John Deere B

just hooked up my John Deere 120 corn snapper to JD B 1948 but when I raise the rock shaft to lift the picker
as soon as I let go of the handle it starts to go down on it's own I can't find my operator manual I thought I have
adjust the metering valve stem to change from cylinder to rock shaft but there are two stems one on top left
and one lower in the center not sure whitch is whitch anyone have a operator manual? what are the settings?
thanks Howard
 
You must already have the correct plugs in your powertrol unit or your rockshaft wouldn't function at all. Low oil level would not cause the picker to drop, but they might not allow it to raise fully. Have you used the rockshaft on this tractor on anything else? I would suspect a leak in the internal cylinder, either a bad cylinder packing or a leaking gasket between the cylinder and the basic housing. It's possible that there is an internal leak or valve in the powertrol valve itself, but I would suspect the cylinder area first. Those old hydraulics are low pressure, so the gasketing is not high tech.
 
It could be that the spool is going past the center position. A weak spring on one side of the spool will cause this.
 
The metering screw on the left side is closed when using a remote cylinder and opened about 2 turns when using the rockshaft. The metering screw is for adjusting the speed of "slow raise". It doesn't sound like the problem since you said the rockshaft picks up very fast.

Besides a leak down at the piston cup/packing or cylinder gasket one of the check valves in the Powr-Trol may not be seating and letting oil return to the reservoir.
 
the rock shaft did work good I think it's in the check valves how hard is it to clean them out? if the packing has a leak all the oil would leak in the rear end right? anyone have a break down of the power trol? thanks Howard
 
If the piston cup/packing is leaking the oil goes back into the hydraulic reservoir.
If the piston cylinder gasket or the seals on the pto shaft where it passes through the front wall of the rockshaft housing are leaking, the oil goes into the rear end.

Look at pages 108-111 of the parts catalog for a breakdown of the Powr-Trol valve box. Be careful when you start taking it apart and keep track of the order of the parts as they come out. It would be a good idea to take the Powr-trol valve box off and work on it on the bench.

Be patient when you open the parts catalog - it takes awhile to download.
Parts catalog Model B
 

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