Hydraulic problems?????

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vinrum

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I just rebuilt a 1974 Bobcat M970. I ran into a few problems while the project was in process, but thanks to the knowledge of the guys on this website, I was either emailed through them or talked through them on the phone..Now that everything is back together, The motor rebuilt, the gas tank patched, I am having problems with the hydraulics(I think)..Under full throttle, I cant get any pushing power or digging power..I will go into a pile of loam, the motor baugs down, but the tires dont spin, It wont even make it up the 8 inch ledge going into my garage, the machine has no balls..The motor is a Continental 6 cylinder..Any Input would be greatly appreciated.. Thanks Steve
 

Tazza

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This is a hydrostatic unit i suspect? from the specs its a monster!!! 74 HP
Do you happen to have a manual on this machine? does it squeel and does the pump get hot quickly?. The symptoms you describe sound like a cloged suction line filter, these bronze filters are usually hidden in the port block, on top of the hydraulic pump.
Give me a few more details and see what we can work out, i'm sure its something simple as its not affecting just 1 side.
I had the filter problem on an old machine, it had no guts at all, but cleaned the filter and it had heaps of power!!!
 

vinrum

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This is a hydrostatic unit i suspect? from the specs its a monster!!! 74 HP
Do you happen to have a manual on this machine? does it squeel and does the pump get hot quickly?. The symptoms you describe sound like a cloged suction line filter, these bronze filters are usually hidden in the port block, on top of the hydraulic pump.
Give me a few more details and see what we can work out, i'm sure its something simple as its not affecting just 1 side.
I had the filter problem on an old machine, it had no guts at all, but cleaned the filter and it had heaps of power!!!
Tazza, Yes this is a hydrostatic machine .All of the other hydraulics work fine. It has all new fluid, new filter. The left side drive seems to be a little slower than the right, when both controls are all the way forward.. I was looking in my manual for a suction line filter but I had no luck finding one.. I have a diagram for checking the pressure in the pumps, would the filter be where I am suppose to put the pressure gauge?? I have not checked the pumps yet, to see how much pressure there is. Thanks Steve
 

sterlclan

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Tazza, Yes this is a hydrostatic machine .All of the other hydraulics work fine. It has all new fluid, new filter. The left side drive seems to be a little slower than the right, when both controls are all the way forward.. I was looking in my manual for a suction line filter but I had no luck finding one.. I have a diagram for checking the pressure in the pumps, would the filter be where I am suppose to put the pressure gauge?? I have not checked the pumps yet, to see how much pressure there is. Thanks Steve
dont know about yours mine is in the port block it has 3 hoses down one side filter is in the center one behind a fittingyou have to take off the hose in front to get at the center one good luck Jeff
 

Tazza

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dont know about yours mine is in the port block it has 3 hoses down one side filter is in the center one behind a fittingyou have to take off the hose in front to get at the center one good luck Jeff
Also, if you replaced the oil you may still have air in the system that will make it a little funny for a while but this doesn't seem to be the case.
As Jeff said, the filter may be hidden on the port block on the left side where 3 hoses enter, there will be a largeer fitting going into the block, the filter is usually hiding in there. This is assuming your machine has this, i would suspect it does though.
I wouldn't fiddle with the pressure testing just yet, testing at the filter will tell you nothing, it will only tell you the charge pressure. To test the pressure you need restricting valves and gauges to learn anything from the test.
Check for the filter first, it is the most common problem these older machines had with their drive system just because no one knew they were there!!!
 

vinrum

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Also, if you replaced the oil you may still have air in the system that will make it a little funny for a while but this doesn't seem to be the case.
As Jeff said, the filter may be hidden on the port block on the left side where 3 hoses enter, there will be a largeer fitting going into the block, the filter is usually hiding in there. This is assuming your machine has this, i would suspect it does though.
I wouldn't fiddle with the pressure testing just yet, testing at the filter will tell you nothing, it will only tell you the charge pressure. To test the pressure you need restricting valves and gauges to learn anything from the test.
Check for the filter first, it is the most common problem these older machines had with their drive system just because no one knew they were there!!!
Tazza, I am having trouble finding that block on the left side, the only block of hoses that I can see on the left side is for the tilt, lift, and aux hydraulics, Could the Filter be in that block??? Please let me know
 

vinrum

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Tazza, I am having trouble finding that block on the left side, the only block of hoses that I can see on the left side is for the tilt, lift, and aux hydraulics, Could the Filter be in that block??? Please let me know
where did the hoses lead to on your block of 3 ports?? Like I stated earlier, I followed the lines coming out of the Hydraulic tank and checked them, and no sign of a filter, I pulled the filter out of the tank again, I soaked it and blew that out also, but no change in the drive... Thanks Steve
 

