4wd not working

[drifter]

New to the forum here and having some trouble with the 4wd.

What i have is:
98 Tahoe 5.7
4 button 4wd "NP8 RPO?"

Here's what happening.

Basically it shows the 4wd is working but its not.

Push 2wd button and works fine.

Push 4hi button light flashes a couple times, goes solid and i hear this sound like its trying to engage but wont.
stop the truck and start driving again and the sound goes away. All the while the light is solid on 4hi.

Push 4lo while stopped and the light flashes for a bit and then goes solid. I can hear and feel the transfer case shift to 4 lo and it drives in 4 lo but the front wheels are not trying.

The front actuator is working when i pulled it out and when the truck is in 4wd and the front end is in the air the drive shaft turns like the transfer case is not engaged.

Not sure where to start since every other Chevy truck i have owned had a manual transfer case.

The front actuator is working when i pulled it out and when the truck is in 4wd and the front end is in the air the drive shaft turns like the transfer case is not engaged.

Thanks
Al

 

[96ProCompTahoe]

you should also have an actuator on the transfer case. theres a few other threads on this, let me try to find one of the for you.

heres one:
http://www.tahoeyukonforum.com/forum/showthread.php?t=17964&page=3

 

[drifter]

Front actuator seems to be working fine. With the switch in 4 hi the light stays on solid and i can turn the front drive shaft by hand. Unless i'm missing something that shouldnt happen.
What bothers me is that when i shift to 4wd from 2wd i can hear the transfer case shift, but it act like it's not shifting all the way or something is broke inside?

 

[SunlitComet]

So you have truck in the air put it in 4lo or 4hi front axles lock together with front driveshaft but while the rear shaft is staionary say with tranny in park you can turn front shaft by hand and your front axles move in same direction while rears do not move?

If correct then you can eliminate the front shaft and all forward for sure. Also eliminated is shift motor and most of internal shaft. What is broken?

Chain, mode shift fork, mode shift gearset or t-case output shaft. In any case out comes the t-case.

If both front and rear shaft move together while in park you probably lost your chain. If I got the your details wrong let me know.

 

[drifter]

With the front end in the air and the rear on the ground.

With the tranny in park and the xfer case In 4hi the light is solid but i can turn the front drive shaft by hand.

So here's another question. with the front actuator engaged does the front diff lock solid?

 

[SunlitComet]

No you could turn one wheel and the other would turn in the opposite if the front driveshaft was held still. It just makes it a complete typical axle with a differential.

Tech data:Front Drive Axle Description
The Front Axle on four-wheel drive model vehicles has a central disconnect feature that, under most conditions, allows shifting into and out of four-wheel drive when the vehicle is in motion. An electric motor actuator engages the central disconnect feature.
The axle uses a conventional ring and pinion gear set in order to transmit the driving force of the engine to the wheels. The differential allows the wheels to turn at different rates of speed while the axle continues to transmit the driving force. This prevents tire scuffing when going around corners and premature wear on internal axle parts. The ring and pinion set and the differential are contained within an aluminum carrier.

---------- Post added at 06:07 AM ---------- Previous post was at 04:57 AM ----------

I almost forgot your t-case should be using a clutch pack instead of a mode shift mechanism and mode shift fork should be replaced clutch pack fork so the clutch assy is also a suspect. Sorry about that.

 

[SunlitComet]

Here is a drawing of wha the whole shifting assy looks like.

 

[drifter]

Got a chance tonight to do some more research.

Jacked up all four corners and pushed 4 hi, nothing on the front end. not even the front drive shaft. BUMMER!

With the engine off I can hear the front actuator engage and the transfer case actuator engage also. Really Bummed now!

Guessing its the clutch pack?

 

[SunlitComet]

clutch pack, engagement mechanism or chain. How did it fail anyway? immediately? over time? any noise or cluncks?

 

[drifter]

Not sure when it quit working. went out all of a sudden though.

Truck's been sitting in the garage for a couple months and then last Monday went to use it and no worky!