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I should know this but - 4 wheel drive ?


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Posted

Okay, so I am a 4wheel newbie, so puleeze cut me some slack.  You guys helped me before! I have a 97 Suburban, with the shift on the fly push the button on the dash 4 wheel drive. After reading the owners manual, I have no problem using the system, but other than the obvious (gear ratio?) what is the difference between 4 Hi and 4 Low? Sorry for the silly question.

Posted

4Hi uses standard gearing...  so you can go highway speeds with front and rear wheels looking for traction.  4LOW changes the gear ratio in the transfer case applying max torque to the wheels.  Great for pulling a boat up the ramp etc or someone out of a ditch...  alot less strain on the drivetrain.  But max speed in OD would probably be about 45 mph at redline...

 

Try four low in a parking lot in a straight line (turning is hard on the drivetrain on dry pavement).  The truck will be in 3rd gear about 15 mph!!!

Posted

I believe you have Insta-Trac and AutoTrac followed later. With Insta-Trac, I do not think you are supposed to shift directly to 4-Lo. You are supposed to go from 2WD->4HI->4LO. And, many think you cannot shift this t-case to neutral, but you can.

Posted

with autotrac you have to be going less than 5mph or be completely stopped to switch to 4 lo

 

4 lo you get alot more torque also

Posted

I use 4 HI and 2HI almost exclusively--on the InstaTrac-and maybe have used 4LO twice.  So, I got out my book and it does NOT say you cannot go from 2HI to 4LO, without engaging 4HI first. So, I stand corrected by myself. It is strange to have to be corrected by yourself ;)

 

In case you ever find the need to go to Neutral, the procedure is:

1: Set park brake.

2: Start the truck

3: Connect truck to towing vehicle

4: Put the Transmission in Neutral

5: Shift the transfer case to 2Hi

6: Simultaneously press and Hold the 2Hi and the 4Lo button for 10 Seconds. The Red NEUTRAL light will come on when the transfer case shift to NEUTRAL is complete

7: Shift the transmission to REVERSE for one second, then shift the transmission to the DRIVE for one second

8: Turn the ignition to OFF

9: Place the transmission shift lever in PARK.

10: Release the parking brake prior to towing..

(My thanks to SteveO for this)

Posted

Thanks guys! I tried out the 4lo in the yard, after it had rained. It really does have some grunt then! Had a blast tearing up the grass! I can't imagine what a 454 in 4lo would do! That must be some massive pulling power. :0

Posted

Not all Insta-tracs could go into neutral.  The first model year or two couldn't...1996 and 1997 maybe?  

 

To add a little to the replies about 4 low, there are several misconceptions about it.

 

1.  It is the best for mud:  As long as you have wheelspin, 4-low is not necessary.  4-low cannot spin the tires as fast as 4-high.  Because of this the tires cannot clean themselves out.  I have, on at least 3 occasions, gotten into a stuck vehicle, shifted the transfer case out of 4-low and driven the truck out.  Four low is great when you are pulling up a boat ramp, hauling a 25,000lb cotton trailer up a hill, climbing rocks (like a jeep), etc

 

2.  It reduces driveline stress:  Only partially true.  The motor and transmission do not have to work as hard in 4-low, but the axles, driveshafts and hubs are seeing roughly twice the power (or about 2.6somethinganother in our trucks).  Trust me.  I know this.  I have blown up stuff.  Like axles, driveshafts, hubs.....

Posted

NEVER use 4wd on hard pavement!  

 

Your wheels need to be able to slip to prevent driveline damage.

 

Trust me on this...unless the newer units "insta-auto-deluxtrac etc.." have the ability to freewheel in turns and such.

 

My wife drove 5 hours in my 1979 Stubby 4WD with the Xfer case in 4 HI.

 

It was fragged.

 

You know it ate the clutch disc out also!

Posted

I unfortunatly do have push button 4wd.  I do not have a nuetral setting with mine.  However, I can put the transmission in Nuetral, set the parking brake and hit the 2LO button.  The system automatically transfers from 2HI to 4HI to 4LO.

Posted
NEVER use 4wd on hard pavement!  

 

Your wheels need to be able to slip to prevent driveline damage.

 

Trust me on this...unless the newer units "insta-auto-deluxtrac etc.." have the ability to freewheel in turns and such.

 

My wife drove 5 hours in my 1979 Stubby 4WD with the Xfer case in 4 HI.

 

It was fragged.

 

You know it ate the clutch disc out also!

I agree, its not going to do any good for the thing, but 4H hasn't hurt anything on any of our trucks over the years driving on pavement with it on.  There are times we've forgotten and left it in.  Other times, like last fall and early spring when its so muddy out, we just leave it in all the time since we go from the road to mud and back so often.  Haven't had to do it with this 2000 since it has the electric engager, but with the '96 that had the heat deal it took FOREVER to engage and we'd just get sick of waiting.  Leave it in, no wait.

Posted
NEVER use 4wd on hard pavement!  

 

My wife drove 5 hours in my 1979 Stubby 4WD with the Xfer case in 4 HI.

 

It was fragged.

 

You know it ate the clutch disc out also!

Rule #2 NEVER let your wife drive your truck...............

 

Doug

Posted

I don't see how anybody could actually drive in 4wd on pavement.  I tried it one time in my truck, and there is no way I could ever do it again.  Whenever you turn in makes horrible sounding noises from the drivetrain, and didn't turn worth a crap.

Posted
I don't see how anybody could actually drive in 4wd on pavement.  I tried it one time in my truck, and there is no way I could ever do it again.  Whenever you turn in makes horrible sounding noises from the drivetrain, and didn't turn worth a crap.

Huh, only real difference I find with it is that it is slightly harder to turn.  Never heard a sound come out of the front end or had any parts break.

Posted

When in 4WD, you LOCK the front axle to the back axle in a part time system! In some full time 4WD vehicles there is a center diff that takes care of different speeds between the front axle and rear axle, but in part time they are mechanically LOCKED! The driveline will bind any time the front and rear axles turn at diffent speeds. Turning a corner on dry pavement causes enough difference in axle speeds to cause binding.

 

You won't explode a transfer case or drive shaft or anything if you run in 4WD on dry pavement for a short time and at low speeds. But, it can causes significant wear if done for longer periods of time.

 

If the front axle was "spooled", turning corners on dry pavement would be impossible. But you can experiment by (from a DEAD stop) turn your wheel all the way one way and LIGHTLY push the gas. As you will be able to tell, you won't get anywhere. Give it more gas and the steering wheel will buck and your tires will squeal. (Use your own judgement in this, I'm not responsible if anyone damages their vehicle)... This is drivetrain bind...

 

The outside front wheel is trying to turn faster than any other wheel, it's linked to the to axle and driveshaft and the rear axle.... it can't make the front axle turn faster than the other axle, so in order for the vehicle to turn through that arc, the truck drags the tire through the arc, due to binding... So as you can see the binding is not just caused by the front end...

 

I don't know if that explains it to your satisfaction or not, but it's the best I can do right now....

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