2 post lift problem

[gizardlizard]

Hi all. I put my truck on the lift tonight and started lifting it up. I lifted the truck a few inches off the ground, gave it a quick wiggle to make sure it was stable and continued to lift. I got the truck maybe a foot off the ground when I noticed the truck was leaning to one side. I got the truck lowered back to the ground and moved out of the way so I could examine the lift. The lift is a 2 post rotary revolution RTP 10. I started to the raise the lift unloaded and after it was up a bit, I noticed that one rod cylinder was hanging down and not lifting the carriage. (This lift has the cylinders mounted inverted.) The other cylinder is lifting both carriages. Sometimes the problem cylinder won’t move at all and other times it moves a little. When it doesn’t move, the good cylinder raises both carriages twice as fast as it is supposed to. Checked fluid level, looked for leaks and found none, checked cable condition and made sure there was not mechanical binding. Anybody see this before? it’s like most if not all the oil from the pressure line is going to the cylinder furthest from power unit.

 

[zkdiesel]

Cylinder is probably mechanically siezed Pull and see if you can stroke it with air pressure

 

[gizardlizard]

Its not seized. About 1 out of 6 lifts it goes all the way up. When it does stop moving, it stops at a different spot every time.

 

[iamhomeless]

Now that is an odd problem. Best bet is to take a couple of videos of the problem and then call Rotary or your dealer on Monday and sent them the clip. Slay post the clip, because I want to see it.

 

[Jlbc212]

My guess - there's air in the hydraulic system and you need to bleed the air out.

 

[dirtydrew420]

I'm no guru here, but it does sound like air in the system.

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[gizardlizard]

I would agree, but after raising and lowering 2 dozen times, same problem. If there was air in there, it should have been pushed out by now. Unless it’s maybe sucking in a little air every now and then adding to the problem.

 

[gregs]

Sounds like it’s sucking air some where. I have seen air leaks that don’t leak fluid. Crack in a line or fitting or seal.

 

[dirtydrew420]

Did you try manually bleeding the cylinders?

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[gizardlizard]

I did not try to manual bleed. How do you do that? Unhooked the return line and push on the rod?

 

[dirtydrew420]

I usually bleed mine at the bolt on the tops of the cylinders.

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[zkdiesel]

Systems are in parallel. Same hydro pressure applied to both sides, one moves, one doesn’t. Check cylinder that doesn’t move for binding or carriage for binding....

 

[gizardlizard]

Correct. They are plumbed parallel. Carriage is not bound at all. Tomorrow I may remove the cylinder, and disassemble for an inspection. Thing is though, sometimes it works fine. Guess I’m still leaning toward air being sucked in from somewhere.

 

[Jlbc212]

Before removing the cylinder look to see if you can find a bleed port. Others here may remember the procedure better, but essentially it involves running the hydraulic pump with the bleed port open and keeping the hydraulic reservoir filled with fluid. With the pump running and the bleed port open eventually fluid should push all the air out. Be ready for a mess.

 

[TurnipTruck]

These lift cylinders PULL to lift and have built-in bleed lines back to the reservoir.
It might be interesting to disconnect the bleeds one at a time to see if a cylinder is leaking through.

 

[gizardlizard]

Lift problem solved. I cracked every connection loose and re tightened. That’s it. Nothing else. Ran lift to full stroke 15 times. Has yet to fail. I installed this lift a year and never had an issue until yesterday. Anyway, all good. Thanks for all the suggestions.

 

[Wrench97]

I've seen it happen, if you can raise the lift all the way up with the truck on it levels itself out if not raise til you hear the low side click over a lock and lower til the high side stops on one.