1999 Suburban 6.5 4wd questions

[mobilevet]

I'm looking at a 99 Suburban 6.5 to buy, but am a bit unsure about the 4wd. This truck does not have the shifter in the floor, but has the "push button" variety. According to the owner it shifts through 2HI, 4WD Automatic, 4HI, and 4LO.

Question 1 - Are these "push button" versions reliable? I'm used to shifters in the floor. Any one got an opinion as to which is better? Which they like better? My gut says that it is just something else to break/not work when you need it and that I may not be happy with it.

Question 2 - What is this "4WD Automatic"? Does this "sense" when you "need" to be in 4WD?

Question 3 - Anyone have experience taking one of these electronic varieties and converting them back to manual? Is it possible? Very expensive?

Thanks for all the advice.

[Jochen Woern]

Hello mobilevet, how are you?

QUESTION 1:
I do have the push button option on my 96 Burb and it works well, never had a problem with it. My wife used to drive a 99 Tahoe Gasser with the same feature, never a problem there. Can not tell you which is better, but I know that the pushbutton works for me.

QUESTION 2:
Yhe 4 WD Automatic is a feature that can be used when on wet roads or icey roads. It will sense which wheel needs the most traction. What it means is that you will NOT be driving in 4 WD drive until the truck thinks it should. (Unfortunately I do not have this option on my 96 Burb but wish I had it since I really liked it on the 99 Tahoe).

QUESTION 3:
I have no experience there, nor does it make any sense to me since I never had any problems with the push button feature. I also like the additional floor space by the manual shifter not being there.

Hope this helps.

[DrumFunKen]

The 4wd on the Floor or button style are literally the same thing.

after 92 they got rid of the locking hubs up front, and manual transfer cases, and went to vacuum style engagement.

So what that means is if you're used to the old skool 4wd where when using the floor shifter it was actually attached to a lever on the transfer case engaging it into 4hi, 4lo, etc.

Now its electronic. With both the push button and floor shifter all you are doing is sending some electricity to a solenoid activating the 4wd by means of vacuum.

Hope that helps.

[DmaxMaverick]

1999 is a good year for 4x4 systems. Earlier years (-96?) had a thermal-engagement system that was sparsely problematic, usually upgraded with a stepper like on the 99. No vacuum since the 80's IFS, pre GMT-400. The "Auto 4x4" is unique. It is not a standard type transfer case, and requires special "Autotrac" fluid. It contains clutches to engage/disengage on the fly automatically, and does sense traction needs (much like the Jeep system). A nice feature for some conditions, and generally very reliable. Expensive to repair, but are fairly durable.

[DA BIG ONE]

Auto 4wd is great & safe, it intergrates into your ABS system, has 3 speed sensors and its own control module to control torqe to 9 clutches and 10 steels for total and smooth automatic 4wd control under all conditions.

This transfercase does not suffer from the wear through failure seen in many newer electronic t-cases and its torque capacity is well beyond anything you would encounter on or off road.

[Dimsdale]

This may be "old school" thinking, but another nice feature of the NV246 Autotrac is that the AUTO setting engages the front axle, leaving only the clutches in the transfer case disengaged until the computer tells it to engage.

Running this periodically, particularly in the summer, allows you to warm up and circulate the axle lubricant, u-joints and axle ends to keep the internals lubed and the seals lubed. Manuals of older 4WDs usually recommended locking the hubs for 25 miles or so to do the same thing. Non-autotrac transfer cases won't allow you to do this.

On the other hand, for the front axle to engage in AUTO, there has to be a certain amount of slippage of the rear wheels, so it is a sort of after-the-fact 4wd, but it is nice to be able to run around in partially snow covered roads without flipping the shift lever back and forth all the time. AUTO will default to full time 4wd (4WD HI) after a certain number of automatic engaging events.

If you still have the drain/fill plugs that require you to insert a hex, there are better replacements with normal square bolt holes. You CANNOT use steel bolts in these cases! Galvanic corrosion will occur.

There was a time when a special Autotrac fluid was required (it was blue), but I think they got away from that. It was needed to address a popping noise that came from the rear output shaft slider, but I am a little hazy on that one.

[DA BIG ONE]

This may be "old school" thinking, but another nice feature of the NV246 Autotrac is that the AUTO setting engages the front axle, leaving only the clutches in the transfer case disengaged until the computer tells it to engage.

Running this periodically, particularly in the summer, allows you to warm up and circulate the axle lubricant, u-joints and axle ends to keep the internals lubed and the seals lubed. Manuals of older 4WDs usually recommended locking the hubs for 25 miles or so to do the same thing. Non-autotrac transfer cases won't allow you to do this.

On the other hand, for the front axle to engage in AUTO, there has to be a certain amount of slippage of the rear wheels, so it is a sort of after-the-fact 4wd, but it is nice to be able to run around in partially snow covered roads without flipping the shift lever back and forth all the time. AUTO will default to full time 4wd (4WD HI) after a certain number of automatic engaging events.

If you still have the drain/fill plugs that require you to insert a hex, there are better replacements with normal square bolt holes. You CANNOT use steel bolts in these cases! Galvanic corrosion will occur.

There was a time when a special Autotrac fluid was required (it was blue), but I think they got away from that. It was needed to address a popping noise that came from the rear output shaft slider, but I am a little hazy on that one.

I had installed an ARB air locker in my front differential so I have full lockup up front when needed "great feature".

As for the special fluid requirement New Process engineers state only other fluid to use would be a full synthetic transmission fluid which has been in mine since replaced new. My original NP246 was damaged by tow truck operator who failed to put unit in neutral.