Switching Drive Mods

Khaos05 · January 29, 2007

Ok...i decided that I would test out my 4wheel drive (not in muddy conditions or anything) so I read the manual and it says prolonged use on hard pavement would damage the components, but I just wanted to make sure I could switch and it would engage. I was going about 4mph, put the truck in neutral, and hit 4Lo it blinked for a second and then engaged. It sounded kind of funny and was really jumpy so I drove for about 20 ft and then put it back in neutral and hit 2Hi...this time it felt like the truck jumped off the ground and made a really loud noise...i was like OHHH CRAP!...it drives fine and the manual says something about excessive noise and bump is normal when engaging and disengaging, but i'm not sure how much they mean...anyone else have any ideas?

Rolandd · January 29, 2007

From what I am reading in your post it sounds like you have an electronic transfer case--the control for the transfer case is a set of buttons near the headlight switch. I am not as familiar with this system so others may correct me. I am assuming that if you follow the same rules as with a manual tranfer case (a shift level is on the floor to control this unit) you should be OK.

You should be able to switch between 2- and 4-high at any speed as long as you are travelling in a straight line. The transfer case has no differential, so it is important that you not attempt to corner tightly on hard surfaces as it will put a lot of stress on the drive line. If you can, rolling slowly in neutral is easiest on the driveline. However, I have often switched back and forth as I go between snow covered and clear streets without worrying.

You need to be not moving or moving very slowly to shift into or out of 4-low. When I can I move to a slight grade, put the truck in neutral, and then shift quickly. If it will not go into 4-low during that shift I will let the truck roll gently and try to pop it into gear. The shift should be quick but not forced.

I have found on some trucks that shifting to 4-low can leave you stuck in neutral with the front of the transfer case spinning because there is no load on it. Attempting to shift into anything will grind. At this point I shut down the engine, let the truck roll a little (this is why I do this on a hill) and shift to where I want to be. Some day they may put syncros in these boxes, but for now they are a but cantankerous. I assume that the electronic transfer cases use solinoids to shift, which may account for the banging.

mkeeney · January 29, 2007

Ok...i decided that I would test out my 4wheel drive (not in muddy conditions or anything) so I read the manual and it says prolonged use on hard pavement would damage the components, but I just wanted to make sure I could switch and it would engage. I was going about 4mph, put the truck in neutral, and hit 4Lo it blinked for a second and then engaged. It sounded kind of funny and was really jumpy so I drove for about 20 ft and then put it back in neutral and hit 2Hi...this time it felt like the truck jumped off the ground and made a really loud noise...i was like OHHH CRAP!...it drives fine and the manual says something about excessive noise and bump is normal when engaging and disengaging, but i'm not sure how much they mean...anyone else have any ideas?

That all sounds normal. The truck is really jumpy in 4Lo because the gear ratio is so low. It's best if you can let the truck roll a little when changing to/from 4Lo.

Khaos05 · January 29, 2007

so y'all dont think it is messed up or that I messed it up b/c it made a loud noise (not grinding just bumping and shaking ) when i went from 4Lo to 2Hi?

WindyCityPilot · January 29, 2007

so y'all dont think it is messed up or that I messed it up b/c it made a loud noise (not grinding just bumping and shaking ) when i went from 4Lo to 2Hi?

Mine does the same thing. No problem here so far. Keep on truckin!

juliedean · January 29, 2007

so y'all dont think it is messed up or that I messed it up b/c it made a loud noise (not grinding just bumping and shaking ) when i went from 4Lo to 2Hi?

Not likely at all. There has been a thread or two about the noise when switching into and out of 4LO. Having read some of the earlier postings and from personal experience, I'd say you just experienced the GM transfer case clank.

The slow roll is really the way to do it; it makes the innards engage more smoothly. If you have the transfer case shift into 4LO while standing still, the clank will be very pronounced and may even rock the truck forward a bit, too, which can be unnerving.

Loomis462 · January 31, 2007

when i shift to low range i always stop and put the shifter in neutral, press 4-lo, let it engage, then put her back in 2 or 3 (beach driving) The shift back into gear will be more pronounced since the overall driveline reduction will be greatly increased.

chevroletmb · January 31, 2007

I assume that the electronic transfer cases use solinoids to shift, which may account for the banging.

they actually don't use solonoids, just an electric motor

itsclay11 · January 31, 2007

when i am switching into 4wd, even with 4hi i stop completely and engage when you can switch at any speed, but with 4lo i stop completely and put into neutral and engage. just to be cautious, it's my baby and i don't want to hurt anything.

Khaos05 · January 31, 2007

cool...now i'm reassured that I didn't screw my week old truck up and that everyone else is as bothered by it as I was...i heard the noise and felt it jump and I was like AHHHH!

c4cruiser · January 31, 2007

when i am switching into 4wd, even with 4hi i stop completely and engage when you can switch at any speed, but with 4lo i stop completely and put into neutral and engage. just to be cautious, it's my baby and i don't want to hurt anything.

My 99 owners manual says with the AutoTrac system, moving in or out of 4LO, you should be moving between 1-3 MPH with the shift lever in Neutral. Guess that way the gears will synchronize with no load on the sytstem.

If you are stopped to shift in or out of 4LO, wouldn't a strain be put on the transfer case once you put the tranny in gear? With no movement of the gears, the tranny would send some torque to the system and you could get an initlal noise or shudder once the truck begins to move as the gears engage.

67ChevyRedneck · January 31, 2007

Maybe it's just me, but my truck shifts into 4LO much easier if I put it in 4HI first, put it in N, roll the truck a couple miles an hour, and push the 4LO button. I do the same thing backwards to take it out. It SEEMS to almost never cause any "noise."

Khaos05 · February 1, 2007

I got to test my 4wheel drive out for real tonight...4inches of snow and ice...absolutely NO problems (plus it's fun watching other people helplessly slide)

Khaos05 · February 1, 2007

Does anyone know how bad it is to turn semi-sharply with the truck in 4Hi? Someone said it puts stress on some front component...i did it a few times tonight while driving around town and it made weird noises...

Trouttrooper · February 1, 2007

Does anyone know how bad it is to turn semi-sharply with the truck in 4Hi? Someone said it puts stress on some front component...i did it a few times tonight while driving around town and it made weird noises...

You have to understand how part time 4 wheel drive systems work. When engaged, both 4lo and 4hi, the front driveline is DIRECTLY connected to the rear driveline. This means that one front tire must turn the same speed as one rear tire). No problem driving in a straight line, until you turn your front wheels. Now all of a sudden all 4 tires want to turn at a different rate. This is where stress comes into play. The tires are fighting against each other and the drivelines. Something has to give. Most commonly what happens is your tires will spin/slip a little to match each others rotation. On dry pavement you have so much more traction from your tires you do run a risk of snapping a u-joint or transfer case damage if you make a sharp turn.

Hearing noises is not uncommon when in 4 wheel drive and turning your wheels. In 4lo you will hear a lot of whining noises coming from the transfer case, again normal.