How to Operate the 4WD?

[steiny93]

Note the difference between driveline "wear" and driveline "damage".

thank you

 

[noodlesandsam2]

My own rules - both with the 01 1500 ( 270K, no issues ) - Auto trac when it is raining, or snow and slippery and on the highway - press the button, never an issue. I switch back to 2WD as soon as it is not slippery - also I try not to do either switching when accelerating. 4W Hi - Deep snow, when Auto Trac is not sufficient. Again, I never stopped for 4Hi, but not when on the throttle.

Honestly, I don't think I ever used 4 Lo, unless it was to try it out in a parking lot. with the 1500 I ran dedicated snows, so traction was never an issue.

Same rules for the 2500 I just got, - he is at 156K, and the last owners must have been pretty gentle, it acts just like the 1500 did.

 

[Matthew Jeschke]

The clutch pack works with the encoder motor to pulse the front diff on and off for the auto function. This same technique is used on other vehicles, not just the GMT800. I believe Subaru uses a similar system, perhaps even the NP246 on some models as well. I've never had issue using it off road w/ delay or any of fore mentioned concerns. I venture that system would react within milliseconds (I used to design control systems as an engineer some automotive as well), faster than you'd even notice. I experienced no driveline failures or wear as previously brought up with my NP246 / GMT800 setup. My truck primarily exists off-road. I also tore down my functioning NP246 tx-case just to rebuild it, upgraded the clutches, put in case saver, etc as preventative maintenance because I spend most of my time in remote mountains were a breakdown off-road can be quite catastrophic otherwise and rebuilding this is somewhat trivial. Long story short, the clutches in both cases I tore down were like new so I don't know what the previous mention is of driveline wear, it seems to be a very well designed system. I've literally went through every drivetrain system on the truck when I built mine and found virtually no where anywhere in the system when I bought the truck. Both front and rear diffs, suspension, 4L60E, Tx-case, & engine. The GMT800 is a VERY well built truck (aside from interior).

My original case was tore down at something like 250,000 miles and the clutch pack didn't show any wear. Literally the auto 4wd clutches maybe had a few thousands wear on the entire pack. Same for the working core I used while I rebuilt my original. I tore it down afterwards. I use my truck in much harder conditions than the average person and it's yet to let me down in 60,000 miles since I bought it.

Where these transfer cases fail is from pump rub. There is a small metal clip to protect the case from the pump. That little clip wears out and the pump eventually digs through the case. A case saver will for all intensive purposes eliminate that problem. Everywhere else the case is built like a beast. I don't know where it would fail. It's built up WAY stronger than the 4L60E (which I went through and built up too). Probably stronger than a 4L80E as well. It's SUPER beefy. I have a post on the forum about rebuilding the NP246.

 

[Fless]

The clutch pack works with the encoder motor to pulse the front diff on and off for the auto function. This same technique is used on other vehicles, not just the GMT800. I believe Subaru uses a similar system, perhaps even the NP246 on some models as well. I've never had issue using it off road w/ delay or any of fore mentioned concerns. I venture that system would react within milliseconds (I used to design control systems as an engineer some automotive as well), faster than you'd even notice. I experienced no driveline failures or wear as previously brought up with my NP246 / GMT800 setup. My truck primarily exists off-road. I also tore down my functioning NP246 tx-case just to rebuild it, upgraded the clutches, put in case saver, etc as preventative maintenance because I spend most of my time in remote mountains were a breakdown off-road can be quite catastrophic otherwise and rebuilding this is somewhat trivial. Long story short, the clutches in both cases I tore down were like new so I don't know what the previous mention is of driveline wear, it seems to be a very well designed system. I've literally went through every drivetrain system on the truck when I built mine and found virtually no where anywhere in the system when I bought the truck. Both front and rear diffs, suspension, 4L60E, Tx-case, & engine. The GMT800 is a VERY well built truck (aside from interior).

My original case was tore down at something like 250,000 miles and the clutch pack didn't show any wear. Literally the auto 4wd clutches maybe had a few thousands wear on the entire pack. Same for the working core I used while I rebuilt my original. I tore it down afterwards. I use my truck in much harder conditions than the average person and it's yet to let me down in 60,000 miles since I bought it.

Where these transfer cases fail is from pump rub. There is a small metal clip to protect the case from the pump. That little clip wears out and the pump eventually digs through the case. A case saver will for all intensive purposes eliminate that problem. Everywhere else the case is built like a beast. I don't know where it would fail. It's built up WAY stronger than the 4L60E (which I went through and built up too). Probably stronger than a 4L80E as well. It's SUPER beefy. I have a post on the forum about rebuilding the NP246.

So you have a faster actuator than what is shown here? Mine is just like the one he tests.

 

[Marky Dissod]

Where these transfer cases fail is from pump rub. There is a small metal clip to protect the case from the pump.
That little clip wears out and the pump eventually digs through the case. A case saver will for all intensive purposes eliminate that problem.
Everywhere else the case is built like a beast. I don't know where it would fail.
It's built up WAY stronger than the 4L60E (which I went through and built up too). Probably stronger than a 4L80E as well. It's SUPER beefy.
I have a post on the forum about rebuilding the NP246.

Where does one get this 'case saver'?
Where do I find your post about rebuilding the NP246?

 

[Matthew Jeschke]

There are a couple different styles.

This is the most affordable style HERE

It slides in and increases the surface area so the protector lasts longer, versus the factory design that is just a small clip going over one of the lugs on the pump half.

This is what I used. It's a new pump face HERE

Either does the trick fine. You can get generic pump half kits for cheaper too.

Honestly, if a person just dropped the case, separated it and changed that case saver, it would likely do the trick. I went the extra mile and replaced all the guts for couple hundred bucks, including upgrading to Raybestos GPZ clutches. If you change out the bearings though you'll have to redo front output shaft seal. It's a two way seal for which you'll need a tool (roughly $100 for the tool) or VERY careful hands to make sure the inner seal lines up with the outer and the shaft.

 

[2591tdj]

Greetings,

I am a complete newbie when it comes to 4WD controls. I bought a 2005 GMC Yukon XL over the weekend and I want to make sure I understand how to operate it properly.

I have a few questions:

1. Do I need to stop the vehicle to engage the 4WD Auto setting? Is it the same for the other settings?
2. Can I drive at highway speeds with the 4WD Auto setting on?
3. Any other insights or tips would be greatly appreciated.

Thank you in advance for your help!

I’ve seen comments on other threads saying that it’s okay to drive on hard surfaces in 4Hi. I made the mistake of forgetting to shift out of 4Hi in my 2005 Z71 Tahoe when I reached pavement and drove 45 miles, mostly at highway speeds but with several complete stops & 90 degree turns. As I reached my driveway the front diff started making a loud grinding, clanking noise. I had destroyed the front diff and had to have it replaced. The repairman said that driving on hard, dry pavement in 4Hi did the damage.

 

[Marky Dissod]

I’ve seen comments on other threads saying that it’s okay to drive on hard surfaces in 4Hi.
I made the mistake of forgetting to shift out of 4Hi in my 2005 Z71 Tahoe when I reached pavement and drove 45 miles, mostly at highway speeds but with several complete stops & 90 degree turns.
As I reached my driveway the front diff started making a loud grinding, clanking noise.
I had destroyed the front diff and had to have it replaced.
The repairman said that driving on hard, dry pavement in 4Hi did the damage.

This forum REALLY NEEDS the 'Helpful' smiley; none of the other 6 smiley options are as appropriate.

Although I do wonder if you could've gotten away with it if you'd never made any turns, still sucks that it happened to you.
Thanks for saying it to us.