743 Hydraulics

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Wis XM

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Apr 27, 2007
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New poster here. I have a early model 743. The Hyd. warning light comes on after 20-30 minutes of running if I have the throttle higher than half-speed. I think it is because of temperature and not pressure because it is not intermittent. It will only go off if I reduce throttle or shut the engine down and wait a while. If I work at less than half throttle, I can go for an hour or more without the light coming on. Engine temp seems fine and doesn't get much over 150 on the gauge. I had the motor replaced last year and the radiator checked at the same time. I just had the unit into the shop because of cavitation and they replaced the hydostatic pump, checked all the seals, etc but found no source for the air in the system. I did not have this problem before it went in. I have checked hyd. oil level (has the two petcocks on side of resevoir) & replaced the filter. The hyd hoses feel very hot but I don't know what is normal. Any ideas on what to check next would be greatly appreciated.
 

Tazza

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When the cab is in the air, what do you see on the hydraulic pump (the one rite at the front)? do you see a square block sitting on top with 5 hoses connected or is there a large hose that runs to a block near the throttle lever?
Did you check the oil cooler? if its gunked up that could cause excessive heat.
What oil are you running? it may be thinning out a little too much with heat.
Let me know and we can work from there.
 

Wis XM

New member
Joined
Apr 27, 2007
Messages
4
When the cab is in the air, what do you see on the hydraulic pump (the one rite at the front)? do you see a square block sitting on top with 5 hoses connected or is there a large hose that runs to a block near the throttle lever?
Did you check the oil cooler? if its gunked up that could cause excessive heat.
What oil are you running? it may be thinning out a little too much with heat.
Let me know and we can work from there.
I see a block that has 5 hoses connected to it. 3 on one side, a larger one going back and 1 coming off the front and going down. THe front one is right beside a sender unit. I did not check the oil cooler. Where is it? I'm running Bobcat brand hydraulic oil and I think they would have replaced a fair amount when they replaced theypump. My earlier post said they replaced the hydrostatic pump but it must have been the hydraulic pump. I can see the new one below the block with the 5 hoses.
 

Tazza

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I see a block that has 5 hoses connected to it. 3 on one side, a larger one going back and 1 coming off the front and going down. THe front one is right beside a sender unit. I did not check the oil cooler. Where is it? I'm running Bobcat brand hydraulic oil and I think they would have replaced a fair amount when they replaced theypump. My earlier post said they replaced the hydrostatic pump but it must have been the hydraulic pump. I can see the new one below the block with the 5 hoses.
Excellent, i'm pretty sure i know what your problem is. The oil cooler is in the back, under the radiator. If you remove the steel covers behind the exhaust flexible tube you will see it and the bottom of the radiator.
Now, with the cab in the air, the left side of the block on the pump. Its best to have a helper here that can use a finger or 2 to plug the hoses if you don't have plugs. You won't loose a lot of oil, but it helps if you have another person to help out.
You need to remove the middle hose and fitting on the left side. To do this, you will need to remove the front hose to gain access to be able to un-do the fitting in the middle. First remove the front and middle hoses, then un-do the fitting in the middle, it will have a larger head than the other 2. Behind here is a spring and a bronze filter. Remove the spring and use pointy nose pliers to pull the bronze filter out. Give it a good clean out with kero or diesel and blow down with air, you can then re-install it. There is a good chance it has never been cleaned!!! Almost no one knows there is a filter hidden in there. This filter is on your charge pressure line, so when the filter is clogged the oil can't get back to the pump fast enough. Usually it works well when cold, but as it warms up it looses power and makes a lot of noise.
Re-install the hoses and you should be set. If not, you may need a new filter.
 

Wis XM

New member
Joined
Apr 27, 2007
Messages
4
Excellent, i'm pretty sure i know what your problem is. The oil cooler is in the back, under the radiator. If you remove the steel covers behind the exhaust flexible tube you will see it and the bottom of the radiator.
Now, with the cab in the air, the left side of the block on the pump. Its best to have a helper here that can use a finger or 2 to plug the hoses if you don't have plugs. You won't loose a lot of oil, but it helps if you have another person to help out.
You need to remove the middle hose and fitting on the left side. To do this, you will need to remove the front hose to gain access to be able to un-do the fitting in the middle. First remove the front and middle hoses, then un-do the fitting in the middle, it will have a larger head than the other 2. Behind here is a spring and a bronze filter. Remove the spring and use pointy nose pliers to pull the bronze filter out. Give it a good clean out with kero or diesel and blow down with air, you can then re-install it. There is a good chance it has never been cleaned!!! Almost no one knows there is a filter hidden in there. This filter is on your charge pressure line, so when the filter is clogged the oil can't get back to the pump fast enough. Usually it works well when cold, but as it warms up it looses power and makes a lot of noise.
Re-install the hoses and you should be set. If not, you may need a new filter.
Thanks! The hyd oil cooler looked pretty clean. It will be a couple days before I get the chance to replace the bronze filter in the block. I'll let you know how it goes.
 

Wis XM

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Joined
Apr 27, 2007
Messages
4
Thanks! The hyd oil cooler looked pretty clean. It will be a couple days before I get the chance to replace the bronze filter in the block. I'll let you know how it goes.
I pulled the bronze filter and it looked pretty clean. There was some larger sediment trapped and since I had purchased a new one, I went ahead and replaced it. I had the same problem afterwards so I pulled the temperature sensor and put in one that controls a temperature gauge I mounted in the cab. So far the temperature has not gotten over 130F so it looks to have been a bad sensor. The gauge will give me a lot more confidence that I'm not damaging the pump. Thanks for all of your help Tazza!
 
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