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Hi All,
I realise that this an old thread but here is my experience in fixing one of these tj4000 jacks.
My neighbour asked me to look at, and perhaps repair a tj4000 which his son had used to jack out some tree roots, when he got the jack back it no longer pumped up.
There was no sign of leakage but when pumped the lifting pad rose and stayed there if the handle was held down, however when the handle was raised for another pump the lifting pad dropped back again. In addition if the lifting pad was held up by hand, and the jack pumped again it would lift again, but drop down to the previous position. He suggested that it was caused by failure of the seals.
I removed the pump piston and cylinder by undoing the hex nut (and that was tight !!) to find that the nylon type seal had disintegrated into a crumbly mess. I cleaned this out ( not good enough it turns out), and ordered a polyurathane U-CUP seal size 6mm IDX 12 mm OD X 6mm high, from Totally Seals on Ebay. Now this seal is really too short, it should be 8mm high, but I packed it with a 12mm OD X 2mm thick O-Ring.
On reassembly the jack still did not work and showed exactly the same symptoms.
Now these jacks have several steel balls which act as valves, no springs,just plain old ball bearings. There is one ball (5mm diameter) inside the pump, below the piston which stops the oil going back into the oil reservoir, but this was clean and in place.
In addition there is another ( probably 5mm diameter) ball in the passage which feeds the oil from the pump to the Ram cylinder which I reasoned could be jammed by a bit of broken seal material. The only way to get to this is to dismantle the jack and undo the big (50mm AF) nut on the Ram end of the cylinder. This turned out to be super tight, requiring a 3 foot long bar to get it undone. OK, undo the nut, remove the Ram look down the Ram cylinder and you should see the ball tucked partly behind the copper sealing washer. In my case the ball did not move but after tapping it down with a punch and washing through with paraffin and compressed air the ball could be lifted and dropped with a magnetic screwdriver. Everything was washed with paraffin and dried with compressed air and reassembled using proper jack oil as an assembly lubricant.
Lo and behold, after refilling and bleeding, it all works perfectly.
Was it worth it ?
Well, in financial terms no, definitely no. But is was fun, interesting and I learned something.
Edited by Monitorman3 on 01/05/2019 at 13:29
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