Bought a used machine. Description was trans failure, won't move. Hauled home and began testing. It had a low charge pressure fault, cold oil about 1000 RPM's had 325 psi. If I read the manual correctly, the charge pressure is regulated in the drive pump, down between the engine and pump. I pull the relief and the plunger is stuck on the valve pin, fretted or worn. I disassembled and polished up so seat moved freely on stem. I also added a shim when I reinstalled, I did not reinstall a gauge, light is still on. It intermittently logs a 15-4, charge pressure excessively low. Not every time. I am thinking I need a drive pump and a pair of wheel motors. Anybody know of anything I might be missing?
Welcome to the Forums rodneyp10! :drinkup Unfortunately I am of no help for you when it comes to the deep internal workings but we are fortunate to have a resident Bobcat expert Wille and he'll be along shorty to help you out.
Unless you have really deep pockets, that ain't a thinking thing, that's a chunk of money. :yup Go back to diagnosing. First of all, just to verify, are you removing the charge pressure sensor at the hydraulic filter housing and connecting your pressure gauge at that port? Second, charge pressure should be 240-260 PSI at high idle and oil at operating temp (140F +/-), 325 PSI is incorrect, remove shims at pressure regulator and get back in spec. Lastly, have a hyd hose shop make you a length of hose so you can connect a pressure gauge and run it to operators cab with gauge, operate the machine and monitor charge pressure, if it remains in spec, and machine operates proper, that charge pressure sensor has been lying to you with the excessive low charge pressure code.
There are no functions on the machine. The bucket will try to roll, about one inch of stroke on the cylinder. The left track will just move, like the brake is on. I resealed the right brake, so with no hydraulic pressure, I suspect the brake has not had enough pressure to start to release. Yes the sensor port is where I checked pressure. It originally had a 15-5 fault, I replaced the sensor and now have an intermittant 15-4. It starts, turns on the buzzer and charge pressure light and shuts down. It will run 30 seconds more at high idle rather than idle, but never more than 2 minutes. My assumption was charge pressure excited a port or valve to allow the functions of the rest of the machine. I assumed I was loosing charge pressure in the drive pump and not allowing other functions. I will get a hose made up to monitor pressure in the cab. I suppose a tee would be good, so the sensor can be installed also.
Maybe I read your first post incorrectly, I thought you were saying you had 325 psi of charge pressure? What's your machine serial number? Is it a high flow machine? Is it standard controls, AHC, or selectable joystick control?
Correct, at high idle it does have 325 PSI and sets a 15-4 fault. 531613295 The control panel on the upper right has a switch that changes the flow, not sure exactly what it says, rocker switch that changes. Not at the machine right now to verify? The control levers attach directly to the drive pump with flat rods. There are electrical switches on the control, they are not pilot operated joy sticks. I believe standard controls.
Hmm, I'm puzzled, if you're getting 325 psi charge pressure, you should not be getting codes for low charge pressure as it's actually higher than it's supposed to be at 245 - 255 psi. It sounds like one of the auxiliary hydraulic valves is partially engaged, but I'm not certain about that. I'll check out that theory at work tomorrow.
I realize if it has 325psi of charge pressure the drive belt must be working but I cant help but wonder if the belt has been checked.
Good point frogfarmer, it's possible the belt could provide enough power to develop charge pressure with no functions being operated, but once you operate a function putting load on belt it could slip and everything go dead. It's worth looking into.
I will check that tomorrow and let you know. Thanks
Ok, checked belt and its tight and the pump continues to rotate. I them disconnected the steel pilot pressure line from the outlet of the filter that feeds the valve bank. I attached a gauge to that port, so now the lift section and valve bank are disconnected, 310 PSI until I pull a track lever, pressure goes to zero. Now I am thinking I am loosing pressure in the hystat pump. I am thinking I bypassed the rest of the machine. Now I remove the number 12 line that comes out of the filter that goes to the hystat pump. I machine a 1/8" orfice and place in hose. I reattach the hose, now I have a restricted line to hystat, thinking I have additional pilot pressure. I lost my gauge port so I can't monitor pressure, still no loader function. I really would like a flow gauge at this point, although I am having difficulity believing the gear charge pump has failed. I attempted to attach a picture. I don't believe it attached.
the main )loader) hyd pump and charge pump are seperate pumps. on the k series machine you have they are piggybacked together on the right end of the hydrostat. and seeing that this is a rental unit from sunbelt, i'd be almost positive that the gear pumps are damaged. most rental houses dump equipment when it's broken/damaged and out of warranty wouldnt be the 1st set of (gear) pumps i've seen that are crapped out :drinkup
So does crapped out mean pumps and motors or just the pump? If the pump failed and sent debris to the motors, they are most likely junk also, correct?
