Lift goes up, but only goes down sometimes.

My tractor is a 1948 8n Ford. I've mowed four acres with it for ten years. Just recently the deck will sometimes only go up, not down. When the deck finally hits full height then it will drop when the control lever is pushed down. I took off the right side inspection hole cover and was actually able to make the tractor do this problem while I observed (very rare to have that happen as we all know) Here's what I did; I started the tractor, put the pto in gear and moved the lever up to lift the deck (after pulling the shaft to the mower) Then I left the deck in a mid lift position for a few minutes with the tractor running. When I went back to lower the deck I was looking in the inspection hole and noticed the long verticle arm that is supposed to transfer the lever movement down to the pump did not move(!)when I tried to lower the deck. I then shut off the tractor and reached in the inspection hole and wiggled the verticle arm. It was free and not binding as evidenced by it feeling "loose" and having some small amount of free play in the yoke it sticks into down in the pump area. This verticle shaft goes into a yoke that acts like a sort of rocker arm to control the pump intake and exhaust of fluid. When the rocker arm is pushed in, the pump lifts the deck, when the rocker arm is allowed to spring back, it lowers the deck. The key point here is that the rocker arm is spring loaded to the exhaust (deck lowering) position. The control arm only has a positive pressure on the rocker arm in the lift mode. When you lower the deck control it merely relaxes pressure on the verticle arm and, hence, allows the rocker arm assembly on the pump to return to it's resting position. Verdict: something in the rocker arm assembly is binding. If you have the Ford service manual it's pictured on page 100 figure FO153, parts 34,35,36,37 etc,..etc..
All this being said still leaves me wondering WHY this assembly is binding. I took it all apart and found nothing unusual, a tiny spot of pitting, and some very slight wear, but nothing that looked like it hadn't already been there for a lot of years. I am wondering if any of the hydraulic experts out there could help? Will a faulty check/safety valve make this valve assembly lock up briefly? Either way, since I've got all of this stuff apart, I'd like to replace the exhaust and intake plungers, or at least the intake plunger spring as it is the only return force to make the pump lower the load. I cannot find anywhere on the internet that sells this stuff. Everyone seems to have the older 9n/2n T shaped valving, but not the 8n stuff. What am I missing? The parts in quesion are numbers 8n697(intake valve spring), 8n698-f(hydraulic pump intake control color code blue), 8n640C(hydraulic pump exhaust valve color code yellow), etc. I hold an airframe/powerplant FAA license and know how to read a micrometer. The valve plungers I have are within spec. I just noticed a post here describing a similar problem but I thought I'd start a new thread anyway. Any ideas?

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• Re: Lift goes up, but only goes down sometimes. Mike (ok) Wednesday, July 11, 2007 (0)

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