4 Wheel Drive

[Woody]

Hey guys... gotta question. Normally I run my truck in auto 4 wh. But yesterday it was raining pretty bad so I put the truck in 4 high. Well, I noticed after that a little creaking and jerkiness to acceleration and was like huh? So I changed it back to auto 4 and then back again after a little while to 4 hi and now it seems normal. What was that? Just wondering if I should be concerned. Thanks guys.

-Woody

 

[RichUF]

(warning...blunt post ahead...no personal offense intended)...

You are not suppose to "normally" run your truck in auto 4WD and you are especially not supposed to run your truck "normally" (even if in rain) in 4 hi.

This assumes that your "normal" means on the pavement, rain or no rain.

 

[bekind]

The creaking and acceleration was your truck trying to tell you not to run in 4x4 on pavement. If you tried to turn sharply on dry or slightly wet pavement the truck will make all kinds of noises. Even in the rain, full time 4x4 is probably not recommended due to the inability of the front wheels to turn differently when turning...

~bekind

 

[Tree_Hugger]

I strongly advise you to read your owners manual on this subject...
No, you probably (virtually certainly) haven't done any damage.

4 High is a 'part time' 4WD system. This means that there is NO center differential. This means that your front and rear axles are locked together and must turn at the same speed. Since your front and rear wheels are not EXACTLY the same diameter, then this cannot happen unless one set of wheels can slip a little, occasionally. This cannot happen on dry pavement, and is fairly unlikely on wet pavement. So stress builds up in your drivetrain (actually in your Transfer Case) and that can break something! Usually it just gives the sort of symptoms you describe, as the stress builds up, and the owner takes it out of 4 High (as you did) and the stress is relieved.
4 Auto is a special situation. You are basically in 2WD, but with your front axle all hooked up and ready to go except for one final link that is electrically disengaged. WHen the computer detecs rear wheel slipping (by different speeds on front and rear axle) it engages that final connection and puts you in 4 high (part-time system, remember). At some point the computer decides to put you back in 2WD. We haven't found out how it decides yet!
(Full time 4WD, or All Wheel Drive, always has a center differential to allow the front and rear axles to turn at different speeds. We don't have that - but the Caddillac EXT does.)
The safe protocol is:-
2WD normally
4 Auto when the possibility of wheel slippage exists.
4 High when the certainty of wheel slippage exists.

I usually run in 2wd, and pick 4 Auto in heavy rain. 4 high only offroad. Sometimes I forget to take it out of 4 Auto for a day or so after the rain stops - no real problem....
HTH.

 

[Lockout]

Here's a little piece of info that was taught to me when I was just learning to 4x4...

Run in 2-wheel drive as much as possible.
Use 4-High to get out of trouble.
If you need to use 4-Low... You probably shouldn't be there, but since you are... Have fun

 

[Blueruck]

I will even try hills in 2wd until I slip and must put it in Auto - I have to have some real water or a deep hole to cross before I go into 4Hi or 4lo

I went through a blizzard last year with 1 - 1 1/2 feet of snow on the roads - used Auto the entire time.

 

[TXAVy]

Great explanation, but I think there's another more important reason for this part...

4 High is a 'part time' 4WD system. This means that there is NO center differential. This means that your front and rear axles are locked together and must turn at the same speed. Since your front and rear wheels are not EXACTLY the same diameter, then this cannot happen unless one set of wheels can slip a little, occasionally. This cannot happen on dry pavement, and is fairly unlikely on wet pavement.

I agree that your front and rear wheels MIGHT not be exactly the same diameter, though if they're all the same wheel/tire like they should be then they whould be pretty darn close.

The bigger problem though comes when you go around a corner. As you turn in a circle the back tires cut a smaller circle than the front tires. This is the same for any car, bicycle, wagon (or any other vehicle with front wheel steering). Check the tracks in the sand if you don't believe me. When you do that, the front and rear of the vehicle are going forward at the same speed (they're attached by the frame), but they're going around two different size circles, so the front tires travel farther than the rear ones. This is what causes all the binding in a 4WD system and anyone who's ever turned a VERY tight corner while locked in 4hi or lo can attest to.

So along with the advice above, I'd recommend not to turn your steering wheel all the way right or left when in 4wd. Short instances shouldn't be a problem, but repeated use that way could cause damage even off road.

