Please explain to me how the front axle works.

[CJEliassen]

I have an 04 4x4 and from reading some other posts and watching its operation, I am a bit confused. When I got around corners, the thing acts like there is no differential, but some people say there is. I have also seen the one wheel stop rotating while the other continued too. This was very jerky, but definiately not a "locked" axle. So, what exactly is up there?



Thanks all.

 

[Bertram65]

The front is an open diff, the wheel with the least resistance gets the power. The front axle is also engaged all the time, there is no disconnect, only the transfer case.

 

[bpenrod]

I agree it is an open design but it seems "tight" for lack of a better word. Like a tight LSD, when going around a corner or turning you can really feel the front end bucking while trying to turn both wheels.

 

[mikepvg]

Yep, in 4X4, up front, it bucks & graps & generally displays its poor design. I sometimes wonder why the Big 3 can't build something as refined as a Toyota. Every Toy I have ever owned ran as smooth as silk in 4x4 on any surface. Go figure.



I guess, it being an American product, we should be happy that it even works!

 

[SRadke]

It's not the differential that causes it to buck. When you turn a corner the front end of the truck has to travel a farther distance than the back (make a larger circle) so the bind that you feel is between the front and rear, not the front side to side. This happens with any 4X4 (exception is for articulated steering or skid steers) and is amplified by a long wheelbase and/or a tight turning radius.



-Scott

 

[RustyJC]

The difference between an AWD (all wheel drive) and a 4WD (4 wheel drive) system is that the AWD system has a center differential to accommodate differences in wheel speed between the front and rear. That's why the AWD system can be used to drive all 4 wheels on dry or otherwise high-traction surfaces and the 4WD system can't (or at least shouldn't be). The 4WD system binds up when turning due to the difference in turning radius (and, therefore, wheel speed) between the front and rear tires.



Rusty

 

[GerryDrake]

Bind

The fact that in forward or reverse, except when going in a PERFECTLY straight line, the front end always travels further than the rear end is the reason that used to be, and still might be, some applications where the manufacturer puts slightly different ratios in the differentials. Had a 68 bronco with 4. 10 in the front and 4. 11 in the rear. Worked great

 

[klenger]

In response to GerryDrakes comment, I have heard that some vehicles used different ratios for front and rear, but I have never had one that did as far as I know. The explanation that I heard for doing it was so that the front axle would have a tendenancy to pull the vehicle rather than for the rear one to push it.



Edit: I've been thinking about this concept and am wondering if anyone has any actual ring/pinion combinations that were actually used with a different ratio in the front than the rear. I made an Excel worksheet to see how many different combinations of ratios would be available within a range of 35-46 for the ring gears and 9-13 for the pinion. I read on a different thread here that one of the gears' teeth count must be prime to force random gear mating (makes sense to me). That being the case, there aren't all that many ratios to choose from.



See attached chart. The yellow cells indicate ratios outside of the range of use for our application. The magenta cells indicate ratios where both gears are not prime. The green cells indicate ratios in common use for our application. Interesting concept and looking for feedback.

 

[JHardwick]

The explanation that I heard for doing it was so that the front axle would have a tendenancy to pull the vehicle rather than for the rear one to push it.

This is so true on mud boggers. They may run as much as a rev (on the pinion) difference front to rear. I think the theory is to get the front to float or skim and dig with the rear.

 

[Bertram65]

Yep, in 4X4, up front, it bucks & graps & generally displays its poor design. I sometimes wonder why the Big 3 can't build something as refined as a Toyota. Every Toy I have ever owned ran as smooth as silk in 4x4 on any surface. Go figure.



I guess, it being an American product, we should be happy that it even works!

No way, any 4X4 without a center differential separating the front and rear differentials will bind on a dry road even with open diffs front and rear. As for Toyotas, great trucks I have owned a few, and many times I have had to back up after driving a while in 4WD in snowy conditions to un-bind the drivelines and be able to shift back into 2WD. There is nothing wrong or unusual with the way the 4X4 system operates in the Dodge trucks.

