753 pump *hums*

[skidsteer.ca]

heatpumpproducts: slightly late reply, but the seal for the pintle levers is a simple lip seal, you will need to remove the centering plate, then the alloy arm that bolts to the yoke. You must fully remove this bolt to enable it to slide off the shaft. You will need to remove all 4 bolts on the cover on the top of the pump that hold the seal. You will need to replace the shaft seal and you will also need to replace the square O ring that seals the plate. It can all be done without disturbing the inside of the pump.
Slightly off topic, but here is a picture of the gland nut from the tilt ram, i had a little trouble removing it!!! ended up needing to use an air chisel and oxy torch. I was lucky enough to still have a piece of alloy that i was able to machine a new one out of, worked out pretty well. Some how the thread picked up and it refused to move. I had a 10' bar holding the body of the ram, i then used a LARGE pipe wrench with a 6' pipe and it still refused to move much more than a few mm every try. Out came the air chisel and it would move slightly every try.

Higher rez pic: http://users.tpg.com.au/tazza_/100_0037.jpg

I don't know if that poppet is for cold weather, I know where the one in on mt NH and its function is to stop the oil flow in the return line until the pressure builds to the charge pressure level. Forget what they call it. Could you take a picture of the Bobcat one and describe the location? Would be good to know where it is and what it looks like.
Did the threads all "roll up" on that gland nut , tight all the way, or was it just tht hard to break loose. I don't like the way they have the undersized 2 pin hole system to remove these. I made a tool for the ones on my old hoe and it was hopeless. Ended up with a big pipewrench and scared the aluminum nut all up. But nothing like that. I need to fix the brake on my lathe so I can thread, incase I need to do that someday.
Ken

 

[jerry]

I don't know if that poppet is for cold weather, I know where the one in on mt NH and its function is to stop the oil flow in the return line until the pressure builds to the charge pressure level. Forget what they call it. Could you take a picture of the Bobcat one and describe the location? Would be good to know where it is and what it looks like.
Did the threads all "roll up" on that gland nut , tight all the way, or was it just tht hard to break loose. I don't like the way they have the undersized 2 pin hole system to remove these. I made a tool for the ones on my old hoe and it was hopeless. Ended up with a big pipewrench and scared the aluminum nut all up. But nothing like that. I need to fix the brake on my lathe so I can thread, incase I need to do that someday.
Ken

When you guys are machining threaded glands or gland nuts take a careful squint at the old threads to be sure they are 60 degree. Some cylinders use buttress threads which are 30 on one side and 90 on the other although if I remember right it was mostly on o.d. threaded tubes.

 

[OldMachinist]

When you guys are machining threaded glands or gland nuts take a careful squint at the old threads to be sure they are 60 degree. Some cylinders use buttress threads which are 30 on one side and 90 on the other although if I remember right it was mostly on o.d. threaded tubes.

Standard inch size buttress threads are perpendicular to 7 deg. incline on the thrust face and 45 to 50 deg. on the clearance flank with a flat or radius in the root. Metric buttress threads are perpendicular to 3 deg. thrust and 33 deg. clearance. This is if they are cut to the standards but manufacturers can engineer the parts with any angle they desire to try and make sure you have to buy OEM parts.

 

[Tazza]

Standard inch size buttress threads are perpendicular to 7 deg. incline on the thrust face and 45 to 50 deg. on the clearance flank with a flat or radius in the root. Metric buttress threads are perpendicular to 3 deg. thrust and 33 deg. clearance. This is if they are cut to the standards but manufacturers can engineer the parts with any angle they desire to try and make sure you have to buy OEM parts.

Ken - it was tight the whole way, the threads picked up and tore off the gland nut, it took about 30 mins to bash it free!!! I will try and get some pictures of the valve location, i have a new valve on order.
I did check the threads with the tool to check the angles were rite, the tool that i ground sat in the threads correctly but the threads that were still there did have that funny geometry of what looked like a 90 degree face and about a 30 degree one too. But the inside if the tube was 30 and 30 from memory making the standard 60 degree (or 55, close enough for me). I figured it was done this way as it was faster to machine?
I really need to learn more about this so i know things are spot on. Not as simple as a standard angle metric or imperial thread!

