743b has no down pressure on boom control???

[Sfdcapt]

Ive read through most of the post and havent found a solution... maybe someone knows how to fix? Or at least where to start? I just bought a 1993 743b and it runs great and everything works great on it other than the left foot controls... When I rock pedal forward just a little bit the bucket will come down but more like its in float (just the weight bringing it down) if I push pedal forward normally then it lifts the bucket up??? Also if I rock pedal backwards just a little it lowers bucket ( again just weight bringing it down) and if I push pedal back normally it raises the bucket. I,ve checked the linkage and everything seems to be right. Tilt and curl work fine and I lift the front of bobcat with tilt but cannot with boom?? It will lift a bucket of dirt with no problem. Any input would be appreciated

 

[[email protected]]

aux hydraulics engaged?

 

[Sfdcapt]

aux hydraulics engaged?

I checked the aux and they are in neutral position, I can move stick left and right and I can hear it engage when I move it..

 

[[email protected]]

I checked the aux and they are in neutral position, I can move stick left and right and I can hear it engage when I move it..

probably just a linkage adjustment...although they do get worn out sometimes.

 

[Sfdcapt]

probably just a linkage adjustment...although they do get worn out sometimes.

I was thinking it was a linkage adjustment at first but it doesn't make since why bucket goes up when I press back of pedal but no matter what position I have foot control in I cannot get bucket to move down under pressure??? I appreciate the input I have plenty of power for lift, tilt, curl and drive just no down pressure on arms Seems to me it like down on arm is in float position?

 

[[email protected]]

I was thinking it was a linkage adjustment at first but it doesn't make since why bucket goes up when I press back of pedal but no matter what position I have foot control in I cannot get bucket to move down under pressure??? I appreciate the input I have plenty of power for lift, tilt, curl and drive just no down pressure on arms Seems to me it like down on arm is in float position?

perhaps the detent could be worn out causing it to just go into float position.

 

[Tazza]

perhaps the detent could be worn out causing it to just go into float position.

Can you feel the spool move and the spring pull it back to centre? Lift the cab and get someone to move the pedal for you while watching the linkage at the spool, make sure it extends and retracts without and obstructions.
The way you are describing it, the functions are reversed.
I also wonder if the nut may have come loose inside the cylinder?

 

[Sfdcapt]

Can you feel the spool move and the spring pull it back to centre? Lift the cab and get someone to move the pedal for you while watching the linkage at the spool, make sure it extends and retracts without and obstructions.
The way you are describing it, the functions are reversed.
I also wonder if the nut may have come loose inside the cylinder?

Thanks, I'll try and take a look at the spools and linkage this weekend

 

[Onemancrew]

Thanks, I'll try and take a look at the spools and linkage this weekend

Did you ever find the cause of this problem? I have the exact same problem. My machine was working fine one day. The next it was doing exactly as you described. I have taken a quick look and it seems the spool valve moves both ways fine... Did you find a blockage in the spool valve when you took it out?

 

[Onemancrew]

Did you ever find the cause of this problem? I have the exact same problem. My machine was working fine one day. The next it was doing exactly as you described. I have taken a quick look and it seems the spool valve moves both ways fine... Did you find a blockage in the spool valve when you took it out?

I think I misunderstood your original post.. My bobcat works normally except the boom wont come down except under its own weight. I have to engage float to get it down. Someone told me that the inner lining of hoses can come apart and cause a blockage in one direction... Although I think that's unlikely. I'm leaning toward it being a spool valve problem? Can anyone help?

 

[Tazza]

I think I misunderstood your original post.. My bobcat works normally except the boom wont come down except under its own weight. I have to engage float to get it down. Someone told me that the inner lining of hoses can come apart and cause a blockage in one direction... Although I think that's unlikely. I'm leaning toward it being a spool valve problem? Can anyone help?

Did you ensure the aux hydraulics are not engaged?

 

[billrbg]

Did you ensure the aux hydraulics are not engaged?

Does that really make any difference? I put in many hours using my 743 with a hydraulic-hammer. Both the aux and lift/tilt actions worked simultaneously. Yes, they may slow down when all are being exercised at once, but definitely no loss of "boom action"; either up or down. I would expect the "B" version to be at least as good...

 

[Tazza]

Does that really make any difference? I put in many hours using my 743 with a hydraulic-hammer. Both the aux and lift/tilt actions worked simultaneously. Yes, they may slow down when all are being exercised at once, but definitely no loss of "boom action"; either up or down. I would expect the "B" version to be at least as good...

It matters when they are being dead headed. With a hammer, the flow will not be fully shut off continuously running over the relief.
When the aux hydraulics is stuck on, things act very weird.

 

[billrbg]

It matters when they are being dead headed. With a hammer, the flow will not be fully shut off continuously running over the relief.
When the aux hydraulics is stuck on, things act very weird.

When I'm using the (909) back-hoe it also seems the aux doesn't affect the lift/tilt. My recollection is that the aux has no effect when just using the standard bucket. It's "wintering" in mud right now, but the next time I wake it I'll be sure to check. You have me curious now!

 

[[email protected]]

When I'm using the (909) back-hoe it also seems the aux doesn't affect the lift/tilt. My recollection is that the aux has no effect when just using the standard bucket. It's "wintering" in mud right now, but the next time I wake it I'll be sure to check. You have me curious now!

when you engage the aux with no attachment connected it does exactly as you say with both functions moving simultaneously

 

[Tazza]

when you engage the aux with no attachment connected it does exactly as you say with both functions moving simultaneously

With a backhoe, the control block has an open centre, so any oil that is not being used, just flows around in a loop back to the machine, it only dead heads when a cylinder is fully extended or retracted.

 

[7LBSSMALLIE]

With a backhoe, the control block has an open centre, so any oil that is not being used, just flows around in a loop back to the machine, it only dead heads when a cylinder is fully extended or retracted.

PORT RELIEF ANTI CAV VALVE. came apart and shot the ball into tube line. need to find it ' check valve there will be visual clues if it came apart. needs looked at anyway.

 

[mmsllc]

PORT RELIEF ANTI CAV VALVE. came apart and shot the ball into tube line. need to find it ' check valve there will be visual clues if it came apart. needs looked at anyway.

When dealing with a bobcat, this issue is probably the only issue that will not keep you from making money. I will not say that it is not annoying, but consider the leaks, or no starts, that won't let you operate & make good money. It does sound like a valve is not operating correctly though. The float valve theory is a very good point. It might be time to remove, disassemble, clean & rebuild the loader control valve. Almost nothing else makes sense. If it can lift a heavy load, then the hydraulic pump (system pressure) is good.

 

[Onemancrew]

When dealing with a bobcat, this issue is probably the only issue that will not keep you from making money. I will not say that it is not annoying, but consider the leaks, or no starts, that won't let you operate & make good money. It does sound like a valve is not operating correctly though. The float valve theory is a very good point. It might be time to remove, disassemble, clean & rebuild the loader control valve. Almost nothing else makes sense. If it can lift a heavy load, then the hydraulic pump (system pressure) is good.

Ok thanks for the replies guys... Sorry I haven't checked back earlier... I am definitely sure aux hydraulics are not stuck as I have a 4 in one bucket for one... And two, I have attached my backhoe and it works as it should perfectly... The only problem I have is tht the boom just will not come down under hydraulic pressure. It only comes down when I mash the pedal into detent... And now after using it for a few days like that it won't even stay in detent no more... Another symptom is if I mash the pedal into detent as soon as the bucket begins to lower if I rock the slightest bit back on the pedal it will have hydraulic power but uncontrollably.