What situation would an everyday driver use 4x4HI over awd?

[bspurloc]

My daughter asks me when she should use 4x4 instead of AWD and I really have no answer.
I really dont know exactly how they are different.

I was under the impression 4x4 is for off roading but rally cars are AWD so now I am confused.

I tell her just stick with AWD.

Everyday driving would be rain, unpaved snowy roads 6 inches of snow or more...
If you were stopped on an unpaved inclined road AWD or 4x4?
If she slid off the road onto snow covered grass AWD or 4x4?

Doesn't 4x4 cause sharp turning issues of the axles slapping?

and this is going to totally sidetrack the whole Primary question, so only answer this if the first one was answered!
when do u use 4x4LO? pulling someone out of a ditch? and yes I know how to get it in and out of 4x4LO I used it to pull my mothers car off a wet lawn she had decided to park on and got stuck...

 

[kjkim93]

Well for the gmt 360 platform you should never actually be in 4x4 or auto in dry situations. Only when the situation calls for it. Using either on dry situations is definitely going to dry out any of the clutches in the transfer case and something will break. Someone with more experience will chime in later on. When the snow isn't sticking or there's some ice and build up i leave it in Auto and let the car figure it out. Whenever there's fleets of snow or a whole pile I put it in 4x4

 

[bspurloc]

Well for the gmt 360 platform you should never actually be in 4x4 or auto in dry situations. Only when the situation calls for it. Using either on dry situations is definitely going to dry out any of the clutches in the transfer case and something will break. Someone with more experience will chime in later on. When the snow isn't sticking or there's some ice and build up i leave it in Auto and let the car figure it out. Whenever there's fleets of snow or a whole pile I put it in 4x4

I didn't know it had an auto option! I seem to ask people this all the time what is the difference?
one spins at least 1 wheel per axle or spins 2 on any axle or something.
She always keeps it in 2wd until it snows or is icy she puts it in AWD, but recently she had to drive on unpaved roads and put it in 4x4.

 

[Sparky]

If traction is good (dry roads, even general unpaved roads since traction is still going to be fine if dry) just use 2WD.

If it is really snowy/icy use 4WD. A4WD would be when it is a mix of dry tracks and snow covered and you don't want to be in full 4WD due to that, however I tend to shy away from A4WD and just use 2WD for that and stay aware of the road condition changes and adjust speed accordingly. A4WD can be a bit on the harsh side when it throws into 4WD and back.

 

[Trkdrvremt]

Hello and welcome. To start let me say I am still new to this platform so I am in no way an expert on this. From what I have personally experienced is A4WD only kicks in the front axles when it detects slippage from the rear wheels. Meaning if you are turning and the front wheels continue to slide in the direction you are moving 4 wheel drive will not kick in. I was playing with the A4WD and 4hi options with the last snow we had. I had it in A4WD and while taking a turn the truck continued going in a straight line due to no slippage to the rear. 4Hi will keep the front axles locked at all time preventing this from happening. Just my . I'm sure the more experienced members will help explain it better..

 

[Envoy_04]

A general rule I follow is if it's bad enough I think I might need the front end pulling, I go to 4hi and keep speeds reasonable, you shouldnt be going at highway speeds if conditions may warrant 4wd anyhow. Auto mode is very harsh sometimes when it kicks in, it will tear something up if allowed to engage harshly at higher speeds. The only time my Envoy sees auto mode is when I turn the selector past it and into 4hi. (Or 4lo, if I'm playing off road)

 

[bspurloc]

so 4WD is best on unplowed/badly plowed roads as it will hold the road going around corners, but you dont want to be in 4wd over 55mph?

I should take her truck out and test it!
I drive a RWD Crown Victoria, and know how to get around without getting stuck. Studded snows and if I need to be on unpaved roads I have chains.

 

[Sparky]

Thing with 4WD is it locks front and rear axles together, so if you're on a surface with good traction that don't allow for slippage (like dry roads) then it causes driveline bind when you go around turns. Slick surfaces when you need 4WD will allow for the bit of slippage for the driveline to not bind up. Just the way full 4WD works.

