Is it possible for a tractor to have limited slip?

[V1Rotate]

The small Terramite TLBs use a hydraulic motor driving an automotive type rear axle with what they call TRAC-LOCK which is a type of limited slip. The front wheels are driven by separate hydraulic motors.

 

[k0ua]

No, even if only one tire is spinning the speed of the tire does not double.
The speed of the tire (one or both) is limited by the engine rpm and gear ratio. Theoretical top speed of the car is the same as the max speed the one tire will spin. Actual top speed of course is less due to friction, air resistance, etc.

See I am not full of crap:laughing::laughing: Well actually I am full of crap most of the time.:laughing: but the twice speed thing is for real, if you one wheel is totally stopped and the other is spinning on an open diffy. that is why in your owners manual of your car, they caution against "excessive" wheel spin as it is hard on your spinning tires to go that fast, as you can easily go over the speed rating of your tire, and it can fly apart. I have never actually seen one fly apart from all that smoke rolling off of it, but I suppose it could happen. But I remember sitting perfectly still and seeing 120 MPH on the speedo. So I guess one tire was going about 240 mph, as there was only 1 black mark on the road.

James K0UA

 

[tcartwri]

K7LN is correct. Don't confuse a planetary unit with a differential. You might want to look into that a little more.

A typical open diff has four spider gears. The two splined onto the axles are considered sun gears and the two pinned to the carrier are the planetaries.

The planetaries are pinned to the case by the cross shaft, and when you abuse an open diff with one wheel peels, the gears will gall to the cross shaft, effectively locking the diff.

:thumbsup:

 

[Ford tractor]

See I am not full of crap:laughing::laughing: Well actually I am full of crap most of the time.:laughing: but the twice speed thing is for real, if you one wheel is totally stopped and the other is spinning on an open diffy. that is why in your owners manual of your car, they caution against "excessive" wheel spin as it is hard on your spinning tires to go that fast, as you can easily go over the speed rating of your tire, and it can fly apart. I have never actually seen one fly apart from all that smoke rolling off of it, but I suppose it could happen. But I remember sitting perfectly still and seeing 120 MPH on the speedo. So I guess one tire was going about 240 mph, as there was only 1 black mark on the road.

James K0UA

I hate to burst your bubble, but what you wrote makes no sense. The speedo is reading the speed of the tire, the spider gears are not multipliers. One wheel spinning is just that, one wheel spinning -- not spinning 2x the normal speed because only one is spinning. Watch the video, it will make it all clear.

Owners manuals tell you not to spin the wheels because "bad expensive things" happen when traction is found. You will also be much less in control of the vehicle while spinning and if stuck you will just dig down making it harder to get out.

 

[k0ua]

I hate to burst your bubble, but what you wrote makes no sense. The speedo is reading the speed of the tire, the spider gears are not multipliers. One wheel spinning is just that, one wheel spinning -- not spinning 2x the normal speed because only one is spinning. Watch the video, it will make it all clear.

Owners manuals tell you not to spin the wheels because "bad expensive things" happen when traction is found. You will also be much less in control of the vehicle while spinning and if stuck you will just dig down making it harder to get out.

Sorry, dont think so.. the speedo is reading the speed of the transmission, not the tire, the speedo gear is in the rear end of the transmission. so if it is reading 120, the transmission is running at the RPM that would make the tires go 120, after it goes thru the differential, and going in a straight line, now, the spyder gears are not turning, on their shafts, they are pushing the side bevel gears ok.. So now if you stop one wheel the spyder gears are now rotating on their shafts as well as still pushing "sideways" from the differential frame, which is attached to the main ring gear solidly by bolts. so you have the rotational speed of the differential frame pushing at 120 plus the spyder gears rotation against the now "dead" tire causing the speed to double.. the spinning tire is now going 240 MPH. thats my story and I am sticking to it.
James K0UA

 

[mjncad]

Here's the video on YouTube.

That's the video, thanks.

I'm sure that was a fake video. Not possible to create enough friction to catch a car on fire from an ice burn out.

I suspect the friction causing the fire was from something else on the car that wasn't kosher.

 

[RickB]

A typical open diff has four spider gears. The two splined onto the axles are considered sun gears and the two pinned to the carrier are the planetaries.