 

[BHolm]

It has already been answered correctly but maybe I can add to the confusion... . I mean help



It is normal to see one front wheel spin and one stop. That is how an open differential works. It is like that so you can go around corners. I have several trucks with lockers. Unless you are on an extremely slippery surface turning is very difficult with a locked front diff because, as mentioned, to turn, one wheel must travel further than the other. 4x4 is a misnomer, most 4x4 trucks drive through the two wheels, one front and one rear, that have the least amount of traction. If you have the LSD rear you get almost 3 wheel drive.



The transfer case locks the front and rear axles together. This causes the bucking when you try to turn on too grippy a surface. Most of the reason it is jerky is because of the u-joints connection being in four places around a circle. A CV joint does it better because of a constant connection around the circumference, but they are a lot more expensive. That is part of a Toyotas smoothness, they run CV's up front not u-joints.



AWD and 4wd were compared well too. AWD has a diff in the t-case. This allows dry road use without binding. AWD is as funny as 4WD, not really true to the wording. My AWD trucks are stuck when one wheel sits on ice for example. With open front and rear diffs and an open center diff the power finds its way out through the one wheel with the least traction. Most AWD vehicles today use the brakes to slow the spinning wheel and transfer torque to a wheel with traction. The other alternative is lockers. I have three trucks with full lockers, the only true way to get real 4wd.



What you have is normal, but it sounds like you may be using it when you shouldn't. Any time you get the bucking and binding you have too much traction and are running the risk of breaking something. Also keep in mind that the u-joints are strongest when the wheels are straight. Cranking the wheel over in 4wd and applying full Cummins torque is a recipie for disaster. If you want to learn more about 4wd systems my buddy Harald has some great write ups on 4x4abc.com

 

[RKerner]

It has already been answered correctly but maybe I can add to the confusion... . I mean help



Most of the reason it is jerky is because of the u-joints connection being in four places around a circle. A CV joint does it better because of a constant connection around the circumference, but they are a lot more expensive. That is part of a Toyotas smoothness, they run CV's up front not u-joints.

The above is the reason. I have run both, from Blazers to 4Runners to Tundras and back to the Dodge. CV joints versus cross and trunion (roller?), no comparison for input speed versus output speed.



My concern is the driveline chatter when spinning the wheels pulling a load in poor conditions at slow ground speeds. I assume it is not good for the final drives but it is hard to avoid when trying to build ground speed so as not ot get stuck.

 

[BHolm]

While the Dodge system is on the crude side, I also think it is pretty durable. Hopping and bucking certainly isn't ideal, but like you say, it may be the only option sometimes. My '03s deliver to construction jobsites, often in snow and mud. I KNOW they have been beat on like this. They do take abuse pretty well. One option is to run low range if you can, to get moving. An auto trans helps here too as the convertor allows more torque multiplication yet and some ability to absorb driveline shock.

 

[CJEliassen]

What you have is normal, but it sounds like you may be using it when you shouldn't. Any time you get the bucking and binding you have too much traction and are running the risk of breaking something. Also keep in mind that the u-joints are strongest when the wheels are straight. Cranking the wheel over in 4wd and applying full Cummins torque is a recipie for disaster. If you want to learn more about 4wd systems my buddy Harald has some great write ups on 4x4abc.com

I have to turn my 4x4 on all the time. Just about anytime I stop I have to through it on to get moving forward again. My 97 dodge was awesome in 2 wheel drive inthe snow. This 04 sucks. I have gone an entire winter without using 4x4 in my 97. In my 04 I can be on dry pavement with one rear wheel on the smallest patch of ice and go nowhere. It is embarassing when you have a huge truck and you get stuck on flat level ground with nothing but a wee little patch of ice. It really seems like dodge is going backwards.