This does mean it is easy to see if 4WD is functional. Put in 4WD in a dry parking lot, turn the wheel, and (slowly) start making a turn. If it feels like it binds and "crow hops" then you know 4WD is working

Generally speaking if the conditions are bad enough that you need 4WD you shouldn't be going 55MPH. Remember, 4 wheel drive is called that for a reason - it helps you DRIVE, but does nothing for you when you need to STOP.

 

[AtlWrk]

A few points I didn't see mentioned:

First, our sister site www.Offroadtb.com has an excellent article in there Tech Docs section about how our transfer case works.

Second, to clarify, we do not have AWD (as in All Wheel Drive) mode--we have Auto 4-Wheel Drive (A4WD) and 4WD. They are distinctly different.

I used to be in the "avoid A4WD mode" camp until the last few winters here in New England. I've used it more in the last month than any other mode because:
a. I have religiously maintained and inspected my transfer case and 4wd drive components.
b. The transfer case engagement when the rear starts to slip is unnoticeable, even on snowy hills--far less harsh on the drivetrain than even a shift from the transmission. YMMV
c. With snow every 5-7days the road conditions change from wet to dry to packed snow to wet to slushy to completely unplowed...etc. every 10 feet.
d. Switching between 2wd and 4wd also engages/disengages your splined disconnect which (despite a full rebuild) I have much less faith in structurally than my transfer case.

With a 2002 MY do you know the maintenance history of the transfer case? Fluids changed every 50k? My advice, when conditions allow, is to have her drive around and practice in each mode. The only absolute rule IMO is no 4WD in non-slippery (dry/just wet) conditions. You can "arguably" stay in A4WD mode indefinitely provided your TC is in good condition, but your gas mileage will suffer and you will see extra wear in your front differential (negligible) and transfer case clutches.

Probably raised more questions than answered

 

[bspurloc]

Thing with 4WD is it locks front and rear axles together, so if you're on a surface with good traction that don't allow for slippage (like dry roads) then it causes driveline bind when you go around turns. Slick surfaces when you need 4WD will allow for the bit of slippage for the driveline to not bind up. Just the way full 4WD works.

This does mean it is easy to see if 4WD is functional. Put in 4WD in a dry parking lot, turn the wheel, and (slowly) start making a turn. If it feels like it binds and "crow hops" then you know 4WD is working

Generally speaking if the conditions are bad enough that you need 4WD you shouldn't be going 55MPH. Remember, 4 wheel drive is called that for a reason - it helps you DRIVE, but does nothing for you when you need to STOP.

Yeah ive heard the axle pops when it was accidentally put into 4low. I thought it was only 4low that hopped in turns but your explanation explains it better.
I was talking with a friend apparently AWD is done in a few different ways and on this vehicle I assume the Chevy way is done the dumb way. His Dodge truck is always in AWD which means when he is on snow and punches it all 4 wheels spin, when that is not optimal he can switch it to 4WD.
That must by how rally cars do it because it makes more sense and follows the meaning of ALL WHEEL DRIVE, not this wheel/axle then that one if needed.

 

[bspurloc]

A few points I didn't see mentioned:

First, our sister site www.Offroadtb.com has an excellent article in there Tech Docs section about how our transfer case works.

Second, to clarify, we do not have AWD (as in All Wheel Drive) mode--we have Auto 4-Wheel Drive (A4WD) and 4WD. They are distinctly different.

I used to be in the "avoid A4WD mode" camp until the last few winters here in New England. I've used it more in the last month than any other mode because:
a. I have religiously maintained and inspected my transfer case and 4wd drive components.
b. The transfer case engagement when the rear starts to slip is unnoticeable, even on snowy hills--far less harsh on the drivetrain than even a shift from the transmission. YMMV
c. With snow every 5-7days the road conditions change from wet to dry to packed snow to wet to slushy to completely unplowed...etc. every 10 feet.
d. Switching between 2wd and 4wd also engages/disengages your splined disconnect which (despite a full rebuild) I have much less faith in structurally than my transfer case.

