Is it normal for these trucks to jump and lurch as the make a sharp turn while in 4x4?

It happend on day as I turned off an icy road onto dry so I thought it might just not to 4x4 on the dry hard stuff.

But today even on snow it bounces the whole truck as it lurches and jerks threw the turn.

It feels like the universals may be binding!?



This is a great site I am learning a lot. Thanks!

 

Yep, normal.

The u-joints ARE binding--especially the ones at the spindles. On dry pavement, it is very noticeable. Whenever the tires can slip, not so bad.

 

Mine does the same thing. Completely normal. My old GMC was twice as bad. -Steve

 

Yep, mine does the same thing if the pavement isn't slick enough. I guess it's kind of tough for an 8000lb rig to scrub off speed differences between axles. It would be sweet if they had a center differential.

 

Mine does it also. In fact, all my 4x4,s I have owned did it. Normal, no worries unless you hear unusual sounds, then worry.

 

Yep, that is normal. Every 4X4 does it. It is, however, not good to let it jump and lurch like that. Binding the front ends up repeatedly will lead to warping, bending, premature front end wear. Sometimes you may have to turn real sharp and can't help it, but you should take it slow and try to avoid it where possible for a long healthy life.

 

Since it's a snap to go in and out of 4wd, try and take it out when before going into sharp turn. Binding places a terrific load on the U-joints and suspension parts.

Ron W.

 

That would help, but it wouldn't eliminate the problem. (BTW, the full-time 4wd's have this feature.)

Some of the problem lies with the use of cross type u-joints to join the front axle shafts to the shaft that drive the front wheels. Any time there is a misalignment between the two shafts, the speed of the driven shaft varies sinusoidally (how's that for a big word? I can't think of any other that will describe it, though.) At times, it's going slower than the driving shaft; others, it's going faster. The average speed is of course the same, but the varation makes the truck jump and buck, too.

That's why the constant speed joint (aka, CV joint) was developed and is used on front wheel drive cars.

 

The early days of semi-full-time 4 wheel drive (GM mated to New Process w/out lockouts) showed that the concept worked well, until you had to fill the tank every other day. When locked in 4 Wheel Drive, the front dif is not designed to give one side or the other through a turn, thus one wheel is trying to turn faster than the other. Some of the Japanese companies are getting close to perfecting the point at which you want the dif to slip and the point at which you want the traction in the full-timers, but still a ways away. That being said, I would rather have it grab once in awhile when rounding a solid dry corner, then giving when one tire is on a rock, and the other is in the air.

Some of the cool designs I have seen are a lot like centrifical clutches, in that when the wheel in the air spins fast enough, it locks the grounded wheel. But again, something else to go out. Keep it simple Dodge and lock it all in when I pull the lever to 4.

 

"That's why the constant speed joint (aka, CV joint) was developed and is used on front wheel drive cars."

Still have the same problem when locked in 4. A lot of the ricers use CV's and you would not be able to tell the difference when rounding a corner in 4.

Easiest way to explain this is the inside wheel in a turn will require less revolutions than the outside wheel. With that being said, something has to give when both wheels are locked to the power train.

You can pull out the kids tinker toy set and test this by using the bearing wheels and an axle, mark the wheels, and make a turn. The inside wheel will turn less than the outside. If they are free of each other (dif in-between), then there is no wheel slip (either the dif takes the slip, or the wheel and tire take the slip).

 

