440B Jumpy Hydraulics

Help Support SkidSteer Forum:

hmw

Member
Joined
Oct 10, 2006
Messages
7
Recently bought a 93' 440B. My problem is the lift arms are jumpy, like the pump is cavitating or getting air and it foams the hyd oil. Even after cycling many times. This machine has had a history of this. The previous owner bought it in 99' and said it did it since he had owned it, he just put up with it. The hydrostatic drive seems to work fine. I put a new engine in it [old kohler was blown up]and while out, i put a kit in the hyd pump being aware of the foaming problem. It didnt help, still works the same. It doesnt make the machine unusable just a nuisance. Anybody else ran into this problem. Also seems everybody on this site says to use 10w30 motor in the hyd system. Is this correct? I'm sure the machine has tractor hyd oil in it. Lots of equipment calls for motor oil and hyd oil is ran in it with no problems. Ex: Ditch Witch calls for 30wt motor oil and we always ran hyd oil in them with no issues. Other equipment calls for motor oil in the hydrastatic drive units, so i think i'll change the oil to 10w30 and see what happens. Just don't feel confident this will fix it. Any thoughts would be appreciated.
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
You need the oil to be thicker for your hydrostatic system, if its too thin it doesn't lubricate well enough and can destroy your pumps. Hydraulic oil is fine for hydraulic cylinders and pumps but for your hydrostatic pumps and motors it just isn't good enough from what i have been told. Stick with 10W30 or 10W40 motor oil, if in doubt call your local dealer, they will confirm what oil you should be using in your machine.
Your hydrostatics are fine? no jumpiness or noises? the only other thing i could think of that could cause your hydraulic pump to cavetate is a restriction in your suction line filter (if there is even one fitted). Usually if there is a blockage it will affect your hydrostatics too as your hydraulic pump is also your charge pump for the hydrostatic pump.
 

hmw

Member
Joined
Oct 10, 2006
Messages
7
You need the oil to be thicker for your hydrostatic system, if its too thin it doesn't lubricate well enough and can destroy your pumps. Hydraulic oil is fine for hydraulic cylinders and pumps but for your hydrostatic pumps and motors it just isn't good enough from what i have been told. Stick with 10W30 or 10W40 motor oil, if in doubt call your local dealer, they will confirm what oil you should be using in your machine.
Your hydrostatics are fine? no jumpiness or noises? the only other thing i could think of that could cause your hydraulic pump to cavetate is a restriction in your suction line filter (if there is even one fitted). Usually if there is a blockage it will affect your hydrostatics too as your hydraulic pump is also your charge pump for the hydrostatic pump.
I'm going to change it to 10w30. Other Pieces of equipment i've worked on use 20w50 synthetic motor oil in the hydro units so 10w30 sounds right. Yes the hydrostatic drive works fine. No noise and not jumpy. It does not have a suction filter only a return one. I Re-hosed this machine earlier this year for the fellow i ended up buying it from. The hose from the tank to pump is only about 24" long. One thing i do not like about the hyd system on this is the return line dumps into a "run" tee at the bottom of the hyd tank. In other words the suction comes out one end of the fitting and the return dumps into the side of the fitting. If any air in the system, [foam] it would get sucked right back into the pump. Also the return oil never gets to the tank to cool. I work for an electric utility and repair all kinds of bucket trucks, digger derricks etc. I have never seen a return ran like this. But it must work, the way the tank is there is no other port to run it in. I think I'll try the motor oil, Not confident it will make the hyd system less jumpy but doesn't hurt to have the right oil in it. Thanks for your reply, I'll let you know how it works out.
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
I'm going to change it to 10w30. Other Pieces of equipment i've worked on use 20w50 synthetic motor oil in the hydro units so 10w30 sounds right. Yes the hydrostatic drive works fine. No noise and not jumpy. It does not have a suction filter only a return one. I Re-hosed this machine earlier this year for the fellow i ended up buying it from. The hose from the tank to pump is only about 24" long. One thing i do not like about the hyd system on this is the return line dumps into a "run" tee at the bottom of the hyd tank. In other words the suction comes out one end of the fitting and the return dumps into the side of the fitting. If any air in the system, [foam] it would get sucked right back into the pump. Also the return oil never gets to the tank to cool. I work for an electric utility and repair all kinds of bucket trucks, digger derricks etc. I have never seen a return ran like this. But it must work, the way the tank is there is no other port to run it in. I think I'll try the motor oil, Not confident it will make the hyd system less jumpy but doesn't hurt to have the right oil in it. Thanks for your reply, I'll let you know how it works out.
Thats the setup on all the machines that i'm aware of, but remember when you extend a cylinder it will displace more or less oil, this will push the foam into the reserve tank or draw fresh un-foamed oil out. Removing the air from the system can take a while, but trust me, it does go!
 

