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front axle will not engage in 4x4

47K views 28 replies 12 participants last post by  davester3500 
#1 ·
I have recently purchased a 2000 GMC 2500. Today we got a lot of snow so i went to put it into 4x4 and the front axle did not engage. The transfer case is working and engaged with the front axle spinning as it should. Any idea on what the problem could be or where to start looking? Thanks.
 
#4 ·
The way I would do it is to remove it from the axle and with it plugged in, have a helper put it in and out of 4WD and see if it is working. The truck will not have to move in order to see if it is working, so make sure the helper holds the brake firmly while you are under the truck. You may want the parking brake on and the rear wheels off the ground on jackstands so there is no way for it to move.
 
#6 ·
Finally got a chance to pull the actuator out last night. It seemed to be working fine but I changed it just to be sure that it wasn't still it and it wasn't pushing out hard enough or something like that. As far as I can tell, the 4x4 is still not working.'
 
#9 ·
I put my phone under the truck with the camera to check the drive shaft and pulled ahead a few feet and when it was if 4x4 the front drive shaft turned. As far as noise, I am not sure but i do know that the actuator is working. I had it pulled out and hit the button and watched it extend out, and I put a new one in just in case and still nothing.
 
#11 ·
Could be possible that the transfer case is bad, and what you're seeing is the driveshaft turning because the actuators have kicked in... but the only reason its turning is because the front wheels are. About the only way I could think of to rule that out would be to lift all 4 wheels and put it in gear.
 
#12 ·
Possible the clutches in your transfer case are bad, I've heard of guys having similar problems where everything feels fine, sounds fine, acts fine when they check things out (like putting the truck in the air & running it in 4hi, all 4 wheels spin but when the truck is on the ground only the back wheels spin in snow, mud, etc). Lot of work to prove/disprove but it might be your problem. I've also heard people say they've had their front diff apart & found a missing washer (probably from somebody who didn't know what they were doing taking it apart & putting it back together) that allows the front diff to partially engage but not enough to actually drive the front axle under load. Good luck!
 
#13 ·
Easiest way if no rack or equipment. Unbolt front driveshaft and put in 4x4 and leave in park. Try to turn front yolk on front diff. If solid the front diff is locked and working. Bolt back in driveshaft and if you jack up truck on 4 jackstands and run in 4x4 if front driveshaft spins t-case is engaged and motor is working correctly. This means you have a problem is the t-case. Depending on t-case you could have a burnt up clutch pack which doesnt hold the torque applied when driving comparedto free spining off the ground or a bad viscous coupling. Eithet way t-case would need tore apart and fixed or replaced. If you pit in 4x4 and turn wheel sharp and slowly try to accelerate. Does truck feel like its binding up?
 
#14 ·
tankrat said:
Possible the clutches in your transfer case are bad, I've heard of guys having similar problems where everything feels fine, sounds fine, acts fine when they check things out (like putting the truck in the air & running it in 4hi, all 4 wheels spin but when the truck is on the ground only the back wheels spin in snow, mud, etc). Lot of work to prove/disprove but it might be your problem. I've also heard people say they've had their front diff apart & found a missing washer (probably from somebody who didn't know what they were doing taking it apart & putting it back together) that allows the front diff to partially engage but not enough to actually drive the front axle under load. Good luck!
+1 on this
 
#15 ·
im having the same problems with my 01 1500. I can turn the front driveshaft when in 2wd freely and I cant turn it in 4 hi or lo. its been on 4 stands and only back wheels turn in 4 hi and lo. xfer case and front axle is engaging, just no movement. iv even had the rear on stands and put it in 4 hi and lo with no movement.. no ses or svc 4wd lights any ideas?
 
#17 ·
...just fyi, cm2491 hasn't logged onto the site in 3 years, you are unlikely to get a response from that user...

If you have got the truck up on 4 jackstands, and in 4hi/lo, only the rear wheels spin under power, and manually turning the front driveshaft turns one/both front wheels, that basically points to the mode fork or chain in the transfer case being broken.
 
#20 ·
If, in 4hi/lo, with all 4 wheels off the ground, and in park, you try to manually spin the front driveshaft:

a) you can spin it -> something is wrong with the transfer case, from the encoder didn't shift, to the shift forks broken, or various gears, or the chain. Ie, the problem is with the transfer case (or before it, as in the manual shift lever or the electric button setup/wiring).
b) you can spin it -> good, the transfer case has shifted into 4wd mode (either hi or lo)

Now, block one of the front wheels so it can't spin, and try spinning the other wheel
1) If you can't spin the other wheel, or the blocked wheel winds up spinning -> excellent, you are in 4wd, and the front diff is locked, and the system is working ok
2) if you can spin the other wheel -> bad, something is wrong with the front axle being locked. In this case, you need to figure out if the actuator in the front diff in moving in/out as you shift between 2wd and 4wd. If it is, then something is busted in the front diff (generally the passenger side shaft, or the locking gears). If it isn't, then it might be the sensor in the transfer case, a wiring problem (between the TC and the front diff), or the actuator has failed.
 
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#23 ·
So I lifted up my truck on 4 stands and put it in 4 high and put it in drive the rear tires spin the rear shaft spins as well as my front shaft spins both with it, but the front tires do not..

I also lowered one of the front tires down to see if I could do the 1 wheels spin method and the other 1 didn't move neither did the shaft. So I'm coming to believe I think it's something in the front differential not locking in Maybe the shifting fork or the gear on the passenger side of the front dif.

Now with that said I know you don't have to take the whole dif out to do it but what would be the easiest way to pull that half off I have seen videos that is another model truck where they take the whole wheel caliper ,hub etc off to get to it but I read in a forum that you don't have to do all that, anyone have a link to a video or a suggestion. I greatly appreciate all the help BTW everyone helps alot.
 
#29 ·
From looking at a youtube video, it does look like your diff does split where the actuator screws in, similar to how it is for my truck, so it's likely just splitting it, you can replace the part/s you need to (not guaranteed, it is possible for something to have broken that requires the diff to come out, it's just much more common for the bits around that split to fail).

I would suggest getting a subscription to the full service manual at a site like alldatadiy.com , to see what has to be done for your truck...
 
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