There are a couple of things left to be done to the rear drive unit such as cutting the chain to length and securing the hydraulic motor in place. We will come back to that shortly but I want to move ahead with the accelerator control linkage. The means of controlling the speed on a hydraulic drive system like ours differs quite a bit from the standard linkage that controls the speed of a gasoline engine. The basic components are shown in the next photo. They consist of the hydraulic control valve, 5/8" pillow block bearings, shaft left over from the steering kit, piece of 1/2" round tube for extending the linkage, and some angle iron and flat plate for a frame. The primary component is the directional control valve. It directs the flow of hydraulic oil by means of a spool which is a metal shaft that moves back and forth. As you can see in the next picture there is a metal handle on the right that is connected to the spool. There is an added piece of metal that acts as a cantilever to increase the leverage of the handle and decrease the force needed to move the spool back and forth. This is referred to as an open center valve because there is a spring that returns the spool to the center position when there is no force exerted from the handle.You will notice that there is a port on each side of the valve. Hydraulic oil is pumped into one side of the valve and exits the other side. The spool is moved manually as needed by use of the handle. Now you will also notice that there are two ports on the top of the valve. Hydraulic fluid is diverted into the ports by moving the spool in or out. Fluid can be diverted through only one port at a time in this kind of valve depending on whether you push the spool in or out. The hydraulic motor I have chosen is fully reversible so the idea is to set up a pedal that will move the cart in forward when the pedal is pushed forward. Can you guess how we might cause it to go in reverse? If you said get out and push then that is not the plan. I want it to be as simple as pushing the pedal forward to go forward and pushing it backwards to go backwards. I know that does not sound right but I will explain in a little while.

First of all we need a way to hold the pillow block bearings in place. Some 1/8" x 1 1/2" angle iron works nicely.

Now here is the left over shaft from the steering kit. I want to use it to pivot the pedal linkage to the control valve. It is a 5/8" shaft with two drilled pieces of metal that form a cradle. One thing I noticed upon closer inspection is that the holes do not line up exactly. That would be no particular problem if it were used horizontally as it was designed to be used. But it causes a problem with alignment when trying to use a clevis and pin. All that needs to be done is to twist one of the arms around slightly in order to line them up. In my younger days I would either wail on it with a hammer or try to use a piece of pipe to twist it into place. after all it just needs to be moved a little bit.

In fact I did go get my trusty pipe leverage to see if it might help.

But that is just not the right way to do it. The arms are held on with just two gnarly tack welds. So all we need to do is get out the angle grinder and grind the welds off.

Then just take the hammer and tap it loose.

Now we can move it into alignment and reweld it in place.

This is a 5/16" clevis with a female thread. It will function as a pivot point for sliding the 1/2" round extender tube between the pedal and the control valve. A short 5/16" bolt will be used to connect the clevis to the 1/2" extender tube.
Here is a shot of the individual components.

Pieces assembled.

Now the 5/16" connecting screw needs to be welded to the end of the 1/2" tube.

Screw welded to 1/2" tube.
Parts assembled with the bearings.