An older 743 Hyrdaulic Pump issue

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dirtbiker245

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Sep 3, 2007
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Well, im tearing into my dads old bobcat. He used to use it for construction jobs and it unexpectedly quit on him one day about 8 years ago. The engine was running, but it wouldnt move. Anyways, he got the thing home and off the trailer. He figured the pump went out so he tore into that. Once he got it all apart he realized that there was nothing wrong with the pump. Then he looked into the book more and round out about the U joint behind the engine, pulled the engine, fixed the u-joint and got that all back together. All during this, the hyrdaulic pump was sitting in a bucket fully dissasembled. Well, he got busy with work and the pump sat in the rain for about 4 years and got completely wrecked. I bought a new pump and have fully cleaned out the port block with kerosene, then dipped it in a bucket of hot water to remove the kerosene, then air blew out all the ports with a compressor. I also cleaned up all the other parts that had been removed this way. I bought a complete new/rebuilt hydraulic pump so I dont have to worry about there being a rust spot in the old one or whatnot. Im about to re-assemble it but just wanted to ask if there is anything I should do before putting it back together... I have alot of mechanical experience, however hydraulics are new to me and I know that they have to be very precise and I dont want to screw something up. Thanks
 

Tazza

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The only thing i would do would be get as much oil out of the system as possible. Without a pump i'm sure most has leaked out.
I would remove the large hoses from the motors and run say diesel and compressed air through them to get any much that may have entered. It wouldn't hurt when the hoses are off to push the machine a bit or jack it up and turn the tyres to get as much oil out as you can.
With the pump out, check your axle seals, are they wet at all? if so now is a good time to replace them and even replace the chain case oil while the pump is out as you have more access. If you just want it working again, skip this bit but i'd clean out the hoses and motors as i said earlier just to be sure.
Top up the tank and replace the hydro filter and you should be set.
Now, the port block, does it sit on the pump or has it got a hose that joins to the port block? if it has a hose its all good, but if there is a square block on the pump ensure the filter inside it is clean or even replaced.
Now, when its all hooked up it may take a bit to get the oil to start to flow. I started the machine for a few seconds then turned it off. I did that a few times till it got fluid through, not too long or you risk damaging the pump from lack of fluid. You could even hang the pump up and pour oil in directly from the charge port or the hydro pump. I did all this when my system was bone dry, pump out, all lines and cylinders out, oil cooler, the whole lot was empty. When you first start it, make sure its blocked and the wheels can turn.
The main thing with hydraulics is keep it super clean. Use engine oil in your machine NOT hydraulic oil.
Any other questions just yell, unfortunately i know 743's inside out...... Many hours work in repairing mine, but totally worth it! great little machine thats easy to work on.
 

dirtbiker245

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Joined
Sep 3, 2007
Messages
31
The only thing i would do would be get as much oil out of the system as possible. Without a pump i'm sure most has leaked out.
I would remove the large hoses from the motors and run say diesel and compressed air through them to get any much that may have entered. It wouldn't hurt when the hoses are off to push the machine a bit or jack it up and turn the tyres to get as much oil out as you can.
With the pump out, check your axle seals, are they wet at all? if so now is a good time to replace them and even replace the chain case oil while the pump is out as you have more access. If you just want it working again, skip this bit but i'd clean out the hoses and motors as i said earlier just to be sure.
Top up the tank and replace the hydro filter and you should be set.
Now, the port block, does it sit on the pump or has it got a hose that joins to the port block? if it has a hose its all good, but if there is a square block on the pump ensure the filter inside it is clean or even replaced.
Now, when its all hooked up it may take a bit to get the oil to start to flow. I started the machine for a few seconds then turned it off. I did that a few times till it got fluid through, not too long or you risk damaging the pump from lack of fluid. You could even hang the pump up and pour oil in directly from the charge port or the hydro pump. I did all this when my system was bone dry, pump out, all lines and cylinders out, oil cooler, the whole lot was empty. When you first start it, make sure its blocked and the wheels can turn.
The main thing with hydraulics is keep it super clean. Use engine oil in your machine NOT hydraulic oil.
Any other questions just yell, unfortunately i know 743's inside out...... Many hours work in repairing mine, but totally worth it! great little machine thats easy to work on.
The port block sits on the pump and I pulled out the filter It looks fairly good, but I think im gonna get a new one just because since ive got it all apart anyways. Im also planning on replacing all hoses while ive got it apart cause I dont want one of them blowing out. I noticed some slight cracks in the rubber on the hoses and even though im sure it was just the outer layer of the hose, I want to replace them all just to be safe. Im planning on using the bobcat for some digging and grading of the garage im building in my back yard, but once Im done with that, its going out to a job site of my dads where it will be run 8 hours a day, 6 days a week so I need to make it as reliable as possible. You said use engine oil instead of hydraulic oil... Could you explain that a bit? I didnt have a chance to talk to my dad about it cause hes been working, however I do see that hes bought the big bottles of bobcat hydraulic fluid.... so... yeah... Let me know. Thanks.
 