skidsteer.ca

Well-known member
Joined
Jan 20, 2006
Messages
3,853
Thats the setup on all the machines that i'm aware of, but remember when you extend a cylinder it will displace more or less oil, this will push the foam into the reserve tank or draw fresh un-foamed oil out. Removing the air from the system can take a while, but trust me, it does go!
You could set up a temporary return ino the fill cap of the hyd tank, (just be sure to submerge it in the oil to reduce foam) until you get the air out.
Ken
 

hmw

Member
Joined
Oct 10, 2006
Messages
7
You could set up a temporary return ino the fill cap of the hyd tank, (just be sure to submerge it in the oil to reduce foam) until you get the air out.
Ken
Thanks for the replies. I've got a line truck to work on right now so maybe I'll get back to the Bobcat this weekend. I didn't say much about it but its a nice machine. I bought it with a hole in the side of the block. [threw a rod]. Had a horizontly opposed Kohler and I replaced it with a "v" style Kohler. Actually fits better than the original engine, more room around the new engine. Had to fabricate a new muffler, throttle linkage and removed all the wiring and made a new wiring harness to fit the new engine. Even used the original harness connector housings over. so it looks like its all original[installed new terminals, no butt connetors]. All wiring is in loom. It has new tires and wheels, I replaced all the hydraulic hoses earlier this year and I built a new bucket for it about 2 years ago for the previous owner, so all in all its a nice machine. Just get the jumpy problem worked out and should be good. Its not unusable but i think it should not work that way. Thanks again. I'll let you know what i find.
 

hmw

Member
Joined
Oct 10, 2006
Messages
7
Thanks for the replies. I've got a line truck to work on right now so maybe I'll get back to the Bobcat this weekend. I didn't say much about it but its a nice machine. I bought it with a hole in the side of the block. [threw a rod]. Had a horizontly opposed Kohler and I replaced it with a "v" style Kohler. Actually fits better than the original engine, more room around the new engine. Had to fabricate a new muffler, throttle linkage and removed all the wiring and made a new wiring harness to fit the new engine. Even used the original harness connector housings over. so it looks like its all original[installed new terminals, no butt connetors]. All wiring is in loom. It has new tires and wheels, I replaced all the hydraulic hoses earlier this year and I built a new bucket for it about 2 years ago for the previous owner, so all in all its a nice machine. Just get the jumpy problem worked out and should be good. Its not unusable but i think it should not work that way. Thanks again. I'll let you know what i find.
Well, I replaced the hydraulic oil with 10W30 and it hasn't seemed to make much difference. I kinda did't think it would but I would rather have the right oil anyway. Next I'm going to hook up my flow meter/pressure gauge in between the pump and valve bank and see what happens. I'll post what i find. I used the machine a little and runs and works good, except for that annoying "jumpy" bucket. Hydros seem to work fine. Going to make a bracket for the front to move trailers around. Unhook the bucket and install it right on the cross bracket. Quick disconnect also.
 

