Have a '97 GMC Jimmy 3 button 4x4. I had a problem with the encoder motor and the actuator. Encoder motor was seized solid so i repalced it with a scrap yard unit yesturday. The actuator had a hole so I locked the diff engaged via visegrips.

I can here the encoder motor swifting between postions except 2HI..when selecting 2HI I hear a click versus the normal clunk. Put the truck on a lift and in 2HI the front wheels still turn..if I apply load to the rear wheels(parking brake), only the rear wheels turn. On the ground in 2HI I can also do a full lock steering no prob without the drivetrain binding up as normal.

My switch light for 2HI I think is burnt in teh button, but when I select 4HI, 4LO...only that button will light up as normal. I assume 2HI would light up just it doesn't when I select it..so thinking bulb is burnt for none of the others come on when 2HI is selected.

Now the noise really sounds like the encoder motor isn't shifting fully to 2HI, and I get a syncro teeth grinding/howling noise. I know the t-box is good cause I've shifted it manually with the motor completely off and driven it like this with no issue.

So I am believing the fault is due to this scrap yard encoder motor I picked up..just to be sure though..there's no special way of installing it.I set the t-box in 4HI manually and used a 1/2 rachet to align the encoder motor..bolted the encoder moter up and test drove it with the above results..

 

The right front axle clutch is partially engaged causing the growl/grinding sound. To repair it correctly, you'll need to put your vice grips back in the tool box where they belong Then replace the axle actuator under the battery tray. The root cause is a faulty transfer case vacuum switch, so it needs to be replaced as well.

 

The actuator had a hole in the diaphram so it's gone, and the switch was stuck closed circuit to engine vacuum in any position. I removed the actuator and blocked all the vacuum lines..I heard of ppl locking up the front diff with vise grips with no issues except a worse mpg(which doesn't bother me), so thought I'd try it being I'm just using this truck for the winter and then selling it..

I know the front is fully engaged with clamping the cable, just what puzzles me is why the front shaft will spin at a 1:1 ratio to the rear shaft if in 2WD on a lift . I can also hear this noise coming from the transfer case when I load up the wheels..it's really as if the transfercase isn't coming fully out of 4wd into 2wd.

 

All of this stuff is related to the original problem, and what you have done trying to "fix" it.

The right front axle is not engaged with the differential. Either your vice grips aren't pulling the axle actuator far enough, or the axle clutch mechanism is bad from grinding.

The axle engagement switch is activated, or shorted out. This tells the TCCM the axle is locked in, and the TCCM turns off the 2WD bulb.

Again, the right front axle is not fully engaged with the differential, or the clutch mechanism is bad.


Normal. This is what enables you to shift on the fly. The front shaft turns when the vehicle is in motion. The differential is driven by the transfer case but it's not "live" until the right axle is engaged.

 

Ok, thanx for explaining.. makes sense about the front shaft spinning for "shift on the fly".. I'm so sure the cable is pulled all the way(I will double check though, doesn't hurt to check)... I can go into 4HI and when I go full lock on the steering the drivetrain will bind up as it should. If the axle was not engaged and in 4HI wouldn't the drivetrain not bind up?

 

The binding sensation is called "crow hop" because the front end feels like it hops sideways. When turning, the front wheels do not rotate at the same speed, and if the front axle is engaged on drive pavement, it will crow hop. If/when it crow hops, it's hard on the front drive train, (transfer case, universal joints, differential, etc) and will cause internal damage. This is one reason 4WD should not be used on dry pavement.

This image shows the front drive axle assembly. Parts 9 through 23 are used to engage & disengage the right axle with the differential.



Bravada does not use this axle assembly. The right axle is always engaged with the differential and parts 9 through 23 are not used.