Hydraulic jack maintenance

[William_H]

Went to jack the boat on trailer and found this jack would not rise. Operate the lever and it rises then falls back. Have filled the oil reservoir and the needle valve to release pressure looks OK. (and is screwed in tight) So many clever people on this forum. Has anyone any experience of dismantling this kind of jack. (or is it a throw away). Seems to be a hex on top of pump. A hex on top of cylinder and possibly the body screwed in to base. Where to start. I presume there is a non return valve some where inside. Thanks in anticipation ol'will

 

[Mister E]

It sounds like the seals in the pump have split. You can get a kit to replace them.

 

[Refueler]

I have similar that does same ... I replaced seals - but TBH - it worked but I could not trust it any more .... so I went out and bought a decent trolley jack to replace it.

 

[RunAgroundHard]

Take it to a White Wizard or Witch to remove the Hexes and it will work. (-;

 

[ash2020]

I'm all for repairing stuff but when safety is the number one priority, wouldn't it be a good idea to splash out 100 quid and get a nice new trolley jack?

 

[Refueler]

I'm all for repairing stuff but when safety is the number one priority, wouldn't it be a good idea to splash out 100 quid and get a nice new trolley jack?

100 quid ?????? Made of gold is it ??

My 3.5T trolley jack was half that in euros !!

But I agree ... I repaired my piston jack and when used - it did not inspire confidence ....

 

[penberth3]

Went to jack the boat on trailer and found this jack would not rise. Operate the lever and it rises then falls back. Have filled the oil reservoir and the needle valve to release pressure looks OK. (and is screwed in tight) So many clever people on this forum. Has anyone any experience of dismantling this kind of jack. (or is it a throw away). Seems to be a hex on top of pump. A hex on top of cylinder and possibly the body screwed in to base. Where to start. I presume there is a non return valve some where inside. Thanks in anticipation ol'willView attachment 176376View attachment 176376

Throw it away. Or destroy it trying to undo the hex cap, then throw it away.

 

[Mister E]

You should not be trusting any jack axle stands are a must.
The problem is not that it will suddenly drop (the screw valve stops that).
The problem is a fail safe and will not raise.
Exactly the same system on a trolley jack.

The seals are under the hex fitting.

 

[penberth3]

You should not be trusting any jack axle stands are a must.
The problem is not that it will suddenly drop (the screw valve stops that).
The problem is a fail safe and will not raise.
Exactly the same system on a trolley jack.

The seals are under the hex fitting.

I disagree. If a knackered old seal fails completely it will drop very quickly.

 

[rogerthebodger]

Looks to me that the piston has rusted which will distort the top seal but if its not leaking oil its problem will be the non-return valve in the pump or the release screw seal cone damaged

I have several up to 50 ton of the same type from China and are easy to repair. If you don't wish to send it to me I I will fix it

 

[Refueler]

You should not be trusting any jack axle stands are a must.
The problem is not that it will suddenly drop (the screw valve stops that).
The problem is a fail safe and will not raise.
Exactly the same system on a trolley jack.

The seals are under the hex fitting.

Close friend of mine ... Volvo 850 estate on axle stands ... car moved - killed him.

 

[William_H]

Thanks all for the replies. The trailer is essentially raised on blocks under the axle. With wheels left on. This to provide access under the hull. Jacks just used to support the back end against tipping. so 5 point support. But yes I will be careful. I do have a trolley jack and 2x mechanical scissor jacks. Winter no 40 doing all this again. getting used to it. I will try the hex to see if I can get any movement. No great loss if it is a throw away. ol'will

 

[Iliade]

Close friend of mine ... Volvo 850 estate on axle stands ... car moved - killed him.

As a youth, I had about ten tons of lorry on axle stands when the huge generator on the vehicle alongside ran away. Bits of generator engine went all over the place and the vibration split one of my axle stands, dropping the lorry onto its side! By luck & agility nobody got hurt... Always put other things under a vehicle in addition to stands if you're working beneath. Dirty great lumps of timber are the preferred support of last resort.

Back to the jack: You could disassemble it, get both the pistons reground, hard chrome plated and finish ground, then reassemble with new seals... But it still won't work because the fault is indeed in either the non-return valve or the screw-in needle valve ;0) As you live in Asia this might be worthwhile to address, but over here, I'd just buy a new one.

For your purposes, would wooden stillages and fox wedges work or are they banned there? Easy to put in a lot of redundancy that way.

 

[penberth3]

........Back to the jack: You could disassemble it, get both the pistons reground, hard chrome plated and finish ground, then reassemble with new seals...

Er, a new jack is about £20

 

[William_H]

Thanks again. Yes a new jack would be cheaper. However for the purposes I use them scissor type mechanical jacks with a much greater range of lift. Mostly this request came out of stubbornness of loving old tools.
Anyway I did open it up. The top hex takes off the reservoir and outer casing with pressure down to hold the seal of the body to the base. All looked ok. The hex on the pump cylinder also came off OK. Found huge amount of sludge and debris seemed to be sitting on top of a filter screen. Cleaned it out and reassembled with new oil and found the same effect still. Put it aside for another attempt another day.
However I remember my Dad saying you never clean brake hydraulics in kerosene/petrol as it damages rubber parts. I thought he said use methylated spirits but I found in this jack case metho dissolved nothing. Might have well used water. Any suggestions. ol'will

 

[Iliade]

A five litre bottle of brake cleaner is only £20 in the UK!

It contains C6-C7 hydrocarbons, (e.g. hexane)

Personally, I'd use parts washer fluid, the one which is largely kerosene, just not letting the seals sit in it for ages. Jack oil is a mineral oil after all.

After reassembly I'd then bin the jack, or perhaps cut it in half for display purposes.