Rear hydraulic lift problems.

KZR455

New User
Hello, I have a Ford 3400 and am having problems with the rear hydraulic lift. It only rises a couple inches and work sporadically. I performed a hydraulic pressure test as outlined in the I&T shop manual. I removed the top accessory plate and rotated it 180 degrees and made a block off gasket. When I start the tractor and slowly close off the added return line the pressure goes up to about 2000 psi for about 15 seconds and then starts to fluctuate all the way down to zero. Within a minute the pressure drops to zero and stays. If I open the return line and start the process over the same thing happens again. Does this sound like a faulty relief valve or perhaps something else? Thanks
 
Hello, I did not get any responses to my rear hydraulic problem on my Ford 3400 and was thinking maybe I didnt explain something correctly or perhaps I need to outline the test procedure that I performed from the I&T repair manual. The procedure described in the manual is to remove the plug from the actual pump and install a tee. A hydraulic gauge goes on one end of the tee and on the other side a valve along with a hose that returns to the rear end filler opening. The accessory plate is removed and is reinstalled backwards along with it gasket that I had to make to block this area off. I believe this would eliminate from the system the safety valve, the unload valve, the control valve, the piston and lift cylinder. From the cutaway schematic diagram it seems all that is left in the system is the suction filter pick up, the hydraulic pump, the pressure relief valve and the flow control valve. To perform the test the manual says to run the tractor at 1600 RPM with the added return valve/hose open. Then slowly close the valve until its completely closed and check the pressure. As described in my first post there were times I was getting up to 2000 psi (500 psi less than is called out for) but it would continually drop to zero. I replaced the pressure relief valve with a new one and now Ive got absolutely nothing registering on the gauge. I dont know if perhaps I got a new faulty valve or maybe its the wrong one. I have not tried re-installing the original relief valve again. As far as other things that can be wrong there are only a few things left in the system with this block off plate installed. This brings up 2 questions. When I run the tractor with this added return valve open it looks like it might be pumping about 1 gallon per minute flow in the test return line that goes back to the filler opening. Does that eliminate the possibility that theres a problem with the suction filter or could it create a situation where theres fluid being pumped but no pressure? The only other thing in the system is the flow control valve. Could that fail in a way where it would completely eliminates all my pressure? Thanks
 
If this diagram is correct for your tractor, it appears that there is one more place for an "over-pressure dump" and that is in the flow control assy, just to right & below restrictor.
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Thank you for responding. Yes that is the same picture I have in my manual. I tried to add it to my last post but I was not able to. Not sure but it might be because I just signed up for this fourm. If something is wrong with this assembly would it cause my pressure to maybe zero? If I pull this flow control plate off what problems might be looking for? Thanks
 
(quoted from post at 18:04:14 04/19/22) Thank you for responding. Yes that is the same picture I have in my manual. I tried to add it to my last post but I was not able to. Not sure but it might be because I just signed up for this fourm. If something is wrong with this assembly would it cause my pressure to maybe zero? If I pull this flow control plate off what problems might be looking for? Thanks
he restrictor knob should be set to max flow I would think and if looking for problem inside the unit, I would try to determine whether or not the knob was in fact opening the flow path. Additionally, the item outlined in red looks to be an over pressure relief valve. I would check it for good spring tension, be sure no trash is holding it open.
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[Hello, thanks again for the input here. I took the four bolts off and house the flow control valve and it seems after reading the manual that the top lift cover has to come off first. Here is what I was going to do unless someone can advise me different. I was going to first drain the fluid and pull the new pressure relief valve that I installed and checked closely that it matches the original one. I was maybe going to try the old one again because it worked to some capacity before. Next I was going to try and check the flow rate with this return hose that had been added with this test equipment. It seems it should be about 4.8 gallons per minute if I understand this correctly. Depending on what happens next I was next going to pull the top lift cover off so I can further inspect the flow valve body. I will also then be able to check the suction filter. Any other recommendations? Also when I originally drained the oil to install the new pressure relief valve it seems I couldve gotten the air in the line from the hydraulic pump and with the block off plate the only place this air could escape might be through the flow control valve. Maybe I could crack open the block off plate to confirm that theres no air in the system. Any other thoughts or suggestions would be very much appreciated. Thanks
 

You where getting odd pressures before replacing the pressure relief valve and now have no pressure, no need to look farther until you get the pressure back
The top accessory plate uses o-rings to seal it, no gasket, with over 2000 psi pressure it can easily blow a channel out in the gasket you made
Id pull that plate off and check the gasket then put it back on with just the o-rings, next I would swap the old pressure relief valve back in to see if I could get back to where it was in the beginning
With the accessory plate on backwards it completely blocks off flow past the flow control valve so you need to establish flow and pressure before looking into the position control valve
Take the return hose you made and stick it in a 5 gallon bucket, start the tractor and run it for 30 seconds, you should have slightly over 2 gallons of oil in the bucket. If not there is likely a issue with the suction screen or the pump
 
I assumed that when I turned the top accessory plate 180 that all the passages would be backed up by solid steel but apparently some will still line up with openings because I did have 2 holes pushed through the gasket I made. I'm not sure what I was supposed to do different. With a 1/4" Tee coming off of the pump, a quarter inch valve and a 1/2" holes I got less than 1 quart of oil pumped at 1600 RPM. I have ordered a hydraulic lift cover repair kit and am going to open this thing up. Thanks again for the help.
 

