4 wheel drive not working

[DesertDog63]

Need help troubleshooting why my 4 wheel drive doesnt work.My Blazer is a 1988 and has manual locking hubs.Is there a way to tell if it's the hubs by turning the front drive shaft?Also,I dont get the dash light telling me it's in 4 wheel drive.

 

[TheBeast_88K5]

- Does the drive shaft spin, while in 4?
- Is it just 4HI, or does 4LO not work either?

When I first bought my truck, the 4HI didn't work.
I could get it to shift into 4LO, but getting it back out was a pain.

The reason being, the previous owner had disentegrated the 4HI shift fork.
Thus, there was nothing to engage the T-case into 4HI,
but you could skip passed the broken fork.

About 90% of the time, it's a shift fork pad that needs replacing...

Rebuilding a 208 is really simple.
Just time consuming.

 

[496truck]

You need to start by getting the truck up off the ground, on jackstands at all 4 corners. From there you can start diagnosing, what's moving, what's not moving.

It's not a difficult system. Start with the basics.

 

[DesertDog63]

haven't hide time to jack it up yet.Yesterday I did drive it and noticed that in 2WD nothing in front turns but in 4WD the front driveshaft and axles turn.Would this be a proper check to assume the manual locking hubs are bad?

 

[496truck]

Try this, leave it in 2hi and lock in the hubs. Have someone drive the truck and you look to see what is or is not turning. Then report back here.

 

[TheBeast_88K5]

^Ya, do that...


Or, go in the middle of nowhere, and walk it, like I do....

 

[DesertDog63]

When in 2WD and hubs UNLOCKED-neither the front drivedshaft or axles turn.

When in 2WD and hubs LOCKED-the front driveshaft AND both front axles turn.

 

[4X4HIGH]

When in 2WD and hubs UNLOCKED-neither the front drivedshaft or axles turn.

When in 2WD and hubs LOCKED-the front driveshaft AND both front axles turn.

Then there is nothing wrong and everything is working properly since in a previous post you stated that the front shaft turns when it's in 4wd.

 

[DesertDog63]

It didn't work in the dirt last time I had it out.Is there something that could have caused that?

 

[1BEATK5]

Try this.
2Wd. Engine off, hubs locked. Crawl under the truck and try to spin the driveshaft by hand. What happens?

Then try this
Hubs unlocked, t-case in 4x4, trans in park. Crawl under and try to spin the driveshaft by hand.
What happens?

These 2 simple tasks will tell you all you need to know. Just pay attention on the first one, if the driveshaft spins, you need to make note of which axleshaft or shafts spin at the same time.

 

[496truck]

A common problem with the NP208 and the similar NP241 t-cases is the shift forks and or pads wearing out and 4wd may not stay engaged. Heck, mine would pop out of 2wd just driving down the street. No power to the wheels and just grinding noises from the t-case.

I'm not saying this absolutely is your problem. Without further diag it's hard to say. But it sounds like a good chance it's time to rebuild the t-case.