Tazza

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where did the hoses lead to on your block of 3 ports?? Like I stated earlier, I followed the lines coming out of the Hydraulic tank and checked them, and no sign of a filter, I pulled the filter out of the tank again, I soaked it and blew that out also, but no change in the drive... Thanks Steve
The filter is not located in the line between the port block and tank.
Does your machine have like a square block on top of the hydraulic pump with about 5 hoses running into it? 3 on one side and say 2 on the front and a pressure switch?
If so, its on the side with the 3 hoses (well it was on mine) it should have a larger head on the fitting that screws into the port block than any of the others have.
If possible take a picture with the cab up, it may assist with telling you where to look.
 

Tazza

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The filter is not located in the line between the port block and tank.
Does your machine have like a square block on top of the hydraulic pump with about 5 hoses running into it? 3 on one side and say 2 on the front and a pressure switch?
If so, its on the side with the 3 hoses (well it was on mine) it should have a larger head on the fitting that screws into the port block than any of the others have.
If possible take a picture with the cab up, it may assist with telling you where to look.
OOH
The block is in the middle, not the left side, the hoses are on the left, sorry for the confusion.
The block on the left is the hydraulic control block, this has nothing to do with your problem. Your problem is purely hydrostatic.
 

vinrum

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OOH
The block is in the middle, not the left side, the hoses are on the left, sorry for the confusion.
The block on the left is the hydraulic control block, this has nothing to do with your problem. Your problem is purely hydrostatic.
Tazza, I have 2 pumps up top where the hand controls connect...Should I be looking for the port block between the 2 pumps?? I was looking in my manual tonight, and it said to check the orfice in the charge pump. Do you think I should try that??
 

vinrum

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Tazza, I have 2 pumps up top where the hand controls connect...Should I be looking for the port block between the 2 pumps?? I was looking in my manual tonight, and it said to check the orfice in the charge pump. Do you think I should try that??
Tazza, should I be looking on the top of the pumps, or down underneath??
 

sterlclan

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Tazza, should I be looking on the top of the pumps, or down underneath??
If yours is like mine on the front of the two back to back pumps is the hydralic pump the port block screws to the top of that pump I belive the hoses go to the drive pumps(charge pressure)the oil cooler and the tank along with returns from the drive motors Jeff
 

Tazza

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If yours is like mine on the front of the two back to back pumps is the hydralic pump the port block screws to the top of that pump I belive the hoses go to the drive pumps(charge pressure)the oil cooler and the tank along with returns from the drive motors Jeff
It should be attached to the top of the hydraulic pump. The hydraulic pump produces charge pressure to feed the hydrostatic pumps.
Have a look at this pic, it should give you a better idea of what you are looking for.
It hides in that big square block on the top of the hydraulic pump behind fitting labeled 10.
Hopefully that will give you an idea.
Sorry if this pic screws the size of all the posts, but it needs to be large or you can't see it.
731%20hydrostatics.jpg
 

vinrum

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It should be attached to the top of the hydraulic pump. The hydraulic pump produces charge pressure to feed the hydrostatic pumps.
Have a look at this pic, it should give you a better idea of what you are looking for.
It hides in that big square block on the top of the hydraulic pump behind fitting labeled 10.
Hopefully that will give you an idea.
Sorry if this pic screws the size of all the posts, but it needs to be large or you can't see it.
Tazza, I got the machine up off the ground...I think I found the blocks that you are talking about...My machine has gear reduction boxes on both sides and attached to them are the drive pumps. and the blocks are located on both sides...Before I jacked the machine up, I put it against a tree, and tried one side at a time, the right side kept spinning, but then I tried the left, and the motor bogged down and the tires wouldnt even spin,,,I am keeping my finger crossed that the screens are clogged...It is just to damn cold out today to be laying on the cement...ha ha ha,....I will keep you posted, and once again I would like to thank you and all the other guys that been giving me input...I would be lost without you guys
Thanks
Steve
 

