Willie sir your help is required ...as soon as i start the engine of the bobcat ...tilt cylinder creeps down ..i interchanged the A , B line at the cylinder end ..now bucket creeps up as soon as engine is started ...we overhauled the control valve ..& tested the system without mechanical link used to operate tilt cylinder ..but the problem remains the same ...also the arm cylinder is not working ...checked the rod end hose of cylinder for pressure while operating the spool manually ..i could see some pressure ...wat can be the reason ...please help
off the top of my head, it sounds like one of the aux solenoids is stuck open :drinkup
Sorry to hear about your trouble ricky. I think crewchief888 would know more about this problem than me, and I agree, a faulty aux valve will cause problems like this. I don't know if a faulty load check valve would do the same, and I wonder about the machine screw that sets the spool centering spring, if this screw came loose it could allow control spool to shift slightly.
i thought about that too willie, but a loose centering spring screw shouldnt stop the boom from operating also. load check would show a slight down boom movement before going up, especially with a load. to quickly check your aux solenoids.. start engine, seat bar down, BICS activated turn on the aux with the button rh handle (thumb) paddle switch push it both directions and hold, then try to use the hydraulics. if they then work, problem is a stuck aux solenoid :drinkup
Got it chief. Maybe I'm reading it wrong, I was under the impression that problem was only in bucket tilt circuit, didn't consider loader arm circuit being affected as well. I've got plenty of experience with replacing seals on control valves, but haven't ran into problems with load checks that often, so wasn't sure what fault effects would be.
I'm thinking if this has a BICS block something isn't right there. On start up, the hyd fuctions should be locked out by BICS. I'm not sure how it could meter oil to the tilt circit while keeping lift inopt, but that is the only thing I can think off. Nothing eles can stop lift from working. Normally even if aux is stuck on, lift will raise, but not lower and tilt will pretty much not work. That said, some machines do act different. One other thought, you said it was rebuild, I wonder what would happen if the spools some how got mixed up?
...also the arm cylinder is not working . or maybe i'm not understanding what he's describing i've been up since 4am, with 2 hrs of sleep last night, and my brain's starting to hurt :laugh :drinkup
Hey, I'm just glad to see two more Bobcat wrench benders here. I'm ready to pass the mantle of Bobcat guru to you guys.
What I want to know was this a simple seal job, or was the vavle pulled and completely stripped down. If it is the later, something(s) has to be assembled wrong. I had a 763 that had a slow powered tilt caused by a slighly stuck aux. I mean slightly. I put an auge on it to watch for flow. At idle it did not turn at all, and full, maybe 1/4 of normal speed. Still, lift worked fine.
Dear frnds.. I took out the control valve and the assembly was cleaned 2 times ...i hope there is no mix up in the spool ...By the way there is no BICS or if it was there it has been taken off ..this problem of tilt cylinder creeping without any pedal operation started after the leaking seal of tilt cylinder was changed..
Arm cylinder is not functionin at all by the pedal it just moves abot 5 mm n then gets stuck...one more thing after the engine starts tilt cylinder rolls in in the neutral position ...and with pedal movement i m not able to roll it down completely ...while operating it feels there is some pressure on opposite side ...and if the accelerator is put on tilt cylinder rolls in with speed at neutral position...There are no auxiliary attachments used so i guess no use of auxiliary solenoids which are mounted on top ...also there is one solenoid in the middle of the control valve ..but i dont know its function
Wats the function of load check valve & port relief valve in bobcat 753 control valve ...willie 59 sir and crewchief888 sir plz reply
Sir tilt cylinder is rolling in at neutral position without any pedal movement ...wat could be wrong here ..the control valve was dismantled 2 times and cleaned and assembled back again
lets see.... aux spool is on top 2nd spool is tilt backside of spool has a spring with an aluminum "bonnet" that can be removed bottom is the lift. this spool has a detent assembly inside the aluminum bonnet, if you disassembled the bonnet, you may have reassembled it incorrectly, or it may be stuck in the float position. the 2 solenoids on top of the valve are the aux, the 3rd one, down in the center of the valve between the fittings is the BICS valve. load check valve stops unwanted movement of the cylinder when the spool is initially moved, ie: to stop a "drop" of the load before going up. port relief valve is a safety system to prevent damage to the cylinder or hoses. most common problem would be a blown oring, but i seriously doubt that would cause the problem you are having. :drinkup even if the aux are not activated, one of these valves could be stuck partially open.
