[mopar70]

I have a customer with a JD 9650 that coasts when travelling down hills. The Hydro doesn't slip or slow down when going up hills and there is no sign of metal or contamination in the hyd filters. The JD dealer says the only fix is to replace the hydro pump and motor, but I can't believe if they were bad that it wouldn't slip or have some other symptoms like noise. Is it possible for anything in the transmission itself to allow a freewheeling condition?

 

[lanwickum]

Wish I had a schematic to look at. Don't see how the tranny itself could cause this. I would guess a valve in the hydro system. Replace the pump and motor sounds a bit extreme. Again, I don't have a schematic to look at.

 

[ilbar]

What if you put a little more oil in the hydro? I wonder if they don't cavitate pointing downhill because of oil level thus causing the freewheeling going downhill. If it was the hydro motor they should give grief going uphill too shouldn't they? I've had the freewheel issue myself and deere changed pump and motor and it still free wheeled.

 

[X80]

Compensator valve...

Ant...

 

[Haystack]

Is the hydro equally as strong without slippage or bypassing in reverse? When going downhill the pressure will be on the opposite lines just as if you were reversing the machine. I would think there would be two relief valves right on the pump, one for each direction.

Swathers have two pairs of them since they are a dual hydrostat. I have had the cone shaped spring loaded plug miss its orfice and get hung up on the edge of the orfice more than once. There could be different style of cartilage relief valves also, but they all usually look like large hexagon plugs on the pump and can be inspected for debris or a broken spring fairly easily.

 

[Don Boles]

Had a 9860 do the same thing.
But it was 9 years ago.
I do remember the shop spent a lot of warranty time on it but I can't remember what they did nor did I consider it fixed when they finally gave up.

 

[mopar70]

a flow chart would be helpful. I have worked on quite a few IH hydro tractors over the years and they used an anti-coast valve in their drive control valve. If I remember correctly Sunstrand used a decelaration valve in the hydrostat unit to control this