LB7: testing the 4WD actuator

[Jak Flash]

Bear with me for a moment....

So I'm new to the Diesel world with the purchase of a 2001 GMC 2500 Crew Cab. I couldn't be happier with the purchase.

Last night I decided to test the 4WD and the indicator light comes on, I can hear/feel the T-Case engage, but for some reason don't have power transfer to the front tires.

I've heard/read that there is an actuator on the front differential, which leads to my question....

How does one check to see if its working?

Thanks for helping me out with this Newb type question.

 

[S Phinney]

Use a test light have someone engage it and see it sends the signal.

 

[Jak Flash]

Will there be 12v continuous ? Or just a short burst?

 

[S Phinney]

When it energizes it will light the bulb. If it is doing that and not going in gear there could be two items that could be wrong. The motor that engages the slider or the slider itself broke/

 

[S Phinney]

If it is not lighting the test light look at the wire coming to it. it clips to the front differential near the oil pan and can get pinched into there.

 

[Jak Flash]

Perfect, Thank you,

 

[Jak Flash]

update: I did a basic check by engaging the 4WD then jacking the front corner up.

spun the tire to see if the driveshaft spins and It does.... when not in 4WD the driveshaft does not spin. I'm going to assume that the 4WD actuator on the differential is working correctly.

So this means that the shifter on the T-case isn't working correctly? could there be any other components that I need to consider as well?

 

[S Phinney]

The fork inside the transfer case could be broken as well. It will not move the slider inside the transfer case if that happens.

 

[Jak Flash]

^ so if that fork is broken would the TCase shift at all?

Reason I ask is I was able to get under it tonight again and the TCase motor is operating. I can hear it as well as the front 4WD actuator. I am also able to attain low gear. Albeit still no power transfer to the front axle.

I'm starting to think that I'm going to be rebuilding a tcase in the near future. F**K !!!

What could be wrong inside the tcase?

 

[S Phinney]

So it will go into 4 lo? The fork is aluminum and it is bsically u shaped. It slides a gear that changes from 2 to 4 wd and high to low ranges. It cost around 300 bucks for parts to do a rebuild on it.

 

[onebaddmaxxx]

Dump the fluid out. If a fork is broke or bent, the plastic pads would have wore off the end causing the fluid to be slushy silver color.

 

[Jak Flash]

So it will go into 4 lo? The fork is aluminum and it is bsically u shaped. It slides a gear that changes from 2 to 4 wd and high to low ranges. It cost around 300 bucks for parts to do a rebuild on it.

Yes it will go into 4 low. Now from the exploded views that I have been able to find there are two forks in the tcase. One for the planetary and one for the front output engagement (engages the chain). Am I correct in thinking this?

What would this rebuild kit include?

Dump the fluid out. If a fork is broke or bent, the plastic pads would have wore off the end causing the fluid to be slushy silver color.

Ok I'll do that. Just ATF fluid into it?