 

[Tazza]

Ken - it was tight the whole way, the threads picked up and tore off the gland nut, it took about 30 mins to bash it free!!! I will try and get some pictures of the valve location, i have a new valve on order.
I did check the threads with the tool to check the angles were rite, the tool that i ground sat in the threads correctly but the threads that were still there did have that funny geometry of what looked like a 90 degree face and about a 30 degree one too. But the inside if the tube was 30 and 30 from memory making the standard 60 degree (or 55, close enough for me). I figured it was done this way as it was faster to machine?
I really need to learn more about this so i know things are spot on. Not as simple as a standard angle metric or imperial thread!

It still hums!!!!
I replaced the valve but the problem is still there, its not as loud, at idle it makes no noise. I'm not really sure what to check next. It did have water contamination when i got it, the oil was slightly milky. I changed oil and the filter, I'm not really happy with it now, it needs another change as it still has a slight white tint to it. I didn't want to fill the system again if i have to dump it again if i need to pull say the pump out.
Does anyone know the noise a gear pump makes when it wears out? I don't think its worn as it has heaps of power and lifts fast. I thought they run quiet still but have lower flow and can't build up pressure. The drive pumps/motors work great heaps of power.
I'm starting to think oil may be part of the problem, I'm using 20W50 in it. The noise is the same hot or cold. I don't want to start the oil debate again! just not sure if its a little thick causing it to make the valve make the noise. It does get a bit warm in Brisbane though so the oil will thin out pretty fast.
Its one of those things you don't want to fiddle with too much just incase you make it worse. I swear it sounds like the pump is caveating but there are no bubbles in the oil tank. The pump heats up like it is but again, no bubbles!

 

[mllud]

It still hums!!!!
I replaced the valve but the problem is still there, its not as loud, at idle it makes no noise. I'm not really sure what to check next. It did have water contamination when i got it, the oil was slightly milky. I changed oil and the filter, I'm not really happy with it now, it needs another change as it still has a slight white tint to it. I didn't want to fill the system again if i have to dump it again if i need to pull say the pump out.
Does anyone know the noise a gear pump makes when it wears out? I don't think its worn as it has heaps of power and lifts fast. I thought they run quiet still but have lower flow and can't build up pressure. The drive pumps/motors work great heaps of power.
I'm starting to think oil may be part of the problem, I'm using 20W50 in it. The noise is the same hot or cold. I don't want to start the oil debate again! just not sure if its a little thick causing it to make the valve make the noise. It does get a bit warm in Brisbane though so the oil will thin out pretty fast.
Its one of those things you don't want to fiddle with too much just incase you make it worse. I swear it sounds like the pump is caveating but there are no bubbles in the oil tank. The pump heats up like it is but again, no bubbles!

Tazza
It does seem that when a gear pump wears the clearances would increase and it would Just get weak. I had one go bad on a roll back truck. The sound it made was similar to when a bearing starts grumbling. I took it apart and seen no visable problem. No polished wear spots. Bushings/bearings were good
The way the gears mesh I would think tne backlash would stay forward. My pump also worked fairly well but did grumble and got hot.I was afraid to run it not knowing when it would fail.
Do you have a mechanics stethascope. With your gear pump conected to your hydrostatic pump it may be hard to isolate the source of the noise.Do you feel vibration
Mike

 

[Tazza]

Tazza
It does seem that when a gear pump wears the clearances would increase and it would Just get weak. I had one go bad on a roll back truck. The sound it made was similar to when a bearing starts grumbling. I took it apart and seen no visable problem. No polished wear spots. Bushings/bearings were good
The way the gears mesh I would think tne backlash would stay forward. My pump also worked fairly well but did grumble and got hot.I was afraid to run it not knowing when it would fail.
Do you have a mechanics stethascope. With your gear pump conected to your hydrostatic pump it may be hard to isolate the source of the noise.Do you feel vibration
Mike

I don't have a scope, i wish i did though.
No vibrations can be felt holding the sticks. but if you grab hold of a tube line you can feel it buzzing. This is one of the things that made me agree it was a problem with a poppet and housing that was replaced after i was informed it was a known issue. I pulled the poppet and spring and the noise went away so i agreed it was the problem. I lost charge pressure doing that so it couldn't stay out.
I figured thats how gear pumps wear, with good power and speed i stull assume its ok, but i can't be 100% sure on that.

