Possibly blew up my front diff

[ihasahoe]

Hey guys made a intro thread so you guys can kinda know where im coming from but from my other forum were required to make a intro thread before we post.

My brother was driving my Tahoe after I picked it up 2 weeks ago and he was heading to a friends so then later on we headed out to palmdale to visit some other friends. While going a crusing speed of 70mph (it was raining really hard) the front my tahoe made this really nasty griding noise and it started kinda moving left and right so i threw on my hazards and panicked and started moving to the right side of the freeway. I managed to avoid any accidents but it was a scary feeling. I started to move the tahoe forward again on the slow lone and it drove fine im like wtf?? Went this at a crusing speed of 65mph but this time it did it again the from felt like it was sliding or something but the steering wheel wasnt moving at all. I asked my bro wtf he did yesterday he said nothing i just drove it and came back. I eventually got him to confess that he pushed the auto 4wd while going freeway speeds around 75mph. He said it did the same thing it was doing right now. I got out and checked around for any visual damaged stuff leaking oil or cracked something but nothing. It also does it like a normal driving speed and I switched it to 2hi again. The moment i drove it i switched it to 2hi. I called a couple of people and was told that sliding I was feeling was one of the two tires from the front wanted to spin the opposite way or was locking up. Then he gave me a huge lecture about what might off happened something about the 4x4 not fully engaging or something lilke that. He sold me to throw it in reverse and push the gas pedal quickly and upon doing that I herd a noise like a clunk sound like something unjamming. Hopefully somebody can tell me what exactly happened and if you need to know anything else just let me know. I appreciate any help guys.

Any possible ideas on the damages my bro did to my truck??
What should I check for and im stuck in palmdale without my tools.

 

[Gordy]

Engaging the auto 4wd does not mean that the wheels are engaged. It is ready for a break in traction from a wheel then it engages. 4hi engages everything, as does 4lo.

You can run in auto 4wd on dry pavement etc will not hurt anything IF the system is functioning properly.


Are you sure the front end is good on it? Wheel hubs, inner outer tie rods etc.

Are all tires the same size, and wear?

 

[ihasahoe]

Engaging the auto 4wd does not mean that the wheels are engaged. It is ready for a break in traction from a wheel then it engages. 4hi engages everything, as does 4lo.

You can run in auto 4wd on dry pavement etc will not hurt anything IF the system is functioning properly.


Are you sure the front end is good on it? Wheel hubs, inner outer tie rods etc.

Are all tires the same size, and wear?

ahhh that makes sense ill look into that. It never did it until my bro hit the auto4wd. It did the same thing even in 2hi so im lost but is there anything i should have the shop look at or something. The tires have a lot of thread left and the dealer printed a copy of the alignment sheet. I just hope its nothing bad or something that costs a lot to fixed since I cant afford 2 broken down cars.

 

[Gordy]

The best I can tell you is that I have never experienced this nor read of it happening. I think it would be worth letting a certified mechanic look into. If serious enough to make you lose, or feel as though you are lossing control of the vehicle. Its not just you that could be injured by catastophic failure of a drive train component.


You can do a check of the front wheels to see if there is slop. Jack up each front wheel give a 3:00 and 9:00 tug push to see if there is slop. Check like that at 6:00 and `12:00 for slop. Usually slop in the later indicates wheel bearing. Slop the other way indicates tie rod components. Also spin wheel to listen for unusual noise which could indicate wheel bearing also.

 

[ihasahoe]

One of my friends came by and he lifted the rear of the truck in the air and told me to put it in drive and the wheels started spinning but there was this grinding sound coming and when the grinding started the wheels started to slow down and it looked like it was twithing as in it looked like it wanted to stop but kept going. I think the rear diff blew up or lost a couple of teeth or something.

 

[Gordy]

Better the rear than the front diff if it had to be one.

 

[Jay]

Probably damaged the encoder motor drive in the front axle. Better pull it off and check things out. But, i remember somewhere that the axle lock shouldn't occur unless under a certain speed. Maybe not, but if so then that's a MAJOR oversight by GM. That's a splined collar connection and can't take a difference in rpm during engagement (once you pull it down you'll see what i'm talking about.)

Pushing the Auto4wd engages the front axle (locks it together via that little motor you see beside the front diff), but does not engage the front driveshaft at the transfer case. The front driveshaft will turn with the tires since the diff is locked, but the tcase isn't turning it unless slippage is detected.