Thread: John Deere SST
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Old 10-21-2012, 09:26 PM
LawnSite Member
Join Date: Oct 2012
Location: Wrightsville
Posts: 2
New user here, I thought I would post some thoughts about my SST16. As you all know there is not to much information out there about how these things work.

The information in this thread has been great, and to add to it:

The way this thing works is that as soon as you touch the forward or reverse pedal, the switches in the back tell the tractor which actuator to collapse. The actuators do not control the steering per se, they just position the mechanical linkage so that the wheels turn properly based on forward or rearward movement of the tractor.

For example:

lets say you are making a slow left turn moving forward, (for simplicities sake) the tractor would be moving counterclockwise as viewed from above.

Low lets say you are making the same slow left turn but in reverse, The tractor should rotate in a clockwise direction from above.

Without its compound linkage the tractor would steer like any other tractor in forward, but the wheel would have to be reversed in order to make the SST behave like a normal steering tractor in reverse (left turn in reverse makes the tractor rotate clockwise on any other tractor with steerable front wheels but the SSt front end would go left when backing up with its wheel to the left). People already didn't like how the SST steering felt, imagine if they would have left out the compensating linkage

You will notice this linkage is hooked to the trans in the same place that the bolt is, that adjusts the straight line tracking of the tractor (the relationship of one axle speed to the other.)

You can watch the linkage do it's thing if you have the fenders off, put the tractor in park, key off:

1:turn the wheel left or right, the linkage going back to the tranny will not (should not) move yet since the actuators have not been told to set up for forward or reverse.

Now, simulate a pedal input (actuator movement) by taking the part of the linkage that the actuators are connected to and move it to the right of the tractor (I believe this to be the "forward driving actuator" but I am not sure, my motor is blown and I am waiting for another ). While holding the actuators to the right side of the arc, turn the steering wheel to the right, now you will see the linkage going back to the trans pulls forward, likewise a left turn on the wheel will move the trans link back.

2:Now push the actuators to the left of the arc, and again turn the wheel to the right, now the linkage moves the trans lever back, likewise a left steering imput moves the trans link forward.

This linkage essentially takes the place of what your brain would be doing on a standard zero turn that has levers that you push forward to go straight, right lever forward to make a forward left turn and right lever back to make forward right turn, or any combination of the above to make the zero turn do what you want.

A standard zero turn has a direct link to each side of the trans for both steering and forward/back motion control, simple really, steering is done by your brain adjusting wheel speed left to right. The SST has a forward/back lever on the left of the trans right near the actuator switches that is mechanically linked to the forward back pedals. While at the same time it has another mechanical link that controls the relative wheel speed left and right wheel.

My SST would zero turn in reverse all day long, but I had to be on the forward pedal pretty hard to get it to start steering in forward, at that high of a speed, it would not "zero" turn on a dime but would turn at normal mowing speed. I was able to get buy, but it was annoying. I was not real sure what was doing what under there till I read this thread and put some things together in my head while looking under the hood of mine. Waiting for my new-ish motor .

I found that the switch tabs on my SST16 had bent slightly (probably from the pivot points not being lubed well, or grass wedged in there), and I could not get a setting on the forward switch per the advice in this thread.

So I got that all squared away, also the last time I had the fender deck off when I bought the thing two seasons ago, I sprayed the actuator bellows with WD40 after reading what little info was out there, saying that they get brittle and crack then wont hold vacume. I am happy to report that mine are still nice and soft and I hit them again with some spray lube to keep them supple.

I hope I explained clearly so that other can understand the voo-doo of the SST16. It really is not very complicated once you know how things work on these tractors.

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