MFWD ?

[cperky]

I was bush hogging today on some hilly uneven rough ground. While crossing a small ditch at an uphill angle I noticed that my right front was spinning but my left front was not. I was in 4wd. At the angle I was at the majority of the weight was on the left front wheel as it was in the ditch and the right front was barely on the ground . My question is:

Do the front wheels have some type of slip allowance or clutch that allows one wheel to spin when the other is not so as not to cause damage?

I also went through the ditch at the opposite angle to see if my left wheel would spin with the weight on the right and it did just the same

Thanks,
Chris

 

[TedLaRue]

cperky,

The answer to your question is "yes". The "some type of slip allowance or clutch" you're asking about is called a "differential".

The differential gear box has one input from the engine, and two outputs, one to the left wheel, and another one to the right. The differential transmits the power from the engine to those outputs (i.e., to the left wheel, or else to the right wheel, or perhaps a little to each). Naturally, if one wheel is up in the air or on ice, all of the power will go to that wheel since it's easiest to turn. So 4WD only guarantees that two wheels will turn (one in the front, one in the back).

The purpose of the differential is to allow the outside wheel to turn faster than the inside wheel when you make a turn. If you make a right-hand turn, the left wheel must turn faster to cover more ground than the right wheel. You may have noticed that it's harder to turn on a tight radius when your tractor is in 4WD.

Your tractor likely has a foot pedal or lever that allows you to lock the differential, which forces both outputs to turn, but probably only for the rear wheels (i.e., if you step down on that lever, then the rear wheels are locked together and will both turn, even if one is up in the air). When you lock the differential, your 4WD tractor is forcing three wheels to turn. That will usually get you out of a ditch type situation.

As a side note, some cars have (or used to have) something called a "limited slip" differential which would sort of automatically apply that differential lock when one wheel had no traction.

 

[CCWKen]

Yes, it's the differential action. It's the same for the rear axle. Without it, you wouldn't be able to turn. The differential transfers power to the fastest moving side or the side with the least resistance.

If you have independent rear brakes, you can stop one side and the other wheel will turn you on a dime with some change leftover. This is also why you should always lock the brake pedals together during transport speeds.

 

[CCWKen]

Ops. Looks like Ted can type a lot faster than I can.

 

[TedLaRue]

Don't overlook this part of CCWKen's post:

If you have independent rear brakes, you can stop one side and the other wheel will turn you on a dime with some change leftover. This is also why you should always lock the brake pedals together during transport speeds.

I thought my post was comprehensive, but I forgot about that important concept.

 

[Doc_Bob]

I was bush hogging today on some hilly uneven rough ground. While crossing a small ditch at an uphill angle I noticed that my right front was spinning but my left front was not. I was in 4wd.

I hope someone explains that most of our tractors are not "true" 4 WD, but FWA. My TN70A has FWA, not FWD.

 

[RickB]

I hope someone explains that most of our tractors are not "true" 4 WD, but FWA. My TN70A has FWA, not FWD.

It is a matter of semantics. In the Ag tractor world, FWD is normally reserved for tractors with equal sized wheels and tires at all four corners. Smaller powered front wheel equipment 'assists' the rear axle, I suppose. A distinction recognized by some, not all who use, build, sell, or describe tractors. MFD is usually synonomous with FWA, but FWA also includes hydraulic drive axles which are mostly obsolete. Some FWA tractors, usually larger than compact size, have limited slip front differentials or locking front diffs.

 

[cperky]

Hi all,

Thanks for the information about the front differential and the fwa/4wd info. It's always nice to get such good information from the group d:> )