743 Bobcat hydraulic arms won't raise

[redtractorlover]

I have a 743 that I just rebuilt the engine in. While I was rebuilding the engine, I removed and cleaned the oil cooler and replaced the hydraulic filter so I have a lot of air in the system I'm sure. The cylinders will all extend but not retract. If I shut the engine off, and partially step on the pedal, it will lower the arms but if I step on the pedal all the way, it will stop lowering. The only thing I can think of is air in the system. I loosened the set screw up near the pressure sensor and ran it for a minute or 2 trying to bleed the system and no luck. I can hear the pump cavitating. Is there a good way to bleed the system? Or are there other thoughts on what might be causing the issue? Before tearing everything apart, I worked fine. Thanks.

 

[fliersmith]

I just spent a lot of time removing water from my hydro fluid (meaning draining and replacing all the fluid). In the process I had to open all the lines to drain the contaminated fluid and of course introduced air. I woud recommend making sure your hydrostatic is topped off, even a little extra fluid. Then raise the arms, put the lock in place. Open the Allen keyed ports at the 90 degree fittings where the hydraulic lines go into the cylinders, I didn't completely remove the plug. Be careful to not get aggressive with the controls. It's easy to break the o rings. I needed to get new ones for a few. I started with the tilt cylinder, It's the highest point with the arms up. One fitting at time. Then I did the bottom of the lift cylinders connection then the top of the lift cylinder connections. Start the unit up and cycle the controls, It's a giant mess but should help work out the air. Don't run the unit very long as to not run the hydro tank dry.

 

[Tazza]

I just spent a lot of time removing water from my hydro fluid (meaning draining and replacing all the fluid). In the process I had to open all the lines to drain the contaminated fluid and of course introduced air. I woud recommend making sure your hydrostatic is topped off, even a little extra fluid. Then raise the arms, put the lock in place. Open the Allen keyed ports at the 90 degree fittings where the hydraulic lines go into the cylinders, I didn't completely remove the plug. Be careful to not get aggressive with the controls. It's easy to break the o rings. I needed to get new ones for a few. I started with the tilt cylinder, It's the highest point with the arms up. One fitting at time. Then I did the bottom of the lift cylinders connection then the top of the lift cylinder connections. Start the unit up and cycle the controls, It's a giant mess but should help work out the air. Don't run the unit very long as to not run the hydro tank dry.

You didn't knock the aux hydraulic lever on did you? (right steering lever)
Air will make operation jittery till it bleeds, but with no load, it should run without much noise.