What is draft control

[Woodstock Walt]

My previously owned Mahindra 4540 had draft control. I tried it with my subsoiler a couple times, it worked surprisingly well.

One thing it was actually really handy for was putting the final grade on our driveway with a landscape rake (no gauge wheels). It took some fine tuning to get it calibrated correctly, but once it was dialed in it worked great for smoothing out the windrows. It would lift the rake just enough to spread the windrow without moving any material along the path of travel, just sluffing the excess off the top and redistributing it side-to-side.

The thicker/heavier the windrow was, the more it would lift to allow for more spreading and less carrying of material. It's hard to describe, but it actually worked really well. However, I mainly just used it because the tractor was equipped with it and I thought it was cool. My new 5155, which replaced the 4540, does not have draft control and I have not missed it yet. For my application, the same result can be produced by carefully controlling the position valve, or better yet adding a set of gauge wheels.

Standard procedure is to leave draft control all the way off when it is not being used. If it is left on while carrying lifted implements, the bouncing of the implements from the movement of the tractor causes the draft control system to constantly react to the dynamic loads applied to the top link. This can cause the system to overheat (straight from the owner's manual). I remember that I accidently left it on while bush hogging one time, and was alerted of its activity from the constant clicking and minute hydraulic adjustments it was making to compensate for the bouncing of the bush hog. When I felt around the 3 pt. system underneath the operators seat, I found that it was extremely hot from the draft control working overtime to constantly trigger the lift function for minute adjustments.

Lesson learned, after that I was vigilant about making sure it was completely disengaged unless I was specifically using it.

 

[Tx Jim]

Not all model tractors utilized upper(centerlink) sensing. JD tractors from '65-'92 had lowerlink sensing which in my experience was a better design. Sensing on these models of JD tractor was accomplished by flexing a rod that draft arms attatched to. When draft mechanism was set to factory spec's the draft sensing operated very well. One drawback of lower link sensing was the opportunity of a hyd oil leak at the bottom of hyd oil reservoir.

 

[Bavarian]

Not all model tractors utilized upper(centerlink) sensing. JD tractors from '65-'92 had lowerlink sensing which in my experience was a better design. Sensing on these models of JD tractor was accomplished by flexing a rod that draft arms attatched to. When draft mechanism was set to factory spec's the draft sensing operated very well. One drawback of lower link sensing was the opportunity of a hyd oil leak at the bottom of hyd oil reservoir.

If I remember the manual correctly, my 2012 6430 has lower link control. They may have used it even longer.

 

[npalen]

That video is incorrect. Position control keeps your implement at the same depth. Draft control actually raises an implement out of the ground, so it cannot be keeping the implement at the same depth.

How draft control works, as explained on my old IH2500b...

There's a triangle formed by three sides:

1- the line of the back of your tractor
2- the line of your lift arms to implement
3- the line of your top link

There's a rock shaft somewhere at the point that your top link connects to your tractor.

Now, let's say you're driving along with a plow in the dirt. You're in soft easy soil, and all of a sudden you come into some harder soil. Your plow has a harder time cutting through the soil, putting drag on the tractor, so the rear wheels start spinning instead of pulling forward.

As the rear wheels spin, they start digging a hole, which lowers the rear of the tractor.

When the rear of the tractor lowers, the implement does not, because it floats.

Since the rear goes down and the implement does not, that puts pressure on your top link. The top link is trying to get shorter but it's solid. It has to maintain the three legs of the triangle. The implement pushes the top link against the rock shaft. The rock shaft activates the 3 point hitch to lift the implement out of the ground. It keeps lifting until the plow comes out of the ground enough to allow the rear tractor tires to stop digging a hole and start moving forward enough to allow the pressure on the rock shaft to diminish and it lowers the plow back into the ground, eventually back to the pre-determined depth that your position control was set at, unless it hits hard dirt again.

The plow causes a constant push and relax on the top link, depending on soil conditions.

You can manually set the sensitivity of the draft control to react faster or slower to conditions.

So, to summarize:

Draft control keeps your tractor from burying the rear tires by raising and lowering the implement as soil conditions change.

Position control allows the implement to drop to a preset depth and no more.

I see what you're saying but wouldn't one want to set the draft control to raise the implement slightly BEFORE the tires start slipping excessively? The draft compresses the top link as it increases and raises the implement slightly to prevent excessive tire slippage.

The larger and more modern tractors have slippage indicators on the "dash" so the operator can adjust accordingly. That information would be worthless, however, in a mudhole.

