Loud Grinding in reverse and now stuck in 4lo

[armgmc]

My truck has the same auto system, however when its in 4 low the traction control and stabilitrak are off and it doesn't try to auto 4 when the dial is not in that position. I don't know off the top of my head what the fuse is labelled as. Once my truck is in 4 low I can't simply switch to other power transfer modes without putting it into neutral first so I have my doubts about it trying to auto 4 when its locked in 4 low.

yeah it didn't grind on me today but it usually does that in 2wd and the stabilitrak and TC does work. not sure how that whole system works though. Would like to have it hooked up to a scanner but im 30 miles from a stealership and don't want to drive that far in 4low. I have a friend that is a mechanic and i'm sure he's got a pretty fancy ODBII scanner so I'll see if he won't bring it home after work tomorrow and scan it for me.

[russellb]

If your friend can scan it that would be best, cause I'm thinking the more you drive it the worse it will get. Given the fact it made a loud grinding noise tells me its mechanical failure right away, so any more driving will only make it worse until you have a catastrophic failure altogether. If you can't scan it, it still wouldn't hurt to pull it off and take a peak inside, could be as simple as a blown bearing. If the fluid in the transfer case has a metallic shimmer to it, then it has seen metal on metal contact for sure.

[armgmc]

If your friend can scan it that would be best, cause I'm thinking the more you drive it the worse it will get. Given the fact it made a loud grinding noise tells me its mechanical failure right away, so any more driving will only make it worse until you have a catastrophic failure altogether. If you can't scan it, it still wouldn't hurt to pull it off and take a peak inside, could be as simple as a blown bearing. If the fluid in the transfer case has a metallic shimmer to it, then it has seen metal on metal contact for sure.

Got the code scanner coming over in a little bit. Took the shift motor off today and the gear on the motor itself that engages the gear inside the TC is locked up. Is that supposed to be like that? I would assume it would free spin but IDK. Found a junk yard TC for $375 but not sure if I want to go buy it without further diagnosis. I tried switching from 4lo to 4hi with gears disengaged to see if something was locked up in the TC but couldn't get the motor to attempt to move for me. I'm thinking those error codes have disabled signal voltage to the TC motor and won't allow it to do anything. Thinking I may need a TCCM reflash or maybe just a new TCCM

[armgmc]

Found something similar to my reversing problem they reference it as "torque reversal" http://www.gm-trucks.com/forums/topic/130945-transmission-problem-speedo-reads-zero-07-nbs/

[gmtech4]

Got the code scanner coming over in a little bit. Took the shift motor off today and the gear on the motor itself that engages the gear inside the TC is locked up. Is that supposed to be like that? I would assume it would free spin but IDK. Found a junk yard TC for $375 but not sure if I want to go buy it without further diagnosis. I tried switching from 4lo to 4hi with gears disengaged to see if something was locked up in the TC but couldn't get the motor to attempt to move for me. I'm thinking those error codes have disabled signal voltage to the TC motor and won't allow it to do anything. Thinking I may need a TCCM reflash or maybe just a new TCCM

you are jumping to a thousand conclusions very quickly ,,you are assuming how it works and what you need ,,,,,you should really stop doing that ,,,,

 

used t case ....... i dont think so tim

 

take it to a tech

[russellb]

Get the motor tested. If its good the you got other problems. The used transfer case could be worse than yours, find out what's wrong first, then explore your options. Do some homework first before you buy anything, if you got the transfer case off the truck and you can afford it, then take it to someone who is competent and can tell you exactly what's wrong with it. Check out YouTube and other websites and see if you can find more information about your transfer case. Information is free, so get lots of it.

[russellb]

Also, when you find out what's wrong, it is possible to have certain parts repaired, like bearing fits, seal fits etc. If a machine shop can repair it for cheaper than new parts then you'll be good that way. Ask for a price quote not an estimate, there is a difference.

[Ramiro Torres]

On 1/1/2014 at 6:34 PM, armgmc said:

Hey guys, first post here. I have a 2007 GMC SLE (new body style) crew cab z71. I've owned the truck a little over a year and theres been a few occasions since i've owned it where while reversing in 2wd or 4wd that something would slip and cause an extremely loud grinding noise almost everytime the wheels spin a little bit (hard acceleration). After realizing this happens I always try to easily accelerate when reversing but sometimes it will do it anyways. I've never had anyone close by to tell exactly where it's coming from but I suspect the transfer case. Tonight I went down to my hunting spot to just check it out and before leaving I thought I'd put it in 4low (turn knob) and maybe keep from spinning as I backed up the hill. after I got out of the spot I was in I tried going back into 2hi or 4 hi but the tcase never would shift back out and the service 4x4 light was flashing on the dash. Wasn't any loud clanks or grinding during all of this so I'm not really sure what went wrong or where to start looking. I'm gonna take it to my shop tomorrow and see what I can find but just wondering if anyone has ever dealt with the problem before. If it weren't for the grinding I'd suspect maybe an actuator but I feel like that's part of my problem. Thanks in advance for any help.

Did you ever find out what was the issue i have 2007 gmc sierra new body style doing the same thing.

[epicureaninc]

Hello All, 

any follow up to this to share?

[Jsdirt]

Just to add a little info, these trucks also eat spider gears for no apparent reason other than GM's propensity for cutting corners to save a nickel. That would cause the exact symptoms the OP described, as would a transfer case failure. Easy enough to pull the rear cover and check the magnet - if you see chunks of metal, get the flash light out, put the truck in neutral, and start checking side gear and spider gear teeth.

 

Same with the t-case - pull the drain plug and check its magnet. Long, thin shards of metal are normal from what I've seen in the "Auto" transfer cases, but any chips or chunks is cause for concern. If nothing's wrong, your gears get new fluid.

[Michael Moss]

My 1999 Chevy Silverado 1500 4 wheel drive is grinding pretty bad in reverse but only in reverse and also recently once you get over 55 mph and have been driving for a few minutes it starts to vibrate in the front end pretty bad

Edited May 25, 2024 by Michael Moss
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