Folks it seems like as soon as I fix one thing another one breaks!

 

I am having 4x4 issues with my truck.  When shifted into 4-high or 4-low the 4x4 light comes on on the dash but the front axle is not engaged.

 

The transfer case obviously shifts into 4-low so I pretty much have a 2-low scenario.

 

I started checking vacuum lines but my HVAC and cruise work fine.

 

The 2 lines that come up from near the transmission are what confuses me.  One of them ties into the main vacuum line on the cowl.  The other has a 90 on it but is not connected to anything, and I can't seem to find what it would look to.  According to the vacuum diagram this may be the TC vent?

 

Any help would be appreciated.

 

Thanks!

The CAD axle, which I believe you have, is shifted into 4WD with vacuum. If one of your lines is disconnected it will not engage the axle.Either that or the spool in the axle itself may be locked up and not moving.

Dave it is a CAD axle.  For the life of me I cannot find where that other line should go.  

I think that there should be 4 on the little vacuum valve block at the transfer. 1 is feed from the firewall junction, 1 is an exhaust, 1 is cad engage, and 1 is cad disengage. I have a feeling someone will post a diagram here shortly. It might be me if I can find it.

Get a pic of the CAD part of the front axle. Have someone shift the truck into 4x4 a couple times while you disconnect the vacuum hoses to the CAD and feel the ends for vacuum? Have you been working under the hood lately? They’re is a vacuum lime that is easily disconnected if moved around while under the hood. This is what happened to me. 

Problem started after an injector install.  Back at the firewall by #6 is where I found the two lines going to the TC.  The white line is attached to the main vacuum line running along the cowl.  The black line has a 90 degree fitting on it and is attached to nothing.

Look real close down by injection pump and lower that where mine was laying. If it happened only after injector install it’s almost certain that a vac line became unhooked. 

 

Read through here. There's a diagram showing where the lines go

7 minutes ago, Manimalmother said:

Problem started after an injector install.  Back at the firewall by #6 is where I found the two lines going to the TC.  The white line is attached to the main vacuum line running along the cowl.  The black line has a 90 degree fitting on it and is attached to nothing.

The one that's not attached could be the vent or exhaust.

Thanks.  So since my light is coming on it sounds more like a problem in the cad itself.  Still leaves me wondering where that line may go, unless it is a vent?

I was going to say, if the light is coming on then vacuum is pulling the vacuum actuator far enough to trip the light sensor but if vacuum is weak maybe it's not engaging all the way. 

If you put it in 4x4 can you spin front driveshaft by hand, if not then tansfer case is working and problem is in vacuum lines or actuator. Being you just did injectors, I'd say it's vacuum line partly lose or could be a hole in a 90 elbow, just inspect it better. All them rubber elbows rot after time.

Here you go   

Thanks!  So according to this the line I found hanging is the vent/exhaust.  Which means the problem is in the CAD or TC output.

You can just put front end on jacks and put a hose on actuator and start (no dirty thinking) sucking and see if it engages by turning driver side tire. Then put that piece of tube on the other line/fitting and see if it disengage. That will let you know where to look next.

Edited February 5, 20196 yr by JAG1

I would pull it completely and inspect the shift fork and the sliding collar. In the case of my 1996 Dodge 1500 the vacuum motor had been struck by an object and then was bent enough that the vacuum motor have issues. (Binding issues). You might find the shift fork is worn or the shoes on the fork are worn.

Ok I just checked everything.  I have vacuum to the cad that switches when 4x4 is engaged.  I then pulled the cad and the collar, shoes, and fork all look good.  Actuator moves freely when the lines are unhook.  Nice and tight when lines hooked up.  Started the truck with the cad dangling and shifted into 4x4.  Fork moved like it should.  I'm stumped.  Also, driveshaft spins easily in 2wd but cannot turn by hand in 4x4.

 

Only thing I can think is the actuator is strong enough to move the fork out of the truck, but doesn't have enough force to move it once installed.

 

Thoughts?

 

Thanks!

Dave

Dave,

 

since you get the 4wd light on the dash, the actuator is moving. (notice the 4wd light switch is at the end of the stroke of the actuator.)  the actuator moved, but did the collar move is our question. 

 

 

Put the front axle on  on jack stands.  (I assume you have an Auto truck, so put it into neutral.) 

