Hi Guys.
Before I start to replay to this thread, does anyone have an alternate part number for the hydraulic pump on the front of the engine? It is a John S. Barnes P/N 3396. Any help would be appreciated.
I'm glad I came upon this forum and can probably provide you with some information as I too, have learned the hard way after purchasing mine at an auction sale here in Nova Scotia. My apologies for not reading all of the replies, so if I am repeating what has already been said, I hope I can at least contribute.
The hydrostatic transmission in the Digit tractors does a number of things.
First of all, there is a small gear type pump incorporated into the upper housing of the hydrostat (where the two hydraulic lines come out and go to the steering ram) This small gear pump offers power to the steering ram and does nothing else. That said, you will have to look deeper into the problem of not being able to move.
The second is the hydrostat itself. Encased in it internally, consists of two components identical in appearance. One is a rotary piston pump with a variable swash plate (connected to the drive shaft) . This pumps fluid to its counterpart, a rotary hydraulic motor just below it. The swash plate is what controls the pistons on the piston pump. In the neutral position, (that is when your forward and reverse pedal is in neutral) this swash plate keeps the pistons in a neutral plain so that no hydraulic pressure is being produced to move the hydraulic motor. When you step on the forward/ reverse pedal, through the linkage, you tilt the swash plate one way or the other in order to translate the rotary motion of the engine to an up and down motion of the pistons to provide the hydraulic pressure to move the hydraulic motor one way or the other. You are simply controlling the flow and the direction of flow to make the hydraulic motor turn.
The safety switches to only one thing and that is to stop the engine from running if anything goes wrong. If the engine is still running and you have no movement, then there can be no flow of hydraulic pressure to the hydraulic motor. Starting with the very basics, does it have enough fluid? Is there a restriction of the supply line (the one going to the lower portion of the hydrostat)? Does a physical check confirm that the forward and reverse on the foot pedal actually move the forward and reverse arm located on the left side of the hydrostat? Is the filter dirty? What color is the oil? If it's black or dark in color that is a sign of overheating. Check output shaft and make sure it's not turning when you step on the pedal. This would indicate the rear differential rather than the hydrostat.
That said, the first thing I would do is to carefully open the (smaller) filter hooked directly to the hydrostat and check it for metal contamination. You can use a hacksaw if you have to, however try to eliminate as much contamination as possible from being introduced. Once this has been done, remove the paper filter element and using a sharp knife, cut the paper portion out and spread it on a piece of cardboard. If there are pieces of brass evident, then chances are that the brass has warn on the pistons at some point. This is usually due to running the machine low on oil.
Another thing is to check the output shaft and make sure that it is the hydrostat and not the rear differential that is the problem.
If you need to buy a replacement hydrostat, I think Heartland sells them for around $4000.00 the last time I checked. I have found a cheaper way to repair the old hydrostat if that is indeed the problem. As there are no longer any replacement parts available (that I am aware of) for the old hydrostat, I have found that part from the older John Deere 300 hydrostat can be reworked and used on the DigIt hydrostat. I'll save that info for another day though.
I have photos of all the internal components if you require them.
Hope this helps.
Yours truly,
Doug in the Maritimes
