453F Air in Hydraulic system UPDATE

[OldMachinist]

Just thought I'd post an update to the problem I was having with cavitation.
http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=3027
I removed the engine and almost all of the hydraulics except for the steel lines to the lift, tilt and aux. fittings. It is so much easier to work on with the engine out and the way it's designed it comes out pretty easy with the hydrostatic and hydraulic pumps attached.
I didn't find anything that made me think I had found the problem. All the orings where there and in good shape. The fittings where all tight. Removed and cleaned all the poppets and check valves. Flushed out the oil cooler and hydraulic tank. I didn't do anything to the hydraulic valve but remove and clean it externally and replace the vinyl caps over the detents.
The hydraulic pump seemed to turn a little free by hand so I put the seal kit in it and I needed pliers to turn it after that.
I reassembled it all with all new orings, fresh oil and three new hoses that required the engine out to change.
When I fired it up it was fixed.
Now if I had to guess what cured it I would say the seal kit for the pump. So even though it was putting out enough pressure the flow may have not been enough. I would recommend anyone with similar problems to have a pressure and flow test done at the dealer.
All together the parts and oil were only $163. I worked about 25 hours on it and that included cleaning 6 years of gunk under and behind everything.

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[Tazza]

EXCELLENT!!!
I'm glad you managed to get it all sorted out, i guess it could have been pulling in air through the plates of the pump which was fixed with new O rings. Glad you took the time to replace the rubber boots on the control block, it keeps the gunk out of them that will cause wear. Cleaning all the caked on grease and dirt was a good move too, with the engine out it makes it ALOT easier to clean it all out.

 

[skidsteer.ca]

EXCELLENT!!!
I'm glad you managed to get it all sorted out, i guess it could have been pulling in air through the plates of the pump which was fixed with new O rings. Glad you took the time to replace the rubber boots on the control block, it keeps the gunk out of them that will cause wear. Cleaning all the caked on grease and dirt was a good move too, with the engine out it makes it ALOT easier to clean it all out.

Thanks for the update, good to know what worked and where to check.
How many hours are on your machine?
Ken

 

[OldMachinist]

Thanks for the update, good to know what worked and where to check.
How many hours are on your machine?
Ken

The machine has a little over 1700 hrs. on it. I bought it from a rental company and it had a few other problems that they couldn't figure out also. It had one wheel hub that kept coming loose and I found that the hole in the axle hadn't been tapped deep enough from the factory. One foot pedal would jam up sometimes and found that to be someone used the wrong hardware to hook the pedal to the seat bar interlock. But the cavitation was only a minor problem when I got it and it just kept getting worse.
I should note that what Bobcat calls the seal kit for this hydraulic pump I would call a rebuild kit. It contains a new wear plate, diaphragm, gasket, seal, check ball and spring. So you replace every thing except the gears and bushings in the pump. Also the service manual says you can service the pump without removing the engine. I wouldn't recommend doing it that way but it says you can do it.
Don

 

[hmw]

The machine has a little over 1700 hrs. on it. I bought it from a rental company and it had a few other problems that they couldn't figure out also. It had one wheel hub that kept coming loose and I found that the hole in the axle hadn't been tapped deep enough from the factory. One foot pedal would jam up sometimes and found that to be someone used the wrong hardware to hook the pedal to the seat bar interlock. But the cavitation was only a minor problem when I got it and it just kept getting worse.
I should note that what Bobcat calls the seal kit for this hydraulic pump I would call a rebuild kit. It contains a new wear plate, diaphragm, gasket, seal, check ball and spring. So you replace every thing except the gears and bushings in the pump. Also the service manual says you can service the pump without removing the engine. I wouldn't recommend doing it that way but it says you can do it.
Don

Hi, new to this forum. Recently bought a 440b with the same symptoms you mentioned. I recently "re-hosed " this machine for a customer. About 3 months later the engine blew up and I bought it from the customer. I am a hydraulic and equip technician for a local electric utility co and i work on all kinds of aerial devices and hydraulic equipment[ bucket trucks, trenchers etc]. I have worked on this machine several times on different repairs including fabricating a new bucket for it and noticed the hyd system jumpy. Of course the customer is not willing to pay to have it diagnost so on it went. Now that i have it and the engine is out [I have a new "v" Kohler to go back] I was thinking about the cavitation problem and had pretty much decided it had to be the pump. On this model the oil tank is below the pump which with any kind of "suction" problem makes it worse. After reading your article I think i will overhaul the pump before installing the new engine. The previous owner said it had been "jumpy" ever since he had it. He bought it used. Its a 95 yr model. It only takes a pump being run low on oil, especially one that has to "draw" its oil, one time to damage plates and or seals. so thanks for the post and I'll let you know how i make out. I still have to fab a new muffler for the new Kohler and then I'll pull the pump out. thanks again