Hey Crewchief; I just read your note again, and it said gear pumps. What is the failure in a gear pump? My experience with gear pumps is they are durable?
The oil goes through the hydraulic filter before it goes to the drive pumps.
on the gear pump failures i've seen, one or more of the shaft bushings have siezed and spun in the pump housing. also seen the splined coupler between the 2 pumps broken,and stripped the splines on the shafts. my conclusion was at some time (recently, typically within 100 hrs or so) the machine had blown a hose, hyd system had been run dry, causing the damage. pull both filters, and dump them into a clean container and check for debris. metal pieces are from the hyd and charge pumps, if you find brass, thats from the valve plates in the hydrostats. :drinkup
Crewchief, I do believe you are correct. Both pump sections show where they have failed. When I first disassembled the pump I looked at the brass plates and they were not chewed to bad. When I was washing, I found the damage to the inlet side of both the charge pump and the hydraulic pump. Hopefully the pictures attached and you can see the damage. Thank you for the assistance.
I'll bet if you look at the bushings where the shafts ride you'll see grooves worn in them from the shafts, that's what causes that scuffing of the gears against the housing.
This is my first hystat so bear with me. If I understand this correctly, the charge oil to the hystat pump is filtered, so no debris should be downstream of the filter. Thus there should be no additional damage to the rest of the system. My concern is if I replace this pump and have additional damage, if I have to buy a hystat pump, I am then in upside down mode from a cost perspective. Should I be looking for any additional problems before I buy this pump?
Yes and no. The oil does pass through the filter before going to the drive pumps, but if enough debris clogs the filter (such as from a failed gear pump) it will pop open the by-pass valve in the filter housing, junk now goes to the drive pumps. Aside from checking filters as crewchief888 suggested, there's little you can do to check the condition of the system short of complete take apart which is simply not practical. As crewchief suggested, remove the hydraulic filter and pour the oil in filter into a clean container looking for debris. Once you've poured the filter empty, pour some diesel, kerosene, or solvent in the filter. Place your had over the end of filter and shake it. Now pour the liquid into a clean container to see what comes out. Operate the machine and do a frequent filter change to see what the condition of the oil/debris in filter is.
once again willie has hit the nail on the head. when you install the new pump, overfill the hyd tank and set the machine sit overnight. this will let oil gravity feed into the pumps so you dont get a dry startup, and cause the same damage to the new pumps. you may want to install a manual guage in the sender port and spin the engine over, without starting it, untill you see pressure, this will ensure the pumps are full of oil :drinkup
Me again.................... Installed a new charge/hydraulic pump. Followed you direction for startup. Initially had about 300 PSI charge pressure and the boom and bucket worked normal. After it started to warm up, same thing as before, 300 PSI charge pressure until you pull a function and no pressure and no function. I am loosing pressure down stream someplace.
without activating hyd functions, you have charge pressure.. does the brake release and the machine drive normally? :drinkup
No, lost track function also. Initially the brake released and the track would function.
removed the drive motor hoses from the pumps and cap the fittings off. start the machine and monitor charge pressure :drinkup
Im not familiar with the T190 system in particular but when a track motors fail internally they can bypass enough oil that the charge circuit can not keep up. No charge pressure means the brakes will not release as they should. At this point I would be doing the stall tests to see if the pumps are capable of producing adequate pressure. Given the fact that the system runs almost closed it is very possible that damage has been do to both pump and motor. Not what someone wants to hear but is the truth all the same.
The issue is concuqured, two drive motors and a charge pump later. What oilm can i use in the T190, is AW 46 hydraulic oil ok?
I use a good quality AW46 oil in Bobcat machines.