funky drive still

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sterlclan

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May 1, 2004
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Recently fixed a bunch of leaks,changed all filters and hyd fluid,still having drive issues just weak turns decent most times after a little use gets groany and weak. I also noticed sometimes bucket movement takes drive almost all away do i need a new pump? or am i missing something? thanks Jeff
 

JustAwrench

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May 9, 2005
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OK-this is the 631 right? Your "pump" is actually a stack of three pumps-two hydrostatic pumps-one for each drive motor(left or right) and your hydraulic pump(also called charge or implement pump) bolted onto the end farthest from the engine. Worse case scenario-your hydrostatic pumps and drive motors are worn out, but these symptoms can also be caused by the little hydraulic pump on the end of the stack. It's easy to remove and inspect. It has a little rotor inside with fiber vanes. If its weak, it won't charge your hydrostatic system with enough oil to drive , hence the groaning. You can also check it with a flowrater at the auxilliaries, if equipped and you have acces to a flowrater, without removing the pump. Sorry if you already know all this. Check the hydraulic pump first, if it checks out, there are some tests for the hydrostats that are easy to do. Let us know, good luck.
 

Tazza

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OK-this is the 631 right? Your "pump" is actually a stack of three pumps-two hydrostatic pumps-one for each drive motor(left or right) and your hydraulic pump(also called charge or implement pump) bolted onto the end farthest from the engine. Worse case scenario-your hydrostatic pumps and drive motors are worn out, but these symptoms can also be caused by the little hydraulic pump on the end of the stack. It's easy to remove and inspect. It has a little rotor inside with fiber vanes. If its weak, it won't charge your hydrostatic system with enough oil to drive , hence the groaning. You can also check it with a flowrater at the auxilliaries, if equipped and you have acces to a flowrater, without removing the pump. Sorry if you already know all this. Check the hydraulic pump first, if it checks out, there are some tests for the hydrostats that are easy to do. Let us know, good luck.
This sounds like what my 731 did, it had a blocked bronze filter that starved the hydrostatics of oil, you did change that filter too? is so, please don't yell at me :)
 

sterlclan

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This sounds like what my 731 did, it had a blocked bronze filter that starved the hydrostatics of oil, you did change that filter too? is so, please don't yell at me :)
.yup I changed that bronze one too Ill look at the hydralic pump are theese things rebulidable or is it better to get one that is already done? when the machine is cold it works like a new one and sometimes it stays good for a long time and sometimes not 5 min.
 

Tazza

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.yup I changed that bronze one too Ill look at the hydralic pump are theese things rebulidable or is it better to get one that is already done? when the machine is cold it works like a new one and sometimes it stays good for a long time and sometimes not 5 min.
If your hydraulics are still working I would say its not your hydraulic/charge pump...... It sounds like when the oil is heating up it is thinning out causing it to either cavitate or bypass the pistons in your hydrostatic pump. This one seems like a question for JustAwrench, i'm sure he would know how to fault find a hydrostatic system better than i can. The only other thing i can think of is an oil problem? it may be too thin or its thinning out too much when warm. A synthetic oil may solve this but don't quote me. The hydrostatic pump is repairable, BUT don't even attempt it without a diagram of the pump. The hydraulic pump is also repairable, they are a simple vane pump. but if your lift arms still work and seem to be strong i would think that it is not the problem (still delivering correct hydraulic pressure). If you pull your lift arms down or tilt rite back and hold it you should hear a whistle sound of the relief valve opening up so you are getting enough pressure. Hopefully i am not wrong here and if i am i'm sure JustAwrench will tell me.
 

JustAwrench

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Man it's been a long time since I worked on one of these, but in reading the thread something came back-read on.--The vane pump is rebuildable, IF the insides of the housing aren't scratched or gouged, and the bushings are still tight-a set of vanes and o-rings and a seal, I seem to remember. You really need to check that pump before you dig too deep into the hydrostats.--What I remembered is trouble we had with the cold-weather bypass poppet in the manifold. There is a plug, spring and poppet in the manifold block, check the poppet for burrs, scratches or a wear ring, anything that keeps it from seating. We were sometimes able to repair the poppet by chucking it up in a drill press and polishing it with emery cloth, but it's good to replace if you can. Anyway, something to check before you pull your hydraulic pump. Tazz is right in all, but a worn hydraulic pump can work OK until the oil reaches operating temperature then have these symptoms. Your problem might be any combination of things. Anyway, check all this stuff, if you're still having trouble, time for hydrostat tests, I guess.
 

sterlclan

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Man it's been a long time since I worked on one of these, but in reading the thread something came back-read on.--The vane pump is rebuildable, IF the insides of the housing aren't scratched or gouged, and the bushings are still tight-a set of vanes and o-rings and a seal, I seem to remember. You really need to check that pump before you dig too deep into the hydrostats.--What I remembered is trouble we had with the cold-weather bypass poppet in the manifold. There is a plug, spring and poppet in the manifold block, check the poppet for burrs, scratches or a wear ring, anything that keeps it from seating. We were sometimes able to repair the poppet by chucking it up in a drill press and polishing it with emery cloth, but it's good to replace if you can. Anyway, something to check before you pull your hydraulic pump. Tazz is right in all, but a worn hydraulic pump can work OK until the oil reaches operating temperature then have these symptoms. Your problem might be any combination of things. Anyway, check all this stuff, if you're still having trouble, time for hydrostat tests, I guess.
thanks as for the oil brand new I will look at the cold weather bypass and the pump once it stops raining weve had 17 straight days now with 2 to 3 inches expected tonight as is now the ground is so saturated i cant work anyway. I will keep you informed Jeff
 

sterlclan

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thanks as for the oil brand new I will look at the cold weather bypass and the pump once it stops raining weve had 17 straight days now with 2 to 3 inches expected tonight as is now the ground is so saturated i cant work anyway. I will keep you informed Jeff
I am ordering poppets and springs Monday Ill let you know if they help. rain stopped black flies came out oh joy Jeff
 

sterlclan

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I am ordering poppets and springs Monday Ill let you know if they help. rain stopped black flies came out oh joy Jeff
new poppetts and springs not any better and the bucket functions almost seem worse? if my aux pump is bad do I have to get it from bobcat or can I get it somewhere else? any ideas as to cost? any tests I can do to see if that is it? figures it stops raining and the machine dosent want to work oh well Jeff
 

