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Discussion Starter #1
Good afternoon,

For today's stupid question, I gots a doozy.

I'm chasing an odd humming/whining noise, which I think is caused by the transfer case being in 4Hi and the front axle being in 2Hi. This started at the same as the buttons on the dash stopped having working, so...

Here's the thing- I have the front end up on stands, and the front wheels turn without rotating the front drive shaft, just like you'd expect. The front drive shaft also turns freely in both directions, an seems to maybe make a bit of that noise i'm chasing (hard to tell at "turn it by hand" speeds).

Seems like if the T/C was in 4Hi, I shouldn't be able to easily turn the drive shaft? This is my first time fooling with a 4wd truck, so I'm not 100% on how everything functions.

I've already replaced the actuator under the battery tray, and I checked the vacuum lines for vacuum with the truck running (I do have vacuum at both the ball attached to the hood and the fitting where to line to the actuator Ts off.)

What other testing procedures do y'all recommend? I really want to chase this noise down and get whatever is causing it fixed today so I can drive her to work tomorrow.

Merlyn


PS: If anyone is in Denver and wants to help out in person, there's a 12 pack of your favorite variety of beer available
 

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First of all, is it a 3 button or 4 button 4wd.
If it is 4 button, can't help you.
3 Button, if the TC is truly in 4HI, the tranny in PARK, you should get no movement in the front driveshaft while turning it by hand. It should only turn freely in 2HI.
Let's go there first.

Bill
 

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Discussion Starter #3
First of all, is it a 3 button or 4 button 4wd.
If it is 4 button, can't help you.
3 Button, if the TC is truly in 4HI, the tranny in PARK, you should get no movement in the front driveshaft while turning it by hand. It should only turn freely in 2HI.
Let's go there first.

Bill
It's a 3 button.

I just changed out the vacuum switch on the transfer case, no joy. Still making the odd noise, still won't switch out of 2wd.

Merlyn
 

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If the encoder motor is working, you should hear it "Clunk" when you shift it into and out of 4wd. Do you hear it??
My question still remains, can you turn the front driveshaft by hand in 4wd and tranny in PARK?
The vacuum switch on the TC has nothing to do with this. All it does is apply vacuum to the right front axle shaft when in 4wd. That's it..

Bill
 

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Discussion Starter #6
I don't hear anything when I press the 4hi or 4lo buttons on the dash. I'll test the motor and the switch to see if one of them is bad.

As for the driveshaft moving, it sounds like that proves that the T/C and axle are both in 2wd. That's good enough for me for the moment. I have until winter to get the 4wd working :: chuckle ::

That noise though...

It sounds a lot like tire noise, if I were running serious mud tires (I'm not). It varies with speed but not with engine load or RPM, so it's something in the drive line. It doesn't change when I transition from pavement to dirt, so it's not tire noise. I can freely turn both the front tires and the front drive shaft with the truck jacked up and the trans in park, so I'm thinking that rules out the T/C?

I just serviced both differentials and replaced both front axles, so those should be good.

The truck is a 1997 LS, 4.3 automatic.

Any ideas?

Merlyn
 

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Discussion Starter #7
Aaaand the dashboard switch is bad.

Odd thing though- I jumpered from 12v+ (Pink wire) to 4hi (Gry/BLK) and heard the TC shift. I jumpered from 12v to 2wd (dark blue) and heard the TC try to shift back. Multiple "clunks" but then when I shift the jumper back to 4hi, nothing.

The noise that is the actual problem I'm chasing, of course, remains constant.

I'm going to replace the dash switch and see if that accomplishes anything significant.

Merlyn
 

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Could be the encoder motor or bad TC.
Did it REALLY go back into 2WD? Did you check the front driveshaft for freedom of movement after the above test?
You still need to check the front driveshaft to confirm your findings whether the TC is in 4wd or 2wd.

Bill
 

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Good afternoon,

For today's stupid question, I gots a doozy.

I'm chasing an odd humming/whining noise, which I think is caused by the transfer case being in 4Hi and the front axle being in 2Hi. This started at the same as the buttons on the dash stopped having working, so...

Here's the thing- I have the front end up on stands, and the front wheels turn without rotating the front drive shaft, just like you'd expect. The front drive shaft also turns freely in both directions, an seems to maybe make a bit of that noise i'm chasing (hard to tell at "turn it by hand" speeds).

Seems like if the T/C was in 4Hi, I shouldn't be able to easily turn the drive shaft? This is my first time fooling with a 4wd truck, so I'm not 100% on how everything functions.

I've already replaced the actuator under the battery tray, and I checked the vacuum lines for vacuum with the truck running (I do have vacuum at both the ball attached to the hood and the fitting where to line to the actuator Ts off.)

What other testing procedures do y'all recommend? I really want to chase this noise down and get whatever is causing it fixed today so I can drive her to work tomorrow.

Merlyn


PS: If anyone is in Denver and wants to help out in person, there's a 12 pack of your favorite variety of beer available
Hello,
I have had the exact same problem. I have changed the switch, actuator, etc. The problem seems to be in weather around 20 f and lower. I am beginning to think it may also be connected to moisture. I just replaced all the front quarter steel from water and salt damage. I think the 2 might be connected. The next step is replacing all vacuum lines . I have had to put most of this on the back burner as I am also rebuilding a 1972 Nova. If the lines don't work I intend to follow up by checking the wiring harness that is associated with the 4x4 system. GOOD LUCK
 

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Discussion Starter #11
Welp, I found the source of my sound... The pinon bearing is shot.

On the bright side, replacing the dash switch on my 4wd seems to have resolved that issue.

Graves
 

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Discussion Starter #12
$160 later...

Bearing noise resolved, and I have a posi rear diff AND disk brakes on the back.

LKQ Pick a Part for the win.

Merlyn
 
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