BOBCAT 843 ARM DRIFT

[ROBERCRAIG]

Hi Guys, I'm new to the forum so please bear with me and my lack of knowledge. I have an older Bobcat 843 and am am perplexed as to why the arms drop slowly when they are raised. I can't find any leaks. I seem to have adequated hydraulic power and all controls seem to work fine. Any ideas on what might be the issue and the fix? Thanks much!

 

[OldMachinist]

Do you mean they drift down while the machine is running? If so then it could be the piston seals allowing fluid pass them or the load check valve not seating. Here are a couple of tests to determine where the problem is.

If the piston seals test ok skip to load check test.

 

[ROBERCRAIG]

Do you mean they drift down while the machine is running? If so then it could be the piston seals allowing fluid pass them or the load check valve not seating. Here are a couple of tests to determine where the problem is.

If the piston seals test ok skip to load check test.

Thank you Old Machinist. I printed the diagram and will run thru these tests tonight. The arms do drift down while running and while machine is off. It seems to have adequate down pressure and up pressure too. I'm hoping the pump itself isn't weak.

 

[ROBERCRAIG]

Thank you Old Machinist. I printed the diagram and will run thru these tests tonight. The arms do drift down while running and while machine is off. It seems to have adequate down pressure and up pressure too. I'm hoping the pump itself isn't weak.

Thanks again for the info. I performed the checks per your diagram and it appears that the load check is failing. Do you know if this is a difficult repair? Not quite sure where to begin. Thanks again!

 

[OldMachinist]

Thanks again for the info. I performed the checks per your diagram and it appears that the load check is failing. Do you know if this is a difficult repair? Not quite sure where to begin. Thanks again!

It could be a piece of debris or a nick on the load check. The repair depends on which control valve you have. The early 843 had a control valve made by Cessna and the later ones where made by Melroe. The Cessna valves look like individual valves bolted together and the Melroe is a single casting.

 

[ROBERCRAIG]

It could be a piece of debris or a nick on the load check. The repair depends on which control valve you have. The early 843 had a control valve made by Cessna and the later ones where made by Melroe. The Cessna valves look like individual valves bolted together and the Melroe is a single casting.

Thanks for the info. It is a Melroe per the serial #plate. Does this mean I simply pull the old load check and replace with new? I learned also that the machine is a 1988.

 

[OldMachinist]

Thanks for the info. It is a Melroe per the serial #plate. Does this mean I simply pull the old load check and replace with new? I learned also that the machine is a 1988.

All the machines were made by Melroe but some had Cessna valves. Here's a image of the Melroe control valve. The lift load check is C1.

If this looks like your valve I'd pull the load check and inspect it for debris or damage. Make sure the arms are down or blocked before working on it.

 

[ROBERCRAIG]

All the machines were made by Melroe but some had Cessna valves. Here's a image of the Melroe control valve. The lift load check is C1.

If this looks like your valve I'd pull the load check and inspect it for debris or damage. Make sure the arms are down or blocked before working on it.

Thank you Sir. I will do what you say. If it turns out to be a Cessna, is there something different I need to consider?

 

[OldMachinist]

Thank you Sir. I will do what you say. If it turns out to be a Cessna, is there something different I need to consider?

If it a Cessna valve I'll have to find a different picture of the load check.

 

[SkidRoe]

Thank you Sir. I will do what you say. If it turns out to be a Cessna, is there something different I need to consider?

Just wondering, before you go elbow-deep into the control, have the cylinder piston seals been eliminated as a possible source of leakage? In my experience in older loaders, this is the normal cause of sagging buckets / booms. Just saying... SR

 

[ROBERCRAIG]

Just wondering, before you go elbow-deep into the control, have the cylinder piston seals been eliminated as a possible source of leakage? In my experience in older loaders, this is the normal cause of sagging buckets / booms. Just saying... SR

OldMachinist sent me some trouble shooting tips that seem to have eliminated the cylinder seals as the culprit. I suppose I could plug the connections at the cylinders and see if the drift continues. Your thoughts?

 

[ROBERCRAIG]

OldMachinist sent me some trouble shooting tips that seem to have eliminated the cylinder seals as the culprit. I suppose I could plug the connections at the cylinders and see if the drift continues. Your thoughts?

NOTICED RECENTLY WHEN ARMS WERE DRIFTING THAT THE LEFT ARM CYLINDER WAS PINGING AT THE REAR OF THE CYLINDER AS ARMS WERE DROPPING. WOULD THAT INDICATE A BAD INTERNAL PISTON SEAL?

 

[waynemags]

NOTICED RECENTLY WHEN ARMS WERE DRIFTING THAT THE LEFT ARM CYLINDER WAS PINGING AT THE REAR OF THE CYLINDER AS ARMS WERE DROPPING. WOULD THAT INDICATE A BAD INTERNAL PISTON SEAL?

mine was doing the same. changed out the seals in the cylinders. all good. takes about an hour to do both.

 

[scottie]

Simple test, raise the arms to full height and switch the machine off, if they drift all the way down then its the o ring and back up rings on the cav valve next to the lift spool, if they only come half way down then its the piston seals.