Bobcat 743 testing lift/curl hydraulic pump

[ozark18]

I tested my pressure at the aux port and it's only about 1500 lbs. I changed the relief valve with no affect. Also have down drift lifting the bucket, curl OK. I'm trying to determine if the pump is bad or the control block. My question; can I test the pressure directly at the pump where the hose goes to the control valve without doing any damage. I haven't put new seals in the control block yet. Some on the forum say that won't affect pressure but would probably fix down drift.

 

[Bswwood]

You can test the pump itself, ideally you would want a flow control valve to do this, however I understand not everybody has access to these tools. The method I'm about to describe can be dangerous if the pump is in good condition. You will not have a relief valve in line. You have already tested pressure at the auxiliary port and ruled out the main relief so it definitely sounds like your pump is bad. Pull the main pump hose off the valve body, using adapters make tee fitting to hook on to the main pump hose, a gauge in one side, a ball valve on the other side and a hose returning to tank. Just remove the cap off the hydraulic tank and drop the hose in it. With the ball valve open start the machine and slowly close the ball valve and see if you make more than the 1500 PSI you are getting at the auxiliary port. Again you have to be very careful because if you close the ball valve all the way something is going to give somewhere. If your pump is low-flow / low pressure then you could probably close the ball valve all the way without killing the engine. Again it's not recommended to do it this way but it is possible. Used hydraulic fittings and a steel ball valve not brass. However if you use brass I guess that could be the relief valve LOL.

 

[ozark18]

You can test the pump itself, ideally you would want a flow control valve to do this, however I understand not everybody has access to these tools. The method I'm about to describe can be dangerous if the pump is in good condition. You will not have a relief valve in line. You have already tested pressure at the auxiliary port and ruled out the main relief so it definitely sounds like your pump is bad. Pull the main pump hose off the valve body, using adapters make tee fitting to hook on to the main pump hose, a gauge in one side, a ball valve on the other side and a hose returning to tank. Just remove the cap off the hydraulic tank and drop the hose in it. With the ball valve open start the machine and slowly close the ball valve and see if you make more than the 1500 PSI you are getting at the auxiliary port. Again you have to be very careful because if you close the ball valve all the way something is going to give somewhere. If your pump is low-flow / low pressure then you could probably close the ball valve all the way without killing the engine. Again it's not recommended to do it this way but it is possible. Used hydraulic fittings and a steel ball valve not brass. However if you use brass I guess that could be the relief valve LOL.

Thanks for the reply. I'll give it a try this weekend. Have to get some fittings together. Seems like a relatively safe way to do it. Can these pumps be rebuilt or just have to replace them?

 

[Bswwood]

Thanks for the reply. I'll give it a try this weekend. Have to get some fittings together. Seems like a relatively safe way to do it. Can these pumps be rebuilt or just have to replace them?

Depends on the damage, personally I just replace

 

[ozark18]

Depends on the damage, personally I just replace

I found a guy locally that says he can rebuild/reseal the pump. I'll see what he says. Looks like a new one is about $600.00.

 

[Tazza]

I found a guy locally that says he can rebuild/reseal the pump. I'll see what he says. Looks like a new one is about $600.00.

The hydraulic pump has a cartridge that can be replaced, talk to loader parts source, see if they can do better than 600. All you need is the cartridge and the outer housing, they are the main parts that wear.

 

[ozark18]

The hydraulic pump has a cartridge that can be replaced, talk to loader parts source, see if they can do better than 600. All you need is the cartridge and the outer housing, they are the main parts that wear.

Got pump back today. They said it was in good condition. Checked out and new seals for $120.00. I'll try to install it tomorrow. Apparently it's a vane type pump.

 

[ozark18]

Got pump back today. They said it was in good condition. Checked out and new seals for $120.00. I'll try to install it tomorrow. Apparently it's a vane type pump.

Got my "rebuilt" pump installed. Having trouble getting it primed. Manual says to operate controls and run engine at low and high speeds. Still no lift or curl. Plenty of fluid. How long do you have to run it before it pumps? Do I need to bleed lines?

 

[Tazza]

Got my "rebuilt" pump installed. Having trouble getting it primed. Manual says to operate controls and run engine at low and high speeds. Still no lift or curl. Plenty of fluid. How long do you have to run it before it pumps? Do I need to bleed lines?

No need to bleed really, the way i primed my pump was with the engine off, operate the lift pedals and extend the cylinders, it pulls fluid through the pumps.
These pumps don't really need priming as the reserve tank is higher than the pump, so gravity helps.