The planetaries are pinned to the case by the cross shaft, and when you abuse an open diff with one wheel peels, the gears will gall to the cross shaft, effectively locking the diff.

:thumbsup:

Sun gears, maybe. Spider gears, yes. Planetaries, no. A differential is not a planetary unit.

 

[k0ua]

To K7LN, Your are correct about limited slip differentials coming on the scene before 1965, I did a little research:

n the 1950s and 1960s many manufacturers began to apply brand names to their LSD units. While Packard pioneered the LSD under the brand name "Twin Traction" in 1956, the most famous of these in the USA was Chevrolet's "Positraction". Since then, Positraction (often shortened to "positrac" or merely "posi") has become a genericized trademark for LSDs in the USA.

Also found a reference to Porsche having one in the 1930's, and Torsen making one in 1958. So I stand corrected, on LSD's.. but the first Posi-Trac by Chevrolet I have ever seen, was in the 1965 model year. I cannot find out exactly when it appeared for sure, but that is the first one I know of.

James K0UA

 

[V1Rotate]

Sorry, dont think so.. the speedo is reading the speed of the transmission, not the tire, the speedo gear is in the rear end of the transmission. so if it is reading 120, the transmission is running at the RPM that would make the tires go 120, after it goes thru the differential, and going in a straight line, now, the spyder gears are not turning, on their shafts, they are pushing the side bevel gears ok.. So now if you stop one wheel the spyder gears are now rotating on their shafts as well as still pushing "sideways" from the differential frame, which is attached to the main ring gear solidly by bolts. so you have the rotational speed of the differential frame pushing at 120 plus the spyder gears rotation against the now "dead" tire causing the speed to double.. the spinning tire is now going 240 MPH. thats my story and I am sticking to it.
James K0UA

k0ua is absolutely correct and did a pretty good job of explaining how the differential works.

 

[TripleR]

This has been a fascinating thread with lots of good information by different posters. I now have a much better understanding of how these things work.

Funny that I have replaced a few "chunks" in cars/trucks over the years without ever knowing how they work.

 

[k0ua]

My first experience was in 1964 when I purchased a posi unit and put it in my 1964 Chevelle. The unit cost me a grand total of $44 plus a couple bucks for 2 quarts of the good lube that was made in those days. Let's hear it for inflation. GM brought out the posi unit in 1957, mainly for the highly successful Corvette and the new fuel injection systems that came out that same year for Chevy and Pontiac.

Thanks for the info, I know by the end of 1960's the posi units were quite common, although they had their limitations. I have the Eaton G80 unit in my new Chevy pickup, I have heard some good and bad comments on this unit. Do you have any thoughts on this type of locker?

It also has the traction control, where it brakes the wheel that is spinning and reduces engine power, I dont know if this works for the front wheels or not when in 4 wheel, I dont see why it couldnt but it may not. does anyone know?

James K0UA

 

[EE_Bota]

that is why in your owners manual of your car, they caution against "excessive" wheel spin as it is hard on your spinning tires to go that fast, as you can easily go over the speed rating of your tire, and it can fly apart.
James K0UA

Sounds to me that's why it says it in your owner's manual. In my owner's manual, they substituted a paragraph about bailing out safely if the car gets possessed by an evil spirit.

I never was much of a hot-rodder, so if it says that in my manual, it's to keep me from spilling my coffee on my shirt if a tire spins a cow patty.

Edit: Direct quote from my manual: "If you feel there is a danger the wheel will disintegrate, and you are sober, the HAL 9000 engine control module is self-aware, and despite advice from the HAL 9000 unit, it is time to exit the vehicle, regardless of speed."

 

[TripleR]

Sounds to me that's why it says it in your own's manual. In my owners manual, they substituted a paragraph about bailing out safely if the car gets possessed by an evil spirit.

I never was much of a hot-rodder, so if it says that in my manual, it's to keep me from spilling my coffee on my shirt if a tire spins a cow patty.

Edit: Direct quote from my manual: "If you feel there is a danger the wheel will disintegrate, and you are sober, the HAL 9000 engine control module is self-aware, and despite advice from the HAL 9000 unit, it is time to exit the vehicle, regardless of speed."

