Floor Jack troubleshooting

[sabinoerc]

I realized I posted to wrong forum so reposted in Tools. I don’t see how to delete here so sorry for duplicate post.

I have an old floor jack from Harbor Freight. A Central Hydraulics Model 34271 if that helps.
It doesn't take a full pump as it get's higher. Smaller and smaller strokes w/ pressure. Longer and Longer to get it to max height.
I thought maybe oil was low. I removed the plug on ram and put some oil in, not much - pumped it a bit to see if I could see any air bubbles, but nothing.
It still did the same thing.
I removed the handle so I could push the pump piston up/down by hand to see how it feels.
I found that as the jack went higher and the ram extended further - the pump piston would **** back down when pulled up. If I held it up long enough - it would take a full "bite/pump".
I've not messed with hydraulic jacks before but assume this is something like a plugged vent? As the ram goes out - something has to come in.
Just sanity checking if I'm on the right track. Checking if this is a known failure mode with whoever knows hydraulic jacks.

The only thing I see which may be a vent is a "do not adjust" cap. There is also some screw/filler but I don't see any vent holes in it. The filler plug is on the ram body and is a rubber stopper type plug.

Thanks in advance for any education/advice/direction.
Ed

 

[b.lucky]

Chances are it just needs the air bled from the jack. Simple to do.

Twist the handle clockwise till tight then open it 2 turns and pump the handle fully a dozen times. Tighten the handle again and raise and lower the jack. Repeat process if needed.

Just had to do this to my Napa brand jack and it only took one time.
Good luck.