Hello,
I have a 94 explorer, this is the first vehicle that i have owned that is 4 wheel drive. I was playing around with it today and when i had it in 4 HI and on the pavement driving slow when I would turn the steering wheel about half way around the front end would start to jump pretty bad. It was fine if i took it out of 4X4 is this normal operation?? I hope it is anyways. Thanks

 

Yes that's normal. DON'T put it in 4wd on dry pavement. It can bind up the drive train and break components. The 4wd was made for slippery conditions (ice, mud, sand, snow, etc.). If you go off road, study up some first. Learn the proper way to approach grades, deal with obstacles, etc.

 

To better understand why it did that, see the article (if FTE will let me post this link) at www.howstuffworks.com

 

Cool! Welcome to the awesome world of 4X4. You will now be enabled to go to strange new worlds, where you have neve gone before - to infinity and beyond!

Sorry - I'm in the middle of blowing a gasket right now from the jetski forum where someone wants to argue the laws of physics with me. Don't people understand that energy is conserved? You can not get more energy of an event than is put into it. It converts from stored to kinetic.

OK I feel a little better now - chatting with folks of reason here.

So sure you can play with the 4WD on the street. Jerry is a little harsh saying you're going to rip your drive train apart. Not really unless you do this day in and day out. Hell I use my 4 wheel low all the time on dry pavement. If I have to move a load like the pallet of brick pavers in front of my house when I was landscaping in a new patio - came out great - I should post a picture. But it's a little easier on the clutch dragging a 800 pound load with the 2.7:1 transfer case advantage.

The key is knowing what you are doing to the truck. Since you are new to 4 wheel drives, I'd probably say don't use it on dry pavement. You see , your year truck and going to 4WD locks the front and rear diffs together. There is no driveline slippage and any deltas in the speed of the tires has to be between the tire and the road surface. this is the bucking you felt. Too much traction on pavement makes the suspension take up all the slack.

Even off road on the dirt you will feel this. If you make a sharp turn the front drive wants to push the tires the same speed but they don't want to do that, Nature of the beast.

Now I have gotten into tough binds off road where I needed to make a sharp manuver so I took it out of 4WD and got situated and then back to 4 low. So again, you need to know what you are doing to the truck.

Hah - I have even gotten stuck off road, 15 miles from a paved road, and nothing but class 4 and 5 hills between us with no clutch master. Blew out right there on the trail in 100 degree Arizona heat. So talk about needing to know how a truck works to get out of there to the paved road and then shift with no clutch on the pavement to get home 30 miles away...now you are in my 4WD court.

 

You guys are great thanks for all the help!!

 

IT IS ?????????????????????????

Damn, and all these years I had it wrong.....

Remember, this is America... You have a god given RIGHT to be ignorant of physics...

(This is NO JOKE... had an argument with a Ford engineer when I was consulting up there about water pumps. He believed, and probably still does given his brain had the density of a granite block, that a centrifugal pump provides higher pressures at higher flow rates.....)

EVERY firefighter can tell you this is not true..... sad

 

Not trying to be harsh, just giving a warning. I still say it's best not to run 4wd on dry pavement. Usually the weak link is the auto locking hubs. I bought a used F-350 4X4 and after a little while the hubs stripped out. I suspect that the previous owner had run in 4wd on hard surface. I didn't state that it would blow out right away, but it is not good for the system.

And to Kraut, as a firefighter and an engineer, I would suggest that your problem presents insufficient variables for validation. A centrifugal pump running at a constant RPM will flow higher volume through a larger outlet orafice or reduced friction loss at lower pressure. However, with a fixed orafice and friction loss, you will be required to generate increased pressure for increased flow, typically via higher RPM and power input (up to a point as determined by the pumps performance curve). (Sorry I couldn't resist)

Now, back on topic, Hope you have great fun with the 4wd. I would suggest that you put it into 4wd periodically to exercise the system. This can help by stirring up the lubricant in the front differential and exercising the electric shift motor ( a quick search of this site will tell you a lot about the shift motor on generation 1 explorers.)

As to the no clutch off road, man that sucks. That's one of those stories that's a lot more fun to tell after the fact. I've had to shift a jeep and a pickup before with no clutch, but it was on the road. Off road I'd have been strongly tempted to leave it in low gear if possible. But that is now one of the fun off road stories to tell your friends and kids (course for the kids it would have to have been snowing and up hill both ways while 100°) .

 

I figured this would happen... I was trying not to turn this into a physics thread. At a given RPM, with a centrifugal pump, you can move a higher volume of water at a lower discharge pressure, or a lower volume of water at a higher discharge pressure (esentially what you said). W/O getting into detail, the curve I saw impled that you could have both, higher pressure AND higher Volume at a given RPM. They guy argued the point till he was blue in the face.

You are correct. It's just shocking that a professiona lengineer didn't see the violation of Bernoulli's law in his own curve.

 

Yeah sure - for sure! I'm not advocating driving around in 4WD locked (no front/back slip mechanism) on dry pavement. But if you have to pull a stump out of your front yard, or move a pallet of pavers like I did - you can defintely save your back by hooking a tow rope to your hitch and utliziing your low range gearing.

What are you guys talking pumps here. Centrifigal vs what - variable displacement or fixed displacement? What about scroll compression pumps? Or better yet, turbo, cryo or diffusion pumps - those ones really suck - if you get my meaning...