With a 2002 MY do you know the maintenance history of the transfer case? Fluids changed every 50k? My advice, when conditions allow, is to have her drive around and practice in each mode. The only absolute rule IMO is no 4WD in non-slippery (dry/just wet) conditions. You can "arguably" stay in A4WD mode indefinitely provided your TC is in good condition, but your gas mileage will suffer and you will see extra wear in your front differential (negligible) and transfer case clutches.

Probably raised more questions than answered

so in the recent snow you drive a4wd? I'm not familiar with her car I thought the dial was 2wd, awd, 4hi, 4lo.
Yeah I just am realizing this isnt actually AWD.
at 195,000 miles I dont think the fluid has ever been changed or any maintenance ever done on the transfer case. I know the car was bought used at I think 75 or 95k from a used car dealership, so if they did anything it was 100k ago. This was probably the first time she has put it into 4wd mode.

 

[bspurloc]

oh wait...
so its A4WD so it sits in 2wd and if the front spins it goes into auto 4HI?

 

[Trkdrvremt]

Yes that is correct..

 

[Trkdrvremt]

Except for it takes the rear to spin to engage not the front...

 

[AWD V8]

The A4wd is NOT AWD. AWD means that you can use it on ANY surface. A true AWD system allows for some slippage to compensate for wheel speed differences in turns. Chevy used an AWD system in the early Astro vans and S-series trucks that was AWD all the time. You could not shift anything. It gave you power to the front and the rear all the time.

The A4wd in our trucks is "Automatic 4 Wheel Drive". This is NOT an AWD system and the manual does not infer that. It does just what the name infers. When the computer thinks you need 4 wheel drive, it connects the front wheels to power. Only when rear wheel slippage is detected will the front be connected. The system uses a clutch to engage and disengage the front. The clutch can also drag at times causing increased wear & tear. That is why, even though the manual says that you can use it anytime, knowing owners recommend that you only use it when conditions are slippery, like patchy snow on the roads or when driving on loose surfaces like wet leaves and you may need traction.

The system sounds good in theory but in reality the rear wheels can slip quite a bit and the front not engage. Some rapid slippage is also needed before the front will engage. My front yard has a VERY SLIGHT incline and it is covered in grass. When backing up my Envoy in the rain I MUST use 4x4 mode, not A4wd. If I use A4wd and move slowly one rear wheel will just spin continuously. And it DOES have a G80 diff. If I slowly increase the speed I will feel little tugs as the G80 engages the other wheel and it improves traction. Still not enough to back my truck up. I give it more gas. Now the truck lurches as both the G80 and the A4wd kick in. I need to put it in 4x4 mode so no wheel slippage is needed at the rear before the front engage.

A4wd is not AWD and Chevy never said it was.

Their are many variations of AWD out there, seems everybody has their own version. Many of the Japanese makes simply use the old GM AWD system design with a viscous coupling between the front and rear, many use a front wheel drive design and only engages the rear wheels when the front slips, just like our A4wd, but they misleadingly call it AWD.

 

[AtlWrk]

The early version of the transfer case switch was labeled with "A4WD"

A later version changed it to just "Auto" so it would be less likely to be confused with AWD.

 

[bspurloc]

Ok yeah this makes things so much clearer! and yes labeling it A4WD unintentionally implies AWD. A very bad label idea. When marketing something the first thing you must take into account is "People do not read" so you must assume they are going to assume. So when you see A4WD u assume that is AWD but GM was avoiding some legal stuff and called it A4WD.

Thanks all for explaining it all!

 

[Wooluf1952]

IIRC, the Envoy and the Trailblazer SS did have an AWD option, but, there was no selector switch.

I believe the Buick and Oldsmobile also had that option.