JustAwrench

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new poppetts and springs not any better and the bucket functions almost seem worse? if my aux pump is bad do I have to get it from bobcat or can I get it somewhere else? any ideas as to cost? any tests I can do to see if that is it? figures it stops raining and the machine dosent want to work oh well Jeff
If your hydraulic pimp is the problem, you don't necessarily have to buy it from Bobcat. It has a standard Type 1A mount(I think) but in any case, a dealer can match it. Displacement and rated pressure have to be matched, though. A dealer can look at the plate or embossed numbers and figure that out, and of course fitting ports. The pump is easy to check if you have access to a flowrater, but if not, it's relatively easy to remove, disassemble and inspect it. If the vanes are worn, shaft bushings are loose, or any scratches are inside, it is at least one of your problems, hopefully all.
 

Tazza

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If your hydraulic pimp is the problem, you don't necessarily have to buy it from Bobcat. It has a standard Type 1A mount(I think) but in any case, a dealer can match it. Displacement and rated pressure have to be matched, though. A dealer can look at the plate or embossed numbers and figure that out, and of course fitting ports. The pump is easy to check if you have access to a flowrater, but if not, it's relatively easy to remove, disassemble and inspect it. If the vanes are worn, shaft bushings are loose, or any scratches are inside, it is at least one of your problems, hopefully all.
From what i was told, minor scoring inside the cam ring is ok, as the vanes wear into these grooves. Chatter marks in the cam ring is BAD as when the vane passes over it, it will bounce causing it to by-pass fluid. As JustAwrench said, Vickers pumps can be repaired and parts can be bought for these without any problems. I am assuming your unit has a vane pump attached and not a gear pump, as if it did that changes everything, when gear pumps wear there is very little that you can do, short of replacing the pump. If you pull the pump apart make sure you get new O-rings for it when you re-assemble it. You really don't need oil squirting out of it. One thing you may try, is pulling it apart and making sure all the vanes move freely, none should be stuck as when they spin inertia will make them flick out and contact the cam ring. Hopefully that is your problem, nice and simple if it is. Clean the rotor and clean the vanes so they move freely (i used an oil stone a rubbed the vanes over it to remove rust off a pump once) You must note the orientation of the vanes too, as they will have worn in. Do them one at a time and replace them the same way as you took them out. Hopefully you just have a few stuck vanes, nice and simple. Replace the 2 O-Rings that are on the pump, and the one that is between the hydrostatic pump and the charge pump, you don't need it to leak oil. Sorry for such a long reply but HOPEFULLY this will help you out. Let us know how you go!
 

Outawack

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Nov 20, 2019
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From what i was told, minor scoring inside the cam ring is ok, as the vanes wear into these grooves. Chatter marks in the cam ring is BAD as when the vane passes over it, it will bounce causing it to by-pass fluid. As JustAwrench said, Vickers pumps can be repaired and parts can be bought for these without any problems. I am assuming your unit has a vane pump attached and not a gear pump, as if it did that changes everything, when gear pumps wear there is very little that you can do, short of replacing the pump. If you pull the pump apart make sure you get new O-rings for it when you re-assemble it. You really don't need oil squirting out of it. One thing you may try, is pulling it apart and making sure all the vanes move freely, none should be stuck as when they spin inertia will make them flick out and contact the cam ring. Hopefully that is your problem, nice and simple if it is. Clean the rotor and clean the vanes so they move freely (i used an oil stone a rubbed the vanes over it to remove rust off a pump once) You must note the orientation of the vanes too, as they will have worn in. Do them one at a time and replace them the same way as you took them out. Hopefully you just have a few stuck vanes, nice and simple. Replace the 2 O-Rings that are on the pump, and the one that is between the hydrostatic pump and the charge pump, you don't need it to leak oil. Sorry for such a long reply but HOPEFULLY this will help you out. Let us know how you go!
Driving my early model Clark 631 yesterday, the right side wheels suddenly stopped. last month I got my brand new Eaton Char-lynn 109-1052-004 drive motor that I installed on that same side. not even 10 hours of service.. while waiting for the pump to be shipped I re-sealed everything after the Hydro pump (I'm not very experienced with pumps and it wasn't broken or leaking so I left her alone). , spool valve and the vain pump (if that is what you call the box mounted on top with the copper filter in it) both got fresh new pieces except the sensors that bench tested just fine.. Problems with the retainer clips holding the draw bar have been a issue for some time a block of wood seems to be doing the trick in keeping that in place, Bucket tilts arms go up and down and I can turn left on a dime.. limped it into the shop and let her sit overnight, I thought for sure the drive motor snapped the chain or stripped the gear but everything is in spec. started it up and the right side is working again, put the seat back on and take it for a spin, and now intermittently the right side wont turn Low or full Throttle nothing forward or back everything else works as it should.. after a couple hard shakes on the stick the right side will move for a bit then quit.. I want to send it to a shop for repairs but the old girl is not something my local Tech's are experiences with. I was hoping Tazz or JustAwrench could give their opinion on new shops working on old iron? or better yet maybe they know a video a guy could watch and learn the process for himself?
 
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