Air in Lifton LS750 Hydraulic system. Help!

[sparky1983]

I have a 2001 Lifton LS750 high tip dumper that was taken apart, sand blasted and repainted. Everything is now back together and engine is running well. However, when put into drive (either forward or reverse) it jerks for a bit at first but then runs very slowly and sluggish. Sounds like the pump is pumping air. Is there a handy way (Bleed screw) anywhere on this machine. Any help would be greatly appreciated.

[Stock]

Why not just crack open the out put pipe a flat or two of the nut, if the pump is noising (cavitation) you have air or a blocked suction filter.

Is the dumper Hydrostatic?

[sparky1983]

Yes it's hydrostatic. Put new hydraulic oil and filter in it when I put it back together. Is there not a bleed screw anywhere? This machine was running perfect before dismantling so I am assuming this isn't a flow divider problem? It stops and starts(jerking) when in drive when cold and then after a while it runs but very sluggish. Cheers.

[Muz]

Yes it's hydrostatic. Put new hydraulic oil and filter in it when I put it back together. Is there not a bleed screw anywhere? This machine was running perfect before dismantling so I am assuming this isn't a flow divider problem? It stops and starts(jerking) when in drive when cold and then after a while it runs but very sluggish. Cheers.

Ah youve done some research then ? try jacking both axles off the ground and see what it does

[sparky1983]

Yeah I was reading up on it. I will jack it up tomorrow and see what happens but I can't see it being a flow divider problem as I can hear air in the pump and when I opened the Hydraulic tank tonight the oil was almost white with little bubbles. Will let you know how I get on in the morning.

[Muz]

Yeah I was reading up on it. I will jack it up tomorrow and see what happens but I can't see it being a flow divider problem as I can hear air in the pump and when I opened the Hydraulic tank tonight the oil was almost white with little bubbles. Will let you know how I get on in the morning.

Could be contaminated with something too ... the filler caps for the diesel and hydraulic looked the same on those machines . hydraulic oil with air in it is not easily compressable

[sparky1983]

Could be contaminated with something too ... the filler caps for the diesel and hydraulic looked the same on those machines . hydraulic oil with air in it is not easily compressable

The oil tank cap on mine is a red plastic with a square top to undo it with a wrench. I put new oil and filter after I put it back together so I am pretty sure nothing else could have contaminated it (although I could be wrong). I hope it's just air in the drive pump (the other smaller pump attached to the front of the big one operates the steering and bucket tip etc as far as I can work out and it seems to be fine). Going to jack it up in the morning and see what happens. Think I will loosen some hoses to see if any air bubble appear.

[Wazza]

Did you put the correct oil type back in the transmission ?? ...

If you know your model details you can look it up here ,or any other large oil company website ..
http://www.castrol.com/castrol/ifram...tentId=7061487

[Muz]

The oil tank cap on mine is a red plastic with a square top to undo it with a wrench. .

Sorry my mistake .. I remember the type now .. if youve just refilled it.. IIRC they did froth up from time to time if anything was disturbed.. it may settle down, what was the oil you put in it ? There is no bleeding can be done

[sparky1983]

Did you put the correct oil type back in the transmission ?? ...

If you know your model details you can look it up here ,or any other large oil company website ..
http://www.castrol.com/castrol/ifram...tentId=7061487

Hi Wazza

Checked that website there (thanks) looks like I was supposed to put in 46 oil but I put in 32!! Will this affect it much? I jacked it up this morning and put it in drive and all 4 wheels are turning at the same speed so I think I can dismiss the flow divider problem? Also when I jacked it up i let it run for a few hours (Still running now) to see if it sorts itself out. I think this has helped as I had filled the oil tank to nearly full and its now below half way and there are no leaks anywear so I am assuming the air is starting to leave the system.

[sparky1983]

Went out to check the machine there and made a disturbing discovery. Even though the wheels are spinning at the same speed, I am able to stop them just by holding the wheel??? Seems as if the oil is bypassing somewhere and the drive motors are only getting some of the pressure? If i hold the wheel on a left side then both wheels on that side stop, same as the right side. The drive motors and hoses have never been disassembled so I cant understand why this is happening. Is there an adjustment or relief valve anywhere that I could adjust and try and get more power to the wheels? Also the engine is labouring under full throttle when in drive so I know the pump is working.

[Muz]

Went out to check the machine there and made a disturbing discovery. Even though the wheels are spinning at the same speed, I am able to stop them just by holding the wheel??? Seems as if the oil is bypassing somewhere and the drive motors are only getting some of the pressure? If i hold the wheel on a left side then both wheels on that side stop, same as the right side. The drive motors and hoses have never been disassembled so I cant understand why this is happening. Is there an adjustment or relief valve anywhere that I could adjust and try and get more power to the wheels? Also the engine is labouring under full throttle when in drive so I know the pump is working.

32 oil will be fine .. if you started with a full tank and ended up with half, that suggests it air locked somewhere, and doing what you did freed up the air lock. Is the sight guage half way down the tank anyway, so the correct level is half way ?

Your problem about stopping the motors isnt really indicative of anything IMO cos the drive pump has a variable swash plate which will not go to full delivery until the drive axles are loaded simultaneously with resistive force

It sounds as if something could be plumbed wrong though.. did you take any hoses off at all ?

[sparky1983]

Didn't take any hoses off the drive motors. Just covered them for respraying. Took the machine off the jacks this evening there and it seems to be running alot better although not as fast as I remember so I think it must just have been air and it's clearing itself out. I topped up the oil and will start it from cold in the morning again but I think its getting better. A few hours work with it should clear the last of the air out I hope. Thanks everyone for your help, its much appreciated. Mark

[Muz]

Didn't take any hoses off the drive motors. Just covered them for respraying. Took the machine off the jacks this evening there and it seems to be running alot better although not as fast as I remember so I think it must just have been air and it's clearing itself out. I topped up the oil and will start it from cold in the morning again but I think its getting better. A few hours work with it should clear the last of the air out I hope. Thanks everyone for your help, its much appreciated. Mark

No problems sparky .. just give it plenty of welly then, fully load it, to get the pump to full delivery to blow out any last cobwebs

[ianoz]

Spammer Muz ?