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Hydraulic lift system Hydraulic, mechanical and electrical components of the lift system
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Old 07-17-2017, 04:00 PM   #1
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Default How to remove and replace the hydraulic lift cylinder.

It was suggested that we put this on as a topic in the lift system section. Thanks to Treeclimber for the write-up.

Hi! I've done three cylinder remove/replaces. Basically, with the trailer lowered, a tarp on the ground/cement--take several pictures of pulley placement, locking bar and guide rod placement, etc. I then blue taped the Front Lower cable "FL" same for Rear Lower "RL". Your piston should be almost fully retracted. I use a plastic wire tie(zip tie, medium duty to tie the cables as tight around the pulleys as I can, remove the bolt and washer and again zip tie them out of the way, try to keep SOME tension on them. CAUTION: the locking bar is not held in with any fasteners, it MAY fall after the next step. Ask me how I know. There is a taper type pin on the guide rod-remove that pin SAVE IT! Slide the guide rod to the street side until the curb side falls out. Once free of the HUGE plate, put the pin back in. Using two open end wrenches, remove the locking nut , then the retainer nut from the piston end. AGAIN CAUTION! the Heavy plate will come down (FAST) upon removal from the piston rod end! AND that locking bar!
Next- street side, This area is not the easy end because of space and ingenuity is needed. Carefully remove the "B" nut on the hydraulic line, cap it or use a zip lock bag to prevent contamination. Keep it out of the way without kinking it. Remove the plastic vent line and allow it to drain into a container. ALSO remove that stainless adapter where the "B" nut was attached. On the piston end, remove the cotter pin, nut, washer and then with what ever safe method you can, remove the large pin and the piston should come free. Safely remove it from the trailer.
When you have it repacked ensure you let then know that it is filled with Dextron 1 thru 6 Automatic transmission fluid-- not a hydraulic fluid. Should be bench tested to 2600 psi.
My preferred shop caps and tapes the piston mounting areas, sand blasts it with 220 grit, re-builds it, tests it to 2600psi then primes and paints it gray. Re-install in reverse order. When you raise it, only go about 3-6" several times to get any trapped air out. Then raise and adjust cables if necessary.
I assure you it's not hard, just makes your brain work (or get soft). Take your time, you'll see how it needs to be done.

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Here is an added note from Jim L concerning transmission fluid:

I want to raise a flag about something treeclimber said in his post. He stated that if the hyd ram was resealed to use dextron 1 to 6 to fill the system. I have in the past thought this was correct also. I have a allison tranny in my silverado an I just started following the Transmission section of the duramax forum. One of the experts who post on that forum was the fluid engineer for Allison that wrote the specification for the transmission fluids approved for use by Allison says that Dextron 6 is not compatable with the earlier Dextron fluids. In 2006 Allison put new types of seals in their transmissions that are compatable with Dextron 6 but Dextron 3 is to be used in transmissions built before 2006. They found out that Dextron 6 that had been put in pre 2006 transmissions caused the seals to harden and caused leaks. For anyone wanting to research this further go to the duramax forum and the oils and fluid section of that forum. The engineer's handle is hzjcm8 and you can search for his post. There are 98 pages on just the transmission fluid subject.
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Old 07-20-2017, 11:21 AM   #2
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Addendum: Reason for removing the fitting from the cylinder after removing the "B" nut is to allow the cylinder to clear the hole in the frame. Thanks jedelen for questioning that step.
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Old 07-20-2017, 02:12 PM   #3
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hey do u still have a pic of the lift lock i replaced my cylinder with a differant one and cant find where the lock holds it up under neath
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Old 07-20-2017, 03:13 PM   #4
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d0w0r, I have no idea if your safety bar is like mine, but we'll try. Every bar I've seen has three "stops", that's what I call them. If I have the pics right, the first is the curb side. I fits loosely in a square hole, and in my case the cable goes underneath. The middle stop is the actual stop for the raised top, it is on the CABLE side of head block (the HEAVY steel block). And the third can be seen at the end of the cylinder. Ya with me? Hope the pics help. The problem is, there is NO way that I know of to install the safety bar without removing the guide rod. The safety bar slips into a pocket above the cylinder, then is slid into the curb side pocket and the cylinder holds it in place, while you re-insert the guide rod. In each pic you'll notice each stop. The bar MUST be in that order to work right. The stop above the cylinder prevents the bar from going too far to the street side, thus preventing it from falling out.
Let us know how it works out.
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Old 07-20-2017, 03:18 PM   #5
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I may add that when you pull the cable inside, your raising the center stop ABOVE the cable block, thus freeing the piston to retract. So you need only hold the cable a few seconds of the lowering cycle.
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Old 07-20-2017, 04:20 PM   #6
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Tree, I think the BEST approach would be to get under the trailer and watch how things work while someone else activates the safety bar (and possibly the lifting mechanism) BEFORE trying any repair to any of this. Of course, if it's already apart, this is a moot point.