Thanx crewchie sir ..i want to no about the function of BICS solenoid...when i removed the solenoid...i could see a cartridge type valve underneath the solenoid ..i wonder wat solenoid has to do with valve....one more thing if load check valves are non return valve type or wat...if they are non return type how oil flow can take place in both way is it pilot operated ....... When i removed the A & B port hose of the cylinder i saw oil coming from both ports in neutral as well as in other position ...now can u give me a clue where the trouble could be ..................
The BICS stands for Bobcat Interlock Control System. The solenoid controls the vavle to "unlock the hyd. If you removed the solenoid and left the vavle in place, that is why the functions do not work, the are not suppose to when the vavle has no power to it. Put the coil back on and that should make it work the lift and tilt work. As for the bucket moving the I wonder is you may have mixed up the electric connectons and plugged the bics connector into an aux solenoid causing it to deadhead.
the bics valve is part of the safety system. it "unlocks" the hydraulics when it is "satisfied" that the following has happened.. key switch in run position operator in seat, and seat switch closed ( if the machine has the original BICS sysyem) seat bar down there are 2 different BICS systems one has a seat switch, and a yellow button in the dash the other deletes (disconnects) the seat switch, and has a green button in the dash. both controllers look similar, but have different functions. the controller is next to the seat at the back of the cab. if everything electrically is working properly, all the lights on the BICS will be on, steady, no flashing. bobcat control valves are open center, if you remove any hose from the valve, you will get oil flow from it anytime the engine is running. :drinkup
Crewchie sir can you send me the hydraulic ckt or schemmatic of Bobcat 753 F series (advantage series )
sorry i cant. no access to confidential files from home computer.
Crewchie sir Can you atleast send me schematic of control valve only...just want to know how in built cartridge type valves work...whether the valve is open center or closed center ...2 or 3 positions ...Schematic of control valve means hydraulic ckt of control valve only...in neutral position oil should go to tank...through oil cooler ..but it is coming to A & B port of cylinder why...i think is the reason why arm cylinder gets locked
i have no access to confidential files from home. the control is an open center valve, when the spool is in neutral oil flows through the valve and evetually returns to tank. however even when the valve is in neutral, if you have any open port, you will get oil flow through it. it's just how the valve works. it's called leakage. it's not enough leakage to cause the cylinder to move, but without the cylinder stopping oil flow it leaks. since the problem started when you removed and disassembled the valve, thats where the problem lies. theres no way for me to know what you may or may not have reassembled incorrectly. :drinkup
Crewchie sir ...can you explain how BICS in the control valve works i mean wat happens when the solenoid energises ..i mean the oil flow...Even if i disconnected the solenoid...i was able to operate bucket cylinder why...I also want to know ..how the load holding takes place ..is it PO check valve or counterbalance valve
did you have this problem before you "rebuilt" the control valve? :drinkup
No sir atleast arm cylinder was working...one thing i have taken out the control valve & i nm checking it...with upper BICS part (block) removed ...i can see that while the spool operates oil comes out in both A & B ports of both tilt and arm line ....up to dis point thing is ok...as soon as i fix the upper half BICS block and energise BICS solenoid ..oil stops coming from B line of both tilt and arm line where the check valves are fitted in cross position while operating spoool ..it drains to tank...so that is why i m asking How the BICS valve functions can you provide me details as to how it stops hydraulic functioning unless energised...without energising solenoid also i can see oil coming from A side of both tilt and arm after operating spool
It sure sounds like the soleniod valve is stuck open...just sayin...
Hello from me.Because, may be i'm new, and couldn't find where i can post my problem ( but the problem is similar to this problem) and i'm writing here. So i have S100 SSL with pedals and levers.So tilt cylinder come down( when the machine is running or is not).When the boom is raised bucket(tilt) falling down, but when the front tires of the machine are suspended in air (push down tilt) the tilt doesn't moove.This mean that the problem doesn't come from the cylinders.The machine is without bucket positioning valve, so the one thing could stop ot run the tilt is hydraulic control valve.The machine is new (200mh) and i really don't know what to do.Please help me.Thanks
I do have a similar problem, on my 753 bobcat, after removed the control valve to reseal a spool ,it can not lift enough to take the sefty bar off
I am having the exact same problem with my 753, after seals were changed, as soon as engine starts bucket tilts down, lifts the machine, I've gone through this thread but no definite answer....did you ever fix it, what was it?