At any time when the lift was down did anyone raise the lift arms up by hand to the fully up position.
Neighbor did that to his 3000 which has the same lift, this allowed the connector link that goes between the lift piston and the rock shaft to drop out of the piston cup.
The lift would raise about 1-2 inches and no more, when you lower the lift control lever the lift arms would go back down that 1-2 inches.
I had to pull the lift top to get it back in place.
 
I do not believe the lift arms were lifted by hand at any time. When the hydraulic lift started acting up the Gannon was attached. I have since pulled the top lift cover off. The bottom of this hydraulic cavity is covered in sludge and around the suction filter its about a half inch thick and covers a lot of the filter. I cant figure out how to get the section filter because the PTO shaft is in the way. Is there a way to remove this or perhaps can I clean it with it still installed?

Also, on some of the lift control linkage there is a pivot pin that runs up against a large cam. I believe this pivot pin is supposed to be round but mine is worn about half way through so I need to replace that. The cam surface looks good. Also someone had just used regular bolts on the seat and it appears the rear bolt is a special bolt that runs through the cover and acts as a guide on the rear link. Is this bolt available or will I have to make one?

About 10 years ago I replaced the hydraulic fluid and it seemed like there was water in it and this may have started a lot of my problems. If I remember right the draft control spring housing was turned so that the opening that exposes the spring was somewhat facing upward and collecting water. At that time I had turned the housing 120 so that the opening was facing downward. It seems on another occasion I still got water in the rear end and had to replace the fluid. I now try to keep the tractor covered when it rains. While I have this apart are there any common spots that might allow rainwater to enter the housing I can look for?

Im looking for a website that shows part diagrams and part numbers. I use to use https://www.mycnhistore.com/ but for some reason I can no longer see the diagrams on that site. Is there someplace else I might find this? Thanks, again
 

Messicks Tractor Parts is a good site to look up parts

I havent been inside of a 3000 style rear axle for a while, but on my 4000s the suction screen cant be removed without splitting the tractor
Temperature changes between the inside and outsides of the axle and trans housings cause condensation sweating that in time adds a fair amount of water to the compartments
Back when tractors were worked long and hard the heat from the oil would turn that moisture into steam that would vent from the tractor
Today they are used less and may have more smaller heat cycles the causes even more condensation sweating
A tractor setting out will get more moisture in it even if its sealed from rain water, think of it like a metal roof, on a cool damp morning when the sun starts warming up the roof it looks like its raining inside my shed
 
Im finally getting a chance to get back to my tractor issues. I got a top cover kit that replaced all the o-rings on the top accessory cover as well as the lift cylinder. I replaced the o-ring and backer on the piston as well as honing the bore that looked pretty good. I pretty much followed the Gingell YouTube video plus I adjusted the linkage in draft control as well as position control. My tractor was so far out of adjustment and has so much play in the linkage that I had to actually modify the adjuster rod get the right specs. I pulled the PTO shaft so that I could get the suction filter out and cleaned out all the sludge and replaced the return filter. After reassembling the arms will now lift but when I put my Gannon it will start to lift it but it cant get off the ground. I again performed a hydraulic pressure test as outlined in the I&T shop manual. This time when I removed the top accessory plate and rotated it 180 degrees I sandwiched some shim stock between 2 layers of gaskets so everything was solid. When I perform the test it starts at about 400 PSI and then starts to jump around a bit and then drops to about 100-150 PSI. If I open the added test return valve and slowly close it, it all starts over again at about 400 PSI. With the engine turning about 1600 RPM it takes about 40 seconds to fill a 1 gallon jug with hydraulic oil.
After adding the top block off plate and looking at the above diagram that JMOR posted it seems the only thing left is the pump pressure relief valve and the flow control valve. I just replaced the relief valve so Im thinking theres no problem there although I did purchase it on eBay. I wish when I had the top cover off that I had serviced flow control valve and adjust the linkage. Does this sound like it could be the problem? There is a main line that runs from the bottom of the case to the flow control valve. This tube has o-rings on both ends and they were not included with the kit so I did not bother taking the tube out.
It seems I have a couple options at this time. I can take the pump off and rebuild it or I could again pull the top cover off and look further into the flow valve and maybe the feed tube. Any recommendations here? With the flow rate being so low Im thinking maybe I need to take off the pump and look into rebuilding it. Has anyone out there ever tried to make a block off plate right at the pump? I understand bad things could happen here but if I leave the return valve open just slowly closing it to see if I could build up 2000-2500 PSI and I could maybe confirm if the pump is good or not. My test return valve a quarter inch ball valve so I would just hope that it would not blow up. Any recommendations would be appreciated. Thanks
 

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