Scissor Lift Cart Repair

[NightshiftHD]

Does anyone here have one of these Chinese scissor lift carts (besides me)? I really like how heavy duty it is, but the hydraulic cylinder leaks down internally (not on the floor) and will not hold the table up in a set position for very long. I do not know anything about hydraulics, but would sure like to know how to fix this thing to hold it's position. I tried draining out the light oil and replacing with SAE 30 weight, thinking the heavier oil might help, but I don't see any improvement. Bill

 

[Rocwin]

Generally one of two things happens when a cylinder drifts down, it either a) bypasses internally, which requires resealing, b) has a leaking/defective holding valve.

If you have a holding valve you can set up the cart and remove a hose/tube from the valve. If you can see oil coming through the valve you have your answer.

 

[wdchyd]

Good Luck if you know nothing about hydraulics......even for an experienced hydraulic mechanic these units are not easy.......the problem internally may be an easy fix but finding it will be a chore....

In a perfect world you'd have to pull hyd unit, strip down to bare bones (while inspecting for bad ram seal or valves not seating perfectly)....then clean flush (clean as if you were doing a carb repair), reseal with new OEM seal kit (IF you can find one)....new ball valves and reseat them too.....

Then if by chance and great miracles, it SHOULD work....

The most common trouble is either the ram seal (from a side pi$$ port on the cyl tube internally for over extend protection) , release valve (not seating), or porous casting in the base not allowing the suction and discharge valves a proper seat (worse case senario).....

If you have good documentation on this unit, my advice would be to find a replacement power unit from the OEM......the chinese stuff was never really meant to be fixed, just thrown away.....

I speak with some, rather lots of experience and knowledge on these as the old hydraulic jacks were meant to be rebuilt over and over again...not the new stuff....

 

[dfkrug]

The most common trouble is either the ram seal (from a side pi$$ port on the cyl tube internally for over extend protection) , release valve (not seating), or porous casting in the base not allowing the suction and discharge valves a proper seat (worse case senario).....
(

The units like this I have seen use a single-acting cyl that depends on
weight for retraction, like my floor jack. If the piston seal is leaking, you
will see the fluid level drop and usually a puddle on the floor from
the oil that got out the vent. Since Bill has no puddle, that would point
to a valve problem. If this is a Harbor Fright unit, I have found their
hyd parts to be available and cheap. PDF parts diagrams can be seen
online in many cases, too.

Now if I would only get to replacing the piston seal in my old floor jack.....

 

[NightshiftHD]

Thanks for suggestions guys. Someone else on another site suggested the holding valve was leaking ... bad fit between the ball and the seat. Suggested the "fix" for that on a cheap Chinese cylinder was to give the ball a good smack with a brass drift ... the ball is hard and SHOULD set the seat conformity to the ball since the cast housing will be softer. I've found a couple balls in this cylinder so I'm gonna give them both a good smack ... then flush some oil from each orifice. We'll see how that goes. Cheers, Bill

 

[NightshiftHD]

The units like this I have seen use a single-acting cyl that depends on
weight for retraction, like my floor jack. If the piston seal is leaking, you
will see the fluid level drop and usually a puddle on the floor from
the oil that got out the vent. Since Bill has no puddle, that would point
to a valve problem. If this is a Harbor Fright unit, I have found their
hyd parts to be available and cheap. PDF parts diagrams can be seen
online in many cases, too.

I got mine from Princess Auto (in Canada) but it looks identical to the one sold at Harbour Freight, and I've downloaded the manual/parts list so I have that. But as you suggest, I'm pretty sure it's the hold valve (ball and seat) that must be leaking past. The release "valve" is just a simple little plunger that presses against the hold valve ball from the opposite side when the release handle is depressed. My first thought was that I had the cable to the handle too tight and causing the release plunger to be partially holding the ball off it's seat, but that's not the case. So that ball for sure is gonna get a smack and see if that makes a better seat. If that doesn't work, I may try a stronger spring holding that ball against it's seat.

 

[wdchyd]

Now if I would only get to replacing the piston seal in my old floor jack.....

How about pics on yours...maybe I could ID it for you....assuming it's an old one..(and not from china)....The old stuff is repairable, while most mfg'rs went out of business the soft parts are still avail....

 

[wdchyd]

If the piston seal is leaking, you
will see the fluid level drop and usually a puddle on the floor from
the oil that got out the vent. Since Bill has no puddle, that would point
to a valve problem.

Not if the reservoir tube is wrapped around the inside ram cyl.....it'll leak down and the oil will just bleed into the reservoir......likely if the unit is fairly new then it would lead to valve trouble....but anythings possible....

I'd like to see that breakdown sheet.....any links..??

 

[dfkrug]

How about pics on yours...maybe I could ID it for you....assuming it's an old one..(and not from china)....The old stuff is repairable, while most mfg'rs went out of business the soft parts are still avail....

My 2T floorjack is from the 70s, I think (Allied), and the problem is the
leak is not bad enough to take it apart (yet). Since I do lose fluid, I
am hopeful that the valve is OK, and only the piston seal(s) is bad.
I will just buy the seal based on size/shape from Hercules/Bulldog.

What do you think of those super-light Aluminum floor jacks? I never
had one, but I can see some advantages, if I used a floor jack more
often.

 

[wdchyd]

Can you take some up close pics of the overall unit and closeups of the hyd unit....(under the saddle and handle)...IIRC, Walker may have made the Allied brand.....

Although I DO NOT fix jacks anymore (so my wife tells everyone) I haven't forgotten how to.....I started out in 1976 doing just that full time for another hyd rebuilder....

I still have many seal kits from days gone by......Hercules doesn't have the stuff you need..(and I am a Hercules Distributor)......well occasionally some stuff matches but old jacks took alot of leather v pkgs and special ucups.....

I'd be glad to help......