Autotrac Stuck in 4WD?
Sep 18, 2011 | 06:07 PM
#13
Staging Lane
Joined: Oct 2008
Posts: 86
Likes: 0
Are the 99s different than other years? You should always be able to turn the front driveshaft by hand in 2wd in any IFS GM 1/2 ton that isn't AWD or stablilitrak full time 4wd.
Reading the original post makes me think the front encoder motor isn't working correctly. You should be able to spin the front driveshaft by hand in 2wd, that's why the encoder motor system exists... it disconnects the differential and front driveshaft to decrease rolling resistance and improve fuel economy while in 2wd.
On my 05 the front driveshaft does not turn while driving in 2wd, just the two CV shafts. In Auto4wd the front driveshaft does turn while driving, as it does in 4hi and 4lo (in other words, you can't spin the front driveshaft by hand in any of these three positions since the front axle it locked by the encoder). I can spin the front driveshaft by hand while in 2wd.
All four of my IFS half tons have worked just like this: a 93 1500, 97 Z71, 01 yukon XL, and current 05 yukon.
There are two parts to how the 4wd works on these trucks: 1) front axle lock via the encoder motor on the front diff, and 2) front driveshaft engagement at the transfer case. The Auto4wd button on the autotracs locks the front axle while still remaining in 2wd... while the axle is locked, the front driveshaft is still disengaged at the transfer case so no power goes to the front wheels until the clutchpack engages. My 93 and 97 engaged the encoder as soon as you shifted into 4wd. And the 97 left me stuck in a field one time since the damned encoder motor quit and wouldn't lock the front axle (front driveshaft was turning in 4hi and 4lo, but the front tires were not).
Reading the original post makes me think the front encoder motor isn't working correctly. You should be able to spin the front driveshaft by hand in 2wd, that's why the encoder motor system exists... it disconnects the differential and front driveshaft to decrease rolling resistance and improve fuel economy while in 2wd.
On my 05 the front driveshaft does not turn while driving in 2wd, just the two CV shafts. In Auto4wd the front driveshaft does turn while driving, as it does in 4hi and 4lo (in other words, you can't spin the front driveshaft by hand in any of these three positions since the front axle it locked by the encoder). I can spin the front driveshaft by hand while in 2wd.
All four of my IFS half tons have worked just like this: a 93 1500, 97 Z71, 01 yukon XL, and current 05 yukon.
There are two parts to how the 4wd works on these trucks: 1) front axle lock via the encoder motor on the front diff, and 2) front driveshaft engagement at the transfer case. The Auto4wd button on the autotracs locks the front axle while still remaining in 2wd... while the axle is locked, the front driveshaft is still disengaged at the transfer case so no power goes to the front wheels until the clutchpack engages. My 93 and 97 engaged the encoder as soon as you shifted into 4wd. And the 97 left me stuck in a field one time since the damned encoder motor quit and wouldn't lock the front axle (front driveshaft was turning in 4hi and 4lo, but the front tires were not).
Sep 19, 2011 | 08:08 AM
#14
Sep 19, 2011 | 04:47 PM
#15
Thread Starter
Teching In
Joined: Aug 2011
Posts: 24
Likes: 0
From: Houston, TX
Is there a way to test the encoder and actuator?
I'm inclined to think the problem is the actuator in the front diff. Found plenty on replacing an actuator on the front diff, and as Dorman makes a replacement part I would assume it happens often.
I'm inclined to think the problem is the actuator in the front diff. Found plenty on replacing an actuator on the front diff, and as Dorman makes a replacement part I would assume it happens often.
Last edited by ReallySatisfies; Sep 19, 2011 at 05:25 PM.
Sep 19, 2011 | 05:37 PM
#16
Are the 99s different than other years? You should always be able to turn the front driveshaft by hand in 2wd in any IFS GM 1/2 ton that isn't AWD or stablilitrak full time 4wd.
Reading the original post makes me think the front encoder motor isn't working correctly. You should be able to spin the front driveshaft by hand in 2wd, that's why the encoder motor system exists... it disconnects the differential and front driveshaft to decrease rolling resistance and improve fuel economy while in 2wd.
On my 05 the front driveshaft does not turn while driving in 2wd, just the two CV shafts. In Auto4wd the front driveshaft does turn while driving, as it does in 4hi and 4lo (in other words, you can't spin the front driveshaft by hand in any of these three positions since the front axle it locked by the encoder). I can spin the front driveshaft by hand while in 2wd.
