Floor Jack Hydraulic Issue

[UOFan]

First, I apologize if this is the wrong area to post this.

Anyways, I’m rebuilding a pro-lift floor Jack, and I’m having issues.

When I go to pump the Jack, it doesn’t move the piston at all. I feel resistance at the last 10% of a pump, almost as if it’s pushing back.

However, if I pull the piston out (by lifting the lift arm up, it stays in position indicating pressure is built up and the spring/check ball is working.

I replaced all seals and Fluid.

I know a little about hydraulic jacks but not much. Is this an indicator of too much fluid,not enough, frozen springs, missing parts? Thank you for any help! Pictures below:

Lift arm staying in place:

Mechanism:

 

[sea2summit]

Sounds like air in the system (builds pressure through the stroke but not enough until the last 10% when it finally compresses)? Not sure if you can bleed the piston or between the reservoir and piston?

 

[UOFan]

Sounds like air in the system (builds pressure through the stroke but not enough until the last 10% when it finally compresses)? Not sure if you can bleed the piston or between the reservoir and piston?

Thanks for the reply, I’m disassembling the damn heavy frame to get the Jack out now, and bleed it. Man these things are bulky

 

[oldnslo]

How many check valves were in the parts you dismantled? If more than one could you possibly have mixed up any parts between them?

Inlet check should have very weak spring so vacuum draws oil into the plunger. If it is not allowing oil in properly it will not lift.

Also need to verify that it is seating properly.

 

[UOFan]

How many check valves were in the parts you dismantled? If more than one could you possibly have mixed up any parts between them?

Inlet check should have very weak spring so vacuum draws oil into the plunger. If it is not allowing oil in properly it will not lift.

Also need to verify that it is seating properly.

I took the entire thing apart. I’m having trouble even getting it to bleed air so I may need to just it all apart again…

The piston and u-seal is seating correctly, or so I thought. I’ll check that too.

 

[UOFan]

So this is where I’m at:

From right to left (bottom first:
- valve release assembly
- (screw 1) cap to max weight adjust. You can see the flathead inside the hole to adjust. I didn’t touch this.
-(screw 2) quick/speed Jack valve (can’t get the balls back out)
-(screw 3) release valve
- pump assembly

Here is the diagram I’ve been using:

From what I see there is only one spring (far left hole on jack). The other spring is on the Jack max weight adjust.

I followed the bleeding instructions from the manual to no avail. Am I missing something?

 

[oldnslo]

Is there ball(s) under the pump assembly? Or worded another way what is flow path from reservoir into the pump assembly and then flow path from pump into lifting cylinder? From the failure mode I suspect some problem with flow path from reservoir to pump inlet.

 

[UOFan]

Well, I just keep rearranging the check balls until I got it to pump the piston (finally).

However, once I push the piston about halfway back into the cyclinder/reservoir, it stops and won’t budge.


I’ve bled the Jack a few times. What causes this? Too much fluid?

 

[oldnslo]

Is the piston spongy or rock solid when it stops moving? If solid that would point towards something blocking the oil from returning to the reservoir.

 

[UOFan]

Is the piston spongy or rock solid when it stops moving? If solid that would point towards something blocking the oil from returning to the reservoir.

It’s rock solid. I can’t budge it with a mallet. I turned it upside down and pushed the piston into my workbench with all my weight and the pump (well, the bracket/piston that the handle pumps) shot out.

What could be blocking it, maybe an incorrectly size check ball that allows fluid in, but not out?