I just picked up this lift and need some diagnostic help. Everything works as it should except the steering barely moves while going forward or reverse. If I stop then steer, the steering works very quickly and moves fully in both directions. Nothing appears to be binding and controls clearly work. It appears to be a hydraulic flow/pressure problem with driving 2 functions at once. Any ideas?
I have a 3220 that does the same. Going to hang around to hear what you find out!
Follow-up- I downloaded the service manual and have been studying it. As best as I can figure, it seems the most likely cause is a defective/shorted diode. I presume these are used to drive the proportional valve when multiple funtions are selected at one time? Unfortunatley, the schematic shows numerous diodes but theres nothing in the manual (that I can find) that shows where these diodes are on the machine? Does anyone know if these are in a central location, integrated into individual haress wires or perhaps on components such as solenoids? Any guidance would be appreciated.
No takers? Emailed Skyjack as well... radio silence. I guess I'll venture in on my own and hope for the best. If anyone knows of a more active or appropriate forum for scissor lifts, I'd be interested.
I've worked a bit on JLG scissors but don't know off hand on the location. This is one of the down sides of having a forum with so many different types of equipment covered, it's really easy to miss posts. FaceBook has a rental equipment mechanics page that I have had some success with.
Thx Excavator- I went ahead and called Skyjack... they were very helpful. They're confident from my description of the issue that they know what the problem is. I'll document it to help future searchers: Apparently- steering while stationary, see's full pump relief pressure (3000 psi) HOWEVER- steering while moving gets greatly reduced hydraulic pressure by design (only about 500 psi). This isn't covered in the manual, it's just a function of the design which uses orifices to control flow, which in turn impacts pressures depending on which functions are selected together. They suspect either A) the steering bushings may be bound up due to lack of grease and/or corrosion OR, B) the steering cylinder may be slightly bent from either a forklift or curb strike. Perhaps it's even a combination of both factors. The point is the binding in the steering system is often masked by full system pressure, and then becomes apparent (and annoying) at the reduced pressures while moving. I'm told this is a fairly common issue. The next step will be to verify this and I'll post when I'm done. I hope this helps others.
"This isn't covered in the manual" it's nice that JLG offers their manuals free on line but there's so much that the manual doesn't cover.
Funny. I joined this forum for the same reason. I got a 3219 that has a steering issue while driving. Checked my pressures and 2900 psi 500 while driving. My voltage is good also. Called skyjack said replace the king pin bushings. Thats a chore they are pressed in . Got it all back together and problem is still there . Looking for ideas , anybody got some?