6x4 Cub

[J-Mech]

I'm guessing that a lot of you guys making suggestions haven't ever driven a tandem axle truck, or a tractor....

Turning brakes aren't going to really make any difference. On a tandem, the center of the turn is dead between the two axles. Mounting one axle higher or lower than the other would cause a no-drive situation and may even cause the differential to lose equal drive and it just spin out. Without a walking beam type suspension, you may lose drive traction on opposite wheels and just spin out. Just like on a tandem axle truck on snow/ice/mud will. That's why anyone who drives a twin screw off road wants a power divider and differential lock. Now, the tandem hydro axles, because of how they are driven, wI'll function as a truck with the power divider kicked in, but a loss of traction on uneven terrain, or even as simple as driving into a building with a "hump" could cause spin out. *IF* you are on flat level ground, no ditches, nothing but flat yard..... as long as there isn't say, a 2"or 3" dip or hole, it may work just fine..... but I see the yard in the background of the pic, and looks like up next to the house has quite a rise to it, and the corn in the background is running downhill to the left, so how flat is it really? Using the ATV tires that you did should actually make it better, as they are low pressure and may have more flexibility for uneven terrain. Not having enough weight distribution on the steer axle would make it hard to turn also. You are quite essentially building a truck, not a tractor.

Syncing the two hydro's together isn't hard at all. Been done more than once by others building articulated 4 wheel drive machines. You can use a cable, or linkage. Whichever is easier.


I think it's a cool project. I'm not opposed to it at all. I just don't want to see a whole lot of time spent to find out that it has drive/traction issues. Just trying to pass on what I know to be true, and get the OP to either consider it, or apply it. Hopefully in doing so save a lot of build time.

[DieselDoctor]

Jonathan, I'm not arguing here, I agree with all your statements about traction but in a semi truck tandem axle with the power divider unlocked, doesn't the wheel with the least traction see the power output due the the differential in the power divider? If the power divider is locked in and the rear centers are no spins, then all four drive correct? So in the case of this project, because the back rear axle is positively driven by the shaft passing directly thru the front rear, wouldn't the back one still be driving even if the front one was totally off the ground and spinning? There is no lost motion or disconnect of the driveshaft as it passes thru the front hydro. Even so, with no suspension at least one or two of the four rear tires will most likely be off the ground most of the time on rough terrain. I think it's a cool project too and like you would like to see the OP succeed.

[Green stripe wide frame]

Originally Posted by DieselDoctor

Jonathan, I'm not arguing here, I agree with all your statements about traction but in a semi truck tandem axle with the power divider unlocked, doesn't the wheel with the least traction see the power output due the the differential in the power divider? If the power divider is locked in and the rear centers are no spins, then all four drive correct? So in the case of this project, because the back rear axle is positively driven by the shaft passing directly thru the front rear, wouldn't the back one still be driving even if the front one was totally off the ground and spinning? There is no lost motion or disconnect of the driveshaft as it passes thru the front hydro. Even so, with no suspension at least one or two of the four rear tires will most likely be off the ground most of the time on rough terrain. I think it's a cool project too and like you would like to see the OP succeed.

In a semi with the power divider locked you get power
being transfered to both axles but still have open differentials, just like a 4 wheel drive pick up locked in 4 wheel. With it locked in, you have it right it goes to the wheel with the resistance.
You'll need three drive wheels on the ground for this thing to move. Unless you put a spool in one carrier.

[J-Mech]

Originally Posted by DieselDoctor

Jonathan, I'm not arguing here, I agree with all your statements about traction

Stan, (That is the right name isn't it? Hope so.) I didn't think you were arguing. I was pretty sure you understood, as you made the comment about it needing walking suspension like a truck. You made a couple statements that prove you understand (below). You and Green stripe (sorry bud, I can't recall your name) seem to get it. I broke down some responses below.

Originally Posted by DieselDoctor

but in a semi truck tandem axle with the power divider unlocked, doesn't the wheel with the least traction see the power output due the the differential in the power divider?

[QUOTE=Green stripe wide frame;434518]In a semi with the power divider locked you get power
being transfered to both axles but still have open differentials, just like a 4 wheel drive pick up locked in 4 wheel. With it locked in, you have it right it goes to the wheel with the resistance. [QUOTE]

Yes, this is correct. Green stripe answered it very well!

Now, for discussion and explanation purposes, an all wheel drive vehicle (AWD) has a transfer case just like a pickup would and it has a differential between the front and rear axles just like a power divider in a truck axle. The power divider is just that, a differential, between the two axles. (Further explanation for other readers.) Yes, on a tandem drive (twin screw as it's called) if one wheel loses traction, all power goes to that wheel and it spins. If you lock in the power divider, then it locks the differential between the two axles and equal power will go to both axles. So, if one wheel spins, the differential in that axle will supply power to the slipping wheel, but power will still be supplied to the axle with no slip and you can drive out. If you have a case of two wheels spinning (one on each axle) then the power divider lock will have no effect. You will also have to lock the differentials to get power going to all 4 drive wheels equally. I know you guys covered it, and understand, but I just wanted to go into it a little farther.

Originally Posted by DieselDoctor

If the power divider is locked in and the rear centers are no spins, then all four drive correct?

Yes, but even with the divider unlocked, all four drive equally unless you are 1.) turning. Or 2.) you have wheel spin.

Just to reiterate, with the divider locked, it supplies power (solid shaft) to both axles equally. Only reason not to have it locked all the time is so that it steers easier.

Originally Posted by DieselDoctor

So in the case of this project, because the back rear axle is positively driven by the shaft passing directly thru the front rear, wouldn't the back one still be driving even if the front one was totally off the ground and spinning?
There is no lost motion or disconnect of the driveshaft as it passes thru the front hydro.