 

[skidsteer.ca]

I don't have a scope, i wish i did though.
No vibrations can be felt holding the sticks. but if you grab hold of a tube line you can feel it buzzing. This is one of the things that made me agree it was a problem with a poppet and housing that was replaced after i was informed it was a known issue. I pulled the poppet and spring and the noise went away so i agreed it was the problem. I lost charge pressure doing that so it couldn't stay out.
I figured thats how gear pumps wear, with good power and speed i stull assume its ok, but i can't be 100% sure on that.

Tazza
Its not your oil 10/30 here in the winter would be thicker then 80/90 in Brizzy anytime of the year. I have never noticed any odd werring noises in the winter. (though I usually park indoors)
There is not a second valve in that area or the new one could be bad??? How is your charge presure, steady??
When a gear pump is shot you can see a huge difference in max (relief valve) pressures from cold oil to warm oil at low engine rpm. They often wear quite slow and will work ok if the loader is reved up, but at an idle the load in the bucket may push the boom down when you press the pedal to lift. (oil flows backwards through the pump) seen this on a 7710 ford tractor.
Ken

 

[Tazza]

Tazza
Its not your oil 10/30 here in the winter would be thicker then 80/90 in Brizzy anytime of the year. I have never noticed any odd werring noises in the winter. (though I usually park indoors)
There is not a second valve in that area or the new one could be bad??? How is your charge presure, steady??
When a gear pump is shot you can see a huge difference in max (relief valve) pressures from cold oil to warm oil at low engine rpm. They often wear quite slow and will work ok if the loader is reved up, but at an idle the load in the bucket may push the boom down when you press the pedal to lift. (oil flows backwards through the pump) seen this on a 7710 ford tractor.
Ken

I can't see how the valve could be bad as its a simple valve body spring and poppet, but you never can tell.
Power is good, so I'd suspect its not the pump. I will need to hook a gauge on the charge line, but it will be a little tricky to monitor when I'm in the machine loading it down, but not totally impossible.

 

[sterlclan]

I can't see how the valve could be bad as its a simple valve body spring and poppet, but you never can tell.
Power is good, so I'd suspect its not the pump. I will need to hook a gauge on the charge line, but it will be a little tricky to monitor when I'm in the machine loading it down, but not totally impossible.

use a long screw driver to listen put the handle in your ear and touch the pointy end to the part(s) you want to hear or a funnel and hunk o hose us po folk need tools too.Jeff

 

[Tazza]

use a long screw driver to listen put the handle in your ear and touch the pointy end to the part(s) you want to hear or a funnel and hunk o hose us po folk need tools too.Jeff

Thats not a bad idea, i may give it a go. I can feel the vibrations on the hoses and tube lines but as its a fluid the vibrations travel, it feels strongest at the hose that goes to the oil cooler. Yes, i have replaced the filter I still need to hook up a pressure gauge to it, its currently on my 751 after i filled it with oil for the first time after stripping it down.

 

[mllud]

use a long screw driver to listen put the handle in your ear and touch the pointy end to the part(s) you want to hear or a funnel and hunk o hose us po folk need tools too.Jeff

Jeff I used the tools you suggest for a long time. I found a cheap mechanic stethascope at a flee market. Works great . $10.00. here is the same one on ebay. Mike
http://cgi.ebay.com/ebaymotors/NEW-...m14QQhashZitem170263394944QQitemZ170263394944

 

[Tazza]

Jeff I used the tools you suggest for a long time. I found a cheap mechanic stethascope at a flee market. Works great . $10.00. here is the same one on ebay. Mike
http://cgi.ebay.com/ebaymotors/NEW-Mechanics-Stethascope-Find-Engine-Noises-Easily_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c39Q3a1Q7c66Q3a2Q7c65Q3a12Q7c240Q3a1318QQ_trksidZp3286Q2ec0Q2em14QQhashZitem170263394944QQitemZ170263394944

I think i'll have to look for one of those locally, i'm sure it would come in handy!

 

[Tazza]

I think i'll have to look for one of those locally, i'm sure it would come in handy!