 

[Lockout]

Agree with most of it but the 4-Low comment...

If you're offroading and you're running at low speeds and need torque to the front wheels you probably want to be in 4-Low. Examples: Death Valley, running over and around rocks at low speeds. (see images below)

Like I said... I was told it while learning the ropes... I don't think someone just learning to 4x would be running Death Valley. I'm just starting to get back into it, and won't really be running it for a little while... Need to lift my truck, get more gear, etc...

Since most people don't really need 4-wheel drive (Yes there are those of us that do use it), a lot of people will try to use it whenever they can. Even if the decide to leave the pavement... as soon as they hit a fire road they kick it in 4-High. They never bother to learn how to use the truck... but they think that they know how to just naturally.

Disclaimer: I made a bunch of generalizations in this post. I know there are many of us here that really push our Avs, and make them perform, both on road and off. My comment were more aimed at the yuppie group that buys a 4x4 and never uses it.

 

[RichUF]

Great explanation, but I think there's another more important reason for this part...

4 High is a 'part time' 4WD system. This means that there is NO center differential. This means that your front and rear axles are locked together and must turn at the same speed. Since your front and rear wheels are not EXACTLY the same diameter, then this cannot happen unless one set of wheels can slip a little, occasionally. This cannot happen on dry pavement, and is fairly unlikely on wet pavement.

I agree that your front and rear wheels MIGHT not be exactly the same diameter, though if they're all the same wheel/tire like they should be then they whould be pretty darn close.

The bigger problem though comes when you go around a corner. As you turn in a circle the back tires cut a smaller circle than the front tires. This is the same for any car, bicycle, wagon (or any other vehicle with front wheel steering). Check the tracks in the sand if you don't believe me. When you do that, the front and rear of the vehicle are going forward at the same speed (they're attached by the frame), but they're going around two different size circles, so the front tires travel farther than the rear ones. This is what causes all the binding in a 4WD system and anyone who's ever turned a VERY tight corner while locked in 4hi or lo can attest to.

So along with the advice above, I'd recommend not to turn your steering wheel all the way right or left when in 4wd. Short instances shouldn't be a problem, but repeated use that way could cause damage even off road.

I'm pretty sure TreeHugger was referring to the turning circle diameter and not the tire diameters, but you never know I guess

 

[Tree_Hugger]

I'm pretty sure TreeHugger was referring to the turning circle diameter and not the tire diameters, but you never know I guess

Actually, RichUF, thanks for the thought , but TXAvy was right, I totally failed to mention (forgot!) the turning circle diameter thing!
It doesn't change much, but adds even more emphasis to the 'only offroad for 4 High'.
Off road though, the trails I go on, I'm in 4 LOW ALL the time, and turning the wheel to the max a LOT. It's fine as long as the wheels can slip somewhere. Not a problem in Tennesse mud!

 

[Woody]

Okay, consider me officially shamed. I didn't know that I shouldn't have it in Auto 4WD, but now comes the really stupid question then... how in the heck do you not have it in auto 4WD? Okay... beat me to a pulp now.

-Woody

 

[RichUF]

Try the little button below the auto 4WD with the 2 on it!

 

[Woody]

Not being in my truck right now I'm going to say this, "Theres a two wheel drive button?"

-Woody

 

[RichUF]

OK, it's taken me 13 posts to say this but here goes...

You're joking, right?

I'll play along...

Yes there is a two wheel drive button

 

[dunes_av]

Ok, many of you I am sure will disagree with my point of view here.

When I am driving on a dit trail I keep the truck in 2wd, as soon as I see it is loose or there is mud ahead I shift into 4 hi. If you put the truck into 4hi before you need to, will avoid the hassles of being stuck. I have only had to use 4low once, and that was in a friends truck.

I am not sure how the hubs on the AV work, but in vehicles I have owned in te past the front wheels must turn in order for the automatic hubs to lock. So if you get stuck and are in 2wd.... shifitng into 4wd will do nothing, as the hubs cannot engage, (my reason for always shifting into 4hi BEFORE I really need to). In other words, get stuck in 2wd, shift into 4wd, transfer case may be engaged, but the front hubs are not, so no power is actually being put to the front. (imagine a truck with manual hubs, leave the hubs unlocked, but put the transfer case in 4wd)

Anyone know how the hubs on the AV work? are they vacume assit? or must the wheel move in oder for them to engage?

