720 prentice running gear

[starmac]

Long shot here, but the guy I work for here has a 720 prentice that locked up one track. They thought it was the brake and it was. the brake had basically welded itself together.
They removed it and the one track will not find nuetral, it just keeps spinning, will do it both directions, probably what caused the brake to get so hot.

Anybody have any suggestions as to what to look for, not just a bunch of logging equipment mechanics around these parts.

[kiko]

 The Prentice 720 has two separate loop systems one for each track.  So basically you have a pump/motor set for each side.  The track motor only turns when the pump supplies oil to it. The problem that it has now, not finding the center , is in the pump for that side, not in the motor.  This probably caused the brake failure. Inside the pump the mechanical feed back to the controller is most likely broken.

[starmac]

Kiko, you are 100% correct on the way it drives, and what we figured caused the brake faillure, which didn't have many hours on is since it was rebuilt. Can we get parts and repair or rebuild the drive pump for that side, or is it a replacement type of deal??

Also it seems like it was losing hydraulic power after running a couple of hours, could this be causing that, maybe overheating the oil, or we looking for a complete seperate issue.

[kiko]

I have only seen one of these machines, so I am not very familiar with them as to say exactly what kind of drive pumps it has.  I believe they are sauer 100cc pumps, if that s the case they can defiantly be rebuilt and I could walk you through it and tell you where to get the parts.  A picture of the pumps ,a parts book break down or a model code off pump would help determine this.  The weak main could be related but hard to say from this far away but likely  from common tank contamination.

[starmac]

Thanks a lot, I think he is going to haul it into town tomorrow, so it will be a few days before I can get the pump info.
This thing has several pumps, some piggyback on others (going by what they have told me) do you know if it has a scavenger pump to get the oil back to the system?

It is kind of a major undertaking to either do any major work where it is, or to haul it into town. I hate to see him haul it in, fix the track problem and try it out, only to haul it back out and the hydraulics slow down after a few hours, and having to make another trip to town.
He priced a new pump just for the one side was in the 10 grand range, ouch. lol
He probably has close to fifty loads of saw logs decked that needs processed now, and really need to put up another 100 or so loads before spring closes us down.

[cutbank]

this sounds like a virtual closed hydraulic circuit that the main pump is the directional control valve for each track. There is an internal pump in the main pumps that supplies pilot pressure ( ones I worked with was 2 bar) to both sides of swash plate to maintain center. Some of the track units I worked on the brake was released by oil flow pressure by trying to move forward or backwards , even if pump is not centering brakes would still release. Are the main pumps dual function both tracks and boom functions if so there has to be an external brake release so when your using boom functions that the tracks wont move until commanded.

[starmac]

The only thing there that I can answer is, that the brakes are released by oil pressure.