Adjusting the draft control on an 8N ford, for example, requires a bit more operator intuition. Listening to the engine RPM drop would be a good indicator when adjusting the draft control lever.

 

[MossRoad]

I see what you're saying but wouldn't one want to set the draft control to raise the implement slightly BEFORE the tires start slipping excessively? The draft compresses the top link as it increases and raises the implement slightly to prevent excessive tire slippage.

The larger and more modern tractors have slippage indicators on the "dash" so the operator can adjust accordingly. That information would be worthless, however, in a mudhole.

Adjusting the draft control on an 8N ford, for example, requires a bit more operator intuition. Listening to the engine RPM drop would be a good indicator when adjusting the draft control lever.

That's the whole point of it. It tries to lift the implement before slippage becomes excessive. Before an operator can detect it. Just the slightest slippage causes the wheels to start digging holes, and that top link angle to try to change and put/release pressure on the rock shaft. The total movement on that rockshaft is very small. The valve is very sensitive. It really works very well.

As others have mentioned, I had top link sensing. There's also lower arm sensing, and electronic sensing. I don't know how those other two systems work, as I'm only familiar with the top link sensing that was on my IH2500b.

 

[npalen]

Are there any less than 40HP new compact tractors offered today with draft control?

 

[rScotty]

That's the whole point of it. It tries to lift the implement before slippage becomes excessive. Before an operator can detect it. Just the slightest slippage causes the wheels to start digging holes, and that top link angle to try to change and put/release pressure on the rock shaft. The total movement on that rockshaft is very small. The valve is very sensitive. It really works very well.

As others have mentioned, I had top link sensing. There's also lower arm sensing, and electronic sensing. I don't know how those other two systems work, as I'm only familiar with the top link sensing that was on my IH2500b.

I like MossRoad's explanation of the way that draft control works, and his experience with it parallels my own.

I'm not sure I agree it is only the sinking of the rear wheels that causes the compression of the top link to actuate the draft control - I admit I haven't thought it all the way through. It always felt to me that the draft control actuated the moment that the front of the tractor got light when the plow hit an obstruction - on that we agee, whether the lightness is the rear sinking or the front rising...

Now that could be due to the tires slipping and digging down as MossRoad says, or it might be that the sudden hard spot was causing the tractor to slow down and try to raise the front end without the tires slipping and digging in - while they still have traction. Either way would put the same compression onto the top link. And we agree that compression is the trigger for most of the draft control valve to actuate.

I don't know about the bottom link actuated draft control that TxJim talks about. I'm sure there are other ways to do it, too. Our old 1958 John Deere has the typical top link sensor for its draft control and works nicely. It has a Cat II 3pt.

If that top link is suddenly under a lot of compression the draft control will actuate with a rapid series of quarter inch upwards movements of the three point arms and it is hard to miss. I've had it sound like a rapid fire machine gun and shake the whole tractor as it successively raises the 3pt arms in a series of short movements.
rScotty

 

[Tx Jim]

If I remember the manual correctly, my 2012 6430 has lower link control. They may have used it even longer.

Your probably correct but my personal experience with JD tractors ceased with JD 55 series. After viewing 6430 parts catalog I think your correct that 6430 has lower link draft electronic controlled draft sensing

 

[MossRoad]

Are there any less than 40HP new compact tractors offered today with draft control?

I do not know.

 

[MossRoad]

I like MossRoad's explanation of the way that draft control works, and his experience with it parallels my own.

THough I'm not sure I agree it is only the sinking of the rear wheels that causes the compression of the top link to actuate the draft control - though I admit I haven't really thought it through. It always felt to me that the draft control actuated the moment that the front of the tractor got light when the plow hit an obstruction - on that we agee.

Now that could be due to the tires slipping and digging down as MossRoad says, or it might be that the sudden hard spot was causing the tractor to slow down and try to raise the front end without the tires slipping and digging in - either way would put compression onto the top link. And we agree that compression is the trigger for most of the draft control valve to actuate.

I don't know about the bottom link actuated draft control that TxJim talks about. I'm sure there are other ways to do it, too. Our old 1958 John Deere has the typical top link sensor for its draft control and works nicely. It has a Cat II 3pt.

If that top link is suddenly under a lot of compression the draft control will actuate with a rapid series of quarter inch upwards movements of the three point arms and it is hard to miss. I've had it sound like a rapid fire machine gun and shake the whole tractor as it successively raises the 3pt arms in a series of short movements.
rScotty

Yes. If the front end gets light that means the tractor is tipping back, which would indeed put pressure on the top link.