JD 3520 MFWD lever disengages hard

[kuboman]

This question brings up something I have wondered about. Some of the 4x10 series tractors only have an electric push button to engage/disengage MFWD. Does the 4WD light stay on until the gears actually disengage, or does it simply shut off when the button is pushed whether the gears are still engaged or not? Obvious problems if it just shuts off with the switch.

I think any that use an electric switch have a hydraulic clutch that engages and disengages the front drive so there is not the same problem than the lever style. The gears get 'wind-up' and all you need to do is reverse the direction for a few feet to disengage with ease.

 

[JD755]

Instead of just wondering I decided to research it. There is no clutch. MFWD is engaged the same way whether it has an electric switch or a manual lever. It is a simple collar shift. With the electric switch the manual lever is replaced with a hydraulic cylinder, and the light is simply turned off/on by the switch. Seems like the cylinder might be harder on the gears. Interesting point is that the MFWD is engaged by default when using the hydraulic cylinder. It requires power to activate the cylinder to disengage MFWD.

 

[kuboman]

Instead of just wondering I decided to research it. There is no clutch. MFWD is engaged the same way whether it has an electric switch or a manual lever. It is a simple collar shift. With the electric switch the manual lever is replaced with a hydraulic cylinder, and the light is simply turned off/on by the switch. Seems like the cylinder might be harder on the gears. Interesting point is that the MFWD is engaged by default when using the hydraulic cylinder. It requires power to activate the cylinder to disengage MFWD.

Learn something every day. Seems like the electric way might be the least attractive way to do it.

 

[Dmac1]

When I bought my first 4wd vehicle a long time ago the same thing would happen when all wheels had good traction. They told me the mechanics call it "wind up" as kuboman mentioned. The pressure on the gears comes from not all the wheels taking exactly the same path but being forced to turn at the same speed. Thus, pressure results and if you run a vehicle in 4WD on pavement (for example) you'll accelerate the wear on the tires.

Another example...run your tractor in the grass locked in 4WD and watch it chew up the yard when you turn! Ok...don't!

Anyway, the same thing happens with any 4WD vehicle that doesn't have a viscous connection somewhere that allows slippage. Would bet that no one has a problem disengaging MFWD when all wheels are on a slippery surface. Turning the steering wheel and keeping the tractor going is one way of relieving the tension.

I doubt that disengaging things when its a little tight will do any damage. Now...if you've got to really lay on it, thats another matter! I'd aim for an easy disengagement though.

On the push button one...you should be able to tell if you're locked in or not via how the vehicle turns when it has good traction on all wheels. If it kinda binds on a turn, its locked in. I'm going to guess the light goes out when the gears come apart. Thats how my old SUV worked anyway and it had pushbutton (which I hated). I prefer a lever.

Dave

 

[JD755]

The information I attached shows the light is simply part of the switch. It knows nothing about whether the gears are engaged or not. I agree you will immediately notice in a turn if they are engaged, but straight line you may not be able to tell. It could be possible to drive a distance on dry pavement and not know it is still engaged. Remember too that the previously attached info shows the tractor defaults to 4WD with engine off. Something good to know if you tow the tractor. There are advantages to simply having a mechanical lever.

 

[Zebrafive]

I don't know about the CUTs, but on the bigger MFWD AG Tractors, they are designed with the front axle turning a little faster than the rear axle. I think this is for easier steering and front tires wearing out faster. So even with out a lot of turning there will be drivetrain "windup"

 

[JD755]

I believe the CUT's are designed the same way for the front to always pull, so you always need at least a small amount of slip. I have owned many trucks with various 4WD designs. Part time with mechanical shift lever and manual hubs, part time with auto-locking hubs, part time/full time with auto-clutches, etc, etc. I can also tell you about the issues with a positive locking differential on the front axle. The key thing is to know what to do and not to do with what you have. I remember a guy many years ago who thought it would be neat to put some oversize tires on the rear of his part time 4WD truck. Later he wondered why his transfer case broke. So the same with tractors. There is always pressure on loaded gears in 4WD and dry pavement will not provide the slip required to unload them for 2WD. So just having a light would concern me, but I always prefer to hear first hand reports from owners. Are there 4x10 owners with real knowledge of their system would could provide some personal experience? I'm always glad to learn more.

 

[Dmac1]

The information I attached shows the light is simply part of the switch. It knows nothing about whether the gears are engaged or not. I agree you will immediately notice in a turn if they are engaged, but straight line you may not be able to tell. It could be possible to drive a distance on dry pavement and not know it is still engaged. Remember too that the previously attached info shows the tractor defaults to 4WD with engine off. Something good to know if you tow the tractor. There are advantages to simply having a mechanical lever.

Ok...thanks for the clarification. I didn't yet take time to study the schematics and sounds like you've got it covered for sure.

What I was getting at though was that he could test it via engaging MFWD, go forward and turn so its bound up a little, then disengage MFWD. He could then see if the light comes off immediately or whether it waits until the gears come apart after the wind up is released.

Interesting about defaulting to 4WD! Definitely something to know...but ya never gotta tow a Deere!!!

 

[Dmac1]

Instead of just wondering I decided to research it. There is no clutch. MFWD is engaged the same way whether it has an electric switch or a manual lever. It is a simple collar shift. With the electric switch the manual lever is replaced with a hydraulic cylinder, and the light is simply turned off/on by the switch. Seems like the cylinder might be harder on the gears. Interesting point is that the MFWD is engaged by default when using the hydraulic cylinder. It requires power to activate the cylinder to disengage MFWD.

Examined the schematics and JD's guidance on how it works. Three things:

This doesn't seem right...it says on eHydros (mine) and PowerReverser (manual shift?) the hydraulic cylinder is involved. So its not just those with the MFWD button that default to 4WD when turned off. If this were correct, we wouldn't have resistance on the lever when we disengage it and its wound up.

I'm not too good with electrical schematics...where is the indicator light for when MFWD is engaged?

Whats an SST machine? It says they're the only ones where MFWD is engaged via lever.

Thanks!
Dave

 

[JD755]

The hydraulic cylinder is on machines with electronically controlled transmissions. This would be the eHydro and ePowerReverser. Some 4x10 machines have the mechanical Hydro or mechanical PowerReverser. Some have the mechanical SyncShift. That one is the SST. All these other transmissions replace the hydraulic cylinder with a mechanical lever that will put the tractor in 4WD only when the lever is placed in that position. The lever will stay in whatever position you leave it.

The light is the circle with the x in it. When you turn the switch ON that provides power to the light, and removes power from the shift solenoid. This shows the light does not know whether gears are engaged, and also why the system defaults to 4WD when the tractor is turned off.

I'm not clear on your question about lever friction. Your 3520 does have a light, but does not have a pushbutton. It has a lever so yes you will feel the friction unlike those that just have a pushbutton. The button was only on some 4x10 series tractors.