Tazza

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The port block sits on the pump and I pulled out the filter It looks fairly good, but I think im gonna get a new one just because since ive got it all apart anyways. Im also planning on replacing all hoses while ive got it apart cause I dont want one of them blowing out. I noticed some slight cracks in the rubber on the hoses and even though im sure it was just the outer layer of the hose, I want to replace them all just to be safe. Im planning on using the bobcat for some digging and grading of the garage im building in my back yard, but once Im done with that, its going out to a job site of my dads where it will be run 8 hours a day, 6 days a week so I need to make it as reliable as possible. You said use engine oil instead of hydraulic oil... Could you explain that a bit? I didnt have a chance to talk to my dad about it cause hes been working, however I do see that hes bought the big bottles of bobcat hydraulic fluid.... so... yeah... Let me know. Thanks.
Well if he has bought Bobcat hydraulic oil it will be rite. These systems run engine grade oil not hydraulic fluid. 10W30 to say 20W50 is ideal. The Bobcat oil is still the same grade as engine oil but it has Bobcats sticker on it. Hydraulic oil is too thin to keep the parts lubricated when the machine gets warm.
You are correct in replacing the hoses if they are cracked. Even though its the outer thats cracked it can cause leaks. Just get a hydraulic shop to make the hoses, they are cheaper than buying genuine hoses.
The filter should be cheap, but if it was dirty you would see that! mine had bieces of all sorts stuck in it. A quick clean and it was running perfect!
If its going to get a bit of use, i really do advise that you check your axle seals. At the very least i'd change the chain case oil (this will also take engine oil).
Any other questions just let me know, i know my 743 in and out
 

dirtbiker245

Active member
Joined
Sep 3, 2007
Messages
31
Well if he has bought Bobcat hydraulic oil it will be rite. These systems run engine grade oil not hydraulic fluid. 10W30 to say 20W50 is ideal. The Bobcat oil is still the same grade as engine oil but it has Bobcats sticker on it. Hydraulic oil is too thin to keep the parts lubricated when the machine gets warm.
You are correct in replacing the hoses if they are cracked. Even though its the outer thats cracked it can cause leaks. Just get a hydraulic shop to make the hoses, they are cheaper than buying genuine hoses.
The filter should be cheap, but if it was dirty you would see that! mine had bieces of all sorts stuck in it. A quick clean and it was running perfect!
If its going to get a bit of use, i really do advise that you check your axle seals. At the very least i'd change the chain case oil (this will also take engine oil).
Any other questions just let me know, i know my 743 in and out
Alright, well thats good to know. I'll run that by my dad. No use in getting ripped off by the bobcat dealer anymore when it takes standard oil. Im gonna check the axle seals and possibly change them anyways. Everything is completely dry cause its been sitting for 4 years... so I wouldnt be able to tell if its leaking or not. And I am gonna change the chain case oil. Thanks so much for your help so far. Im sure i'll be back on here needing more help sometime soon. lol.
 
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