richie

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Tazza, I got the machine up off the ground...I think I found the blocks that you are talking about...My machine has gear reduction boxes on both sides and attached to them are the drive pumps. and the blocks are located on both sides...Before I jacked the machine up, I put it against a tree, and tried one side at a time, the right side kept spinning, but then I tried the left, and the motor bogged down and the tires wouldnt even spin,,,I am keeping my finger crossed that the screens are clogged...It is just to damn cold out today to be laying on the cement...ha ha ha,....I will keep you posted, and once again I would like to thank you and all the other guys that been giving me input...I would be lost without you guys
Thanks
Steve
Please post your progress! I have the exact same problem with my mustang. I've already had everything apart and read pressures at different points but still don't know whats wrong. My right side drives good and my pump pressure to the motor is approx. 200# should be between 180 and 220. The pressure out of the pump on the left drive is almost 500#,but I don't know why and so far haven't found a good explination. Only a suggestion to take the motor to be checked. Anyway like I said I have the same situation, left side will drive, but has no power. Also the longer it runs the worse it gets. (as the oil warms up) Hope there is some help out there!! Thanks to all you guys trying to help!!!
 

Tazza

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Please post your progress! I have the exact same problem with my mustang. I've already had everything apart and read pressures at different points but still don't know whats wrong. My right side drives good and my pump pressure to the motor is approx. 200# should be between 180 and 220. The pressure out of the pump on the left drive is almost 500#,but I don't know why and so far haven't found a good explination. Only a suggestion to take the motor to be checked. Anyway like I said I have the same situation, left side will drive, but has no power. Also the longer it runs the worse it gets. (as the oil warms up) Hope there is some help out there!! Thanks to all you guys trying to help!!!
It coulds like a case drain filter, see if you can trace the small case drain hose from your hydro motor (the small hose). If it goes through an adaptor or something that a small bronze screen could fit into. If it gets worse with heat i'd be willing to bet its a filter! i had the exact same problem with a 731, cold it worked well, warm it would squeel like a pig and refuse to move under load.
 

richie

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It coulds like a case drain filter, see if you can trace the small case drain hose from your hydro motor (the small hose). If it goes through an adaptor or something that a small bronze screen could fit into. If it gets worse with heat i'd be willing to bet its a filter! i had the exact same problem with a 731, cold it worked well, warm it would squeel like a pig and refuse to move under load.
I had the case drainline apart that comes from the side im having problems with, I didn't see anywhere there could be a filter or screen. After it leaves the left side pump it goes into a tee where the right side pump ties in. This would be the only other place for something like a filter. I'll have to do some work to get to it, but I'll check at the tee. Thanks! What you say makes good sense, I only hope it's that easy!!
 

vinrum

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I had the case drainline apart that comes from the side im having problems with, I didn't see anywhere there could be a filter or screen. After it leaves the left side pump it goes into a tee where the right side pump ties in. This would be the only other place for something like a filter. I'll have to do some work to get to it, but I'll check at the tee. Thanks! What you say makes good sense, I only hope it's that easy!!
Hey guys, I havent forgot to post my progress, There hasnt been any..ha ha ha..I will get back to it this weekend, and post the results..

steve
 

vinrum

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Hey guys, I havent forgot to post my progress, There hasnt been any..ha ha ha..I will get back to it this weekend, and post the results..

steve
Well, I finally tackled the project today, I needed a little time away from it.. I took the blocks of the drive motors, and I didnt find any screens, just a few relief valves. with 2 small hoses going into it..Anyway I took it all apart, and soaked it for a while, Put it back together, It is better then it was, but I am still stumped about the screen..I followed the two hoses back, and they go to a valve to let the hydraulics freewheel. Please let me know if you have any other Ideas
 
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