4wd don't work

[scooter5991]

have a 99 chevy and the 4wd does not work. I shift it to 4wd and i can hear the actuators work on the front drive shaft and the encoder on the rear. I can also shift into 4 lo and it goes there but the front wheel still won't work. I also lifted the front wheel off the grond and in park and 4wd I can turn the front drive shaft and the front wheels will turn. No service 4wd light is on

[777stickman]

From your post I might think that it's something in the t-case since you can spin the front drive shaft with it in park and in 4wd.

Do the indicator lights come on showing that the shift into 4HI or 4LO is completed? Is it a push button or floor shift? Do you have "auto 4wd"?

[scooter5991]

Yes the lights indicate that it does indeed go into 4wd. and it does have the automatic 4wd

[327chevy]

I have the same truck and pretty much the identical problem only mine will work in auto 4wd but like yours not in 4 hi or 4 lo.I asked a mechanic friend and he says it sounds like the shifting forks inside the trans case are not fully shifting.I'm hoping to yank mine out sometime this summer or early fall to see what's going on inside but will likely just buy a rebuild and slap it in rather than tear into mine.I've priced the parts to rebuild mine and by the time all is said and done it is almost as cheap to do a swap plus there's less down time with the truck.

[777stickman]

1st thing for both of you is to drain the t-case and replace it with the GM "autotrac ll" fluid. This fluid is blue in color. Also check the fluid you drain out for metal particles. Drive it around for a couple of weeks. May help, may not. The auto 4wd t-cases have clutch packs in them for the "auto" function.

With the lights telling you that the encoder motor is going to the selected position (not blinking) then there may well be an internal t-case problem.

[j cAT]

Originally Posted by scooter5991

have a 99 chevy and the 4wd does not work. I shift it to 4wd and i can hear the actuators work on the front drive shaft and the encoder on the rear. I can also shift into 4 lo and it goes there but the front wheel still won't work. I also lifted the front wheel off the grond and in park and 4wd I can turn the front drive shaft and the front wheels will turn. No service 4wd light is on

the encoder motor is the componet that engages the front axle to the rear...this is usually the problem...

the transfercase fluid trac II needs replacing when the color is gray...when the transfercase fluid gets to old this will cause many of these problems and possibly a new transfercase..

the front diff actuator locks the front axles together,,,this has nothing to do with loss of 4WD...the encoder motor does that..

[327chevy]

Originally Posted by 777stickman

1st thing for both of you is to drain the t-case and replace it with the GM "autotrac ll" fluid. This fluid is blue in color. Also check the fluid you drain out for metal particles. Drive it around for a couple of weeks. May help, may not. The auto 4wd t-cases have clutch packs in them for the "auto" function.

With the lights telling you that the encoder motor is going to the selected position (not blinking) then there may well be an internal t-case problem.

Way ahead of you there I changed the fluid over a year ago and nothing has changed as in the way it works.I know all about the internals of the auto trac and the clutches which is why I'm a little hesitant to tear into it and why a replacement is a better option.Not that I'm inept mechanically it's just that I don't want to be without the truck for too long a period of time and I could probably swap one in a day.

[scooter5991]

Thanks for the advice. I figured the T-case was bad inside but I wanted to see if there was something that I may have missed. I just bought the truck and it was a repo and has had the #%$@ beat out of it.

Thanks again

[ratchets]

Old thread I know, but I am having the same problem as these guys. What is the function of the encoder motor? Why would I hear the truck shifting when I go to 4hi, but I have no power at the front wheels? I guess my only hope is to change the fluid in the t-case, and if nothing else the t-case itself?

[j cAT]

Originally Posted by ratchets

Old thread I know, but I am having the same problem as these guys. What is the function of the encoder motor? Why would I hear the truck shifting when I go to 4hi, but I have no power at the front wheels? I guess my only hope is to change the fluid in the t-case, and if nothing else the t-case itself?

the issue you have maybe many things. first as always get the drive train failure codes. you maybe hearing the locking actuator. this only locks the front axles together as one. see post #6

[ratchets]

I'm assuming there would only be drive train failure codes if the service 4wd light was on, which mine is not. I disconnected the plug from the front axle locking actuator and I still here something engaging. I assume this has to be the encoder motor?
When I select 4hi or 4lo the light will blink and then stay lit. just a little more info

[j cAT]

Originally Posted by ratchets

I'm assuming there would only be drive train failure codes if the service 4wd light was on, which mine is not. I guess I could disconnect the front axle locking actuator and see if I hear the sound....
When I select 4hi or 4lo the light will blink and then stay lit. just a little more info

when in 2wd hi the light is on next to 2wd button ? WHEN YOU SELECT 4wd the lamp flashes and then is on next to the 4wd button ?

with checking for those codes this would be the correct proceedure if you are sure it is indeed not in 4wd..the transfercase could be internally broken where the encoder moves but the fork does not.

lift front wheels off ground when in 4wd can you rotate any front wheels ? if so then it is defective. also check that the front wheels are locked together.

[ratchets]

Originally Posted by j cAT

when in 2wd hi the light is on next to 2wd button ? WHEN YOU SELECT 4wd the lamp flashes and then is on next to the 4wd button ?

Yes.

I am sure it is not in 4wd because when i put it in 4wd and spin in dirt it is only the rear tires that are spinning.

Thank you for the fast replies!!

And if you notice, I changed my previous post...

[j cAT]

Originally Posted by ratchets

Yes.

I am sure it is not in 4wd because when i put it in 4wd and spin in dirt it is only the rear tires that are spinning.

Thank you for the fast replies!!

And if you notice, I changed my previous post...

if you remove the encoder you can check this out. post back what was broken.

[ratchets]

I believe this ---> http://www.chevyavalanchefanclub.com...c,41895.0.html
is the t-case in my truck, and if so it shows how it works

EDIT: The transfer case above is the 05+ upgrade. They talk about the differences in the article.