NAA lift won't move

k15n1

New User
Have 54 NAA with piston pump. Having trouble with the hydraulics.
The main problem is that the lift suddenly stopped working. Here's a historical account, which stretches back about 2 years.

(Was posted on N Board. Re-posting here in hopes of getting more insights.)

Several years ago, I plowed my garden with a 2-bottom Oliver 3241 plow. Exciting times. Had no trouble lifting the plow but there were some odd things. I had always had some bobbing, even with just the blade---but only a few times a minute. But back to plowing. I wanted to use draft mode so I put the selector into the horizontal position, moved the control lever down, and started plowing. When I moved the selector, it would jerk the plow all the way up, briefly. Later that day, I was running a bush hog and 15-30 min later I noticed that the mower was lowering. Corrected several times with position control lever but eventually it was just dragging on the ground. I unhooked the mower and drove back to the garage.

I eventually was advised to do the usual maintenance---the cam follower pin, the pin that bears on the piston skirt (very bent), gaskets, etc. When I took off the lift cover, I found that the turnbuckle was not turned vertical. This could cause the linkage to jam. Fixed that and all of the other stuff. Also got distracted learning how to spray implement paint on various parts, built a bead blasting cabinet, etc. Then the wife signed up the kids for soccer, the basketball. Next thing I know, I'm coaching instead of tinkering. A year goes by. I eventually get the lift cover back on, find the bolts, re-wire the tractor, replace the starter, weld a lug back onto the block. You get the point.... trying to do too many thing at once.

Recently, I got it all together and found that the lift arms don't move at all. Tested for prime in the pump by running a hose from the pump to the filler hole on the sump. Pump seems fine. Checked for oil splashing down from the ram cylinder. None. Even checked for a spray against the front wall.

Verified that the back-pressure valve stud is seated against the o-ring on the ram cylinder. Safety valve down in the sump was not tripping.

Eventually, I blocked the back-pressure valve tube with my finger. Immediately, the lift arms move up, with no load, not even the rear links.

Now I suspect that the back-pressure valve is stuck open. I take it out and notice that there is a clear path between the ram-cylinder-o-ring contact and the tube. Did some light percussive maintenance and get the spool free.

https://drive.google.com/file/d/0B3wfQHEAycNcczFtdWExVkVTb1E/view?usp=sharing

After getting it free, I re-installed the back-pressure valve. It didn't seems to make any difference. Still can use my finger on the outlet and the lift works right away. So I guessed that the valve was breaking open below the FO-19 spec of 45 psi. I'd estimate that about 45 psi of finger pressure was sufficient to get the lift to go up, judging from the tube diameter and how hard I had to press. But when I press on the spool, when I was cleaning it, much less than 45 psi was required to depress the spool.

Now I decided to try putting a spring under the acorn nut. After trying several lengths, the lift appear to mostly work. However, it DRIFTS UP without any load. At first, I thought this indicated too strong a spring so I cut off half a turn until the spring pressure was very weak. Even with the weak spring, it still drifted up. If I removed the spring, the upward drift stops and the lift arms were inoperative---the original problem.

With the weak spring installed under the acorn nut, I noticed that if I stand on the lift arm (200 lb) and the control lever is down, it will drift down as fluid is released from the ram cylinder. If I raise the control lever, the lift will stop going down, corresponding to the position of the control lever. But it cannot lift me.

I started over with a much longer spring. The lift drifts up but if I stand on it, it acts normally. When the lever is down, the lift sinks. When I pull up on the control lever (still in position mode) the lift goes up. If I turn up the idle, the response is a little more snappy but the difference isn't huge.

Then, I figured, I can at least move the plow to the neighbors yard. Closing on this house is Friday and the Buyer is walking through on Thursday. No pressure. Hook up the plow with the tractor off. Start... pull back on the control lever and it lifts the plow, about half way. I put it down and try again and it doesn't lift as far. I get a pressure gauge and put it on the jack tapping port (on the lift cover). Try to lift again and get 200 psi. Subsequent attempts get even less pressure and almost no motion of the lift. I look into the filler hole and see fluid gushing when I move control lever up. I think I saw something like a 1/2" diameter stream toward the back of the tractor. Seemed like it was coming from near the control valve. JMOR suggested looking at the check-valve and after looking at this assembly, but after examining it, I do not think it would produce the type of spray pattern I observed. Also, I found a blown gasket between the ram cylinder and the lift cover. Could this be a result of excessive back pressure?

https://drive.google.com/file/d/0B3wfQHEAycNcTWZBd0dvU1YtUDA/view?usp=sharing

I got another back-pressure valve from ebay. Was 20 $ and I didn't have high hopes. It also looks stuck open... can blow through it without resistance. Nothing moves. It's rusty and smells bad. Oh well, it was worth a try.

Here's JMOR's drawing of the back-pressure valve:

http://i192.photobucket.com/albums/z232/JMOR_photo/NAA%20HYD/hyd_NAA_backpress_relief_flow.jpg

Can anyone make sense of this?
 
Obviously, fix the blown gasket. And no, excessive backpressure didn't cause that. That gasket is always exposed to full system pressure, which can be over 2000 PSI, depending on load being lifted. I see no gasket material on those two bolt holes toward top of picture.....no gasket there will cock the mating surfaces and blow the gasket as pictured.
 
Yes, I see what you're saying.

I assume the gasket bit that tore off must be fished out of the sump. That will be fun!
 
AFter studying these diagrams, (link below) it seems that the back-pressure is only needed to hold the unloading valve into the closed position. When the control valve isn't asking for lift, pressure from 6 should move the spool and turn off oil to the cylinder. And at the same time, pump pressure should be moving the unloading valve right with pressure at 8. It's not until later that the back-pressure valve is in the circuit. Once the unloading valve has shifted to neutral, it's in parallel with the path 2-8-7. The fluid could take the path of least resistance without the back-pressure valve.

http://forums.yesterdaystractors.com/viewtopic.php?p=7812099&sid=903d3fae36a64eab22a5942da1c3d5c5

So why does the lift go up when I block the back-pressure valve outlet, even when the control lever is down----no lift is requested. Doesn't make sense at all. I suspect that the unloader valve is stuck.

...

OK, I disassembled the control and unloading valves. Everything was mostly fine. The unloading valve moved smoothly. The o-ring looked fine. There was a small ring of rust in the bushing near the neutral position. I polished it lightly with some 600 grit paper. There was some corrosion on one spot at the other end of the bushing but it seemed to be very slight pitting, nothing that would prevent the valve from moving.

https://drive.google.com/open?id=0B3wfQHEAycNcWEV6VlNMRGhJUXc

honed:

https://drive.google.com/open?id=0B3wfQHEAycNcM0dwbjQ1VFg1NGc

pitting:

https://drive.google.com/open?id=0B3wfQHEAycNcOENxWUx6bUFpSTA

Well, I don't know what's wrong. I think there's multiple things that could be the matter. If the gasket was leaking, I could have missed it because I never chained down the arms, asked for lift, and watched for oil dripping down.

On the other hand, the gasket couldn't be the whole problem, either, because the lift arms didn't work at all, even with no load (and there was no oil leaking down during my initial tests).

I think the back-pressure valve is fairly unimportant for what I'm trying to do. It appears to be mainly for maintaining position. From the diagrams, I think it mainly serves to hold the unloading valve in neutral. Without it, I think the unloading valve might jog left on occasion, which would result in the lift jerking up a bit. But as soon as the left side of the spool is pressurized, it'll slide right and back into neutral. With no leak down, I guess your implement could get pulled all the way up. So yes, I think the back-pressure valve was broken but I don't think it's the smoking gun. It's an interesting symptom but maybe not the cause.

Anyone have any ideas?
 
If system were in neutral/hold position and lift were commanded, and there was no back pressure, then there would be no pressure to move the unloader and lift would never occur. So, yes, back pressure is important & its only function is not to "just hold unloader in place".
Why if using finger to elevate backpressure will the lift raise even with touch control lever down? If you mean "down" as in a "lower" command, then, it shouldn't raise as the cylinder dump path will be open. If on the other hand you are commanding a "neutral/hold" and use finger to elevate the backpressure & you manage to increase it enough to open the check valve, then it will lift (dump path now closed by control valve).
 
Bought fiber gasket material from NAPA (1/64") that was suitable for oil and cut out a new gasket to go between the ram cylinder and lift cover. Made 2 matching washers for the opposite side of the casting. Removed ad hoc springs that I had added to the back-pressure valve. When I tried it out, it seemed to work and DID NOT DRIFT UP. Hooked up the mower and monitored pressure while lifting slowly. Everything worked fine but I was somewhat afraid to break it so I didn't beat on it.

I don't know why the lift was drifting up. I don't know how the combination of the leaking gasket and high back pressure could produce those symptoms. I took everything apart in the mean time and inspected all spools, seals, etc. I did find a ring of rust around the control valve, which I polished off with 400-grit sand paper. Otherwise, no obvious problems. When I put it all back together (correctly) it seemed to work.

Then I called back a potential buyer who came a few hours later. Then I went back to packing a moving truck. Later on, I sold the tractor, 2-bottom plow, 5' disc, blade, 3-row cultivator, and bush hog for 3,700 $. I think it was a pretty good deal for him and I've never been so happy to have completed a sale that I was losing money on. The people who bought our house had a walk-through scheduled 30 min after I sold the tractor. So I'm out of the tractor business for a while. Probably will get another when we get settled in NC. So long and thanks for all the advice. You especially, JMOR.
 
(quoted from post at 19:16:57 05/14/17) Bought fiber gasket material from NAPA (1/64") that was suitable for oil and cut out a new gasket to go between the ram cylinder and lift cover. Made 2 matching washers for the opposite side of the casting. Removed ad hoc springs that I had added to the back-pressure valve. When I tried it out, it seemed to work and DID NOT DRIFT UP. Hooked up the mower and monitored pressure while lifting slowly. Everything worked fine but I was somewhat afraid to break it so I didn't beat on it.

I don't know why the lift was drifting up. I don't know how the combination of the leaking gasket and high back pressure could produce those symptoms. I took everything apart in the mean time and inspected all spools, seals, etc. I did find a ring of rust around the control valve, which I polished off with 400-grit sand paper. Otherwise, no obvious problems. When I put it all back together (correctly) it seemed to work.

Then I called back a potential buyer who came a few hours later. Then I went back to packing a moving truck. Later on, I sold the tractor, 2-bottom plow, 5' disc, blade, 3-row cultivator, and bush hog for 3,700 $. I think it was a pretty good deal for him and I've never been so happy to have completed a sale that I was losing money on. The people who bought our house had a walk-through scheduled 30 min after I sold the tractor. So I'm out of the tractor business for a while. Probably will get another when we get settled in NC. So long and thanks for all the advice. You especially, JMOR.
ou are most welcome & glad to be able to help. Thank you for the followup response....all of us out here always appreciate that!
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top