most common problem with 4x4 vacuum acuator system?

GreggNoble · 11-04-2009, 12:12 PM

hi, guys, i have lots of vacuum comin out of the pump but when i remove the hose from the pump and suck on it the suction doesn`t hold ,so i guess i got a leak but i filled the whole line system with light oil thinking the oil would show me the leak but an hour later i still can`t find it.
Just wondering if there is a popular location where the leak occures and is it possible that the leak is in the acuator itself therefore oil wouldn`t work to find the leak. we have had snow already here in Newfoundland canada and i got to get my 4wd working
i`m considering the cable system for the acuator,but 1,d like to know how big a job it is to install where accually on the acuator does it hook up? thanks

SSolderitch · 11-04-2009, 05:53 PM

The transfer case has the vacuum switch on top of it. That switch turns on the cad axle.

I had found the transfer case filter/breather behind the valve cover and it was pluged. It is for the transfer case but [/color]it is wye into that vacuum switch. It must alow vacuum/pressure to vent when the switch cycles. May prevent the switch from fully opening or closing?
I ran no filter for 1 week, then bought a small 1/4" fuel filter from NAPA for $3

test procedure: vacuum pump working? - heater controls ok? vacuum going to tcase switch? vacuum comming out the 2 lines from tcase switch? my guess is 1 for cad engaged (4x4) and the other for 4x2. Good connection to test is above the skid pan, I saw rubber boots. TEST SWITCH. then if ok move to front axle, test lines. test cad.

If the cad moves it will turn on the 4x4 light. Do you have a light? Test the light with a jumper in the plug, because many have had broken wires & NO LIGHT. Must Confirm a working light.

GreggNoble · 11-04-2009, 07:53 PM

Thanks for that. my heater controlls &cruise controll works fine but the actuator wont move. i also have a 2001 3500 flat deck and when i such on the hose that goes to the vacuum pump on that truck the suction stays there but on the 2500 it will leak off.
does it need a lot of suction to move the collar and lock the axle?
does the collar ever stick? or the gear too coarse to mesh right away?

Extreme1 · 11-05-2009, 02:54 AM

Your vacuum leak is the problem. Start at the top and work your way down as described above or at the bottom and work up. Mine had leaky hoses between the T-case and the actuator. I drove it for a couple years with it occaisionaly popping out of 4X4. That wrecks the splines on the axle shafts and then they don't work with good vacuum.

Just about anything can be the problem, start testing at one end and work your way to the other.

GreggNoble · 11-05-2009, 12:05 PM

thanks guys,i noticed that none off you gave up on the stock system and went with the cable system,does it have it problems too?

SSolderitch · 11-05-2009, 05:41 PM

My stock set up works ok, only had a 4x4 light issue with a broken wire. CAD actuators are on ebay for $65 if I remember corectly. Plug the lines at the cad and see if vacuum is ok...probably a bad diaphragm. pull the unit check fork,collar,etc.

JMcCoy · 11-10-2009, 06:10 PM

I pulled my cad and it was full of water. Probably could be drained and reused. I just replaced it. I about 9 yrs later I sucked water in the system and lost 4wd. By the time I got pulled out, I sunk into the Florida Muck. Water then intruded the transmission via a B&M trannny plug kit (garbage). That cost me a tranny. It also gave me an excuse to get an ATS tranny

Do yourself a favor. Get rid of the CAD and get the Posi-lok cable. I did and it is great. Hope this helps

Extreme1 · 11-11-2009, 01:45 AM

Quote:

Originally Posted by JMcCoy

B&M trannny plug kit (garbage).

I agree. I put one in my Trans Am pan and it leaked right away. Still does. Now I just weld a 1/2-20 jam nut to the inside and install a NAPA drain plug. No leaks. That what the T/A will get next time it's apart.

GreggNoble · 11-11-2009, 02:08 PM

One off the reasons this is such a problem is that the bolts that keep the whole unit on the front axle are twisted off and once i break the seal and take it off will i ever get it to stop leaking ,and its a big job to drill out those broken small bolts.
i don`t know how the cable works but i assume that you have to dissassemble the complete vacuum system from the axle.

JMcCoy · 11-12-2009, 02:42 AM

Purchase the cable system. If the bolts are stripped or broken, addrss it. Drilling and tapping is not that hard. Just do it. You will be glad you did.

(This was a motivational speach)

DieselDoghouse · 11-16-2009, 12:49 AM

Water in CAD?? see posts RE: replumbing and moving vent up to firewall. I know it sounds like witchcraft but no system intended to siphon relief air in should be positioned less than 2 feet off the roadway!! Knock wood Mine is working great for quite a while—my vent is at the firewall/hood gasket… if I'm taking water there I have BIGGER problems!!

JMcCoy · 11-16-2009, 10:55 AM

The problem is not the vent tube. It's the low quality vacuum connections: at the CAD, the transfer case, the pump, and everwhere in between. All you need is a pin hole(since it's vacuum you will never find) from dry-rot, lack of clamps, or any other means it wil fill with water. There is no way around it; the vacuum CAD is junk. The cable will at least make a bad thing acceptable for "mild" off road use. If your a pavement pounder, keep the vacuum system.