sheriffav8r

My 4WD light hasn't been lighting when in 4WD. I checked the indicator plug and the light goes on when it is depressed. The collar and fork work smoothly and the vacuum motor plunger moves freely and stops when I plug one of the vacuum holes. I think the fork isn't pushing the collar all the way to the left when it is shifted into 4WD. Do vacuum motors go bad or is there an easy way to test if it is a vacuum line problem? All of my other vacuum stuff works so I don't think it is the vacuum pump. I'm kinda stumped as to what to try next....

Dartmouth 12V

It is quite common for the vacuum lines to get damaged or pulled off. The CAD can go bad if the diaphram in it wears out which happens.

So are you getting 4wd?

izzwardo

How are the replacable tabs on the fork? When I was having 4wd problems, I looked at the fork and one of the tabs on the fork wore away. So when I was engaging 4wd, the remaining tab on the other side was hitting the collar and bending the shaft that came out of the vacuum motor. It was hard to see, but I could tell that the shaft was bent. So I had to replace the vacuum motor. Everything works fine now. If you can, take the vacuum motor out and inspect the shaft where the fork is attatched to and see if it is bent at all. If it is, it might not be engaging 4wd all the way.

sheriffav8r

I am getting into 4WD, but if I turn on asphalt it clunks and pops out of it for a second. I guess that is just the collar sliding back to the right under torque. The replaceable tabs looked fine and everything slides very smoothly. I'll check the vacuum motor itself next. Any idea how much they cost and where to get one besides the dealer?

justme-

that motor from the dealer when I priced it was around $400. They're available after market for WAY less. I have a site saved on my work computer with a good price- can't remember the name tho. I ran for over a year with the trail fix (reversing the fork on the motor rod) engaged until I finally sprung for the cable lock instead. I might just go back to vacuum next year (before anyone asks how I like it)
BTW replace the shift fork pads while you're in there- for the $1.00 or so they cost, it's cheap insurance.
If the collar pops off on pavement in 4WD the vacuum motor probably isn't pushing the collar all the way over.

sheriffav8r

I'd like to check the vacuum lines before I buy a new vacuum motor, but it sounds like the motor just isn't pushing the fork all the way over. With it popping out of 4WD on pavement and the 4WD light not coming on, I think that may be my problem. Is it possible to hook up a stronger vacuum source to the motor to check it? Which line engages it, black or red?

justme-

Stronger source- sure a mighty vac hand pump. There is no stronger on board source. I'm not sure which is which- mine was seized solid when I pulled it.

Also, there is a vacuum switch on the top of the t-case- the vac hoses go to it and it sends vac to the axle. They are known for sticking. You may want to pull it and make sure the ball is free (you'll understand when you see it.) If it's sticking it may not be letting full vac through.

z28clone

My light isnt coming on either. I have vacuum off the engine, im getting vaccum pressure between the lines. I changed the vacuum switch as well. When i hook a vacuum pump to the CAD, i can get the 4wd light to come on, and if i move it to the other nozzle on the cad, i can get it to shut off. Ok, with these symptoms, what could be my problem? do i still have a vcauum leak somewhere? In my case, Does the light indicate that there is vacuum, or when it is engaged? Truck still drives like its in 2wd, and when shifted in 4wd, front driveshaft is engaged.

sheriffav8r

z28clone,
How much vacuum are you getting out of your red and black hoses at the CAD motor? I know you should have vacuum at one line all the time (either 4WD engaged or disengaged, depending on the shift lever). It sounds like you might have the "engage" vacuum not working which may be the transfer case vacuum switch shown here: http://www.1aauto.com/1A/4WDrive/Dod...WA00005/651282
The vacuum motor is here: http://www.1aauto.com/1A/4WDrive/Dod...WA00007/659453