I had a similar problem with an 8 ton shop crane. I bought it from
Northern Tool (formerly known as Northern Hydraulics. They sold me a
Kit that didn't even come close to fitting. The piston was so sloppy
when I took it apart that I brought the jack back to them. They didn't
care. They offered to sell me a new, USA made jack, which I bought.
It has worked well for 3 or 4 years now. It is double acting!. Not
happy with Northern Tool for not standing behind the original jack, but
they told me that they no longer carry the Chinese model that failed.
Maybe they have on in the size you need.

Pete Stanaitis
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Ignoramus16322 wrote:
The hydraulic jack on my crane has two problems:

1) it leaks around the small (pumping) cylinder
2) When I open the valve, it opens too abruptly, so the crane drops
instead of going down slowly, I totally hate this.

So. I would like to buy a replacement jack, preferably something of
"high quality", chrome plated cylinders, made in USA or some such. Are
there any suppliers who sell similar but better jacks?

Pictures are he

http://igor.chudov.com/projects/Harb...t-Truck-Crane/