Floor Jack Acting Up.

[George7941]

This jack has not been used for about fifteen years. It was out of oil, so I filled it with ATF yesterday and it pumped up normally without any load. Today it goes up an inch every time I pump but comes right back down on the back stroke. As a result it cannot be pumped up at all.

The release valve, the one operated with the end of the handle, seems to be working normally. When released the jack does not rise at all and when closed, it moves up one inch when the handle is moved down but comes back down when the handle is lifted up.

Oil level is right up to the bottom of the fill plug.

My best guess is that the check valve on the outlet of the hydraulic chamber is stuck . How do I get to it to inspect it?

 

[Vercingetorix]

Don’t trust your life to that. Dump it and buy a new one.

 

[KJSmith]

It probably has air trapped in it. I had a friend rebuild my craftsman and it did the same thing.
I can't remember the procedure to get it out.... but I think you remove the fill plug and put weight on the jack and try to raise it.

Google can be your friend here.

Don't trust your life to any floor jack....use jack stands as needed.

No need to throw away a floor jack that is repairable.

 

[Mcbeem5]

Try looking up on utube how to bleed air out of hydraulic jack, I had an old jack that did nothing and did the bleed procedure and it work great!

 

[George7941]

I really do not think air is the issue here. Air entrapment leads to sponginess and there was no sponginess at all Move the handle up and the jack moves up, move the handle down and the jack follows faithfully and consistently. Keep the handle up and the jack does not move at all, does not drift down.

Jack is working again. I drained the ATF I had added and replaced it with Nuto32 hydraulic oil that I had lying around. I took the plunger off its bore and cleaned it. The inlet check valve was just a ball bearing. Could not get to the outlet check valve, I think it is accessed by taking the relief valve off. Before I got to that the jack started working.

One possibility is that the ATF caused some rubber swelling and the switch to hydraulic oil helped.

One question. The lip seal on the plunger can move about 3/16 of an inch on the plunger body and it looks like it was designed that way to allow movement. What is the purpose?

?

 

[Wolfen]

you have a bad "o" right and air trapped, the O ring alone is enough for me to toss it on teh scrap pile and get a new one, I use bottle jacks, my favorite is teh 20k from Harbor frieght, I have never had a problem lifting my 1996 ranm 2500 with it, and ALWAYS use jack stands, even with a screew jack
Jack stands are your friends

 

[George7941]

Working on my jack brought up another question - how do these jacks breathe?

When the ram is pushed out by pumping the handle, the internal volume increases. Some air has to be let in to maintain atmospheric pressure inside the jack. All the ports on my jack look pretty well sealed - the port for the release/lock valve, the port into which the plunger pump screws in, port for the overload/relief valve and the fill port. I don't see any air getting past any of the four ports.

 

[ajchien]

Working on my jack brought up another question - how do these jacks breathe?

When the ram is pushed out by pumping the handle, the internal volume increases. Some air has to be let in to maintain atmospheric pressure inside the jack. All the ports on my jack look pretty well sealed - the port for the release/lock valve, the port into which the plunger pump screws in, port for the overload/relief valve and the fill port. I don't see any air getting past any of the four ports.

many of the less expensive floor jacks do not breathe, they are sealed. You’re correct, without a breather a vacuum develops inside the reservoir. This fights against the pump when trying to transfer oil to the inner cylinder. It does cause more wear to the seals, worn seals lead to the jack can sucking in outside air through various seals. The vacuum can also cause a quicker drop of the jack when the release valve gets opened.

 

[97prizm]

View attachment 251984
This jack has not been used for about fifteen years. It was out of oil, so I filled it with ATF yesterday and it pumped up normally without any load. Today it goes up an inch every time I pump but comes right back down on the back stroke. As a result it cannot be pumped up at all.

The release valve, the one operated with the end of the handle, seems to be working normally. When released the jack does not rise at all and when closed, it moves up one inch when the handle is moved down but comes back down when the handle is lifted up.

Oil level is right up to the bottom of the fill plug.

My best guess is that the check valve on the outlet of the hydraulic chamber is stuck . How do I get to it to inspect it?

Aren't they supposed to be filled with jack oil not atf? You can get seal rebuilding kits if you know the manufacturer.