My 463 has been doing it for several winters off and on. More regular this year. Its only used for snow removal using a bucket, blade or blower. When it started doing it, it was only after it was good and warm. Usually not as bad using the auxil. hydraulics. Now when its cold. Haven't seen any function loss except maybe alittle weak on the tilt side of operation. No leaks. Tilt will settle some overnight. Not too bad though. Fluid and filter changed regulary. Sounks like pressure is by-passing or maybe cavitating?? Will check valve to pedal adjustments tmw. Anyone point me to a forum regarding this issue? Any ideas or thoughts. Thanks, Steve
Hydraulic Hiss or Buzz
- Thread starter skayser2
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skidsteer.ca
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If I recall corectly there was a 750 something Bobcat doing this a while back and I think in the end it turned out to be the charge pressure relief valve. Usually this is located near the hydraulic filter. Its job is to restrict the oil returning to the tank from the gear pump until it has created 150 psi(or whatever your charge pressure should be) of back pressure in the return line then dump the oil to the tank.
This charge pressure is necessary to supply oil to the hydrastatic pumps, and doing it on the return line fron the hydraulic gear pump allows them to get 2 pumps in 1 so to speak.
Ken
Thanks for the input. Been thrashing over the hydraulic schematic for several days now and trying to recreate how and when the buzzing starts. I see the charge pressure valve and understand how it's suppose to work. Should I see one side or both operating erratically when the charge pressure is low? If so, I'm not really seeing that. I have noticed that the tilt (rod end side) seems to be alittle weak and sometimes looses "hold" if I'd angle the blade at the same time. Lift seems to be okay. It's a small machine as you know, and I work it pretty hard, even with just snow removal. I've never seen the hydraulic temp light come on but wondering if it just can't cool the hydraulic oil fast enough. I'm either running the blower or the angle blade. The blade is out there a ways so there's some weight there on both those units, 300-350lbs. I usually run the engine about 3/4 throttle. Maybe higher than normal temp combined with the tilt hold leaking by?? I did find the auxillary hydraulics cable mount bolt loose but that valve has a detent so I'm thinking that has little to do with it. I"ll check the temp sending unit next and make sure it's working. How about the cooler by-pass valve? Guess it opens at 625psi to by-pass the cooler. Ever heard of problems with it? If all else fails it'll have to go to the dealer for pressure checks. Thanks again!!
Checked the temp and charge pressure switches. Lights come on when the switch wires are grounded. Dosen't verify the switches are completely working correctly but assures the lights work though the connections. Picked up a gauge and will verify charge pressure next. Charge relief should be at least 85psi according to my manual and the charge switch 17-21psi. The tilt does leak more than it should. With the 350lb blower tilted up it will settle to the ground in a few hours. In your opinion, load check valve or spool valve problem? Or both? Cylinder internal leak is also a possibility I suppose. Also noticed more so lately, that the auxil. couplers are harder to hook up, with the machine running or not. Seems the lines are pressurized. Moving the lever either direction dosen't seem to help. A small amount of oil will leak from the female coupler (machine side) eventually allowing hookup. Seems like alot going on here that maybe contribute to the system "buzzing". Another thing, Ha, the machine dosen't need to be moving for the "buzz" to continue. Hopefully that will help rule out insufficent charge pressure. Any thoughts on any of this stuff? Thanks, Steve
Plan to start checking valves and spools soon. Started making a slight "clicking" noise, very seldom from the right side. Possibly right drive motor or maybe the belt tensioner pulley?? Can anyone direct me toward a cheap (plastic) cap and plug kit? Hate to be a PITA. Thanks
I read somewhere here that one could replace the hydraulic oil with motor oil? Am I correct? I posted earlier that I get a hissing in the system after I work it awhile and it's good and hot. It all works fine but the hissing gets pretty annoying and could be causing future damage? Wondering if the hydraulic oil is just losing vicosity and it's ability to work efficiently once it get too hot. I pulled the cooler and fan and cleaned them this summer. Checked the charge preasure and it appears to be fine also. I mainly use a snow blower and angle plow. I change the hydraulic oil and filter once every other year. Only 700 hrs on the unit (463). Thanks, Steve
The hydraulic oil they run is about the weight of engine oil. Some people swear by the stuff you get from the dealer, i run standard engine oil. I have never had an issue with it.
The hiss/buzz i don't know if it would be from the oil or not. Does it do this when there is no load? like standing still, sticks in neutral?
Tazza, it dosen't start buzzing until it's good and warm. I use it for snow only so everything is happening pretty fast and furrious. After it starts buzzing it usually doesn't stop until I drop it back to idle and then once in awhile for a short periods. Let it set awhile as if to cool down and it's okay for awhile again. I usually run about 3/4 throttle but the higher it goes the worse it is. What weight engine oil do you use? I plan on trying it this winter and see what happens. It's only 10 or so gallons per minute so maybe I'm just over working it and exspecting too much from such a small machine. Thanks, Steve
As you are in the snow, you don't want oil that's too thick as it goes like honey when really cold. Ken may be a better person to give advise on this as he is in Canada, so he would have a far better idea of what grade oil would be best. I live in Australia, it never gets below freezing.
The buzz is weird, its almost like a cold weather by-pass valve. I had bought a used machine that howled like this. It was oil going over the cold weather by-pass valve because they installed the wrong hydraulic pump. When its working right, and when the oil is cold and thick, it goes over this valve to allow oil still to move while it warms up. Yours seems to be working the oposite way, very odd.
Okay, after about eight years and 750 hrs of occasional "buzzing and hissing" coming from the hydraulic system after warm up and rapid use, we might have it solved it, or at least for the time being. Only use the unit (463) for snow removal and change the hydraulic oil and filter every second year. Engine oil at the end of the season. Always followed the maintence manual instructions. After refilling after a fluid change......manual says "Stop engine and check the hydraulic fluid level at the dipstick and fill to the full mark on the dipstick". This is always how I checked it in between changes. This last time, I just happened to check the level with the engine running.......didn't even show on the stick. Added a full quart or better to get it to the full mark on the stick. Was afraid it would run out the tube when shut down but nothing yet. Used it all day yesterday without any unusual sounds like cavitation or starving (hissing and buzzing). I always checked it with the engine off before but will be sure and check it running from now on. Makes sense as you check you truck trans fluid when it's running. Anyway, thanks for all your ideas and insight. Anybody run across this issue before? Thanks, Steve
Took a few measurements today of the hydraulic tank and fill tube. Top of the dipstick tube is 20 1/2" from the floor. Top inside of the hydraulic tank is 22 1/2" from the floor. The tank is 12" deep and not uniform in shape I'm sure. The factory "full" mark on the stick is 16" off the floor. I'm sure they allow for thermo expansion by not completely filling the tank. Anyway, added another mark 1 3/8" above the factory full mark as thats how far the low mark is from the full mark. Also have noticed lately that when the lift arms are high, the bucket tip-up takes awhile to work and weak, until I lower the arms anyway. Out of fluid when it's that high?? Hope the pumps not damaged. Not sure if thats something new or not. Will use it awhile and watch it. Thanks, Steve
