I test drove an 07 suburban LTZ 4wd 5.3 the other day and as im going through my inspections i notices that when i put it in 4 lo dropping into neutral and then switching to low at a stop...i put it in D and theres a bump kinda felt like someone tapped me from the rear then i start to give it gas and hear the engine revving and the rpms moving but the truck moved very very sluggish. gave a little more gas and no change. put it back in 2wd and tried again with 4lo...same. so ofcourse i was concerned about the 4wd system because the truck was gorgeous and very clean with a decent price tag

 

Greetings trainwreck91, welcome to the Forum.

Our Burbs are notorious about clunking when changing in/out of 4WD-lo, though it's hard to say exactly, since I didn't hear it personally.

I'd say that any sluggishness and possible hesitation to change to Lo, probably comes from non-use of the Transfer Case, and there are a lot of vehicles out there, whose Case Fluid has never been changed. Shellac can build up, and cause problems from non use. Though I use 4-hi often, I rarely need to use Lo. Given that, I try to drive it a couple blocks in Lo about once a month, just to keep it stirred up

It doesn't sound like you have a major problem there, that fresh Fluid and a few changes to get it working smoother again won't fix up, with an occasional change to keep it maintained.

If you have the NP246 Case (very likely), keep in mind that it's about a 2.72 increase in gear ratio. One might mistake the extra throttle pressure needed to come up to speed with sluggishness. That's not the case though, you've just put it in "Tree Climbing Mode"

 

"Tree Climbing Mode"

haha. very true! When I put my burb in 4X4 LO it climbs hills in 1st gear at idle. Had fun when we pulled our boat lifts out. Came up with an easy method involving 100FT of cable and a pulley around a tree. Plus a VERY steep driveway. All I had to do was put it in 4X4 LO and "D". Then hit the brake.

 

Just to take the inference a step farther...
When we're in 2WD, our 1st Gear final ratio is 11.41
In 4WD-Lo it's 31.04

That's like adding another 490 Horsepower to the engine

As stated previously, I rarely use 4Lo, but, it gives me a great deal of confidence knowing that capability is just a button away.

 

So 3mph is normally em while stepping on the gas. Because it felt like it didnt wanna go anywhere?

 

By the way I came home and tested my expys 4 lo and it was totally different. I mean the chevy was having a hard time getting to 10 mph. I know it's not meant for high speed but it just felt stuck. Not what I'm used to

 

Well, when in 4Lo, you definitely don't go anywhere fast, but...

The only area of "resistance" that there can be, is in the Transfer Case it's self. It's a Chain Drive, and I can see if the Fluid was goopy enough, it just may act like you're talking about. The only thing you can do is a Fluid Change on it, and see if it clears up. After the change, you'd want to drive it a mile or so in 4Lo, just to get the new Fluid working in it good.

Is there any of this "resistance" when in 4WD-Hi ?

PS:
That Case takes a special Fluid...AutoTrak II, about 2 Qts.

 

no resistance in 4hi

 

That might just be different gear ratios between expy and suburbans. I know when I use 4lo in my F250 it won't go fast at all, don't think it has been over 5mph in 4lo, but the brakes can bearly hold it at a stop. There might even be differences between Suburbans with the 5 speed and ones with the 6 speed autos due to gear ratios, but I am not sure about that.

 

Bluedog,

There are only 4 speed and 6 speed Suburban. And yes, my burb doesnt make it much past like 45mph in 4LO. I have the 4 speed. And the final gear of the 4 speed is a little different than the 6 speed because the 6's are paired up with 3.08's or 3.42's. No the traditional 3.73's.