I have been having a problem with my cat 248 skid steer that I have not been able to fix. Starting a few months ago sometimes when you start the skid steer up it will make a rapping noise from the piston hydraulic pump for the loader controls and high flow. I figured I had hole in my suction line between the tank and the pump so I tipped the cab up and inspected / changed the pieces of rubber in the suction line and figured that would solve it. It was better for a bit and then went right back to it and seemed worse. When it first happened it was only when I first started the machine, as it got worse it would do it if I shut off the machine for 2 minutes sometimes. This confused me even more since it has a pressurized tank even if there was a hole in the suction line it would leak oil not let air in since 2 minutes would not be nearly long enough for the tank to cool down and depressurize. At this point I was getting pretty confused so I called the local hydraulic pump rebuilders who are very well respected and asked them what they thought and the guy I spoke to was sure it had to be the suction pipe inside the tank since if the hole was above the oil level but inside the tank it could still put and air bubble in the suction line while the tank was pressurized. I thought this was a good possibility so I over filled the hydraulic tank and parked the machine leaning pretty hard to the side where the suction line leaves so that I knew the entire suction pipe inside the tank was under oil and left it for the night, in the morning it rapped worse then ever. At this point I am at a complete loss as to what would be causing the problem. The only thing I have figured out which also makes no sense at all to me is that if I part the machine with the bucket up hill it will never rap when I start it back up. When I can finally figure this out I am going to take the pump out and have my pump rebuilders check it out because I know how bad for piston pumps it is to suck air but I would really like to figure out what is causing it first so that I don't ruin a freshly rebuilt pump. I was just curious if any of the cat experts or hydraulic experts have come across anything like this, thanks in advance.
Checked a couple serial numbers, all show first off a breather for the hyd tank and second a suction strainer which needs checking. Also overfilling the tank can cause problems due to lack of sufficient air space. The noise you hear may be the pumps inability to suck oil, rather than air entering the system. Just for giggles try it with the hyd tank filler cap loose or off, see if that changes anything?
Thanks for your reply. The strainer is clean, I had it out of the tanks when I was changing suction hoses. I would certainly be interested in checking the breather but I could not find one anywhere on the tank. Where is it?
Also here is my serial number if that helps. 6LZ00920
Early serial number..... Doesn't show exactly but there is an elbow and hose off the top of the tank: The hose runs down to the bottom somewhere, not sure if it connects to something or has a breather, or an overflow?
I have seen that and it has been confusing me for some time because the hose goes into the chain case on the left side of the machine which seemed like an odd place for it to go. I will check that out. Thanks again!
Okay! Well, for sure there's a breather on the chain case, lol. Later serial numbers had breathers but the style and location kept changing... wonder why?