Engine/Transmission (1994 - 1998) 4x4 not working please help

[CodySanders]

ok i have had many issues with my gearbox as some may have read but now that everything is great with that i have a new issue. after getting truck back i had a bad vibration i couldn't figure out. i pulled about a 14k trailer yesterday and found out the problem. my rear u joint broke they left it loose or lost my bearings andy installed anyway. i put it into 4 low to move it just out of the road (after removing the rear shaft). i have done this a few times before and just enough to get the truck to safety. well this time i heard a loud band and no movement. i got the truck off the road and put in a new u joint on the rear. the vibration is gone now and the truck is running great(no vibration anymore), but i have no 4x4 still. front shaft will spin in 4x4 but does not engage. i have heard a clunk several times before but not had anything break. also my 4x4 light has always worked once in a while never consistently. anyone have a idea or had this happen?

 

[PBJ2500CTD]

Cody,
Time to break into the t-case or take ot to a shop. Sounds like the linkage or shift fork broke.

 

[LVJUNIOR]

I would pull the CAD housing off of the front axel before I tore the transfer case out. It is possible that you had a weak vacuum on the CAD and it barely engaged the splines on the coupler. Then when you added power to the front axle the coupler sliped off of the splines and made the bang.



I'm not saying this is the problem but the cad takes 5 minutes to pull the cover and check in lieu of a couple of hours and a friend to pull the transfer case and open it up.

 

[CodySanders]

i had a little time to drive it today without a trailer. when i engage 4wd and low range 4wd i get low to work and no 4 wheel. i do hear a pop or cluck every 5 feet or so. i am thinking something is not fully engaging? what am i looking for when i pull of the diff cover or what is the cad if that isn't the diff cover? any pictures or a good discription? if my front shaft spins in 4wd wouldn't it be the diff side not engaging?

 

[PBJ2500CTD]

Arrgh... might be the chain... or just pieces-parts floating around inside. That sounds very un-good.

 

[LVJUNIOR]

the CAD is not in the diff cover.



Cad stands for central axel disconnect. the passenger side front axle is actually two pieces. The cad is half way between the rotor and the differential on the back of the passenger side of the front axle tube. It has a vacuum motor that works off of a vacuum signal from the transfer case to move a fork side to side. The fork mates to a slip coupler with internal splines which match the external splines on the axle halves. The internal splines of the coupler are always engaged with one side of the axle. When you shift into 4wd the coupler slides over the unengaged side of the axle to lock the two halves together.



If you have a weak vacuum signal it may not slide all of the way over allowing it to slip (pop) out of engagement. You may also have damaged splines causing it to sip out.



It is very easy to take the CAD housing off. If I remember correctly it is 4 10mm bolts remove them and pull it straight back. Just be carfull putting it back on though. If the fork is not lined up with the coupler when you tighten the bolts up you could bent the fork or the CAD housing.

 

[LVJUNIOR]

if my front shaft spins in 4wd wouldn't it be the diff side not engaging?

Your shaft should spin even in 2wd since the hubs do not unlock like the chevys do the diff is always rotating

 

[Dave M]

Here is a pic of the CAD with the housing off and axles out when I replaced my axle seals. Also a pic of those axles and cad housing laying on ground.

 

[PBJ2500CTD]

i had a little time to drive it today without a trailer. when i engage 4wd and low range 4wd i get low to work and no 4 wheel. --- if my front shaft spins in 4wd wouldn't it be the diff side not engaging?

When you say the front shaft spins, is that when the truck is driven forward, or by having it in 4wd and turning the front shaft by hand? (silly me, I took it to mean the drive shaft would rotate by hand in 4wd) The 4wd light not coming on points more to the switch, CAD, or vacuum leak. I'll have to break out the FSM to see where the light swich is activated from. Update: It appears the switch on the transfer case controls the light as well as vacuum routing.

 

[LVJUNIOR]

The 4wd switch is on the CAD housing. It is activated by pressure from the CAD fork. The wires are vulnerable and can be ripped out by driving through brush

 

[PBJ2500CTD]

The 4wd switch is on the CAD housing. It is activated by pressure from the CAD fork. The wires are vulnerable and can be ripped out by driving through brush

Thanks for filling in my blank brain statement LVJUNIOR.
The transfer case switch is activated when the shift lever is moved from the 2WD position. This switch routes the vacuum signal to the axle shaft vacuum motor, positioning the sleeve to lock the right axle shaft halves , and actuating the 4WD light switch (at the CAD). The axle shaft shift fork and vacuum motor are held in place by e-clips. Maybe an easy fix if one of them let go. Dave M and LVJUNIOR have identified the most likely problem, by symptoms, and easiest fix, too.

 

[Dave M]

I don't know what you mean by E clips but let me tell you what I found when I removed the axles. The fork in the pic connected to the CAD housing has a pad on each side of fork that slips into the groove of the bevelled shift collar. It just pops in or out of the collar but is not clipped on. It is just a tight fit in the groove of the collar that can be pulled and snapped out of the groove.



I talked with Dan at Quad 4x4 and he explined that the vacuum switch always has vacuumn applied whether the axle is in 4x4 or not. When in 2 wd the vacumn pulls the internally splined collar to the right side of CAD (toward the right outer axle and the left intermediate axle is not connected to the right outer axle since the collar is only on the right axle. The collar fits across and is internally splined onto the intermediate and right axles when in 4x4. When in 4wd the CAD vacuumn is applied to the housing so that it shifts the bevelled collar to the left to engage the left intermediate axle while also engaging the right axle. The collar is splined over both axles thereby causing the right wheel to turn while in 4x4.



Dave

 

[LVJUNIOR]

Dave

The e-clips are the little snap rings that hold everything.



Cody,

Did you ever get it all figured out?

 

[PBJ2500CTD]

Dave,
I believe the clips are shown in Figure 61 of the 1998 FSM - Front axle section. There should be 2 small e-clips for the shift fork and one large one to retain the vacuum motor. I don't have an IPB for the 98. When I look into the 02 IPB it shows some indiscript circular band item that is termed snap ring. Anyway they are clipped in by some device that may have evolved over the model years. The vacuum motor is a push-pull device as Dan described. This is to insure the positive engagement and disengagement of the sleeve.

 

[CodySanders]

sorry i haven't been able to respond to you guys. i have a school fund-raising business for work and right now it is very busy cause all schools do a sale in the fall. i won't be able to look at this till the weekend (i am working two crews and about 16 hrs a day). i am of the opinion that is is the vacuum line to the cad and the fork is just barley hooking in and then pops back out. i will pull it apart this weekend and see. thanks for the help. i will post what i find on sat.

 

[Dave M]

The shifts forks have pads that snap onto the collar. If the pads are worn it may cause it to slip out of the collar. Also the bevelled collar could be worn also. I suspect it is just a vacuumn problem.



The parts can be ordered from Home. Take a look there to see what these parts look like.



Dave

 

[CodySanders]

ok i got it fixed up now. it was the cad i replaced the gold thing that the vacum lines went to and the internal parts kit as well. thanks guys for the help. 4x4 light even works now.

 

[LVJUNIOR]

Congratulations Cody glad it was a cheap fixm

 

[DieselDoghouse]

Congrats on the fix Cody - the gold thing is the vacuum shift motor - they often start to corrode and can develop leaks - see prior posts about water entering the system and repiping the vacuum lines to get the vent line (which always draws air in whenever a shift if performed (either direction) up up up away from the road!!! IMHO a useful fix - my vent is now up on the firewall not strapped behind the transmission!!