Yes. That is absolutely correct. One axle can come completely off the ground, and as long as both tires on the opposite axle are still in solid contact, then it will still drive.

Originally Posted by DieselDoctor

Even so, with no suspension at least one or two of the four rear tires will most likely be off the ground most of the time on rough terrain. I think it's a cool project too and like you would like to see the OP succeed.

Originally Posted by Green stripe wide frame

You'll need three drive wheels on the ground for this thing to move. Unless you put a spool in one carrier.

Yes, both of these are correct. 3 wheels will need to be in contact, OR one whole axle. So, if the correct 2 come off the ground, it will still drive. More on this below.



Now, it wouldn't seem that this would really be an issue. But believe me, go off road with a twin screw truck, and even with suspension, and a loaded trailer, it doesn't take much to get one wheel on each axle to lose traction. Kick the power divider in and it gets much better, but even then, it still isn't very hard to lose traction. Example: I was backing a semi into my driveway at home last fall. Just backing off a gravel road, into a gravel drive that goes just slightly uphill, and lost traction altogether. Once a wheel spun, it dug a hole, and wham! Stuck. Power divider in, (truck doesn't have diff lock) and it still couldn't do it. I finally got the truck to move forward just enough, that I could pull forward and go back again (a little faster this time) and got into the drive. But it really is amazing how with a big truck, with suspension, and plenty of weight, it will spin out and your done. That's why I'm so certain that this thing will need at least some sort of flex between the two axles. One tire on it goes up on a hill/bump whatever, it can pull traction from two wheels pretty quick. Now, if the truck had ag tires on it.... maybe it would have been fine. Again.... with those ATV tires, there may just be enough wheel flex to make it work. I haven't been around JD Gators much, but they are an ATV with tandem drives. I do not know what type of drive system they have, but they seem to work pretty well. Also, Terra Gator makes a 5 wheel sprayer/spreader that has a tandem drive rear. It doesn't have any suspension on the rear, but it has floater tires which have a lot of give. I would also assume since it's an off road vehicle, that it has both a divider lock, and diff lock.

[DieselDoctor]

Jon - yeah I understand the concept. I've been a heavy truck mechanic for 41 years now. I wanted to present the issue in the form of questions to help everyone understand. I knew from past posts that you have heavy truck experience. Few people realize that more tires on the ground can actually hurt traction, and I'll use the example of trucks with a tag axle (non-driving axle(s) solely for weight carrying capacity). When trucks with tag axles are on rough terrain, the first thing the driver does is lift the tag up to the transfer the weight and help keep the drive axles on the ground. I had thought about the JD Gator too. They have a walking beam of sorts and are chain driven between the two rear wheels on the same side and use flotation tires as well. From the looks of things on the Gator the front axle does all the work and probably has an open spool. I doubt you'd turn it if it were a no spin.
Stan

[DieselDoctor]

I had a quick thought about using "turning brakes" on the tandem drive. On new class 8 trucks with automatic traction control, the computer automatically applies the individual wheel brake on the wheel that is spinning thereby forcing the power to the opposing wheel with traction. If this Cub Tandem (?) has turning brakes and has the open center differentials as they are from the factory, couldn't the builder step on the brake of the side that is spinning and force power to the other side? I can see this would be a constant issue, stepping on the proper brake every time a wheel lifts and spins. Just a thought.

[DeltaCub]

Originally Posted by DieselDoctor

Jon - yeah I understand the concept. I've been a heavy truck mechanic for 41 years now. I wanted to present the issue in the form of questions to help everyone understand. I knew from past posts that you have heavy truck experience. Few people realize that more tires on the ground can actually hurt traction, and I'll use the example of trucks with a tag axle (non-driving axle(s) solely for weight carrying capacity). When trucks with tag axles are on rough terrain, the first thing the driver does is lift the tag up to the transfer the weight and help keep the drive axles on the ground. I had thought about the JD Gator too. They have a walking beam of sorts and are chain driven between the two rear wheels on the same side and use flotation tires as well. From the looks of things on the Gator the front axle does all the work and probably has an open spool. I doubt you'd turn it if it were a no spin.
Stan

The JD 6x4 Gator frame actually allows the front drive wheels to be slightly off the the ground. Thus when empty and the posi is not engaged is drives and turns very easily. However, that dynamic changes once significant weight is in the cargo box or two fatties are in the seats. All six tires are low pressure ATV tires that are designed with traction and flotation in mind.

[DieselDoctor]

That's interesting. Having the suspension lift the front rear axle when empty would make it much more nimble for turning. I've never actually been close to one, only pictures.

[J-Mech]

Stan, I knew you were a heavy truck mechanic. I wasn't over explaining for your benefit.
For the record, I too have the same experience you do, I just have more like 20 years in it.... but I also have been a mechanic for Case IH, grew up farming (and still do), had my CDL since I was 19, and worked on industrial machines (dozers, backhoe, trackhoe, ect), oilfield equipment and on automotive. My training was in diesel heavy duty, but when I had my shop I also worked on automotive. (Not bragging, just stating experience.)


I did not know that the Gators frame was set up so that the front axle was slightly higher. I have worked on them before, but not at any extent. I didn't remember that they were chain drive. That set up would make for a good steering, and good off road capabilities.

A walking beam like a grader uses would be best..... but might be too costly and time consuming a build. Not really any easy way to make walking beam suspension either. Using one drive axle, with a chain drive to the other axle would really be the simplest. Or even one drive axle that chain drives all 4 tires like the Gator.

Either way, it will be an interesting build to watch and see how it turns out!

[V30crewcab]

what about building some tracks to go around each pair of wheels, then you only have to deal with left or right loosing traction, and then use the brakes to help steer. that would be interesting.