All four of my IFS half tons have worked just like this: a 93 1500, 97 Z71, 01 yukon XL, and current 05 yukon.
There are two parts to how the 4wd works on these trucks: 1) front axle lock via the encoder motor on the front diff, and 2) front driveshaft engagement at the transfer case. The Auto4wd button on the autotracs locks the front axle while still remaining in 2wd... while the axle is locked, the front driveshaft is still disengaged at the transfer case so no power goes to the front wheels until the clutchpack engages. My 93 and 97 engaged the encoder as soon as you shifted into 4wd. And the 97 left me stuck in a field one time since the damned encoder motor quit and wouldn't lock the front axle (front driveshaft was turning in 4hi and 4lo, but the front tires were not).
Reading the original post makes me think the front encoder motor isn't working correctly. You should be able to spin the front driveshaft by hand in 2wd, that's why the encoder motor system exists... it disconnects the differential and front driveshaft to decrease rolling resistance and improve fuel economy while in 2wd.
On my 05 the front driveshaft does not turn while driving in 2wd, just the two CV shafts. In Auto4wd the front driveshaft does turn while driving, as it does in 4hi and 4lo (in other words, you can't spin the front driveshaft by hand in any of these three positions since the front axle it locked by the encoder). I can spin the front driveshaft by hand while in 2wd.
All four of my IFS half tons have worked just like this: a 93 1500, 97 Z71, 01 yukon XL, and current 05 yukon.
There are two parts to how the 4wd works on these trucks: 1) front axle lock via the encoder motor on the front diff, and 2) front driveshaft engagement at the transfer case. The Auto4wd button on the autotracs locks the front axle while still remaining in 2wd... while the axle is locked, the front driveshaft is still disengaged at the transfer case so no power goes to the front wheels until the clutchpack engages. My 93 and 97 engaged the encoder as soon as you shifted into 4wd. And the 97 left me stuck in a field one time since the damned encoder motor quit and wouldn't lock the front axle (front driveshaft was turning in 4hi and 4lo, but the front tires were not).
Sep 20, 2011 | 06:09 PM
#17
Sep 20, 2011 | 06:10 PM
#18
from what ive gathered, it spins no matter what, but theres not really "power" sent through it...once you hit 4x4 you get the power sent to the shaft and the front diff actuator locks it in..
Sep 20, 2011 | 07:33 PM
#19
Staging Lane
Joined: Oct 2008
Posts: 86
Likes: 0
Ok you guys HAVE to be talking about the CV or half shafts that attach to the wheels, which are permanently splined to the hub, so the CV/half shafts always turn with the tires (you can't turn them by hand)... i just went outside to my 05 yukon with autotrac 4x4 system and turned the front DRIVEshaft by hand very easily... the large shaft connecting the transfer case to the front differential. I know the 4wd works cause i just used it two weeks ago going to my favorite hunting area. My last three GM trucks were the same.
If you can't turn the front driveshaft by hand in the 1/2 ton trucks while in 2wd, somethings broke. Which is why i asked if the 99s or there abouts are different.
If you can't turn the front driveshaft by hand in the 1/2 ton trucks while in 2wd, somethings broke. Which is why i asked if the 99s or there abouts are different.
Sep 20, 2011 | 09:10 PM
#20
TECH Fanatic
Joined: Feb 2009
Posts: 1,635
Likes: 1
From: Baton Rouge, LA
Ok you guys HAVE to be talking about the CV or half shafts that attach to the wheels, which are permanently splined to the hub, so the CV/half shafts always turn with the tires (you can't turn them by hand)... i just went outside to my 05 yukon with autotrac 4x4 system and turned the front DRIVEshaft by hand very easily... the large shaft connecting the transfer case to the front differential. I know the 4wd works cause i just used it two weeks ago going to my favorite hunting area. My last three GM trucks were the same.
If you can't turn the front driveshaft by hand in the 1/2 ton trucks while in 2wd, somethings broke. Which is why i asked if the 99s or there abouts are different.
If you can't turn the front driveshaft by hand in the 1/2 ton trucks while in 2wd, somethings broke. Which is why i asked if the 99s or there abouts are different.