That is one negative aspect of a 4 wheel drive system. The whole system get put in a terrible strain while turning, and the sharper the turn the more the strain. When the front axle is locked in (cad) and the transfer case is in 4 wheel drive the front and back axle are mechanical connected Thur the transfer case. In snow, sand,mud this is not a problem. The traction the wheels see is not enough to cause a bind, they simply slip or slide. On dry surface there is more then enough traction to not allow the wheels to slip and hence there is a binding situation. When a vehicle turns, all four wheel turn in an different arch, and at a different rate. Normally this would not be a problem. The front tires would simply turn independently and at there individual rates. The rear to some degree would be the same, some rears are equipped with a limited slip differential. These units employ clutches or cogs to lock the two wheels together. They have a preset rate at witch they will slip, and in a tight turn that rate is exceeded, and the two wheels turn independently. The problem comes when you are on a high traction surface and in four wheel drive with the front axle engaged. Now all four wheel will still want to turn at there own rates, but the system is mechanically locked together, and the transfer case will not allow it. Most time on short duration open road situations there will not be a problem, just a little tugging in the turns, or under steer. But in low speed tight maneuvers, the binding is very much felt, and can lead to damage. The weakest link in the system is the transfer case, it has the front and back locked together and feels all of the strain. Most commonly, the chain the drives the connected front axle will break.
One very good cure for all of this is the installation of a "2WLow " kit. It has several advantages. One, then traveling of roads where the traction level is always changing from clean and cleared road, to snow covered or questionable. The transfer case can be left engaged in 4high, but the front axle can be switched from engaged to dis-engaged by a mere flick of a switch. This easily and quickly lets you lock in the front axle as needed, and do without the wear and tear of a lock system. The other great benefit is the ability to use the truck in 4 wheel low, and disconnect the front axle. This is a great help when backing a heavy trailer, the low gear makes is much easier on the truck and driver. And the front axle stays UN-engaged, so there is not binding or fear of damaged parts.

 

I may be wrong, but it was my understanding that the difference in speed between the inside wheel and the outside wheel would be handled by the differential (whether in 4x4 or not), and bucking while turning in 4X4 is more due to the difference in speed between the front and rear axels.

That is, since the rear of the truck takes a wider radius turn than the front, the average speed of the front wheels would be different than the average speed of the rear wheels, but since the front and rear axels are locked solidly together when in 4x4 it bucks as it forces something to break traction. Giving it a little throttle, if it is safe to do so, may reduce the bucking. Otherwise, just pop out of 4x4.

Some of the recent cherokees had a selector for part time 4x4, full time 4x4 (uses a viscous coupler between axels) and 2wd. They kind of had the best of both worlds, since the axels could be solidly locked together when you really needed traction, but you could also run in all wheel drive which would allow limited slip between axels and wouldn't buck or harm the drive train even turning on dry pavement... I wonder why more vehicles don't have that feature?

 

"I may be wrong, but it was my understanding that the difference in speed between the inside wheel and the outside wheel would be handled by the differential (whether in 4x4 or not), and bucking while turning in 4X4 is more due to the difference in speed between the front and rear axels."

Yes, that is right! When you turn, the rear dif will take the slip of the lower wheel. The forward speed of the locked wheel wheel is also the same factor as the outside locked front wheel, all pushing at different speeds. Easiest to explain with just the front wheels and will still get the picture that the problem is that the slip is sent to the wheel as opposed to the differential.

Key I suppose is the understanding that all of the wheels don't turn at the same speed, and something has to take slip.


In my poor college days, I had a 77 Jimmy w/ full-time, which incorporated the third dif in the New Process transfer case. I lost a U-Joint on the back shaft and only had enough money for beer reserves that month, thus drove around locked in 4 wheel drive turning my Jimmy into a front-wheel drive truck. I still had the buck in the front, but like you point out, to a lesser degree.

 

The way you described it is how i've always understood it too. It would be really nice to have a center differential like the Jeep. Like cp said above, it won't totally eliminate the binding on sharp turns, but it would help out substantially. Correct me if i'm wrong, but if my memory serves me correctly I remember feeling a slight bit of binding in a friend's Jeep even when it was in the "full time" 4wd mode. I guess DC just wanted to keep the design as simple as possible in our rigs. That or there isn't a center diff strong enough to handle the torque of the Cummins.

Which makes me wonder......What kind of setup is the new Jeep rescue with the Cummins 600 going to have. Maybe this center diff could be retrofitted pretty easily in the Ram since the frames are supposedly similar.

 

It all sounds right!

I never noticed this much one my GMC 1ton, it was so heavy in the rear I did not need 4x4 so much.

This truck is hader to drive in the snow/ice. The high torque, light rear and heavy front make it a challenge to keep hooked up.

I added 360 pounds to the back and this is helping a bit. If I ever get to install the gooseneck hitch this will add 150 pounds of so.

I sure am glad the truck I bought had the 4x4 switch, I did not want it but it sure does make it easy to switch in and out!