4wd don't work

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

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"?

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

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.

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.

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..

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.

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

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?

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

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

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.

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...

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.

I believe this ---> http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,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.

I will remove the encoder motor the next time I get some free time, hopefully tomorrow, and post back as soon as I do.

Thanks again man

I believe this ---> http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,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.

so what are YOU going to do ? are you going to get dirty or have someone else get your money to correct this ?

ratches, do you have the 'auto' 4wd button along with the 2HI 4HI & 4low buttons? If so the clutch packs in the transfer case could be burned up.

You should do what j cAT recommended and jack up the front end with it in 4wd. Can you turn the front driveshaft by hand or with channel locks? If you spin one front wheel does the other front wheel turn in the opposite direction? If the front wheels turn in opposite directions then you know the front diff and actuator is ok and the problem is with the transfer case or encoder.

David

so what are YOU going to do ? are you going to get dirty or have someone else get your money to correct this ?

I am going to do it myself. I'm going to drain the fluid to see what is in there right now. I have a bad feeling it is the clutch inside. How bad are they to replace?

From what I've been reading, the encoder motor has an internal brake that can go bad. Hopefully that is the problem and I can just replace the motor.

I do plan on lifting the front end and see if I can turn the front wheels while it is in 4wd, but I'm quite sure I will be able to. Also, I already replaced the front actuator thinking that was the problem.

I'll be working on it again on saturday.

More information:
http://www.carkb.com/Uwe/Forum.aspx/chevy-truck/917/99-Silverado-with-ATC-automatic-transfer-case-doesn-t-engage

I have a final due tomorrow and one Im taking on Monday, so needless to say I'm not getting to it until next week, probably weekend.

Haven't had time to do much yet, but I did pick up the front with it in 4wd hi and i could turn the front wheels by hand. when i turned one forward, the other went in reverse. So the front axle actuator is working. I also can hear the encoder motor working as well.

I am taking it to a transmission shop for a free daignosis tomorrow, so we will see what they say. Then I'll do my own diagnosis on it this weekend.

transmissino shopped confirmed it is in the transfer case. while they had it in the air i could see the front wheels were getting some power, but when he held the brake a little the rear would turn but the front wouldnt. Not sure what that means exactly...

Anyone have any advice for pulling the transfer case? I am going to start on that tomorrow. I am going by the haynes manual.

I pulled the truck up on ramps and drained the transfer case fluid. It's completely black. Now I have unbolted the c-clips that are holding the rear drive shaft to the differential, but the drive shaft will not budge. Is there something I am missing?

I pulled the truck up on ramps and drained the transfer case fluid. It's completely black. Now I have unbolted the c-clips that are holding the rear drive shaft to the differential, but the drive shaft will not budge. Is there something I am missing?

with the transfercase fluid black and your 4wd issues I would say you need a rebuild of the transfercase....

removal of the drive shaft lift rear wheels off the ground then with some wood and a hammer tap the c clamp area/use some penitrating oil.. mark drive shaft so you can install as removed..

black is the clutch material ...this must be replaced and all that material removed..Inspection of the transfercase for case for the wear thru issue is recommended..

Thanks for the reply J. I sprayed some pb blaster on the u-joint and let it sit, then pried it on out with the help of my trusty BFH. The trasfer case is now out.

I knew(or assumed) the black fluid meant the clutches were bad . Not sure what you are reffering to when you say "wear thru issue". Because of my lack of experience I plan to take it back to the transmission shop and let them inspect it. Hopefully they won't BS me. After they get it open I will get them to show me what they see is wrong and replace the clutch packs(again assuming).

My next question, and question to the shop doing the inspection, is what would have caused the malfunction? In the link I posted it had some good info, and I plan on draining the front diff to see if I find any metal (signs of a bad bearing). What else would you suggest looking into?

Thanks for the reply J. I sprayed some pb blaster on the u-joint and let it sit, then pried it on out with the help of my trusty BFH. The trasfer case is now out.

I knew(or assumed) the black fluid meant the clutches were bad . Not sure what you are reffering to when you say "wear thru issue". Because of my lack of experience I plan to take it back to the transmission shop and let them inspect it. Hopefully they won't BS me. After they get it open I will get them to show me what they see is wrong and replace the clutch packs(again assuming).

My next question, and question to the shop doing the inspection, is what would have caused the malfunction? In the link I posted it had some good info, and I plan on draining the front diff to see if I find any metal (signs of a bad bearing). What else would you suggest looking into?

the leak thru of the transfercase is a common failure. the fluid pump clip can wear a hole thru the case on the passengerside. on the internet you will find some very good pictures showing this.

on the transfercase failure cause. operating on dry solid pavement any 4wd, tires not rotated or replaced as a set,tire pressures not maintained,fluid replacement 30,ooomi.,this can create these failures..

checking the fluid condition at the oil change intervals, replace when it looses the blue color...

I got the transfer case back in. When it was out I saw that where the pump normally wears through the case there is a steel strip protecting the case. I had a transmissino mechanic install new bearings and shifter fork pads? and new clutch pack.

4wd works great now! THANKS GUYS!

But now I have a new problem...

There is a vibration starting around 40 getting the worse around 50 and seems to go away around 60. When I was installing the rear drive shaft a bearing cap fell off the rear u joint. I just threw it back on there and when I checked it again today one of the needles was loose in there. I put it back in place but the vibration is still there. I plan to replace the u joint tomorrow. I'm worried it is something else though...

I got the transfer case back in. When it was out I saw that where the pump normally wears through the case there is a steel strip protecting the case. I had a transmissino mechanic install new bearings and shifter fork pads? and new clutch pack.

4wd works great now! THANKS GUYS!

But now I have a new problem...

There is a vibration starting around 40 getting the worse around 50 and seems to go away around 60. When I was installing the rear drive shaft a bearing cap fell off the rear u joint. I just threw it back on there and when I checked it again today one of the needles was loose in there. I put it back in place but the vibration is still there. I plan to replace the u joint tomorrow. I'm worried it is something else though...


prior to drive shaft removal I use spray paint to mark the shaft /yoke to insure it goes back as it came out..

next having tape when shaft is removed tape up the end caps...

since the cap fell of it would take only one needle bearing to be missing for vibs to occur...now you need to replace the U joint...

on the transfercase check fluid condition/color every oil change..when it gets dark replace...

thanks for posting the damaged internal components..

prior to drive shaft removal I use spray paint to mark the shaft /yoke to insure it goes back as it came out..

next having tape when shaft is removed tape up the end caps...

since the cap fell of it would take only one needle bearing to be missing for vibs to occur...now you need to replace the U joint...

on the transfercase check fluid condition/color every oil change..when it gets dark replace...

thanks for posting the damaged internal components..

I marked the yoke and shaft with a sharpie to make sure I put it back on correctly.

I definently learned my lesson about securing the end caps, hopefully it will be a while before I have to do it again.

I replaced the U-joint and the vibration is now gone!!

I'm taking it on the beach this weekend so hopefully it everything goes well.

Thank you and everyone else for the help!

I marked the yoke and shaft with a sharpie to make sure I put it back on correctly.

I definently learned my lesson about securing the end caps, hopefully it will be a while before I have to do it again.

I replaced the U-joint and the vibration is now gone!!

I'm taking it on the beach this weekend so hopefully it everything goes well.

Thank you and everyone else for the help!


sounds very good !