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Old 12-14-2021, 07:27 AM   #1
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Default Final steps hydraulic lift repairs

I've removed the cylinder, had it to the shop, and now am in the final stages of the repair. Boy, was it ever fun to 1. get that cylinder out and 2. to put it and all the parts back in properly.

Not being a hydraulics mechanic, I am hesitant to proceed beyond my current, nearly-ready point in the repair. I am sure there are many folks here with experience repairing hydraulic cylinders on trucks or farm/construction equipment who can assure me my concerns are overblown (or not).

I am puzzled though as to how the air in the cylinder will get out once I turn on the pump to raise the top. The fluid pressure feed the cylinder enters the cylinder midway up the side, not at/near the top. I can imagine that if near the top, the air could get worked out through raising and lowering, but on the side (at the 3 o'clock position, viewed from one end, if you will) it seems that air would always be trapped above the level of the inlet.

Common sense and basic physics suggest that the cylinder should be full of Dexron fluid when operating. Does the trapped air work its way out through the seal on the piston? Would that not damage the seal? Should I try to put as much Dexron into the cylinder before closing it off and putting pressure to it? (Oh boy, that sounds like it could be not especially easy and also messy.)
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Old 12-14-2021, 10:02 AM   #2
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I've not had to do that repair, others, such as Treeclimber have done it though. I'm sure one of them could tell you the precise way to "bleed" the system. I suspect it might be something like opening the lowering valve and then running the lift motor until hydraulic fluid comes back into the reservoir. That's what I'd try if I had no other guidance.

- Jack
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Old 12-14-2021, 12:11 PM   #3
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The fluid path to the cylinder is a dead end, in and out through the same steel tubing, so the fluid will never return to the reservoir with the pump running constantly, only when the pump is off and the weight of the top pushes the piston back to the lowered-top position and the fluid back to the reservoir.

Unless the cylinder can 'burp' out the air as the top is raised and then lowered over several iterations, maybe it can clear out some of the air, but probably not all, given the location of the inlet fitting on the side of the cylinder.
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Old 12-14-2021, 01:24 PM   #4
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OK, you are much more knowledgeable about the hydraulic path than I am. Possibly, the air that's in there gets flushed out with use, or, it might act more like a cushion as pressure builds? I'm sure if the pressure builds high enough, the air will be compressed to the point that it's effect might be negligible?

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Old 12-15-2021, 04:25 PM   #5
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Can anyone with experience removing and replacing the hydraulic cylinder relate their experience with respect to removing the air from the system so it functions properly? That is the last step I have to do to be able to stand up in my 2004 17T again. I have some other repairs to do that will be very difficult without the ability to stand up.

My concern is that the port for the fluid from the pump is located on the side of the cylinder, not on/near the top. If it were on top, bleeding the air out would be a relatively simple matter, messy maybe, but simple. I do not know where other models/sizes of HiLo have the hydraulic fluid inlet to the cylinder located, perhaps they are all the same, but maybe not. If they are all the same, or if the cylinder on your HiLo is on the side and you successfully got the air out following a method similar to what Treeclimber recommended (multiple short episodes of lifting and dropping the top, just a few inches each time), I would like to hear your experience. Or maybe you did not do it that way and still had great success.
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Old 12-15-2021, 04:43 PM   #6
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I've been known to be wrong before, but it may be self purging, if I remember correctly. Several cycles of up and down and fluid level checks should do it.
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Old 12-17-2021, 04:45 PM   #7
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Apparently it is self-purging as there were no hydraulic problems raising the top following the procedure of making a few small steps (6" or so) up and down before lifting all the way.

Adjusting the cables is another matter. So far, the corners are all within about an inch, but I'm not sure that is acceptable. There was a certain amount of threading exposed on the adjusting screws/rods for the lifting cables when I disassembled the lift mechanism. There was also a certain amount of 'slack' in the cables at that time. After putting it back together, the cables have fewer threads exposed and the cables have more tension on them. It is almost as if the cables shrunk while the repair was being done on the cylinder, which is of course, nonsense. The pulleys all seem to be working as they should, though one could stand replacement (anyone know where to get the part?) and the top goes up without complaint. I just don't understand why I don't have the same lack of tension in the cables when the top is down.....
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Old 02-24-2023, 08:57 AM   #8
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Default Replacing hydraulic cylinder

Hi Lvnv, I saw that you live in Central Florida. I live in NCFL and was hoping to contact you about this repair . I have an Ď03 Hi Lo, 2704 model. Itís been raised on 2x4 supports for a couple of years, and I need to get it mobile again. Can you contact me so that we could talk about this? Thanks.
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Old 02-24-2023, 12:20 PM   #9
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lvnv, congrats on replacing the hydraulic cylinder!

As far as cable slack goes, mine doesn't really have much of any slack in the cables with the top down, if that helps. When you adjust the cables, you just want the bulb seal to meet the lip on the top outside of the lower half. Don't try to make the internal trim strips line up. You MAY have to take the trim strip off the inside lower half to see the bulb seal when you make this adjustment. You have to take that strip off to lubricate the cables where they pass over the upper pulleys anyway, so it's good to do this now and then. Don't try to get the top higher than this - it will cause damage to the area where the cables attach to the top half if you do.

- Jack
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