Working on a JD 270 Skid Steer, recently put in a new hydrostatic (tandem) pump, as the old one had way to much by-pass over the case drain. The problem was first noticed as loss of power and stiff control levers (mechanical) especially under load.

Since putting in the new pump it works better, with much more power, but the control levers are still stiff and under load get stiffer. Going against a loading dock its impossible to move the levers as though there is a back pressure or deadheading.

The problem is even more noticeable in the high speed function (this unit has two speed drive motors).

Its impossible to go up against a loading dock and engage the drive to bog down the engine as its impossible to move the levers, where as with a similar machine one can stall out the engine this way. Backing up an incline the levers are stiff, but the machine moves up the incline, when going forward downhill the levers are very soft, which indicates that the levers get stiffer with load.

The new pump case drain is well within the acceptable spec. This is a closed loop circuit, with the motor case drain feeding into the pump case drain and the pump case drain feeding into the suction line which feeds the charge pump.

Any advise and help would be appreciated.

Andi

As far as I know the pump is acting exactly as I would expect it to if it is an Axial Piston design.

However, I have no idea how a John Deere system is designed, never saw one, so it could have had some hydraulic assist that is not working or does not have high enough pressure to work correctly since the new pump assist pressure is not adjusted correctly. STRICTLY A GUESS.

If you have a hydraulic schematic of the circuit it could probably shed some light on the reason for the difference in the operatiing charecteristics.

When KevinJ reads your post he may have some input since he works a lot with Hydrostatic drives.

Thanks for the reply Bud. Not sure on if it has a hydraulic assist, but I don't think so, will check it out though. The pumps and motors are manufactured by Eaton, have not yet talked to them personally though, only to the JD rep who has.

I included a TIF of the schematic. let me know if that works for you, otherwise I can convert to PDF when I get home.

Would appreciated any and all input as we are stumped as of right now.

Andi

attachment didn't seem to take, so here it is again.

Andi

You don't seem to be having any luck attaching a
file-at least I can't open anything.
Maytag

Don't know why, it told me both times the attachment upload was successful.

Andi

See if this works

IFPBcoverColor.doc (77 Kb, 24 downloads)

Andi;
How big is the file? The first one I tried was over 300K and it said it refused it.

Are you putting in the right path to the file? Try Browsing for it if you have not been doing that.

The file is only 17.6 KB, I pasted it into MS Word, will see if that works this one is now 38.5 KB.

JD_270_Series_II_-_Hydrostat_Schematic.doc (38 Kb, 40 downloads)

Thanks for the advise Bud, that was the trick, needed to send it as other then a TIF picture file.

Let me know what y'all think. JD has come back to say that its behaving normal, but it isn't and the customer is certainly complaining.
One can actually push the levers on other machines going against a loading dock either stalling it out or digging the tires into the ground. And yes going against a dead stop is an unrealistic condition, but it emphasizes the point that under load the levers get stiffer with the amount of load.

Andi

This message has been edited. Last edited by: Andi.Mell,

From the schematic there is no boost oil shown so that is probably not the difference in operation. That does'nt mean it's not there just not shown. It only takes one Letter and/or Number in the Pump Part Number to change how the Control is operated.

Is there any physical difference in the pumps, such as, how the volume control (Pump Stroke Control} is connected?

Distance Trouble Shooting is difficult at best and often impossible to do.

Is there a local Fluid Power distributor you can contact? I often helped individuals with problems, especially those who worked at a good customers facility, but often to anyone who called. An Eaton-Vickers distributor would be best choice.