Running in 4x4

[kf6kmx]

Ok, heres a question.. Someone asked me this and I wasnt sure.

On our 4x4's, what is the limit to run in 4hi on the highway without hurting it?
I hadnt thought much about it, but they have a fullsize and it has the "Auto" mode for bad weather to let the truck select 4hi as it needs it.
So, what is the limitation on the drivetrain we have to run in 4hi in bad weather (how slippery does the road need to be... just wet; standing water; snow; ice; ??)
Are we using basically the same transfer case, but without the computer software to monitor tire slip and engage an 'auto' mode? I'm guessing that the fullsieze (its in a 2500HD, Avalanche, and Tahoe, that I've seen.. Also was told the Trailblazer has it.. apparently everything except the S10) is reading the ABS sensors to see if a wheel slips and then kicks in 4hi? A friend with an Avalanche said he uses it in the moutains and he thinks it partially engages his 4x (axles lock in) but doesnt go into actual 4wheel at the xfer case until it needs it.

I know older 4x systems had to be able to slip a tire, especially in cornering, or it could damage itself.

The topic came up at work this week when we had our storms go through here and our parking lot had standing water in it with a lot of little foreign cars sliding around on the slick street. (We had one slide out of its parking spot and end up backing itself onto the sidewalk (came out of a parking spot, went about 20 feet and jumped the back wheels up on the sidewalk with the engine off.. and of course, you KNOW that were parked right next to me! .. good thing their wheels were straight at least!)
Although we think it was owner error and they really DIDNT set the brake (stick shift) that they said they did.. it wasnt THAT much water..

[barch97]

On our 4x4's, what is the limit to run in 4hi on the highway without hurting it?

you kinda answered your own question...

I know older 4x systems had to be able to slip a tire, especially in cornering, or it could damage itself.

The trouble with running in 4wd is turning. the outside wheels spin faster than the inside wheels in a turn. the road surface needs to be slippery enough to allow the tires to slip so that they can spin at the same speed.

This really shouldn't be an issue on the "highway" though. Most of the "highway" is straight and turns are quite subtle. In my experience however, at highway speeds 4wd doesn't really make a whole lot of difference. It's the stopping and starting of slippery local roads that requires the extra pull of front wheels.

[Retep]

...On our 4x4's, what is the limit to run in 4hi on the highway without hurting it?

If road conditions require the need for 4hi, and you driving fast enough to be concerned with damaging something, than you are driving to fast to begin with.
I think the fastest I have drove with 4hi engaged is around 50 mph. This was on a stretch of highway that had been plowed but still had areas with slushy wet pavement.

...I know older 4x systems had to be able to slip a tire, especially in cornering, or it could damage itself.

This is true with any direct coupled 4x4 system including ours. That is why you never drive in 4hi or 4lo on dry pavement.

Pete

[kf6kmx]

...On our 4x4's, what is the limit to run in 4hi on the highway without hurting it?

If road conditions require the need for 4hi, and you driving fast enough to be concerned with damaging something, than you are driving to fast to begin with.
I think the fastest I have drove with 4hi engaged is around 50 mph. This was on a stretch of highway that had been plowed but still had areas with slushy wet pavement.

...I know older 4x systems had to be able to slip a tire, especially in cornering, or it could damage itself.

This is true with any direct coupled 4x4 system including ours. That is why you never drive in 4hi or 4lo on dry pavement.

Pete

More than the speed, they were talking about, like when we had the downpours, leaving it in 4hi as they drove through town because of the slick roads and sliding while turning in some intersections and taking off. Myself, I usually stay in 2hi most of the time (from years of having nothing but a 2wd, I tend to forget I have the option of 4hi to help on slippery roads ) but they said they turn their 'auto' on at the first sign of rain and leave it on until its dry (sounds like overkill to me) and they asked at what point we can turn on 4hi since we don't have auto, and I hadn't really given it enough thought/research so I thought I'd ask
only times I can recall using 4hi on-highway (country road actually) was 1) when there was about 1/8" of hail on the ground, and 2) right after I bought the truck we had a storm go through that had about an inch of standing water on some of the country roads in low spots.. I drove about 8 miles in 4hi at around 45.. The extra 'pull' from the front seemed to help it when it would hit a larger puddle to not really notice, just powered through it..

[kf6kmx]

This really shouldn't be an issue on the "highway" though. Most of the "highway" is straight and turns are quite subtle. In my experience however, at highway speeds 4wd doesn't really make a whole lot of difference. It's the stopping and starting of slippery local roads that requires the extra pull of front wheels.