OldMachinist

Well-known member
Joined
May 24, 2006
Messages
2,748
Well, I replaced the hydraulic oil with 10W30 and it hasn't seemed to make much difference. I kinda did't think it would but I would rather have the right oil anyway. Next I'm going to hook up my flow meter/pressure gauge in between the pump and valve bank and see what happens. I'll post what i find. I used the machine a little and runs and works good, except for that annoying "jumpy" bucket. Hydros seem to work fine. Going to make a bracket for the front to move trailers around. Unhook the bucket and install it right on the cross bracket. Quick disconnect also.
I have a 453F that used to act just like yours. I replaced all the hoses, o-rings and put a rebuild kit in the pump and fixed it. I suspect that the pump kit and the o-ring at the hydraulic tank outlet fitting were to blame.
To check for air in the system if your machine is similar to mine and has a filter block. You can remove the filter drain plug(The pressure at that port is less than 100 psi.) and install a valve and clear hose long enough to reach the oil tank breather port. Start the machine and open the valve if the problem is air cavitation you will see bubbles. This will return the oil to the tank with out being sucked right back into the pump and also seemed to temporary fix it on mine until I shut it off and let it sit for awhile.
Let us know how it works out
 

hmw

Member
Joined
Oct 10, 2006
Messages
7
I have a 453F that used to act just like yours. I replaced all the hoses, o-rings and put a rebuild kit in the pump and fixed it. I suspect that the pump kit and the o-ring at the hydraulic tank outlet fitting were to blame.
To check for air in the system if your machine is similar to mine and has a filter block. You can remove the filter drain plug(The pressure at that port is less than 100 psi.) and install a valve and clear hose long enough to reach the oil tank breather port. Start the machine and open the valve if the problem is air cavitation you will see bubbles. This will return the oil to the tank with out being sucked right back into the pump and also seemed to temporary fix it on mine until I shut it off and let it sit for awhile.
Let us know how it works out
thanks for the reply. This machine has no original hoses. I re-hosed it completely this past spring for the customer i ended up buying it from. After i bought it, with a blown up engine I put a kit [seals, wear plate] in the pump. One o-ring was damaged but the gears and housing looked good, even the wear plate looked good. No difference in performance though. After using it a couple days, it doesn't foam the oil anymore. I suppose that could have been from it sitting for a while and completely apart. No foam now but still jumps same as before. Interesting thing i noticed about this pump is there is no actual shaft seal. only plate seals. The splined input shaft is open to the hydro end housing with one small spring and ball in one port. I think this is normal since this pump could never have been taken off before. But what is also means is that the pump can "suck" some from the hydro. Air is easier to draw then oil. I think I'm going to hook up my flow meter and pressure gauge and see what happens. funny thing is performance doesnt change between engine speed or hot/cold, always the same. Thanks again
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
thanks for the reply. This machine has no original hoses. I re-hosed it completely this past spring for the customer i ended up buying it from. After i bought it, with a blown up engine I put a kit [seals, wear plate] in the pump. One o-ring was damaged but the gears and housing looked good, even the wear plate looked good. No difference in performance though. After using it a couple days, it doesn't foam the oil anymore. I suppose that could have been from it sitting for a while and completely apart. No foam now but still jumps same as before. Interesting thing i noticed about this pump is there is no actual shaft seal. only plate seals. The splined input shaft is open to the hydro end housing with one small spring and ball in one port. I think this is normal since this pump could never have been taken off before. But what is also means is that the pump can "suck" some from the hydro. Air is easier to draw then oil. I think I'm going to hook up my flow meter and pressure gauge and see what happens. funny thing is performance doesnt change between engine speed or hot/cold, always the same. Thanks again
Thats a normal setup. The drive shaft is under low pressure, the high pressure is created on the outer parts of the cam plate i think they call it. The only other thing is to check the O ring between the hydro pump and the hydraulic pump. But if it was bad, i would expect to see oil seaping out between the housings.
 