 

[Sparky]

GMT360 Envoy never had AWD as an option, just 4WD like the Trailblazer. Maybe the older S10 based one did.

I forgot about the Trailblazer SS, good catch.

Buick, Olds, and Saab all had AWD option, no 4WD.

 

[Wooluf1952]

GMT360 Envoy never had AWD as an option, just 4WD like the Trailblazer. Maybe the older S10 based one did.

I forgot about the Trailblazer SS, good catch.

Buick, Olds, and Saab all had AWD option, no 4WD.

I wasn't sure about the Envoy. When I was researching to buy in 2002, I remember AWD was available, but, it must've been in the Olds.

 

[AWD V8]

People get it all wrong all the time. They say it's AWD but they rally do not know the difference. Just like when you see an ad for a Trailblazer and the engine is a V6

 

[Mooseman]

I have the AWD, which is really the same as the A4WD on the TB and Envoy, and I HATE IT! I had 4x4 on my TB and this AWD system sucks. Can't turn it off, the front wheels are always engaged, which means loss of MPG with the extra drag of the front diff and shaft always spinning. And when it engages when the rear wheels slip, BANG, the truck just lurches from the all of a sudden traction.

With the TB, I would put it in 4hi in snow and no worries. Sometimes I would forget to take it off on bare wet roads and sometimes even at highway speeds, I had no problems although I might have noticed some crow hop on tight turns.

I hate this system so much that I am looking at finding a way to swap the AWD transfer case with a 4x4 one and trying to make the encoder motor work one way or another. To start, I will be able to add a front disconnect and actuate it with a simple switch. The ultimate would be to find a way to work with an actual switch and TCCM but that will cause problems with my BCM and Stabilitrak.

 

[Bow_Tied]

Moose, I wonder if something is wrong with your system? I work with a guy that has a 9-7x 5.3 AWD and he doesn't have that sort problem with his.

 

[The_Roadie]

I wouldn't trust anybody driving that thing much without changing all fluids (TC and both diffs) and checking the nature and amount of fluids that run out. I thought all the regulars here got the transfer case memo. Or the stink-eye from me if they waited until 50,001 miles to check it.

 

[Wooluf1952]

Why do I feel like I just got yelled at by the teacher?

 

[Mooseman]

I don't think it's a problem. It's the nature of the system and how it works. On snow, the rear wheels just spin and then the fronts engage as if popping a clutch. Even if it were to engage more smoothly or gradually, I still don't like not having the fronts engaged all the time when I want them.

And yes, I changed the fluid when I first bought it

 

[Bow_Tied]

Fair enough. I am not personally familiar with the AWD system as I have the Auto4x4 version which doesn't do that unless you are on the throttle too much.

 

[Mooseman]

Maybe that's MY problem

 

[AtlWrk]

Interesting...I assumed there was more of a difference between the NP4 (Saab, Ranier) "AWD" transfer cases and the NP8 (Trailblazer, Envoy) selectable 4WD TCs. Looking at the internals now they're almost identical with the exclusion of the low-range planetary reduction gears in the NP4. Turns out the AWD transfer cases really are just "Automatic 4WD" as GM calls it. These are definitely not true AWD systems with a viscous coupling or extra diff in the transfer case. Can't help but think the arguments against Auto mode hold a little less weight if the NP4s spend their entire life in this mode

 

[Mooseman]

When my rear diff blew out, I tried to get the NP4 TC to stay in the locked mode by engaging it and then pulling the fuse. It didn't work because it would eventually go back to 2WD on its own. Looking at the NP8 4x4 wiring schematics, those have extra wiring to a brake in the encoder motor that I have a feeling holds it in the selected mode that the NP4 doesn't have.

If the NP4 were to stay locked permanently, it would be the same as 4hi on an NP8 so you would have the crow hop and binding as well as lower MPG.

