641 still loses Hydraulics prime

noticed a few hings.

Briefly for those not familiar with prior posts; 640 rebuilt lift cover due to erratic behavior, after rebuild hydraulic pump losing prime easily; rebuilt hydraulic pump as well as lift had been operating slowly. Still loses prime. I probably need to take the lift cover off again to readjust lift as arms don't drop low enough in position control, nor high enough in draft control. Worked well enough brush hog today and start to try to use a disc plow.

When pipe plug on high pressure outlet of pump is loosened, switching from position control to draft control produces a torrent of bubbles and sometimes some frothy oil at the pipe plug.

Could I have screwed something up in the top cover rebuild ghat is making it loose prime so quickly? How to troubleshoot loss of prime; I read the archives and I think Dean mentioned that most frequent cause in his thinking was wear on the pump wobble shaft, but no discussion of check/fix.

Thanks in advance!

One other thing: when I rebuilt the pump, I left the wobble shaft and bearing alone- I just rebuilt the input and output valves. I can go back and redo the bearings/seal; just wasn't eager to do so as FO-20 seems to suggest special tools were needed.

Hi Bill,

I was reading you other post about your pump too. Its starting to sound like have blown the seal on your pump. Usually that seal will wear a groove in the wobble shaft to. When that happens, your pump pulls air instead of oil into the pistons. If you want to try to replace that seal you can do it without special tools, but it will take a shop press.

I would plan on replacing the wobble shaft, bearing cup and cone, needle bearing and seal. They are all available after market for a reasonable price.

Getting the seal out is the hard part, it is behind the bearing cup that is pressed in. You can use a welder an put a bead of three on the cup and it usually pops out or grind the cup down to nothing in several places than hook that cup out. One that is done you get the seal and needle bearing out. They all press back in. The wobble shaft has the bearing pressed onto it, that is where the shop press comes in.

If you are up to it, we can help.

Also, I saw the post about gear shearing the key and spinning on the wobble shaft. That's easy to check with the pump off, did you check it when you overhauled the valves?

Kurt

Kurt,

thanks for your reply.

- I think I have the "ball bearing" pump, not the
"roller bearing" pump, if that matters.

- I didn't disassemble the wobble plate, but I did
grab the gear and the wobble plate and they seemed
locked together pretty well.

- I have the FO-20 and the Ford manual.

- Will re-tear it down.

BIll

I have a pdf version of the piston pump supplement manual that features the ball bearing version of the pump. If you want a copy just let me know and I'll send it.

That ball bearing pump is rare. It might a challenge to get the bearings.

thank you. I have the Ford Tractor Shop manual
which shows it. I might well be wrong....

We'll see when I get it apart. Also, might
(might?) not trash the bearing on removing it to
get at the seal.