Auto-Trac binding, dragging

concours · February 1, 2007

My '01 Sub has the Auto-Trak (couldn't get a loaded one without it) and at first it worked good... shortly after I bought it used (65K miles) I changed the fluid using the gen-u-ine GM blue Auto-Trak fluid specified. Since then, it binds while turning (tires make scrubbing noises heard with the windows down and you can feel the increased resistance) like a conventional 4WD system on dry pavement. It doesn't "gallup" but rather the transfer case clutches do finally slip. It is a tire wasting, fuel gobbling monster, problem is, it wasn't always like that. Before the fluid change it seemed OK. I'm wondering if I have the wrong (revision level) fluid in there... any tech have the proper info.....?????

bobcat5544 · February 1, 2007

Changing the transfer case fluid wouldn't cause your problem. Did you change the fluid in the front diff.

Chanks7 · February 1, 2007

My dads 2000 does the same thing, its been doing it since about 60k miles and is still doing it now at 230k. All fluids changed regularly, doesnt bother him so he has left it alone. Curious to see if you figure this one out.....good luck.

KB06YUKONXL · February 4, 2007

Go to the dealer and see if there is a TSB about adding a can of the GM friction modifier to the front diff. DID you get the correct front diff fluid?

95Sierra2500 · February 4, 2007

Your front differential is engaged when you put it in the autotrac mode. This will create this 'binding' you describe as the front tires are trying to turn at the same speed. It's normal.

concours · February 5, 2007

Your front differential is engaged when you put it in the autotrac mode. This will create this 'binding' you describe as the front tires are trying to turn at the same speed. It's normal.

Ok, I was in a big hurry when I posted, left out lots of info. The binding I'm feeling is in 2WD mode, not auto-trac. I'm a seasoned 4x4 veteran, 35 years of owning, driving, plowing, off-roading, lockers and limited slips, etc. I've set-up ring and pinion gears, rebuilt transfer cases and such. What I'm looking for is some pattern failure or common mess up.

A couple things jump out at me here.. at least two posters mentioned front diff. lube, and one mentioned friction the modifier additive. Yes, I did change the front diff. lube and used Mobil 1. I'm pretty darned sure I researched (that's why I got the Auto-Trak fluid and not just Dexron for the T-case) and the factory recommendation for the diff. was merely a GL5 80-90. I know the front diff is a regular "open" with no clutches (limited slips don't work in the front of street driven trucks, don't ask how I know this, LOL).

I just checked the P/N of the fluid I put in (bought an extra qt.) and it's "Auto Trak II P/N 12378508" is this the right stuff? Old stuff? Any TSB's on this topic?

bobcat5544 · February 5, 2007

THERE ISN'T ANY TBS ON THIS, BUT IF YOU ARE IN 2WD AND IT IS BINDING ON TURNS THEN THE FRONT DIFF ACTUATOR IS NOT DISENGAGING. WHICH IS COMMON.

concours · February 6, 2007

THERE ISN'T ANY TBS ON THIS, BUT IF YOU ARE IN 2WD AND IT IS BINDING ON TURNS THEN THE FRONT DIFF ACTUATOR IS NOT DISENGAGING. WHICH IS COMMON.

HOO-RAH!!! Now were cooking with gas... Do you think my choice of gear oil is an issue? Or do the electric actuators usually poop? I know the early electric/thermal actuators always failed retracted (disengaged), but I suppose the new style stepper motor actuator can crap anywhere.... although I should be getting a code.

I also changed the dash selector switch long about the same time this happened... ( had the intermittant "service 4WD" message)

bobcat5544 · February 6, 2007

Do you know what code was stored for the 4x4 system?

You won't get a code for the front diff actuator unless there is a circuit malfunction. The plunger can stick and the 4x4 module will not pick it up.

What you can do is get under the truck with it in 2wd and tries to turn the front drive shaft by hand.

(Note make sure the truck is doing what you stated before you do these test)

* If the front drive shaft turns freely then most likely it is the front suspension (check the hubs and ball joints)

* If it does not turn freely then disconnect the front drive shaft from the transfer case only and then try to turn the drive shaft while connected to the front diff. If it does not turn then the front diff actuator is still engaged (replace the actuator)

* If does turn then try to turn the transfer case front out put yoke. If that does not turn freely then your problem is in side the transfer case. (Possible causes shift actuator did not shift out of 4x4, bent or broke shift fork, and a few others parts.

concours · February 8, 2007

Thanks guys for responding. Tonight I did a few tests.... pulled the actuator out, plugged it back in and shifted into 2H, 4H, Auto 4WD and it extended and retracted properly. I pushed the plunger in with an extension bar, good. I jacked up the RF wheel and it was properly disconnected,freewheeled fine, when I pushed the plunger in by hand, the splines engaged smoothly and the wheel was connected to the diff. I re-installed the plunger and left it jacked up, repeated tests with case in 2H, RF freewheeled. Auto 4WD, RF turned with resistance (clutches in the t-case resisting). 4H , RF was locked to rest of the driveline. Summary, front axle disconnect functioning as designed.

I don't know what code was stored in the AWD system.... I just changed the switch and the message went away.

matt_o_70 · May 26, 2007

Guys,

I am new to GM's and just acquired a 2000 Bravada with the smarttrak. It has the same problem. Is the smarttrak the same thing as auto-trac? (transferr case says new process gear 136GM)

The car is brand new to me when I drove it the previous owner said it has always been doing this for him and that everyone told him that this was normal. He did have the fluid changed and says it made no difference. I checked it it is blue (autotrack2) in the transferr case.

all my experience is with toyota's and I did not believe that this was working as intended! So I am glad to read here that there may be a fix for this.

I plan to jack up the truck and check for where this is coming from.

1) Anyone know where (web-site?) I can read up one the details of smarttrak or auto-trac If they are the same?

2) What service manual would you suggest? as a former toyota technician I am looking for a complete manual, I have never been impressed with the Hayes for imports. Are they any better for domestics?

thanks,

Matt

matt_o_70 · May 26, 2007

Just jacked it up and the transfer case front to back is locked - I can not turn the front freely with out the rear wheels off the ground.

I have seen pictures of the encoder motors on e bay, can I pull this off and turn something back to disengage the front axel? I assume that this is the motor that engages the front axel?

matt_o_70 · May 26, 2007

I just changed the fluid and was surprised to notice an immedieate improvement, I won't yet say it is gone, as I have much driving to do before I am convinced of this, There still is more drive line drag than I would expect.. but again this vehicle is new to me.

I took a look at the transfer case motor and see it says something to the effect of "running it while not connected to transfer case will damage the motor" What's the deal?

Can I test this motor somehow? is this motor turning the shaft to vary the amount of force applied to a clutch pack?

What is the normal range of motion of this shaft?

can I unbolt the motor and manually turn the transfer case shaft to various position, to test the drive line somehow?

Is there a manual someplace that covers this system that can be had reasonably?