Bobcat 753 F series trouble

[ricky agarwal]

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

[crewchief888]

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

[willie59]

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.

[crewchief888]

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

[willie59]

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.

[Bobcatdan]

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?

[crewchief888]

...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

[willie59]

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.

[Bobcatdan]

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.

[ricky agarwal]

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..

[ricky agarwal]

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

[ricky agarwal]

Wats the function of load check valve & port relief valve in bobcat 753 control valve ...willie 59 sir and crewchief888 sir plz reply

[ricky agarwal]

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

[crewchief888]

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.


even if the aux are not activated, one of these valves could be stuck partially open.

[ricky agarwal]

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 ..................