NEED 763 CONTROL VALVE HELP

[TNHOTROD]

MY 763 LIFT ARMS WILL NOT STAY AS SOON AS I LET OFF THE PEDAL THEY START DROPPING . BOTH CYLINDERS WERE REBUILT BY LOCAL BOBCAT DEALER..SO IM ASSUMING IT IN THE CONTROL VALVE. ANY HELP WOULD BE APPRECIATED THANKS CHRIS

 

[thetool]

Motor carriers leaking into the chaincase, but they're new. Lift cylinders drifting down, but they've been rebuilt.....
Did you take the machine into Bobcat for this work, or pull the components yourself and carry them in? Do you have all your hoses hooked back up right?
If the dealer did the work on the machine, they should have told you what was wrong when it was still drifting after they rebuilt the cylinders. It could be a lot of things.
If the dealer changed out your motor carriers, they should have told you why it's still leaking into the chaincase. It's not the motor.
If you're doing the work yourself tearing into this, that and the other without a manual, well, you're never going to get it figured out.
If you had a manual, you could answer 90% your own questions.
I'd check the lift-arm by-pass valve, it's the valve that comes up through the seat, should have a red knob. If that's leaking internally, your boom will drift down, engine on or off. This could also be a lot of things, main relief, port relief, load check, messed-up cylinder rebuild, control spool, lift lock, etc.
What works on your machine?

 

[TNHOTROD]

Motor carriers leaking into the chaincase, but they're new. Lift cylinders drifting down, but they've been rebuilt.....
Did you take the machine into Bobcat for this work, or pull the components yourself and carry them in? Do you have all your hoses hooked back up right?
If the dealer did the work on the machine, they should have told you what was wrong when it was still drifting after they rebuilt the cylinders. It could be a lot of things.
If the dealer changed out your motor carriers, they should have told you why it's still leaking into the chaincase. It's not the motor.
If you're doing the work yourself tearing into this, that and the other without a manual, well, you're never going to get it figured out.
If you had a manual, you could answer 90% your own questions.
I'd check the lift-arm by-pass valve, it's the valve that comes up through the seat, should have a red knob. If that's leaking internally, your boom will drift down, engine on or off. This could also be a lot of things, main relief, port relief, load check, messed-up cylinder rebuild, control spool, lift lock, etc.
What works on your machine?

CHAINCASE PROBLEM IS FIXED.. YES BOUGHT COMPLETE CARRIERS FROM BOBCAT. PROBLEM WAS THE LARGE BLACK SEAL ON ONE SIDE WAS INSTALLED INCORRECTLY. THE BACK OF THE SEAL WAS PUSHED ALL THE WAY AGAINST THE SNAPRING THAT HOLDS THE BEARING. THE LIFT CYLINDERS WERE REBUILT BY A BOBCAT FIELD SERVICE TECH THAT CAME OUT.. THE MACHINE STARTING FILLING THE CHAINCASE FULL OF OIL AFTER THE NEW CARRIERS WERE INSTALLED.SO WHO WOULD OF THOUGHT IT WOULD HAVE BEEN THE BRAND NEW COMPLETELY ASSEMBLED CARRIERS I HAD JUST BOUGHT. SO THEN MACHINE GOT PUSHED TO THE SIDE .THIS MACHINE HAS BEEN SITTING ALMOST A YEAR WITHOUT BEING TOUCHED. AND I AM JUST GETTING AROUND TO FIXING IT. TODAY I REMOVED THE PORT RELIEF VALVE AND A COUPLE OF THE OTHER VALVES THAT LOOK SIMIALAR TO IT . I DID FIND ONE OF THE ORINGS BAD AND REPLACED IT. MADE NO DIFFERENCE AT ALL . IF I TAKE BOTH LINES OFF THE MANUAL BYPASS AND PLUG THEM IT SHOULD TELL ME IF ITS THE PROBLEM RIGHT?? EVERYTHING ELSE SEEMS TO BE WORKING ON THE MACHINE NOW.. BUT WHO KNOWS MAYBE I WILL GO OUT TOMORROW AND SOMETHING ELSE BE A PROBLEM

 

[thetool]

CHAINCASE PROBLEM IS FIXED.. YES BOUGHT COMPLETE CARRIERS FROM BOBCAT. PROBLEM WAS THE LARGE BLACK SEAL ON ONE SIDE WAS INSTALLED INCORRECTLY. THE BACK OF THE SEAL WAS PUSHED ALL THE WAY AGAINST THE SNAPRING THAT HOLDS THE BEARING. THE LIFT CYLINDERS WERE REBUILT BY A BOBCAT FIELD SERVICE TECH THAT CAME OUT.. THE MACHINE STARTING FILLING THE CHAINCASE FULL OF OIL AFTER THE NEW CARRIERS WERE INSTALLED.SO WHO WOULD OF THOUGHT IT WOULD HAVE BEEN THE BRAND NEW COMPLETELY ASSEMBLED CARRIERS I HAD JUST BOUGHT. SO THEN MACHINE GOT PUSHED TO THE SIDE .THIS MACHINE HAS BEEN SITTING ALMOST A YEAR WITHOUT BEING TOUCHED. AND I AM JUST GETTING AROUND TO FIXING IT. TODAY I REMOVED THE PORT RELIEF VALVE AND A COUPLE OF THE OTHER VALVES THAT LOOK SIMIALAR TO IT . I DID FIND ONE OF THE ORINGS BAD AND REPLACED IT. MADE NO DIFFERENCE AT ALL . IF I TAKE BOTH LINES OFF THE MANUAL BYPASS AND PLUG THEM IT SHOULD TELL ME IF ITS THE PROBLEM RIGHT?? EVERYTHING ELSE SEEMS TO BE WORKING ON THE MACHINE NOW.. BUT WHO KNOWS MAYBE I WILL GO OUT TOMORROW AND SOMETHING ELSE BE A PROBLEM

First things first: You were told before you ever posted about your motor carrier seal. Now you've got three open posts out there with different problems and it seems none is solved yet. May make folks wonder it it's all inter-related.
I would reply to my motor carrier leak post, state that the problem is fixed and what it was, and thank all the folks who replied. This way everybody learns, which is the purpose of this board, I think.
Under the cab, if you remove the hose from the by-pass valve that tees into the small return lines, and cap it at the valve, if the valve is bad, this will isolate it. If you have the boom up be sure you have the boom stop in place before you go removing any lines from that valve. If you don't have a boom stop, do it with the boom on the ground.
What happens with this is the valve gets mis-aligned with the hole in the seat pan, it catches when you raise and lower the cab, and bends the stem. You can perhaps see a bent stem when the knob is missing, without even raising the cab.
So if this is the problem, and you replace the valve, make sure it's aligned with the seat pan hole.
Let us know.