I have a 1982 Bobcat/Melroe 843 with the Perkins diesel. I started having trouble last weekend with the hydraulics - lifting the bucket became real jerky, and the it also only wanted to drive one side of the machine or the other. It acted like it was starving for fluid. I checked the fluid and it was milky white which I found out means water in the fluid. Well, I have it in a heated shop (65 degrees) and have drained and filled the hydraulic reservoir three times now. (running the machine for 10 minutes or so in between each drain cycle) The fluid coming out now is not milky white anymore, but it is frothy, like it has air bubbles in it. They settle out after awhile, but I'm wondering if in addition to having water in the line, I also have an air leak which is causing the pump to suck air causing some cavitation?? I have changed the main hydraulic fluid filter, but there is a 40 micron brass filter on the side of the pump that I bought also. The problem is, I can't get the nut/fitting off the side of the pump to change that filter. It was 3/4 stripped from the previous owner, and now it's almost completely stripped with me trying to get it off of there. I noticed in the basic manual that I have, that there is also a hydraulic oil cooler in this machine. I don't even know where it's at, but I wonder if that might also be casuing the air leak? I'm not sure if it's a liquid cooled heat exchanging type of cooler or what, but at this point I'm not sure what area to focus my attention on to find out what's going on. After these fluid changes, the system seems to be driving better, but I still have a quite noticeable jerking action when raising the bucket and frothiness in the reservoir Any advice greatly appreciated. Thanks - Justin
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OldMachinist
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If you don't have a leak on the suction side of the hydraulics the air will bleed out and things will get smoother. Try driving it at half throttle while lifting and tilting the bucket without hitting the travel limits then letting it sit for a few hours or overnight to let the air settle out. Repeat if needed. Since it seems to drive okay the brass filter maybe okay but you should still try to get it changed at some point.
As OM has already stated, drive it around to get the air out, run for a little bit them leave for a hew hours, of not over night.
The oil cooler will be under the radiator, you will need to remove inspection covers to see it. Small amounts of air can enter areas where hoses or cylinder are leaking fluid, but you probably just got air in when you replaced the oil and filters. Run it, time should get it all out.
Thanks for the replies guys...I'll be working on it again in a few days, and I'll see how it goes.