Grey

 

[Tree_Hugger]

No hubs at all.
Old tech.
Outmoded concept.
4 Auto will successfully do exactly what you describe attempting with hubs.
And, by the way, you should have locked your hubs, but not neccessarily engaged 4wd, as soon as you got offroad in your old truck.....

 

[dichris]

I would like to add to the comment about being in 2 wheel most of the time...

2 Wheel mode - All the time except, the following,
Auto 4X - when slippery condition exist
4H - When even more slippery condition exist and not on pavement...
4L - When high torque is required and NOT on pavement... Unless your mad with the owner of the driveway your on and the pavement is really hot, just remember to turn the front wheels hard and watch the pavement get ripped up....( make sure its NOT your driveway )

Oh yeh!! I wanted to say is, Its good to go into Auto 4X and 4H mode periodically to help lubricate and make sure the system is functional. 4L I engage about once every 6-8 weeks.... to make sure its worked a bit...

 

[TXAVy]

Oh yeh!! I wanted to say is, Its good to go into Auto 4X and 4H mode periodically to help lubricate and make sure the system is functional. 4L I engage about once every 6-8 weeks.... to make sure its worked a bit...

I'd heard (and agree) with putting it in 4wd once in a while to make sure all the parts are lubed, but had never heard that about 4-Lo. I thought was exactly the same mechanically as 4-HI except that the transmission is limited to 1st gear only. If so then all the same parts move and lube themselves in 4-HI as 4-LO.

 

[Bisonovich]

actually in 4 lo i thought the final drive ratio was changed and not that it was limited to just first gear otherwise 4hi in 1st instead of drive would work the same but it doesn't

 

[RichUF]

I don't have the right terminology to go with this, but 4LO is definitely another "set of gears" or whatever...I think in the transfer case. Anywho, there is a definite clunk or more like a metalic ping when engaging and disengaging 4LO (yes I roll @ 1-2 mph like the manual says).

I'm a newbie 4WD'er, can you tell? Only had it in 4LO a couple of times to see if it was working is all. Need some opportunity to practice a little.

 

[yellowz71]

4wLo works great to pull bushes out. I started in 2w tires started to spin, went to 4HI no spin but was not doing the job, 4Lo pulled it right out. I was pretty fun.

 

[bekind]

I was in and out of 4lo this weekend while playing in the mud and you can definently feel it kick in. I would describe it as a whirling noise then a clunck, it did this everytime i went in and out, never had a problem...

~bekind

 

[RichUF]

mine actually pings like hitting the drive shaft with a wrench or something...not worried about it though.

 

[ygmn]

4LO is a different gear in the transfer case.....it changes the final ratio and well makes the truck go slow and pull like the dickens.....

IT would be worth at least running a bit in it once year to make sure it still works....and to clean the gears of gooky stuff.....

HTH

 

[TXAVy]

Gotcha, sounds like the creeper gear on my grandfather's f@rd tractor. It was just a little 12 or 16 hp engine, but he used to pull stumps out like they weren't even attached to the ground at all. Even really big stumps came right out but you had to know the trick on how to pull them. I've never done it myself, but it was a sight to see.

He'd first cut the tree down leaving about a 3' or so stump. The nice tall stump helped give some leverage in yanking it out. He then wrapped a chain around the top of the stump and hooked it to the tow bar on the back of the tractor which he also raised up fairly high. He then pulled the chain tight and then slowly let the clutch out in the creeper gear. The chain and stump couldn't move, but the tractor would try to walk right out from underneath itself, slowly pulling the front end up in the air. After he had about 3'-4' of air under the front tires he'd push in the clutch so the tractor would start to fall, and then pop it back out again before the tires touched down. This basically put all the weight of the falling tractor right on the top of the stump and more often than not it popped right out. No stump ever survived 2 or 3 yanks like that without coming out.

I don't recommend doing this if you aren't familiar with it though, as i'm sure it would be REALLY easy to roll the tractor right over on top of yourself if you did it wrong. Very fun to watch when you're a 10yr old kid though.