:laughing::laughing::laughing::laughing::laughing:

 

[Bird]

I really hadn't thought much about whether any tractors have limited slip differentials, since my Kubotas had the common differential lock pedal. But going back to the middle ages when we had a 1940 John Deere L, I can remember a number of times I tried pulling something it couldn't move, but the rear tires would dig holes in the ground and they never spun together. One would turn aways, stop, and the other one would turn a short distance, and stop; just back and forth, so I assume it must have had some kind of limited slip. And of course, the tractor would rock back and forth when it was doing it.

 

[dcyrilc]

I really hadn't thought much about whether any tractors have limited slip differentials, since my Kubotas had the common differential lock pedal. But going back to the middle ages when we had a 1940 John Deere L, I can remember a number of times I tried pulling something it couldn't move, but the rear tires would dig holes in the ground and they never spun together. One would turn aways, stop, and the other one would turn a short distance, and stop; just back and forth, so I assume it must have had some kind of limited slip. And of course, the tractor would rock back and forth when it was doing it.

I had both rears and both fronts going at the same time with the tractor walking back and forth sideways. It's possible that it was due to limited traction, but I would think that once I started throwing the gravel and with the duels on that it would be hard to have the lack of traction equal and keep it that way.

 

[V1Rotate]

I really hadn't thought much about whether any tractors have limited slip differentials, since my Kubotas had the common differential lock pedal. But going back to the middle ages when we had a 1940 John Deere L, I can remember a number of times I tried pulling something it couldn't move, but the rear tires would dig holes in the ground and they never spun together. One would turn aways, stop, and the other one would turn a short distance, and stop; just back and forth, so I assume it must have had some kind of limited slip. And of course, the tractor would rock back and forth when it was doing it.

With an open differential the tire with the least amount of traction will spin. I think what may have been happening to you is that after one tire had been spinning for a bit, it would gain some traction and stop spinning. The other tire would start to spin because it now had less traction than the first tire.
This process then continued.

 

[Bird]

With an open differential the tire with the least amount of traction will spin. I think what may have been happening to you is that after one tire had been spinning for a bit, it would gain some traction and stop spinning. The other tire would start to spin because it now had less traction than the first tire.
This process then continued.

I'd say that's entirely possible. It was kinda of like a dog digging in the ground with first the right paw, then the left, and keep on alternating.

 

[Bird]

be hard to have the lack of traction equal and keep it that way

I agree, but I guess it would be possible.

 

[EE_Bota]

Here is my best guess:

Sometimes I wonder if your issue boils down to "why didn't I get stuck?"

What I mean by that is:

In any case that the tractor is not stationary, you are not stuck.

In any case you are not stuck, all wheels are turning, even if the tractor is just skidding sideways.

In any case you ARE stationary, but the traction difference is not great enough side to side, all wheels on that axle will be turning.

If the rears are doing this, in all cases where the traction is unequal in the rear, a moment is applied that has to be countered by the steering wheels, and in some of those cases the moment may not be countered effectively, causing the front wheels to slide, making it unlikely either front wheel can stop.

It could be that if each side is slinging and shearing different material, one side speeds up and the other slows down, but only in proportion to how hard each material is to sling and shear. Wheel stoppage can be thought of as the upper bound of the range of speeds two wheels encountering variable resistance can assume.

A four wheel drive tractor just seems to be more dynamic than a two wheel drive. Even on dry soil, the fronts run a slightly different speed, and one axle is more dynamic than the other, and which axle that is varies continuously during a mud rodeo event like you described.

This has been a great topic. The only way it would be better is if you went out and did it again just to film it for us.

Edit: Would it be true to say: In an open differential, for most practical purposes, the average torque on each wheel is the same, and the average power is the same, except in the case of the wheel stopping, when power goes to zero? So the rpm varies from side to side except in the special case.
.

 

[dcyrilc]

This has been a great topic. The only way it would be better is if you went out and did it again just to film it for us.

.

Hmmmm.................

...my daughter did just get a digital video camera for Christmas.

But then with my luck, I'd pull the trailer part way out to try to get another shot at it and not be able to even get it back to where it is now. Maybe I should stay quit while I'm ahead.:laughing: