3400 stuck lift now unstuck

Greg Wolodkin · Nov 27, 2011

Well sort of, anyway. Couldn't remove the lift cover as the arms were stuck in the up position. Removed the inspection plate and could see that the piston was in place and the dog bone was where it should be. Moving the lift arms the small amount that they'd move, I could see the dog bone move but it would stop when it hit the piston. Jumped to the conclusion that the piston was seized up due to moisture and time.. hit it with PB Blaster and came inside to read old ytmag posts looking for advice.

Though I didn't believe it until I saw it with my own eyes, it was a hydraulic problem and the unload valve was stuck. Put a rag over the port on the cover plate and backed the bolt out while holding the arms up. With the bolt removed, the arms dropped like nobody's business, sending oil all over the top of the lift cover I had so carefully cleaned up already. Still need to rebuild the cover and clean up the unload valve but I've done that before.. should be no problem.

Judging by the thick layer of grease around the brake cross shaft, I think I'll go ahead and change those seals while I'm here. That's how I got my 4000su to stop marking its territory.

It looks like the axle trumpets may be leaking as well.. no active leaks, just layers of grease there that make me think it will leak more after I clean it up. Is it pretty easy to get in there and renew seals and gaskets? Anything else worth doing if I go that far? (Note too in the third picture there's a half-baked attempt to safety wire two of the bolts on the trumpet)

RickB · Nov 27, 2011

A stuck unload valve is waaaaay more common than a seized lift piston. I can't say that I'm at all surprised that was the problem.

Greg Wolodkin · Nov 27, 2011

I'm still learning.. this forum is a huge help!

wayde · Nov 27, 2011

Brake shaft on 3400 don"t go into sump,like 4000SU cross shaft does.Look some where for oil leak.

JMOR · Nov 27, 2011

(quoted from post at 15:58:02 11/27/11) Well sort of, anyway. Couldn't remove the lift cover as the arms were stuck in the up position. Removed the inspection plate and could see that the piston was in place and the dog bone was where it should be. Moving the lift arms the small amount that they'd move, I could see the dog bone move but it would stop when it hit the piston. Jumped to the conclusion that the piston was seized up due to moisture and time.. hit it with PB Blaster and came inside to read old ytmag posts looking for advice.

Though I didn't believe it until I saw it with my own eyes, it was a hydraulic problem and the unload valve was stuck. Put a rag over the port on the cover plate and backed the bolt out while holding the arms up. With the bolt removed, the arms dropped like nobody's business, sending oil all over the top of the lift cover I had so carefully cleaned up already. Still need to rebuild the cover and clean up the unload valve but I've done that before.. should be no problem.

Judging by the thick layer of grease around the brake cross shaft, I think I'll go ahead and change those seals while I'm here. That's how I got my 4000su to stop marking its territory.

It looks like the axle trumpets may be leaking as well.. no active leaks, just layers of grease there that make me think it will leak more after I clean it up. Is it pretty easy to get in there and renew seals and gaskets? Anything else worth doing if I go that far? (Note too in the third picture there's a half-baked attempt to safety wire two of the bolts on the trumpet)

Sorry, but the unloader valve has zero to do with whether the lift arms will lower or not. Better check elsewhere while you have it apart.

Greg Wolodkin · Nov 27, 2011

(quoted from post at 01:50:17 11/28/11) Brake shaft on 3400 don"t go into sump,like 4000SU cross shaft does.Look some where for oil leak.

The shaft I'm talking about is D1NN2473B, goes through the belly of the tractor to actuate the left side brake from the pedal on the other side of the tractor. It's not identical to the 4000 but looks similar in function. With the lift cover off, I can watch that shaft rotate when I step on the left brake pedal. And there's 3/4" of crud buildup around the points where it enters the belly of the tractor.

I'm sure it's not the only leak, but it definitely looks like one of them.

Greg

Greg Wolodkin · Nov 27, 2011

(quoted from post at 01:52:41 11/28/11)
Sorry, but the unloader valve has zero to do with whether the lift arms will lower or not. Better check elsewhere while you have it apart.

Thanks. So far all I know for sure is what I learned from these threads:

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=ford&th=471662

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=ford&th=489516

and I was able to lower the lift arms by letting oil out of the port on the cover plate.

Now that I have the lift cover off, I'll go through it, replace all the O-rings, etc. and make sure the unloader valve and the control valve are clean. I'll also double-check the schematic when I'm back in the shop.. see what else would prevent oil from getting out of the cylinder when "down" is requested in position control mode.

Thanks again!
Greg

JMOR · Nov 27, 2011

(quoted from post at 21:34:07 11/27/11)

(quoted from post at 01:52:41 11/28/11)
Sorry, but the unloader valve has zero to do with whether the lift arms will lower or not. Better check elsewhere while you have it apart.

Click to expand...

Thanks. So far all I know for sure is what I learned from these threads:

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=ford&th=471662

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=ford&th=489516

and I was able to lower the lift arms by letting oil out of the port on the cover plate.

Now that I have the lift cover off, I'll go through it, replace all the O-rings, etc. and make sure the unloader valve and the control valve are clean. I'll also double-check the schematic when I'm back in the shop.. see what else would prevent oil from getting out of the cylinder when "down" is requested in position control mode.

Thanks again!
Greg

es, the unloader valve is a most misunderstood critter.

Ronnie Graves · Nov 27, 2011

photo #4 that valve Holds the lift up when turned in turn it fully open !

RickB · Nov 28, 2011

Sorry that you don't understand the lift circuit operation.

Greg Wolodkin · Nov 28, 2011

JMOR is right. Should have looked at the schematic more closely to begin with. When the troubleshooting section of the 65/75 service manual had nothing to say about a lift that wouldn't lower, I had assumed the worst.

I've highlighted in blue the path from the piston, past the aux port, and through the control valve to reach the sump. That suggests the control valve, no?

For lowering, it looks like the flow control valve only regulates how much fluid goes through the unloader valve and back to the sump. (Though I did back that valve all the way out in the hopes of lowering the lift, with no luck).

I'll look at everything closely while I've got it apart and report back. Thanks for all the advice, past present and future!

Greg

JMOR · Nov 28, 2011

RickB, By your statement, you just revealed your lack of a working knowledge of this hydraulic system. Many good things about this board, but people who give advice that is incorrect do a dis-service to others. If I don't "KNOW", I either remain silent or if no one tried to help the party for extended period of time, I may make a suggestion, always prefaced with "I think" or "maybe" or some sort of caution indicating that this is how I 'think' it works versus a flat out statement of fact. This approach would serve all well.

JMOR · Nov 28, 2011

"I've highlighted in blue the path from the piston, past the aux port, and through the control valve to reach the sump. That suggests the control valve, no? " Control valve is where I would look.

RickB · Nov 28, 2011

Using modifiers is good practice, I usually do but didn't this morning, sorry. I don't knowingly post bad info, if you have read much that I have posted here over the last decade or so, you would know that. Freeing up stuck unload valves has gotten many inoperative hitches with Greg's symptoms working for me over the years. I guess I don't know enough to know what I was doing wrong all that time. I was good enough to be the go-to hitch guy at a New Holland dealership for about 14 years, now I am in parts sales.

JMOR · Nov 28, 2011

(quoted from post at 18:13:45 11/28/11) Using modifiers is good practice, I usually do but didn't this morning, sorry. I don't knowingly post bad info, if you have read much that I have posted here over the last decade or so, you would know that. Freeing up stuck unload valves has gotten many inoperative hitches with Greg's symptoms working for me over the years. I guess I don't know enough to know what I was doing wrong all that time. I was good enough to be the go-to hitch guy at a New Holland dealership for about 14 years, now I am in parts sales.

wouldn't have responded as I did, Rick, but for your response to me where I said (and it is still true) that the unloader valve has nothing to do with ability to LOWER the lift. {RickB, "Sorry that you don't understand the lift circuit operation."}
I do understand & the unloader valve has nothing to do with ability to LOWER the lift.
cheers!

3400 stuck lift now unstuck

Greg Wolodkin

Member

RickB

Well-known Member

Greg Wolodkin

Member

wayde

Member

JMOR

Well-known Member

Greg Wolodkin

Member

Greg Wolodkin

Member

JMOR

Well-known Member

Ronnie Graves

Member

RickB

Well-known Member

Greg Wolodkin

Member

JMOR

Well-known Member

JMOR

Well-known Member

RickB

Well-known Member

JMOR

Well-known Member

Similar threads