DBO - the lost transfer case thread

[MJEasly]

I had prepared a response but something happened to the thread. Looks like Jim had a server issue of some sort.

Anyways, I wanted to respond to your questions about the autotrac transfer case.

To summarize: My service 4wd light is on. The case has a very difficult time shifting from 4hi to 2hi (I have not found a way to trick it either, it is pure luck if it returns to 2hi). It shifts fine from 2hi to auto and 4hi. The switch light will blink several times and a clicking noise similar to a noise a relay would make can be heard from behind the dash. The front end has slight torque steer in 2hi and pulls slightly to the right. The wheel is way off center. There is now a thump in the driveline and a constant,slight vibration like the transfer case is engaged/driveline drag. The encoder motor was replaed about a year and a half ago.

IIRC, the front end actuator or the driveline sensors could be the culprit.

I plan on placing the truck on jack stands this weekend in order to investigate further with testing.

[DA BIG ONE]

Originally posted by MJEasly:
I had prepared a response but something happened to the thread. Looks like Jim had a server issue of some sort.

Anyways, I wanted to respond to your questions about the autotrac transfer case.

To summarize: My service 4wd light is on. The case has a very difficult time shifting from 4hi to 2hi (I have not found a way to trick it either, it is pure luck if it returns to 2hi). It shifts fine from 2hi to auto and 4hi. The switch light will blink several times and a clicking noise similar to a noise a relay would make can be heard from behind the dash. The front end has slight torque steer in 2hi and pulls slightly to the right. The wheel is way off center. There is now a thump in the driveline and a constant,slight vibration like the transfer case is engaged/driveline drag. The encoder motor was replaed about a year and a half ago.

IIRC, the front end actuator or the driveline sensors could be the culprit.

I plan on placing the truck on jack stands this weekend in order to investigate further with testing. When it gets stuck in 4wd hi and will not shift back, shut down truck for about 1 minute, as you restart it you should be able to shift it into 2wd.

You want to determine what is not disengaging the t-case or frt differential?

You have an open carrier, then when you grab frt driveshaft while truck is parked, it should spin if t-case is in 2wd, or neutral. If it does not spin then disconnect frt driveshaft at frt flange w/truck off ground to see if it the t-case, or frt diff causing issue. Keep in mind excessive wear will cause binding.

I'd check all the drivetrain mounts, making sure frt diff has not shifted right, or left because of loose bolts (2 big ones)attaching frt diff extension housing to chassis on pass side. Look at all the drivetrain mounting bushings for damage, or drivetrain conponents contacting chassis causing vibrations, or whatever?

Frt diff, and t-case should only move as much as the hard rubber mounts allows to reduce vibrations

Take a sample of each ones fluid, look for metal, and or burnt fluid.

All three sensors are located on t-case, rear driveshaft sensor and speed sensors are located on top and back of t-case, the frt driveshaft sensor is near the frt t-case output shaft.

W/encoder motor off t-case it can be shifted w/wrench from high to low range, center being neutral, do this to see if anything is binding inside t-case.

[MJEasly]

Well I finally had a chance to crawl under the truck and do some testing. I placed the truck up on jack stands so I could observe what was actually happening with the transfer case.

Initial observations:
- Transfer case and surrounding undercarriage is wet with tcase fluid. Looks like the rear driveshaft seal is seeping. I wonder if there is a slip-yolk eliminator for the auto-trac case?
-There is some play between the front and rear drive shaft when engaged in 4wd, about 1/8 to 1/16 rotation between the two.
- Powering down the truck causes the encoder motor to make a short noise.
- Transfer case will not shift into neutral (hold 2hi and 4low for 10 seconds)
- In auto mode, the front driveshaft is engaged and turns with the rear drive shaft. The front axle appears to be engaged (driver side tire will turn in the oppposite direction when passenger tire is turned).
- Started truck and went through a shifting routine. ABS light came on and the tcase went into 4lo. Turned off the truck for 5 minutes or so and restarted. Tcase now in 2hi.
- Front axle is disengaged in 2hi. Spinning one wheel does not turn the other wheel or driveshaft.
- Getting into 2hi is hit or miss. No technique ever works twice in a row.
- Only consistent shift is from 4hi to Auto and back. Not sure if anything is actually happening, though.
- Auto mode locks front drive shaft and wheels (axle).
- Pulled speed sensors and inspected. Wiped clean, tested for continuity and replaced.
- Swapped the 4x4 switch with a known working switch with no change in operation.
- All electrical connections seemed tight.

Tests:
2hi to 4hi - Encoder motor makes noiseand apparently shifts the tcase into 4hi. Driveshafts are locked.

4hi to 2hi - Encoder motor makes noise like it is trying to disengage and does this 2 times. 2hi light blinks about 12 or so times before going back to 4hi.

4hi to Auto - encoder motor makes a single long duration noise. Auto light shows instant engagement after a blink or two.

Auto to 4hi - No noise from encoder motor. 4hi light blinks once and burns steady.

4hi to 4lo - 4lo light blinks about 40 or so times and then gives up. No encoder noise.