Terry1

New member
Joined
Feb 14, 2010
Messages
1
thanks for the reply. This machine has no original hoses. I re-hosed it completely this past spring for the customer i ended up buying it from. After i bought it, with a blown up engine I put a kit [seals, wear plate] in the pump. One o-ring was damaged but the gears and housing looked good, even the wear plate looked good. No difference in performance though. After using it a couple days, it doesn't foam the oil anymore. I suppose that could have been from it sitting for a while and completely apart. No foam now but still jumps same as before. Interesting thing i noticed about this pump is there is no actual shaft seal. only plate seals. The splined input shaft is open to the hydro end housing with one small spring and ball in one port. I think this is normal since this pump could never have been taken off before. But what is also means is that the pump can "suck" some from the hydro. Air is easier to draw then oil. I think I'm going to hook up my flow meter and pressure gauge and see what happens. funny thing is performance doesnt change between engine speed or hot/cold, always the same. Thanks again
Hi I noticed you have jumpy hydraulics on a 440B. I was woundering if you ever found the problem. I also have a 440B with jumpy hydraulics. I wish I could help you but I am the one that needs help. I see you had this problem in 2006, I was hoping that you had the problem fixxed. Anyhow if you have any info for me that would be great. Thank you
 

Arik434

Member
Joined
Mar 8, 2017
Messages
23
I have a 453F that used to act just like yours. I replaced all the hoses, o-rings and put a rebuild kit in the pump and fixed it. I suspect that the pump kit and the o-ring at the hydraulic tank outlet fitting were to blame.
To check for air in the system if your machine is similar to mine and has a filter block. You can remove the filter drain plug(The pressure at that port is less than 100 psi.) and install a valve and clear hose long enough to reach the oil tank breather port. Start the machine and open the valve if the problem is air cavitation you will see bubbles. This will return the oil to the tank with out being sucked right back into the pump and also seemed to temporary fix it on mine until I shut it off and let it sit for awhile.
Let us know how it works out
I'm going to bring this post back from a decade of being dead, as my machine is acting very similar. OldMachinist, Could you actually run the machine while bypassing oil back to the reservoir through the temp valve that you put in the filter block? I seem to be somehow sucking massive amounts of air into the system. I can watch it almost immediately bubble up though the case drain ports in the tank. I have replaced any of the suspect hoses, and all o-rings on the suction side. I am going to try your test to see if that helps at all, but I am already confident its air in the system...just no clue how that much can be getting in there--especially without any oil leaks.
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
I'm going to bring this post back from a decade of being dead, as my machine is acting very similar. OldMachinist, Could you actually run the machine while bypassing oil back to the reservoir through the temp valve that you put in the filter block? I seem to be somehow sucking massive amounts of air into the system. I can watch it almost immediately bubble up though the case drain ports in the tank. I have replaced any of the suspect hoses, and all o-rings on the suction side. I am going to try your test to see if that helps at all, but I am already confident its air in the system...just no clue how that much can be getting in there--especially without any oil leaks.
Sadly you won't be getting a reply from OldMachinist, we lost him a few years back now.
Opening a line from the filter block is a way to speed up purging air in the system, something is either sucking in air, or you have a bad pump or a restriction in a suction line filter.
If the pump is pulling in oil, and there is a restriction, be it a plugged filter or other obstruction, it will actually make the oil foam up.
 

Arik434

Member
Joined
Mar 8, 2017
Messages
23
Sadly you won't be getting a reply from OldMachinist, we lost him a few years back now.
Opening a line from the filter block is a way to speed up purging air in the system, something is either sucking in air, or you have a bad pump or a restriction in a suction line filter.
If the pump is pulling in oil, and there is a restriction, be it a plugged filter or other obstruction, it will actually make the oil foam up.
Oh man, sorry to hear that. On a positive note, I think I finally MAY have solved my issue. I replaced the pintle shaft seals and I am Now getting very little air and foam in the tank. I think this is normal air that needs to get bled out now, and preliminary testing had the hydraulics working nice and smooth. Amazing. Now I need to get the rest of the machine back together and put it to work and see how it goes. The service manager at my dealer mentioned that these were a common source of air leaks on these old machines, and since they point up, you don't see any oil seepage. Bobcat only sells entire seal kits--which are $260 for each pump!! Luckily, I was able to take the part number of the old shaft seal and source a couple new ones on eBay for $20 bucks each. Thanks to everyone for all the suggestions!
 

