Has this happened to you?

[Soundguy]

Though it is probably minutia.. if we are talking ag or industrial tires, there will be tractional differences depending on the direction of the tire.. IE less tractrion on an ag tire in reverse direction.. etc..

Soundguy

 

[AlanB]

At the risk of getting a little "tough love" myself. I've had a similar experince with a JD 855. I was using the FEL to move sand out of a large ditch. I would drive straight down the ditch so the tractor was level side to side. Fill the bucket (which was way to big for that little tractor) full of sand and back out. More then once (let the tough love begin) when I reversed up the hill one of the rears would start to lift. I quckly stopped and dropped the bucket which was less then a foot off the ground, emptyed a little sand and tried again.

What I think was happening:
1. The weight in the FEL made the rear very light (to spite the BB I had for counter weight)
2. When you back up a hill the center of gravity is shifted further forward taking more weight off all ready light rear wheels
3. The front tires (4wheel drive) have to exert more torque to move the tractor up a steeper hill. That rotation further lightens the rear.

1,2,3 combine to cause the rear to just start to lift (CG just over the front tires). Since the front end is not fixed the front tires don't provide any initial resistance to tipping sideways, and the rears both have effectivally zero weight on them any minor inbalances in the tractor (load just barly off to one side, ground not perfectly level, engine torque, steerwheel off to one side or the other, etc. etc. all forces that usually don't make a big diffrence) cause one wheel to lift just before the other. Some tractors may naturally have slightly more weight on one side e.g. an extra gallon of fluid in one tire etc. that makes the same wheel lift consistantlly. In my example it was the right rear that always came up first.

If the above theroy is correct and someone lacked the "pucker factor" to stop quickly whne the first tire lifted off the ground eventually the front pivot would hit a stop and both rear tires would leave the ground, the tractor would then pivot on the front tires until the FEL hit the ground.

Numerous factors would control weather the tractor would rest on the FEL and front tires and stop or flip sideways. Personally I don't care to find out. Just one tire in the air is enough to need to change my shorts.


So thats my theroy, let the debating begin.

Heck, sounds plausible too me,

would not bet on what I had on at the moments it has happened as counterweight could have been nothing, or BB or PHD. My tires are not loaded.

I can sit here and think about letting it go till it hit the pivot stop of the front axle, but I am too much of a wuss to let it go that far I think.

For me when that back wheel starts grabbing air, it is time to stop and re-evaluate the situation.

 

[bones1]

I think Gryantaylor has it right as well.I can picture just what he is saying.

 

[Gryantaylor]

Heck, sounds plausible too me,

would not bet on what I had on at the moments it has happened as counterweight could have been nothing, or BB or PHD. My tires are not loaded.

I can sit here and think about letting it go till it hit the pivot stop of the front axle, but I am too much of a wuss to let it go that far I think.

For me when that back wheel starts grabbing air, it is time to stop and re-evaluate the situation.

I don't think "wuss" is the right word. "Too Smart" is a better choice. I have a bad habit of pushing equipment too the limit. But when the wheels start leaving the ground its time to stop moving and start thinking real hard about the physics of whats going on.

When I was moving all those buckets of sand out of the ditch I was wondering what if I kept going would the tractor just end up on the bucket and front tires or on its side. While I'd still like to know the answer I'm not going to risk my life to find out and I'm not suggesting anyone else does it either. that said if anyone already has first (or second) hand experince about what happens I'd like to here it.

 

[slowzuki]

The tipping has nothing to do with engine torque, there is a pivot on the front axle, it is really hard to get a balance such that both rears come up.

The load in the bucket was just too heavy. You notice it in reverse but if you were going forward and slowed down it would happen, same is if you tried to stop going down hill.

Want to repeat it safely? Drive your tractor into a pile of sand and lift the loader. If you have a really weak loader on it won't be able to lift the rear but most will pop it up then it will tip to one side as the sand spills out of the bucket.

Want to try it some more? Hook one side of the bucket under an immovable object and lift. the opposite rear tire will lift.

BTW it is harder to get a 2wd to do the original tip because it will loose traction first. You have to back up a hill with increasing steepness with enough speed to get you past the point of losing traction. Then she'll go up just the same. Be careful, it will begin a fast descent down the hill until enough weight gets on the rears to stop it.

 

[jmc]

The tipping has nothing to do with engine torque,...
The load in the bucket was just too heavy.

Ken,

While what you describe could cause something like this, I have my doubts in this particuliar case. I had to bring this log up onto the driveway over rough ground and I don't recall that squirrelly feeling of an overloaded bucket. We'll probably never really know for sure.

Thanks,

John

 

[pat32rf]

Don't forget that when that rear axle looses traction the tires can start to try to rotate in OPPOSITE directions. This causes some real tricky torque reactions. I have one short (40') steep hill off the side of my driveway where i am quite often in 2wd. The hill is sandy and if I forget to hit 4wd before starting down with a loaded bucket things get exciting if I back off the go-pedal on the hydro.

 

[mars1952]

Hello,

On several occasions with my former tractor, (Ford 1920) I had the left side of the tractor come completely off the ground when pushing hard in reverse. It's kind of un-nerving and it's one of the reasons I like vehicles with clutches- when things go wrong, pushing in the clutch often helps. Anyway, the first times it happened was when using a 3PH implement I built to uproot small trees. It was a sharpened steel channel to push in under the root ball in reverse, then pop out the tree with the 3PH lift. Another time, I had a heavy log in the FEL and was starting to back up a hill. If I hadn't used the clutch, I'm pretty sure the tractor would have rolled over. I'm wondering what causes it and if its a general problem with compact tractors or just that Ford. It's hard to imagine that little engine had enough torque to inadvertently lift the whole side, and if so, why only in reverse?

John

Hi: I have read or skimmed all the posts in this thread so forgive me if I missed something.

Engine torque can definitely lift a wheel off the ground. Think of a two wheel (rear) drive car burning rubber. The right rear wheel always spins. Burn rubber in reverse and the left wheel will spin. When you use your tree uprooter the same thing can happen. The 3PH can float. The digger stops, the tractor keeps going and gets lifted. The torque aids the lifting of the left tire and tries to keep the right tire on the ground. A heavy load on the loader will take weight off the rear wheel and engine torque will preferentially lift the left wheel.

How is your tractor ballasted? If your rear tires have an unequal amount of liquid in them it could exacerbate the problem. In general it sounds like you do not have enough ballast.
Good Luck, Marshall

 

[SteveInMD]

It's really pretty simple...always keep the tractor pointed up hill when you have a load in the bucket. Go backwards down hills and forwards up.

The center of gravity of a tractor on flat ground is further back than a tractor pointed down hill. When the center of gravity moves too far forward the rear will become unstable. Usually one wheel will lift off the ground before the other, after that the tractor can easily tip over.

 

[irwin]

Front axle lead (or slippage) is necessary on front wheel assist tractors in order to realize the benefits of front axle tractive assistance. Desired front axle lead is expressed as a positve increase in front axle speed over that of the rear axle, usually in terms of percentage (ideally +1%-+5% for most front wheel assist tractors). Lead percentages outside of this range will lead to problems such as accelerated tire wear, difficult steering, loss of tractive assistance from the front axle as well as increased drive train wear with premature failures. Negative lead (or slippage) will, from the outset, totally negate any potential advantages offered by front wheel assist.


I copied this from a tire info site awhile back..it goes on much longer...I don't know about your situ..but i'd think in reverse a dominate front drive wheel could cause one rear wheel to lift in the right (or wrong) circumstance.
I'll never find the site again but I have alot of it copied if anyones interested.

tim