Some of the sounds you may be here is made ventilation or by the formation of an empty space that is within a solid object. When the ventilation or aerating happens it contaminates your hydraulic fluid. The sound it makes is like banging noise that compresses and decompresses when it radiates around in the unit. When you have air in your reservoir tank it will look like it has foam on top and seem kind of bubbly. You may need to start looking for air coming maybe in an inlet port, hose or an intake line. If you have fittings or clamps, make sure to see if it taking in air. May just need tightening up.

Hoses may be the culprit, if so check for wear and tear like thinning, aging and cracks. If that is the case, simply replacing it may fix your problem. Another source may be your reservoir itself if the fluid is too low, creates like a whirlwind in there, just fill it up back the proper level. Another place you may want to check for leaking in air or for leaks of any kind is your shaft seal. If the seal is broken, it will need to have a new one put on.

Sealing off can prevent you problems down the road with your fluid in system, components, wearing out your seals not having the proper grease which could cause you to overheat. Sometimes manufactures of reservoirs put in safety precautions like an alarm to your dash board to let you know your level is to low, especially if your machine is going up high inclines a lot.

When you have the empty space within the solid object going on that is where the amount of fluid you have is being used up quicker than you can supply it. This takes place because the complete pressure in any part of the circuit to go down, in turn the condensation pressure of the fluid. And it will buckle in from the compression and cause some knocking.

This type of problem can cause the metal to erode, which flakes off and gets into your fluid and your parts. And if you don’t pay attention to these noises soon enough it will cause major damage to your pump or motor which in turn will shut you down. That will delay your task at hand.

So at the first sign of hearing a noise, investigate it out and not let it go for long periods of times. Don’t think it will just run a little longer. Having debris in your lines or your pump will just tear it up and cost you major time and money to repair it. It does not take much to tear up a seal, hose, tear pistons or mess up plates within your system due to contamination from aeration or cavitation.

If you need more info on this subject, call us at 800-361-0068 or email us at

sales@hydrostatic-transmission.com