Auto to 4lo - Same as 4hi.

Auto to 2hi - Encoder motor trys to shift and gives up after 2 attempts. Light defaults to 4hi instead of Auto.

Thoughts:
- The pull or excessive torque steer I was experiencing must be from the alignment. The truck tracks and brakes straight. The wheel is off center and I think it is unrelated to the tcase. Probably damaged the front end when I put a wheel in the ditch the other day.

- There is a clunk sound related to the front suspension that at first sounded tcase related (front axle engagement). All brackets and mounting assemblies appear tight, straight and solid. It may be the brake pads clicking around in the caliper, but it sounds a little too substantial for that.

- Fluid sample seemed fine. Adding tcase fluid is a bear. Tcase fluid level was very low. I wonder if that can set off a service light?

- This may be ABS or other sensor related. I checked all sensors for visible damage but all seemed ok. That just means ther isn't any visible damage.

- Looks like I have exhausted my ability to fix this tcase and I'll be making an appointment with the dealer to have it fixed. I anticipate serious problems and have a funny feeling that my case is toast.

What a way to ring in the new year.

[DA BIG ONE]

Is t-case fluid level correct? If not, top it off w/GM's NP246 fluid that has special additives for the t-case clutch pack (10 clutches)

You should look at doing repair or change out yourself case weighs 85 lbs. Here is what I was told be more than a few dealers, "the t-case is expected to last 150,000 miles under normal usage", New Process says if taken care of (proper pm) they last a long time and many more miles that dealers claim.

Only shafts I know of are front ones special built for lift kits, rear driveshaft output is slip only, but I'm sure if you have deep pockets some custom fabricator can do, but it would still need the slip joint somewhere else in shaft! I suggest if you do anything to rear shaft, get it modifed to accept u bolts at u-joints instead of the strap crap on it now!

Bottom line the dealer wants $3,000.+ for t-case, do it yourself a new t-case is under a grand, then figure in your labor, or some good shops labor.

There is an issue with rear case wearing through from the inside and causing leak, and because its magneisum no one wants to weld it to fix leak, later cases have a hardened protector to prevent the wear through, sonnex http://www.transmissionspecialty.com/ should have the upgrade part.

Rear case and other common wear parts can be bought aftermarket, at http://www.drivetrain.com/transfercasesparts.html#New%20Process%20Model%2024 6

Front case uses a 2 piece bushing that requires a special tool to install http://www.omegamachine.com/html/New_Process_246_seal_installer.html

Best price new, or rebuilt is from the factory distributer under a grand new, at http://www.transfercases.com/

[ 01-05-2006, 10:41 AM: Message edited by: DA BIG ONE ]

[MJEasly]

Thanks for the info. I'm hoping it is a sensor or something like that. I'll post what I find out, and if it comes to replacing the case, I'll take pictures.

[DA BIG ONE]

Originally posted by MJEasly:
Thanks for the info. I'm hoping it is a sensor or something like that. I'll post what I find out, and if it comes to replacing the case, I'll take pictures. If not high miles, burnt clutches/steels, or damage from lack of lube, it maybe a loose chain issue as you mentioned the driveshafts turned slightly different "frt/rear shaft speed sensors would detect this". So instead of shifting to a % of torque the encoder motor would give full engagement of t-case always" meaning autotrac would not work properly in auto mode.

The t-case encoder motor uses a slider shifting system just inside case, this in turn moves a clutch fork setup to fully lock t-case, or give a certain % of clutch engagement using shaft speed sensors, abs, ecm to determine the actual %.

I made an error in my response to your first question about case functions, I was using my case function as the standard, it's not because I have a locker and the carrier design drives the frt/driveshaft always, even when in 2wd. Because of this my auto function does not work as designed and locks the clutch pack to full tq.

[MJEasly]

Turns out to be a bad wiring harness, damaged by the dealership when they changed out the encoder motor.

[DA BIG ONE]

Originally posted by MJEasly:
Turns out to be a bad wiring harness, damaged by the dealership when they changed out the encoder motor. Glad to hear you got it working, how about the leak?

I did check w/NEW PROCESS TECH yesterday, they said any good synthetic ATF can be used in the NP246. So, the case does not have to have the GM only special fluid!

[MJEasly]

That's good to know.

Concerning the leak, I put a new GM OEM rear yoke seal on the back and cleaned the case. I did this yesterday and have drips on each of the lower case bolts and some other low areas. Not sure if this is normal, but I can't seem to find the source of the leaking.

I'll keep an eye on it and see what develops.

[DA BIG ONE]

Originally posted by MJEasly:
That's good to know.

Concerning the leak, I put a new GM OEM rear yoke seal on the back and cleaned the case. I did this yesterday and have drips on each of the lower case bolts and some other low areas. Not sure if this is normal, but I can't seem to find the source of the leaking.

I'll keep an eye on it and see what develops. If it is the case leaking then it needs your attention say every other week to check fluid level, then figure from there if its worth just topping off fluid, or needs gaskets?

Again, good to hear its was not a big $$$$ issue.