Ok, small update.
The cause of the hum has been found BUT i don't know what is causing it, does that make any sense?
The charge pressure is far too high, i threw a gauge on it and it was off the scale that reads up to 260, it would have been at least 300 PSI as it was off the scale. It should be set to 200. There is a charge pressure relief on the back of the pump which i removed to ensure it wasn't stuck and it was perfect. I installed one off another pump i have, no change. I then removed the spring and poppet that should have brought the pressure rite down to near zero, but no it was still over 260 PSI.
The charge pressure is measured after the oil cooler and filter head so as far as i'm aware it can't be a restriction in either of those. All i can think is its something inside the pump where the oil goes to the main hydraulic pump through the other piston pump sections.
As i don't have any parts breaks downs for this machine i can't check if there are any anti-cav valves in that section that could have gotten stuck and causing problems. I'd assume the insides of the hydraulic hoses wouldn't just close up without any heat to damage the hose.
It still works and works well but i still want it to be rite and to not be so noisy! i don't know if higher charge pressure will cause damage down the track either.
Any ideas guys?

 

[sterlclan]

Ok, small update.
The cause of the hum has been found BUT i don't know what is causing it, does that make any sense?
The charge pressure is far too high, i threw a gauge on it and it was off the scale that reads up to 260, it would have been at least 300 PSI as it was off the scale. It should be set to 200. There is a charge pressure relief on the back of the pump which i removed to ensure it wasn't stuck and it was perfect. I installed one off another pump i have, no change. I then removed the spring and poppet that should have brought the pressure rite down to near zero, but no it was still over 260 PSI.
The charge pressure is measured after the oil cooler and filter head so as far as i'm aware it can't be a restriction in either of those. All i can think is its something inside the pump where the oil goes to the main hydraulic pump through the other piston pump sections.
As i don't have any parts breaks downs for this machine i can't check if there are any anti-cav valves in that section that could have gotten stuck and causing problems. I'd assume the insides of the hydraulic hoses wouldn't just close up without any heat to damage the hose.
It still works and works well but i still want it to be rite and to not be so noisy! i don't know if higher charge pressure will cause damage down the track either.
Any ideas guys?

are there any elbows in the charge line? how about restriction (read garbage or other crap) in the pump where the charge line goes? or is there no charge line at all? have you had the pump apart? could be seal residue in the wear plate section....Jeff

 

[Tazza]

are there any elbows in the charge line? how about restriction (read garbage or other crap) in the pump where the charge line goes? or is there no charge line at all? have you had the pump apart? could be seal residue in the wear plate section....Jeff

Hi Jeff
There is an elbow where the line connects to the side of the main pump, this is the return line from the oil filter which is regulated by a charge relief set to 200 PSI on the side of the pump. I don't have any parts lists to show me if there are any flow restricting orifices, but i would guess there weren't any as its low pressure and regulated by the relief. Are you thinking there is possibly a restriction in the elbow?
I haven't pulled the pump down as i have great drive and lifting power. There is an oil feed hole between the piston pump to the hydraulic pump, all i can think is that its blocked some how but i have no idea what could be so big to clog a hole of that size.
What do mean seal residue from the wear plates? are you talking the main piston pump? all the sealing surfaces use O rings or paper gaskets, there shouldn't be any sealant around to cause any problems and if there was i figured it would be so small as to pass through the oil holes.
I think I'll need to check the main oil hose from the filter to the pump. I have had a hose that was restricted inside but that was after it was licked by fire just a little bit, it was enough for it to close up the inside of the hose though. The outside looked fine, just a little soot.
At least i know what is causing the noise, i just need to find whats causing the problem thats causing the problem *my head hurts now thinking about that*

 

[sterlclan]

Hi Jeff
There is an elbow where the line connects to the side of the main pump, this is the return line from the oil filter which is regulated by a charge relief set to 200 PSI on the side of the pump. I don't have any parts lists to show me if there are any flow restricting orifices, but i would guess there weren't any as its low pressure and regulated by the relief. Are you thinking there is possibly a restriction in the elbow?
I haven't pulled the pump down as i have great drive and lifting power. There is an oil feed hole between the piston pump to the hydraulic pump, all i can think is that its blocked some how but i have no idea what could be so big to clog a hole of that size.
What do mean seal residue from the wear plates? are you talking the main piston pump? all the sealing surfaces use O rings or paper gaskets, there shouldn't be any sealant around to cause any problems and if there was i figured it would be so small as to pass through the oil holes.
I think I'll need to check the main oil hose from the filter to the pump. I have had a hose that was restricted inside but that was after it was licked by fire just a little bit, it was enough for it to close up the inside of the hose though. The outside looked fine, just a little soot.
At least i know what is causing the noise, i just need to find whats causing the problem thats causing the problem *my head hurts now thinking about that*