Idle the truck (so you have vacuum) (or supply the vacuum yourself with a hand pump. <--- I like to do it this way so i don't have to listen to all the rattling...)

put truck into 4 hi or lo (transmission still in neutral.)

prevent the TC output shaft or input to the front differential from turning.  (you can do this with a pry bar in the universal joint somewhere)

Spin the left front tire by hand.  The right front should spin the opposite direction.  

take the transfer case and shift it out of 4wd  to neutral or 2 wd.

Spin the left front tire. the right front should not move. (it is no longer connected to the differential)

 

If the above works fine....  Problem is most likely in TC, but you can check it out. (try by hand first, but you can do this with engine running and a friend watching.)

Jack up the rears to match front.   put TC in 4wd put trans in neutral.   turn the FRONT drive shaft (axle to the TC)   the rear drive shaft should try to turn.   If you have a buddy, you can do it with the engine on. In the 4wd modes. the front TC output should turn in 2 wd on the rear should turn.  (idle is fine you don't need much)

 

There are shift fork dogs that go bad in the tc (you coulda wadded up the chain but that usually is catastrophic and externally visible)  I don't think ours has a clutch in it (some of the later model gms do)  or there could be gear problems in the planetary, but I think you would HEAR that....

 

GL

HTH

Hag

Well is appears to be in the TC.  I jacked up the front last night and the CAD is working as it should.  Axle engages and disengages like it should.  In 2wd I can turn the front driveshaft by hand.  In 4wd driveshaft cannot be turned by hand.  I wasn't able to get the whole truck up on stands.  Ran out of jackstands.  

 

The TC isn't making any bad noises in 2wd or 4wd.  In 4lo I still get the reduced gearing to the rear end.  What could be broken in the TC that still allows the gear reduction to the rear but no front output, even though it engages the front driveshaft?  I would think a broken chain would be making a ton of noise and be extremely noticable.  

 

Thanks

Dave

Dave,

Take a look at this post here.  (this is a DHD yours may be a DLD or some other, but they all work similarly.  You only need to know exactly what you have when you go to get parts.)

Well it is one of two things....  No chain or no dogs. (or broken fork...)

 

look at the exploded view. Notice that there are two forks 51 and 54  one is range and one is mode.  I think your range fork is working (you get high and low) , but your mode fork is not.   It could be that the fork pin 53 is now missing.  (fork just slides on the shaft)  this is rare.  The more common failure is the pads 49 and 50 are gone.  there is just not enough stroke to engage the synchronizer sleeve 29, to engage the drive sprocket 20.  

 

You are going to have to split the case to see what your problem is... it is not in the tailshaft section. 

 

I agree usually a chain will ball up in an area too small for it and cause catastrophic damage.  I imagine it is possible to break and go to a safe spot.   I am betting the mode fork is your culprit.

 

GL  HTH

 

Hag

I don't understand, if you shift transfer case in 4x4 and front drive shaft engages then there is nothing wrong with tc. If your cad engages with vacuum then there is nothing wrong there ether. How are you testing your 4x4 anyway, I mean how do you know it's not working 

Edit 

Or are you saying you put it in 4x4 and front drive shaft doesn't move at all. Have you tried rear wheels off the ground with engine off in neutral and tcase in 4x4 try spinning rear driveshaft, does front driveshaft spin also?

Edited February 8, 20196 yr by Dieselfuture

Ok.  Currently the truck has all 4 tires off the ground.  Transmission in neutral, TC in 4hi.

 

If I spin the back wheels forward and backwards the driver's front goes forward and backwards.  Passenger front doesn't move.

 

If I spin drivers front forward rears go forward.  Passenger front does nothing.

 

If I spin drivers front backward passenger front goes forward.  Rears go backward about half a turn and stop moving.

 

If I spin passenger front forward drivers front goes backward. Rears go forward.

 

Engine running in drive, 4hi rears go forward drivers front moves forward, passenger front doesn't move.  Same in 4lo.

 

I assume this is because of the open diff in the front.

 

It looks like it's working on jackstands.

 

This all started when I went to move my camper last weekend.  It had sunk in the yard and I put it in 4high to move it.  Both rears spun but the front did not spin in the mud.  Had to put it in 4 low to get the camper out, but it turned just fine.

 

Driving around the yard if I put it in 4 low it turns like it's in 2wd and doesn't buck at all.

 

 

 

 

I think everything is working properly, you must have front and rear open differentials meaning no limited slip or lockers. If you're sitting still and putting it in 4-wheel drive and you already stock front wheels most likely will not engage. If I know I'll need four-wheel drive I engage it ahead of time.