I'm working on a bobcat 753, brought in for bad hydraulic leak, seal for lift spool was leaking, I removed the the control valve and replaced both seals on both spool, lift and tilt, so 4 seals. Reinstalled, no more leak but as soon as the engine starts, bucket dumps lifting the machine, no matter if it's locked or not , of I try to counter it using the pedals, it stalls the engine. I also have a heard time getting it back down, key off hold the pedal it moves a little then I have to wait a couple minutes and do it again several times before I get the wheels back on the ground. I took pictures before and after and nothing is connected differently, I also disconnected all electrical connections to the valve, same problem. Before I take it put again, anyone have this issue before or have any ideas?
Did you accidentally put the spools back in the wrong bore or accidentally put the tilt spool in backwards? What about the spool centering springs? Reinstalled correctly? Spool caps back in the correct locations? No random check balls, springs or orifices came flying out during disassembly?
I brought it to a hydraulic shop to have the seals put in, the lift spool has a spring and balls for a detent, so it has a different end cap and they are in the same place they were. I spoke with the tech, who is experienced and knows what he is doing, he assured me that it assembled properly. This is a job I'm doing at home, but for work we deal with him often and he is good so I believe him, said all he did was pull the spools, cleaned it up and changed the seals.
Looks like external linkages to actuate the valve when I look up pictures of the valve on Google. The linkages aren't misadjusted are they? The fact it was fine before it left and if you're 100% certain all the lines connected to it are correct I would have to say the issue is something was assembled incorrectly within the valve. With the spools centered in the neutral position there should be zero flow out to the circuit.
The spool is centered as far as i can tell, has full motion when I move the pedals, I tested the locks and they are both working, with the linkage disconnected it still happens. The llinkage was my first thought as well. I could use a little more explanation on the centering spring, I have come to the conclusion that it has to come back out even though I don't want to. Don't normally do side jobs at home but thought I would help someone out assuming it was gonna be a line or fitting leaking, man was I wrong lol
Bear in mind I'm just some guy on the internet that isn't there to actually see, check or confirm anything. Just from what I can gather in the posts it really sounds like something isn't correct inside that valve.
From what he tells me all he did was pull the spools, change the seals and put them back, cleaned it up but didn't take anything else apart. I'm going to take it out again and take it apart myself and check it. Is it possible that one of the aux solenoids or anything else could cause this problem? It's not a nice job to get it out and I know from the last time I can't do it in frame.
Can anyone tell me if a faulty aux solenoid or pressure release cause this issue?
I have pulled out the valve, separated it, removed and cleaned load check valves, relief valves, checked the spools ...put everything back and still have the same problem
Well first thing to fix is your hydraulic lock out solenoid is not working. It's on top of the valve under the floor pan. Next you need to check out the linkage for the bucket dump. When I worked at a Bobcat dealer the lock out solenoids would go bad all the time.
When you say the lock out solenoid, are you referring to the two that lock the spools in place, or the single located in the face of the BICS section between the 4 ports? I tested the spool locks they are good, I disconnected the linkage, first thing I tried.
If the bucket is dumping even with the foot controls disconnected at the control valve, then you got a problem with that spool.
I had it to a hydraulic shop and had the seals changed, he tells me there was nothing visibly wrong with the spools, he is very knowledgeable, my work sends hydraulic components to him regularly, I also had it apart since then and can't find anything out of place, removed and cleaned every component, put everything back in, still the same problem, I also swapped the 2 pressure reliefs, and the the 2 aux solenoids and still dumping on start up. It will raise the machine, shut it off and it will hold, no creeping down for days, turn the key on, lower the arm, use the pedal and lower it. 15 years of turning wrenches and never been this stumped
Hey guys. I have looked everywhere and was about to give up till I ran into this discussion. I am having the same problem. I do not work on bobcats but at a request of a very good clients of mine I dove into this project. It’s a 751 he bought at an auction and he wanted me to do a full overhaul. So I did. Upon inspection I determined almost all of the hoses had to be replaced since they were cracked, some leaking, some not. And since I had to give him a machine in good working condition that would not leave him hanging I went ahead and removed the valve control to replace oring and seals. Needless to say the valve control was filthy and it actually had pieces of old oring inside of it. Long story short o did the job, have no leaks but now my tilt line to the down side is activated without any commands. I just had this happen to me today and this is the first I read this topic, so I will work on it tomorrow based on what I read here, but if you guys have any suggestions of what I should focus on it would be much appreciated.
Maybe should have started a new thread but how are the aux. hyd's activated? Wondering if they are a 3rd function on the control valve. Is your machine hard to start like the hyd's are activated? If the aux. hyd's were turned on or even the valve not centered could make the other hyd's do weird things. Also wondering if you have a self leveling valve on your Bobcat. It automatically tilts the bucket down when lifting the boom so you don't dump material in your lap. If all the valve linkage is disconnected at it still tilts down, the tilt spool either isn't centered (or installed wrong) or if you have optional self leveling, that valve needs adjusting or repair.
I replaced the bics solenoid on the control valve and the problem went away.