My 4wd won’t work

[Chebbyfan]

2004 Silverado, new transfer case encoder, and now transfer case shifts to 4wd, new front diff actuator, and it works with the switch.  I verified before installing.  Scan proved both speed sensors on transfer case are working properly.  I have verified front diff to engage by pushing in locking mechanism inside differential.  Jacked up in the air (no load) the front will spin, under load (on the ground) the 4wd does not seem to engage properly.  I’m at a loss and cannot figure out what to do next.  Can someone help me please?

[davester]

which 4wd mode are you trying to use, and which transfer case does your truck have?

maybe try putting it in 4hi, drive forward a few feet, then stop, turn off engine, jack up one front wheel, and try spinning it by hand.

Edited March 6 by davester

[Chebbyfan]

17 hours ago, davester said:

which 4wd mode are you trying to use, and which transfer case does your truck have?

maybe try putting it in 4hi, drive forward a few feet, then stop, turn off engine, jack up one front wheel, and try spinning it by hand.

I’ve tried 4 hi and 4 low.  I can hear the transfer case shifting so I know it’s working.  It is an auto 4 transfer case 246 I believe.  What I don’t understand is how it works in the air (on jack stands) but not on the ground 

[davester]

Did you do the test?

[Chebbyfan]

12 hours ago, davester said:

Did you do the test?

What test?

[davester]

what I wrote in my earlier post.

[Chebbyfan]

On 3/7/2026 at 3:04 PM, davester said:

what I wrote in my earlier post.

No, I haven't.  i know for sure its not engaging when the back wheels spin on gravel and the fronts do nothing

[davester]

Well, it's just throwing out random guesses if you don't want to diagnose the problem.

[Chebbyfan]

On 3/9/2026 at 3:15 AM, davester said:

Well, it's just throwing out random guesses if you don't want to diagnose the problem.

OK, I did what you said to do. I jacked up the passenger front and it had some tension on it, so I got underneath of it and watched the front driveshaft spin while I was turning it by hand.  So why won’t it engage while driving it?

[richard wysong]

Well if it was in park and in 4wd you shouldn't have been able to spin the front driveshaft so the problem is probably in the transfer case, remove the encoder and manually shift it into 4 hi and try it. if it still doesn't work you may have a broken shift fork in the TC.

[davester]

Yup, being in 4hi mode, spinning the front wheel, and the front driveshaft spinning = some problem w the transfer case.

 

richard's suggest is good, also check that when the truck is in 2h, you can reach under the truck and manually spin the front driveshaft.

[Chebbyfan]

Well I took the switching motor off the side of the transfer case and switched it manually.  Obviously something not working inside transfer case.  Checked fluid and it was over full telling me the seal between trans and transfer case probably bad too, but fluid was grey in color and sparkly.  Guess I’ll be replacing that soon.  I’ll drive it for a couple weeks yet until I get the chance to change out.  Thanks for the help everyone.

[davester]

I would suggest:

-changing the fluid, just to get the sparkly bits out, might make what's still good a little happier and less likely to catastropically fail

-hit a junkyard and get the same TC from a truck there, or buy a used one, then swap it in when you have some time.

 

You might, if you want, put in bearings/seals and a pump rub kit (cheap pressed metal plate is fine for fixing this problem).  It's fairly straightforward to do, and doesn't need a lot of special tools.  You can find youtube video's on doing it, to see if it's in your wheelhouse, if you want.

 

And if you are going to do the swap yourself, do not do it by yourself.  The TC is an awkward shape, and doesn't like staying on a transmission jack, and it needs to be both tilted front to back, and rotated to get it in out.  It is super easy for it to fall off the jack, and it will mess you up if it does.