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Hydraulic lift system Hydraulic, mechanical and electrical components of the lift system
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Old 07-15-2010, 03:44 AM   #1
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Default Repairing Lift Cylinder

I have just purchased a 2003 17' Hi-Lo. The previous owner was not maintenance minded and had a bent guide rod and a jammed cylinder in the up position. I have disassembled and the cylinder is being repaired. From review of this forum I have a good idea of how to get it reassembled. The comes the commissioning and getting it up and running. So here are some questions.

1. Bleeding: After filling the reservoir with ATF and running the unit up and down, is there any procedure to bleed air out of system. I have no components to do this, so all I can see is to run it a few times.

2. Lift cables: These need adjustment to get all level. What is a practical tolerence to get all measurments the same, front to back, and side ways. Say plus or minus 1/2" or 1/4". Seems like it can be somewhat loose. I want it right but why screw around if it can be a little loose.

3. Plastic Line: I have a plastic line, 1/2" dia from the cylinder back to the reservoir. Is this the return line for lowering the top? Or is it a line to bleed back any fluid that leaks around the piston ? Looks like it can't take a lot of pressure.

4. Tracks: My 17' unit has tracks on the outside at front and back of unit. On the door side there are two tracks along side the door. There is no track at the front of the unit. Looks weird but if everyone else with a 17' has this I can live with it.

Any answers appreciated. I am going over the entire unit, hitch to spare tire to get it shipshape. Fixing loose and corroded connections, cleaning, lubricating, etc. Retired aircraft maintenance man and the lift system looks like a low-tech landing gear system. Lots of fun!

Thanks, Ed Lansing
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Old 07-15-2010, 03:51 PM   #2
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1. Raising the top while manually holding open the valve to lower the top (found on the pump itself...on my 1988 it's a 3" metal spindle that when held forward, opens the return valve allowing the cylinder to decompress) will purge any air or other contaminants from the system.

2. The procedure for adjusting the cables is in the owners manual and described in other threads here. I do it just by eyeballing the inside of the trailer and seeing that the top and bottom line-up. Depending on how much OCD you have, this can be either really easy or impossibly difficult.

3. My cylinder only has one line from the pump to the cylinder. I'd guess the second is a fluid return line...but check your owner's manual or call the factory to make sure.

4. Tracks on my 20' are just as you describe.

I've removed the cylinder for rebuild and replaced my lift cables on my 20' 1988...let me know if you have any questions before you dive in!
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Old 07-17-2010, 02:25 PM   #3
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[QUOTE=johnpeace;1561]1. Raising the top while manually holding open the valve to lower the top (found on the pump itself...on my 1988 it's a 3" metal spindle that when held forward, opens the return valve allowing the cylinder to decompress) will purge any air or other contaminants from the system.

2. The procedure for adjusting the cables is in the owners manual and described in other threads here. I do it just by eyeballing the inside of the trailer and seeing that the top and bottom line-up. Depending on how much OCD you have, this can be either really easy or impossibly difficult.

3. My cylinder only has one line from the pump to the cylinder. I'd guess the second is a fluid return line...but check your owner's manual or call the factory to make sure.

4. Tracks on my 20' are just as you describe.



Excellent answers, very helpful. Here are additional insights.

1. Bleeding: My pump has a small manual valve on the pump for lowering. Just like the valve on a manual hydraulc jack. I'll use this to help in the bleeding process. I talked with Tom a few weeks ago ( before they closed ) and he said " run it up and down about ten times for bleeding "

2. Adjusting cables: I will try for all cables the same tension, the top level with the bottom , plus or minus 1/4' to 1/2" via the eyeball approach.

3. Interesting answer. If you have only one line it must be for both raising and lowering. Fluid flows both ways. I note that the Hi-Lo Manual says to flush out any dirt or crud by running pump and opening the lowering valve simultaneously.

My unit has a second line, 1/2" plastic that looks like a simple drain. It can't hold any pressure. It comes off the cylinder at the other end from the aluminum pressure raising and lowering line. Here is a theory. If any fluid leaks past the piston it will be trapped on the other side of the piston and could eventually lead to the piston not traveling enough. Could lead to the piston not going far enough for the safety bar to engage. Bad news since the only thing holding the top up is pressure which could leak. Solution is a plastic drain line to return fluid to the reservoir. Regret nobody to call at factory at present. Last week I tried numerous times and got no answer or response.

4. Tracks around the door. Since the door is a big cutout in the top, I believe the tracks are for added stability during raising and lowering. Helps to keep the top from sagging.

Thanks for the answer, GREAT FORUM

ED LANSING
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Old 07-17-2010, 03:07 PM   #4
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Quote:
Here is a theory. If any fluid leaks past the piston it will be trapped on the other side of the piston and could eventually lead to the piston not traveling enough. Could lead to the piston not going far enough for the safety bar to engage.
That's a pretty good guess...but I don't think it's that spot-on.

If fluid gets around the piston, you need to have your cylinder rebuilt ASAP. There's not a good enough seal where the ram exits the cylinder housing that fluid trapped in front of the piston wouldn't be able to get out...more likely it'd be pouring out all over the driveway.

A hose to catch potential leaks seems silly...since the cylinder shouldn't leak at all and if it does it's indicative of a huge problem in the hydraulic system.

<shrug>
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