yup if the charge pressure goes through the elbow and it was plugged that would cause restriction... you mentioned that the drive motors had crappy seals, could some of them gotten stuck in the slots in the wear plates where the charge fluid goes in? Ive seen hoses get a flap of rubber inside and plug up. Ive never worked on a pump that new on my relic the charge pressure goes into the center of the piston pump through an elbow,mine had what looked like glass in it when I first got the machine.....we all know where that led me.................be smarter than the machine .......Jeff

 

[sterlclan]

yup if the charge pressure goes through the elbow and it was plugged that would cause restriction... you mentioned that the drive motors had crappy seals, could some of them gotten stuck in the slots in the wear plates where the charge fluid goes in? Ive seen hoses get a flap of rubber inside and plug up. Ive never worked on a pump that new on my relic the charge pressure goes into the center of the piston pump through an elbow,mine had what looked like glass in it when I first got the machine.....we all know where that led me.................be smarter than the machine .......Jeff

one more thought....you replaced the cold weather valve ...Did you change the spring too? I thought the cold bypass regulated the charge pressure with "thick" or cold oil,what regulates it when it warms up?the charge relief? if so would a weaker spring in the charge relief lower that pressure?

 

[Tazza]

one more thought....you replaced the cold weather valve ...Did you change the spring too? I thought the cold bypass regulated the charge pressure with "thick" or cold oil,what regulates it when it warms up?the charge relief? if so would a weaker spring in the charge relief lower that pressure?

Hopefully something is wrong in the hose or stuck in the elbow. The drive pumps make no noise and work flawlessly so i hope no seal particles are stuck. The seals went to like powder so i believe they would be too large to get stuck in the slots in the wear plates (or i hope not).
The cold weather by-pass from what i was told is there for when the oil is too thick and it allows it to by-pass the oil cooler/filter and go straight back to the tank. Its set to 400 PSI which is double the charge pressure relief. I did replace the valve body, poppet and spring, i thought just in case! This valve does nothing to regulate charge pressure, the charge relief is built into the pump.
The thing is, the machine still operates really well, but has that rotten noise! There is what i thought was a problem with the aux hydraulics that they sort of stick, you release the button and it doesn't stop instantly but was told they use charge pressure to release so i think they could be related.
I will try and get the hose and elbow off tonight and see if i can find anything. I really hope it was a simple as a damaged hose.
Thanks for the input!

 

[Tazza]

Hopefully something is wrong in the hose or stuck in the elbow. The drive pumps make no noise and work flawlessly so i hope no seal particles are stuck. The seals went to like powder so i believe they would be too large to get stuck in the slots in the wear plates (or i hope not).
The cold weather by-pass from what i was told is there for when the oil is too thick and it allows it to by-pass the oil cooler/filter and go straight back to the tank. Its set to 400 PSI which is double the charge pressure relief. I did replace the valve body, poppet and spring, i thought just in case! This valve does nothing to regulate charge pressure, the charge relief is built into the pump.
The thing is, the machine still operates really well, but has that rotten noise! There is what i thought was a problem with the aux hydraulics that they sort of stick, you release the button and it doesn't stop instantly but was told they use charge pressure to release so i think they could be related.
I will try and get the hose and elbow off tonight and see if i can find anything. I really hope it was a simple as a damaged hose.
Thanks for the input!

Ok, took the return line from the filter to the pump off, plugged the port on the pump. Hooked up a bottle to catch the oil from the hose to the filter, started it and checked the gauge, no pressure. Filled the bottle in about 5 seconds so the restriction isn't in the hose. I then checked the elbow to the pump and its also clear.....
I'm going to pull the pump and motor on the weekend if the weather holds, i need to get this problem sorted out, its driving me crazy! I had a look at the pump i have for my 763 thats currently in pieces and there is a hole from the input shaft to the inlet of the pump. The restriction must be here somewhere or someone replaced the shaft bearings and left the seals on them.... I have no idea what the previous owner could have done.
Anyway, time will tell.