I forgot or maybe it was never mentioned, several questions, so please forgive me if these are repeats...,
First, these machines are capable and designed to go full speed going forward AND reverse. So the treadle pedals need to be able to move the directional control on the variable volume pump an equal distance in both directions, wether that be cable operated or hydraulically operated.
Second, I have NO hands-on experience with hydraulic treadles, only the hydroback cable on my machine. I'm pretty familiar with it.
With that said...
- does your machine use a hydroback cable from the treadle to the variable volume pump, or is it hydraulically controlled?
- did you block it up off of the ground and try operating the treadle to see if the whine happens with all 4 wheels off the ground?
- The reverse treadle pedal is shorter than the forward treadle pedal, and it should be easier pushing the forward pedal than the reverse pedal due to leverage. BUT... it shouldn't be that hard to push the reverse pedal. Something is amiss.
- If it's a cable operated treadle, try turning the machine off and observing the action of the direction lever on top of the variable volume pump and make sure it can go the same distance when the pedals are pushed full forward and full reverse as measured from the center neutral position. It should be easy in both directions and full travel. If not, there's a problem with the pump, or the cable, or the treadle.
- Also, there are three grease zerks on the cable operated treadle. If you have cable operated treadle, make sure they are all greased and free moving. You could disconnect the cable at the variable volume pump direction lever and see if the treadle pedals move freely by hand in both direction while the cable is disconnected. That would help eliminate the treadle and hydroback cable as problems.
- If it's a hydraulic treadle, I recall mention of the early models with hydraulic treadle being too sensitive to movement and PT added springs under the treadle pedals to put more resistance against your feet so it wasn't so sensitive. If so, see if there are springs under each pedal somewhere.
- Also again, check for any debris under and around the treadle area. Mine frequently gets small sticks and brush in there that can build up under a pedal, making it impossible to push to full travel. I have to remove them after heavy brush cutting.
Hope those suggestions help.