I've found a couple times on highway where the front end pulling helped.. in having a lot of standing water from heavy rain and a crosswind, it seemed to help avoid problems from the crosswind.

[HenryJ]

...Are we using basically the same transfer case, but without the computer software to monitor tire slip and engage an 'auto' mode?...

We are not running the same transfercase, and there are differences.

Basically our (NVG 233-NP1) transfercase is like running a spool. It is a two speed selectable transfercase. It is locked front to rear with no way to slip.

The auto/awd (NVG 136-NP4) transfercase is like a limited slip. For the s-series it is listed as the one speed automatic transfercase. It uses clutches and a pump to engage and disengage the front drive. It can and will slip when there are differences between the front and rear drives during a turn.
It has it's own VSS to monitor differences in rotation from front to rear. So basically if the rear slips the front kicks in automatically. When it is in four high they are engaged all the time.

For street duty the auto has advantages obviously, but for real 4x4 offroading our case is the one to have.

Don't get me wrong the auto will work, and may never slip when you don't want it to. The other is just more positive.

As for a lack of low range. I really thought that the Tahoe auto that I have had the low range too? Maybe the S-series for 2001 doesn't? Of that I am unsure.

I have engaged 4 hi at highway speed on snow pack roads, and ice. I do prefer 2wd until a lack of traction requires 4x4 though.

[kf6kmx]

...Are we using basically the same transfer case, but without the computer software to monitor tire slip and engage an 'auto' mode?...

We are not running the same transfercase, and there are differences.

Basically our (NVG 233-NP1) transfercase is like running a spool. It is a two speed selectable transfercase. It is locked front to rear with no way to slip.

The auto/awd (NVG 136-NP4) transfercase is like a limited slip. For the s-series it is listed as the one speed automatic transfercase. It uses clutches and a pump to engage and disengage the front drive. It can and will slip when there are differences between the front and rear drives during a turn.
It has it's own VSS to monitor differences in rotation from front to rear. So basically if the rear slips the front kicks in automatically. When it is in four high they are engaged all the time.

For street duty the auto has advantages obviously, but for real 4x4 offroading our case is the one to have.

Don't get me wrong the auto will work, and may never slip when you don't want it to. The other is just more positive.

As for a lack of low range. I really thought that the Tahoe auto that I have had the low range too? Maybe the S-series for 2001 doesn't? Of that I am unsure.

I have engaged 4 hi at highway speed on snow pack roads, and ice. I do prefer 2wd until a lack of traction requires 4x4 though.

Thats like me.. I'm so used to 2wd trucks, that I'm usually slipping pretty good before I remember, DOH, I got 4x4....

The Avalanche that they have has 2hi/Auto/4hi/4lo/Neutral (press 4hi and 2hi together to get into neutral).

Good, I can tell him we have a better xfer case than the auto on the avalanche, he always likes to point out that his window comes out (oooh..ah... and his wife, who drives a 4x4 Ram 1500 crewcab likes to point out that her truck has a bigger bed..)

[HenryJ]

... I can tell him we have a better xfer case than the auto on the avalanche, he always likes to point out that his window comes out (oooh..ah... and his wife, who drives a 4x4 Ram 1500 crewcab likes to point out that her truck has a bigger bed..)

I wouldn't say better. It really depends on what you are doing. For streeting, and even baja running the AWD has it's advantages.

I see that the latest StylinConcepts catalog has "Breeser removable rear window kits", so if you really are jealous of that Avalanche rear window, you can have one too

As for a big bed...I have one, but it is in my bedroom just where I like it

[kf6kmx]

... I can tell him we have a better xfer case than the auto on the avalanche, he always likes to point out that his window comes out (oooh..ah... and his wife, who drives a 4x4 Ram 1500 crewcab likes to point out that her truck has a bigger bed..)

I wouldn't say better. It really depends on what you are doing. For streeting, and even baja running the AWD has it's advantages.

I see that the latest StylinConcepts catalog has "Breeser removable rear window kits", so if you really are jealous of that Avalanche rear window, you can have one too

As for a big bed...I have one, but it is in my bedroom just where I like it

Never said I was jelous of the window In fact I figure that is going to start leaking eventually..

I figure the positive xfer case in ours is better for the main driving around here.. off road in dirt, some mud, snow, etc..

I dont even know if they have ever taken that dodge crew offroad.. i

[Walt]

I regularly run 75-80 on the interstate, and have used 4hi numerous times in rainy weather at those speeds, with no problems yet

[F9K9]

I have always "popped" it 4WD when I am making a turn from a standstill into traffic when it's raining, traffic is heavy and the "call" may be a close one.

Never hurt my ZR2 in 6 yrs so am continuing it's tradition