ZekeSkyree
Active member
- Joined
- Nov 9, 2023
- Messages
- 31
I have an 1989 Bobcat 642 serial number 11905. I got it used and it was in tough shape as it had little to no maintenance, but it was functional.
During the summer, while using it, it blew a hose (i believe the pressure hose from the gear pump - this may be important later), and when i looked at the state of the other rubber hoses decided to replace them all and perform some badly needed maintenance. I spend a ton of time cleaning the engine and pump area. All the drains were covered with inches of compressed mud and hydraulic fluid. Once i had everything pretty clean, i pulled the engine (and cleaned it), so i had better access to the lines. While out, i tuned it up, which included valve lash. and replacement of a rusted out coil as well as inspecting the U-joints, which were fine and only needed greasing.. Once done it ran perfectly .
After replacing the hydraulic filter and 40 micron filter, I started pulling lines and replacing them. I took pictures and even a few videos to make sure i got the locations right. After i put the engine back in and fired it up, i noticed a leak in the front, which turned out to be the gear pump. The pump housing split wide open. After buying a new pump and installing it i fired it up. It started and died. It died, because the gear pump was hydrolocking. I saw the pressure hose jump and heard the engine bog. Looking back, i think the initial blown hose, though old, was probably a victim here and that the problem is that there is an issue with the block that the gear pump feeds, or rather that the fluid is not returning. After looking at the manual and not being a hydraulics guy, i "believe" that the valve block it feeds "should" be sending unused fluid back and is not. There is a bypass valve in the block and i am not sure if that would be a place to start, or if there is something more fundamental wrong.
I have double checked all the hoses and "think" everything is correct. If i focus on the gear pump circuit (excluding the drive motor circuit), i think it is a pretty simple diagram. I have included a drawing of what i have and connections. Let me know if you have any questions or need more information. I can also post anything from the service manual as a reference.
Looking for any advice on this. Do you think i may have a hose in the wrong place? Do you think there is an issue in the valve block? I am very new to Bobcats and am definitely not a hydraulic guy, so before i break another expensive pump, i am hoping someone can put me on the right path.
Thank you.
During the summer, while using it, it blew a hose (i believe the pressure hose from the gear pump - this may be important later), and when i looked at the state of the other rubber hoses decided to replace them all and perform some badly needed maintenance. I spend a ton of time cleaning the engine and pump area. All the drains were covered with inches of compressed mud and hydraulic fluid. Once i had everything pretty clean, i pulled the engine (and cleaned it), so i had better access to the lines. While out, i tuned it up, which included valve lash. and replacement of a rusted out coil as well as inspecting the U-joints, which were fine and only needed greasing.. Once done it ran perfectly .
After replacing the hydraulic filter and 40 micron filter, I started pulling lines and replacing them. I took pictures and even a few videos to make sure i got the locations right. After i put the engine back in and fired it up, i noticed a leak in the front, which turned out to be the gear pump. The pump housing split wide open. After buying a new pump and installing it i fired it up. It started and died. It died, because the gear pump was hydrolocking. I saw the pressure hose jump and heard the engine bog. Looking back, i think the initial blown hose, though old, was probably a victim here and that the problem is that there is an issue with the block that the gear pump feeds, or rather that the fluid is not returning. After looking at the manual and not being a hydraulics guy, i "believe" that the valve block it feeds "should" be sending unused fluid back and is not. There is a bypass valve in the block and i am not sure if that would be a place to start, or if there is something more fundamental wrong.
I have double checked all the hoses and "think" everything is correct. If i focus on the gear pump circuit (excluding the drive motor circuit), i think it is a pretty simple diagram. I have included a drawing of what i have and connections. Let me know if you have any questions or need more information. I can also post anything from the service manual as a reference.
Looking for any advice on this. Do you think i may have a hose in the wrong place? Do you think there is an issue in the valve block? I am very new to Bobcats and am definitely not a hydraulic guy, so before i break another expensive pump, i am hoping someone can put me on the right path.
Thank you.
