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Dale2

Member
You answered a question on a 601 ford loosing prime on the hydraulic pump not long ago. I have replaced the seal, the wobble shaft as it had a groove worn in it. Replaced needle bearing and wobble shaft bearing. I also replaced the orings on the transmission housing and the 2 at the pump. I have the accessory plate turned around and a pressure gauge in the port. When I start the tractor and loosen the bleed screw on the pump . The pump picks up prime. when I tighten the plug the pressure comes up to around 1900 to 2000 psi and within 10 to 15 seconds will drop back to zero. To get the pressure to come back up I have to shut off engine and start the bleed process again. Do you think the relief valve item 94 in drawing fo269 in the I T manual could be sticking open or should I be looking else where.
Thanks
Dale
 
That's a head scratcher right there. If the relief valve was at fault, I don't think the pressure would drop to zero. That said, pre 1965 tractors are not my area of expertise.

Have you tried operating the tractor normally to see how it performs?
 
The lift will not even try to work. The tractor has set for about 4 years.
Thanks for your thoughts.
 
Explain "I have the accessory plate turn around" Do you mean the plate under the seat on the right front corner of the lift chest? Do you have that plate turned a half a turn? WAY?
 
yes the accessory plate is turned half way around and gasket is blocking the holes, like the I T manual describes.
 
I have now found that there are always air bubbles coming from the pump, so I assume I am sucking in air. Has anyone ever seen the o rings between the transmission housing and the lift compartment leaking air?
 
The unload valve is located inside the lift cylinder piston assembly, and is the first thing I'd suspect if it doesn't lift at all when you know that you have pump flow. The IT manual should show you where it is.
 
Bern have you ever seen the o rings between the transmission and the lift compartment fail? I have found air bubbles are always in the pump output
 
I do not have a copy of the I&T manual but I guess turning the plate would be a way to check maximum pressure. I would suggest bleeding the hydraulic system till all the air is gone by running a hose from the pump to the fill plug at the reservoir until all air is gone , then check for maximum pressure. I doubt very much if the o rings at the back of the transmission are letting in any air .
 



as the pressure comes up, it will open the relief valve, and try to raise the lift. On the lift, when equal librium is obtained, the the control valve opens... either of the two valves can have a bit of rust, so that when the open, they hang up... staying open...

in some cases I have found that operating the tractor over and over, and moving the lift lever back and forth, I eventually got the valves to work loose and start operating correctly... its a crap shoot but it does work in some cases, where a tractor has set for a long time.

A while back drove a 740 down the road with a shredder bouncing and dragging, and after about three miles, the control valve worked loose and all was good. so,,, you never know...
 
I doubt that the o-rings have failed, since they are static. I myself would be looking for air leaks in the inlet tubing above the oil level, specifically any cracks in the pipe or manifold itself.

Or, it's possible that the seal in the pump you replaced somehow got damaged on installation? That could certainly cause it to suck air.
 
Thanks Bern Yes the seal could be leaking as I remember there was ascratch in the housing where the seal sat.
 
Bern thank you and everyone else for their comments. I took the pump back apart and found I did not seat the seal fully. Fixed that and the pump primed up and the lift is working. So now to wait a few days and make sure the pump does not loose prime. That is the problem I was trying to fix in the beginning.
Thanks to all
Dale
 
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