the vacuum line coming from the differential all the way up to the intake manifold.

The plastic lines like to get brittle and crack over time.

Why would he get rid of it just because the 4WD doesn't work? Seems like a waste of a perfectly good 2WD truck to me. Thats all most cars are, its all my truck is and I get by just fine in Michigan.

Click to expand...

Ok I finally got around testing the lines with a vacuum pump. Tested right around 20, and I believe that's good. Truck went into 4wd, and then would not come out. Did some investigation and found my vacuum valve on the transfer case was shot, and Replaced it. Now it comes in and out of 4wd, but seems to take longer then it use to.

Ah, don't even get me started on that mother****er vacuum switch on the transfer case. I threw everything I had at that sucker and even with a foot plus wrench I couldn't budge the thing. I ended up just buying a 4x4 Posi Lok kit since I was contemplating getting one for a while anyway. Now that switch can keep it's happy ass in the transfer case until the end of time for all I care, LOL.

Without going into too much detail, the Center Axle Disconnect, irregardless of actuation (vacuum or mechanical) requires that the splines on the inner and outer axle shafts are perfectly aligned before the collar will slide over the outer shaft and allow power transfer. This often requires that the truck moves a few inches or even feet after shifting into 4wd before the front axle will engage. What sucks about this is if you're totally stuck in 2wd and can't move at all, you better pray that the axle shafts are aligned as you sit. As I've learned the hard with my Posi Lok, if the rear wheels have no traction, as soon as the shift collar touches the outer axle, the "loose" torque causes the collar to spin and grind against the shaft instead of sliding over it. It's identical to a manual transmission that's kind of in gear but not firmly; the selector is contacting the input gear but isn't firmly engaged and just spins against it.

If you wanna make it pretty much foolproof, you can permanently engage the axle in about 10-15 minutes with a 1/2" socket/ratchet and a metal pick tool.

Get it engaged in 4wd then shut the truck off and pull the cad cover, the housing where the vacuum lines run. When you pull it off the collar will be engaged, you can do this manually I'd the 4x4 isn't working but it's easier to get it engaged first if you can. The fork has 2 little e-clips that hold it in place. With the cover off, move the fork to where you can pull the driverside e-clip using the pick. Slide the fork past that clip and reinstall clip. Bolt housing cover back in with the fork engaged in the collar.

Fork won't move in either direction after doing this, staying permanently engaged.

If you're worried about extra wear/mileage from this, the 02+ 3/4-1 ton trucks and 96+ jeeps run a full solid shaft and I've converted mine to solid shaft as well. No differences.

Or you can always do the posi-lok or maintain the factory system. They're all fairly reliable for the most part and all are easy to work on. Good luck on that **** vacuum hub design on the ford lol