olwhitey

well i just put a new clutch in couple weeks ago. The problem i have now is my truck wont kick into 4wd. i read somewhere that there is something on the front axle that has to engage as well as the transfer case. there is a couple of lines going to the front axle from the tcase, guessing it has something to do with the engagement. anybody have any ideas what could be keeping it from kicking in?

JAX

These trucks have a Center Axle Disconnect system that is vacuum operated. The long side axle is actually a 2 piece shaft (someone correct me if I am wrong here) and there is a splined coupler that is always on one of the shafts. When you shift into 4wd, the coupler slides over the other tube via the vacuum module that has the lines coming to it from the t-case. This locks the two shafts together. A popular upgrade is going with a "Posi-Lock" system which replaces the vacuum model with a cable actuated device. You run the cable into the cab and switch into 4wd that way. This gives you the added benefit of 2wd low range as well. Another option (and much more expensive) is to convert your front end to a locking hub style axle with serviceable wheel bearings (the way our trucks all used to be) like the kit from Dynatrac. This also gives you a 2wd low range, and supposedly a slight gain in fuel mileage. I think if I could afford it, I'd switch over to locking hubs just to get rid of these junk unit bearings.

Dinner

Did you hook up all the vacuum lines back on top of the transfer case?

You could also start the truck, having the truck in Neutral, E-Brake on and in 2wd hi. Climb underneath and disconnect vacuum line plug that is attached to the CAD (the actuator) on the front axle by those little snap rings. Now in 2wd Hi, you should have vacuum through the RED line. Climb back up, switch the transfer case to 4wd hi or low (doesn't matter) and climb back under. You should now have vacuum on the BLACK line. If you do not have vacuum on one, the other, or both. I would disconnect the lines where plastic/rubber fittings meet the steel on the Transfer Case/Tranny Cross Member. If you have good strong vacuum there when disconnected. Take shop air and slightly pressurize the red and black lines (have them still disconnected from the CAD) and check for leaks. If there is any, fix them and try your 4wd.

If you still don't have vacuum at the fittings where plastic meets the steel. I would trace all vacuum lines leading from the pump to the top of the T-Case. Or it also could be the CAD itself is faulty if you have vacuum on both the red and black lines.

This is also why sometimes your truck will be in 4wd, however the light isn't on. This is usually caused by weak vacuum on the Black Line side or dieing CAD. With the Vacuum, there is enough vacuum to pull the fork and collar over onto the second shaft. But there isn't enough to pull it over all the way to illuminate the dash light. With the CAD, it's just due to wear and tear.

olwhitey

thanks for the ideas. is the CAD something i can replace or is it better to go ahead and do that posilock cable thing if it needs replacing? ill go down later and check the lines like said. b4 i did th clutch, my 4x4 light would flicker on and off. could this b because of weak vaccum and it barely pulling over enough to turn it on?

and yea i connected the lines on top of the tcase. although i dont think they are on all the way and maybe not sealing well.

Dinner

The CAD can be replaced, it is held onto the front axle by 4 Bolts, however I believe it is around $100 if I remember right. It is very easy to replace, its just the cost of it. That's why you want to make sure you have good vacuum at both red and black lines before you replace the CAD.

The 4wd light flickering tells me that either it is weak vacuum, or the CAD is faulty. The fork has to be all the way over in 4wd mode in order to "trip" the 4wd light on. If it is a little bit off, the 4wd light could flicker because it is not making 100% contact on the points.

I'm not sure how the Posi Lock Cable system works, but I'm assuming it is mostly a PTO style cable that you run down to your axle from a lever inside the cab. I'm not sure if this keeps the old 4wd light in operating condition or if you have to wire in your own switch and light.

sheriffav8r

Here's what I did after replacing the actual CAD (about $100):

https://www.dieseltruckresource.com/...d.php?t=198399

The heart is www.grainger.com part 6jj43 for $41.
Tee off of your main vacuum line (I used drip sprinkler connectors) and run a vacuum line down to the axle. I mounted my solenoid in a plastic box just above the axle to keep grime out of the components. A lighted red covered spst switch is mounted on the transfer lever cover. The vacuum is run to the normally open side of the solenoid and continues to the open side of the CAD (right). Once power is applied to the solenoid it transfers vacuum to the closed side of the CAD (left) to engage 4WD. So far this has been pretty bulletproof and I am happy with the ability to have 2WD LO and engage 4WD whenever I want to.