Cherry Picker Air-Over-Hydraulics Pump Repair?

[tom86951]

I have a Habor Freight Cherry Picker from about 2007. The hydraulics work fine when pumped manually, but the pneumatic pump doesn't work and is a rusty mess inside. HF doesn't seem to sell replacements. I tried a new o-ring in the cover, but the air just escapes from under the lid. The piston in the middle doesn't seem frozen but very gummed up. Can it be rebuilt? Tips or links that might help?

 

[nadogail]

Cleaning up the gummy deposit on the piston should not make things worse and may make things better.
Making the flat plate that holds the O ring in place more flat just might help. I am assuming that you have chosen the correct diameter and thickness for the O ring. Skinny O
Rings don’t seal well.

 

[andyvh1959]

Most o-rings for hydraulics are designed for 0.015" to maybe 0.020" compression when in the assembled condition of the application. Also, O-rings are typically fitted to slightly overfill the space into which they fit, so the O-ring is slightly force fitted into the location. If the O-ring OD is too small it has to expand too far under pressure to make a seal