 

[Eric04]

When I purchased the TB I noticed the A4WD setting and thought, "who would use that?". I've since spoken to several people who have used this setting in their Tahoe or TB when road conditions are intermittently crappy and like it. To each their own. I've found the TB does pretty well on plowed roads/light snow in 2WD. Deeper snow/ice usually means 4HI. Ultimately I'd rather make the decision than have the ride make it for me.

 

[Grimor]

so you're saying i shouldn't be going 70 in 4wd?

 

[The_Roadie]

You shouldn't be doing 70 in conditions suitable for 4hi.

 

[Grimor]

You shouldn't be doing 70 in conditions suitable for 4hi.

you sound just like the judge....

 

[kkeo211]

In Virginia I normally use A4WD because we don't typically get enough snow where all of the roads are covered with snow. We normally only get a few inches and the roads melt at different spots so there are both snow covered and clean road surfaces at the same time. If it's all snow, I will use 4HI.

My question is, what is the best way to engage either A4WD or 4HI? The manual says that I can switch from 2HI to A4WD or 4HI and back at any speed but for 4LOW the envoy should either be in neutral or moving under 2mph, with the preference being the car moving 2mph or lower.

I normally switch from 2HI to A4WD or 4HI going around 5mph. Is this okay or should I also switch while in neutral. I is rare that I use anything other than 2HI so I don't really know what is best.

Thanks!

 

[Sparky]

You can at any speed yes, but usually I try to switch when not moving very fast just to make it "easier" on the engagement. Not really sure if it is or not, but the theory sounds good in my head

No need to be in neutral when making the switch.

 

[kkeo211]

You can at any speed yes, but usually I try to switch when not moving very fast just to make it "easier" on the engagement. Not really sure if it is or not, but the theory sounds good in my head

No need to be in neutral when making the switch.

Thanks for clarifying this. Regardless of what the manual says, I would hesitate to switch modes while going 55mph. It just seems strange, but maybe that's just me being overly cautious.

 

[Sparky]

Well, to be fair if you're needing 4WD then you probably have no business doing 55mph

 

[Bow_Tied]

In Virginia I normally use A4WD because we don't typically get enough snow where all of the roads are covered with snow. We normally only get a few inches and the roads melt at different spots so there are both snow covered and clean road surfaces at the same time. If it's all snow, I will use 4HI.

My question is, what is the best way to engage either A4WD or 4HI? The manual says that I can switch from 2HI to A4WD or 4HI and back at any speed but for 4LOW the envoy should either be in neutral or moving under 2mph, with the preference being the car moving 2mph or lower.

I normally switch from 2HI to A4WD or 4HI going around 5mph. Is this okay or should I also switch while in neutral. I is rare that I use anything other than 2HI so I don't really know what is best.

Thanks!

I think we should be in neutral for sure when switching to 4Lo. The 2mph simply means that a gentle roll forward of that speed lets the gearing mesh nicer than at a dead stop (less grinding/clunking). I have a Jimmy with the auto tcase and regularly do that, coast in neutral and as I drop under 3mph I engage 4Lo. Very effective. I use neutral to come out of 4Lo as well in the same manner and it works great.

Engaging 4Hi - again with my Jimmy have countless years doing this at speeds up to 50mph. I generally don't use 4Hi at that speed as I shouldn't need it if I can go that fast safely. The big thing I do for engaging 4Hi or going back to 2 Hi is to be essentially coasting. If you are off the throttle then the tcase has way less drivetrain load to withstand during the shift. Kind of like you wouldn't shift to drive from neutral or vice versa under heavy load.


The Auto4x4 is the same way. Don't shift into it under throttle. When in auto4x4 the tcase will shift for you - don't hard throttle in places where the tires might spin (leaving a stop sign for example) just be easy on the gas and should shift nicely. You may feel it grab, but this mitigates the bang shift.


I have not had our Envoy for very long, but it performs exactly the same way.


HTH.

 

[kkeo211]

Well, to be fair if you're needing 4WD then you probably have no business doing 55mph

yeah, 55 may be a little fast. Probably more around the 15 to 25 mph range.