NAA Hydraulic Gurus Needed

[Ian074]

'53 NAA Piston Hydraulic pump
Problem: When 3 point is holding weight (back blade for example) it was slowly leaking down about 2 inches and then catching itself and jerking back up. It took about 45 seconds to cycle.
This week I lifted the cover and went to work.
New Piston
New NH o-ring and backup washer installed correctly on piston
Honed cylinder
New cam follower pin
Removed, cleaned and polished control valve
Removed, cleaned and polished unloading valve. This was the older type unloading valve with no o-ring
Cleaned and polished all bores
Replaces back pressure valve and installed new washer in seat
Lightly oiled everything on re installation
Control valve and unloading valve worked smoothly in their bores
Visually, nothing seemed amiss.
Put the whole shebang back together
Result: I'm still getting leak down and a jerking correction. However, now it is only going down about 3/4 inch and the cycle is about 1 and 1/2 minutes. So I guess I corrected things about halfway.
What am I missing here? Weak control valve spring? I was very careful and everything seemed to work and move okay. I could see absolutely no leak from the ram. My sometimes faulty logic says it has to be in the control valve or unloading valve area. Right?
Could it possibly be that everything is just worn too much to operate correctly? How about an adjustment?
As it stands I can use it okay. It is just that it so frustrating to not be able to figure this out.
Guess I'll go have a few beers. Maybe something will come to me.

 

[JW Axtell]

I'm afraid that I can offer no help. But, it seems we have the same systems right down to the unloading valve with no o-ring. And, I also have a small leakdown and catch that's driving me nuts.

 

[souNdguy]

That slow bobbing is semi-normal operation of the unloading valve as it regenerates the curcuit after the lift leaks down enough for the valve to 'sense' it.

IE.. you have a bit of a leak.. and it is puimping the lift back up to correct for it..

soundguy

 

[Ian074]

(quoted from post at 10:05:13 04/03/09) That slow bobbing is semi-normal operation of the unloading valve as it regenerates the curcuit after the lift leaks down enough for the valve to 'sense' it.

IE.. you have a bit of a leak.. and it is puimping the lift back up to correct for it..

soundguy

Hmm.... Semi-normal?

 

[ZANE]

That original type unloading valve with no O ring was a recall in 1955 and later years also. Not all of them got replaced as you know. The reason they were recalled was because of the symptoms you have. Slight leakdown. Another problem with them was too close tolerance with the bushing and the least bit of grit would stick them. The rubber O ring can compensate for a little dirt!

Just be thankful it doesn't stick all the time and use it.

Zane

 

[JMOR]

Zane, JW Axtel & self have been cussing/discussing thistopic on another thread and if you have time, would you take a look at the last 2 or 3 posts, diagram, questions/speculation, etc. and comment please.
http://ytforums.ytmag.com/viewtopic.php?t=457158&start=15

It ends something like this:
Well, velly intersting! I'm going to take a WAG at this point, maybe 2 WAGs.
1) The path to the unloading valve from the back pressure valve is on the high pressure of bypass valve and the path is internal to the casting, making the tube on the bypass on the low pressure side of bypass & dumping into the sump.
2) There was an early and late design, where we are dealing with the late version & in the other, or early version, the bypass valve was not at all as we see it( acorn nut, tube & all), but was rather integral to the top cover casting.
Just thinking out loud.

 

[Ian074]

(quoted from post at 18:39:12 04/03/09) That original type unloading valve with no O ring was a recall in 1955 and later years also. Not all of them got replaced as you know. The reason they were recalled was because of the symptoms you have. Slight leakdown. Another problem with them was too close tolerance with the bushing and the least bit of grit would stick them. The rubber O ring can compensate for a little dirt!

Just be thankful it doesn't stick all the time and use it.

Zane

Thank you. It is usable. It's nice to know that after all that it wasn't something I missed. Ironic too that I paid particular attention to that unloading valve with cleaning and polishing.As stated I got half the travel out/

 

[JW Axtell]

(quoted from post at 08:39:12 04/03/09) That original type unloading valve with no O ring was a recall in 1955 and later years also. Not all of them got replaced as you know.
Zane

Is it feasible to install the newer (o-ring) type) to the units that didn't get the upgrade? Or does it require a whole different ram cylinder assembly?