SkidRoe

Well-known member
Joined
Dec 10, 2009
Messages
1,885
Oh man, sorry to hear that. On a positive note, I think I finally MAY have solved my issue. I replaced the pintle shaft seals and I am Now getting very little air and foam in the tank. I think this is normal air that needs to get bled out now, and preliminary testing had the hydraulics working nice and smooth. Amazing. Now I need to get the rest of the machine back together and put it to work and see how it goes. The service manager at my dealer mentioned that these were a common source of air leaks on these old machines, and since they point up, you don't see any oil seepage. Bobcat only sells entire seal kits--which are $260 for each pump!! Luckily, I was able to take the part number of the old shaft seal and source a couple new ones on eBay for $20 bucks each. Thanks to everyone for all the suggestions!
Glad to hear you got it fixed. Good catch on the pintle seals, I sure would have overlooked that one.
One thing I do notice about my 440b is that if it sits for a while, it is like the gear pump loses it's prime. It is regained again within seconds as soon as you start it, but it takes a few minutes of use for the air to work its way out of the system again. The place that you notice it the most is in the boom lift cylinders - they will be a bit jerky for the first couple of times that you lift the boom.
I have never really labeled this as a problem, more of just an idiosyncrasy of an older machine with a bit of wear in it.
Cheers - SR
 

Arik434

Member
Joined
Mar 8, 2017
Messages
23
Glad to hear you got it fixed. Good catch on the pintle seals, I sure would have overlooked that one.
One thing I do notice about my 440b is that if it sits for a while, it is like the gear pump loses it's prime. It is regained again within seconds as soon as you start it, but it takes a few minutes of use for the air to work its way out of the system again. The place that you notice it the most is in the boom lift cylinders - they will be a bit jerky for the first couple of times that you lift the boom.
I have never really labeled this as a problem, more of just an idiosyncrasy of an older machine with a bit of wear in it.
Cheers - SR
Ok, good to know. Being an engineer (like you), I've found a bunch of design ideas that I don't care for with this machine. Then again, its well over 30 years old and it's a lot of stuff to package together in a tight small machine. I do think that mounting the oil filter upside down is a bad idea though and only drains out every time you shut it down. Thanks again to SkidRoe for helping me along with this. I figured that with such a similar machine, he would be the best source of info--and I was right. Hopefully the next person to come along searching out an air leak will consider these seals. It definitely wasn't obvious to me, and I guess I still don't understand why my charge pressure is really good, but they could still suck air! At this point, I don't care! Arik
 

Skidsteer1

Member
Joined
Nov 24, 2019
Messages
6
Oh man, sorry to hear that. On a positive note, I think I finally MAY have solved my issue. I replaced the pintle shaft seals and I am Now getting very little air and foam in the tank. I think this is normal air that needs to get bled out now, and preliminary testing had the hydraulics working nice and smooth. Amazing. Now I need to get the rest of the machine back together and put it to work and see how it goes. The service manager at my dealer mentioned that these were a common source of air leaks on these old machines, and since they point up, you don't see any oil seepage. Bobcat only sells entire seal kits--which are $260 for each pump!! Luckily, I was able to take the part number of the old shaft seal and source a couple new ones on eBay for $20 bucks each. Thanks to everyone for all the suggestions!
Did you do the shaft seal to ? I did the pintal seals and I'm getting foam air hydraulic oil still.
 
Top