- Jack
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Old 07-21-2017, 07:52 AM   #7
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Jack, in this case the bar is Not installed. The top could, of course, be cycled, but the bar cannot safely be installed while up. I, mentally, (could be a problem!) went through each step of r/r of the cylinder and vividly remember the bar clunking me in the head! Without removing the guide rail, I don't see how it could be done. Unless you cut a big hole in the floor and install from the top. NOT!
I seriously recommend each owner, crawl under and watch the evolution of the cycling of the top, up AND down, NO beer prior please!
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Old 04-26-2019, 07:47 AM   #8
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Default Heavy plate.

I will be removing my cylinder soon and have been reading the forum for advice, in the first post its mentioned that there is a nut holding on the plate, mine looks to be threaded directly to the plate, is this normal? I am working on a 1977 model.
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Old 04-26-2019, 04:43 PM   #9
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Tug, mine was also threaded to the plate and for some reason a nut capped off the threaded portion. I guessed those extra threads (about 1/2") were for some adjustment. I counted the exposed threads and replaced with the same count. I still can feel the safety bar! Again I caution all about falling safety bars. As you'll find out, it's not hard removing the cylinder, just take your time and get creative with your tools. My hyd shop had it rebuilt and tested to 2600 psi in a short time. Let them know to test it with Dextron 3, 4, or 5 tranny fluid.
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Old 06-16-2020, 06:40 PM   #10
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I removed the cylinder from my 2001 Towlite this morning and dropped it off for a rebuild. As per my usual methods, I didn't read up or research how to do it, I just jumped in and did it. I recognized that the plate would be heavy and gravity would bring it down on my head in a painful way so I staged a plastic bucket (upside down) for it to rest on - so no problem there. Once I had everything disconnected from the cylinder and the heavy end plate safely down without injury, all that was left to do was to wrestle the cylinder out of there. That's when I found out (the hard way) that the safety bar will fall on your head once the cylinder is removed! Hahah - I literally feel your pain Tree! Thanks for trying to warn me though.
Still, it was not a difficult task and my experience should not stop others from attempting it. A second set of hands helps but is not necessary. Tree's description for doing it is pretty accurate and if you just look at it you can figure it out. Admittedly, I originally thought it would be less work than it was - but I still had it out in 90 minutes working by myself.
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Old 08-16-2020, 06:14 PM   #11
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Sorry, new to forums. We'll see how this goes.

Mine's stuck in the raised position. Will not go up. Appears to be a leaking seal on the jack (clear tube is returning fluid).
My question: Does anyone have the part numbers for the seal(s) on this jack, or any info towards that end.
Thank-you
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Old 08-16-2020, 06:45 PM   #12
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Also, any idea as to how much the top half of a 22' would weigh (+-).
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Old 08-16-2020, 06:46 PM   #13
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craztjoe, hope I get thru this without losing internet. Good and bad news. Sound like you'll have to rebuild that cylinder. Good news is you could do it if you've the knowledge and tools plus a way to pressure test it to 2600psi. Bad news, you HAVE to remove the cylinder to do it. With it stuck in the up position, the safety bar WON"T be there to hold it. There is no way to lower it without the safety bar retracted. So the top must be raised with strong people and 2 x 4s placed under each corner, or four farm jacks. Remove the cylinder and have it rebuilt, reinstall and be done with it. s
Sorry for the bad news. I worked as a hydraulics man in service and wouldn't do it myself.
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Old 08-16-2020, 07:39 PM   #14
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Thanks for the reply. I will probably raise it with threaded rods from the piston(cable roller) plate to the frame. I might be able to lower it with the threaded rods (turning nuts for days). I will remove the whole jack if possible. Otherwise I'm going to try to remove only the piston and cylinder cap and seal(s). If I get the parts I will rebuild it. I haven't looked closely on the cylinder for numbers, yet. Doesn't seem to be a lot of info on this stuff, (none on the jack). Monarch is out of business. Mason-Dynamics has some stuff. Sucks to be me, today. Thank-you
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Old 08-16-2020, 11:17 PM   #15
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Crazy, you COULD raise it by using the tongue jack alternately to raise and lower the front and back of the trailer. Place 2x4s at the corners of the top at the front to the ground and lower the tongue. That will lift the front. Put 2x4s between the front outriggers and the top to maintain that lift. Then, place 2x4s at the rear of the top to the ground and raise the tongue, which should lift the rear. You'll need new 2x4s on the rear outriggers to maintain the lift on the rear, and you can then put new 2x4s between the ground and the top front to lift that end more as you lower the tongue again. Repeat as needed. You'll probably have to be careful to not add too much uneven lift at one time.

I know this sounds complicated, but someone did it this way and posted a thread about it a few years ago. He did it to separate the halves, I think to replace the bulb seal? Anyway, think about it - it may be easier than what you were thinking of.

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Old 08-17-2020, 09:05 AM   #16
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Jack, thanks for your reply. I've done a lot of equipment moving. I know this top isn't that heavy, maybe 1500#. I'm not a big fan of using 2x4's vertically, but you gave me a great idea. I will send pix in a week or two.
However, I am pretty determined to rebuild it myself. Especially if I can't get the cylinder out. I don't expect turn around time to be of my liking from the repair shop, if I can find one where they don't look at it, moan and start praying. Looks like nobody has any info on this jack(no name or numbers-Chinese?). Mason Dynamics would help, but they are in Michigan. We'll see. I do appreciate Treeclimber's advice, though. It ain't over. Thanks, again.
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