Hi, I'm new to this forum and I think there are very knowledgeable folks here. My problem is that my bobcat 773 drives very good and strong but the bucket lift and tilt are very slow and weak. It started gradually after I replaced a hydraulic hose that controlls the right lift cylinder. It is located at the back door on the right side there are 2 short hoses, I replaced 1 of them. Since then it appears the bucket lift slowed and the tilt also slowed. I have a grapple bucket on there and the claws are also slow and weak. Today I have to rev the engine near wide open to move the bucket up, but its still very slow. At idle the bucket will not move upward are tilt at all. Its full of fluid, the hydraulic pump belt and tensioner are good. Brand new hydraulic filter. All lights are on, ie. seat, seat bar, ect. Emergency brake is off. It can push against a tree and spin the tires. No warning lights on. Cranks easy, sounds good. No weird noises when I attempt to lift the bucket. Oh, and yes the hose I replaced was with the same size hose. Please help, its driving me crazy. Thanks, kerry
Help Support SkidSteer Forum:
frogfarmer
Well-known member
- Joined
- Jul 30, 2010
- Messages
- 359
May have gotten some foreign material in the system that is stuck in the safety bypass valve. Did the system run dry due to the hose breaking or was it a preventative maintenance repair? If the system ran out of fluid the pump may be gone. Did you check the new hose to see how clean it was before the install? New hoses are bad for debris inside.
Hi, no the system did'nt run dry. The hose was replaced because it was leaking. No i did'nt check for debris in the new hose. thanks for your reply. kerry
Sadly it does sound like a pump issue, hopefully its just air. For a small hose i can't see there being any issues though.
As you said it was a gradual decline, it sounds more and more like the pump. A good test would be a pressure gauge on your aux hydraulic couplings. Even if you remove a line to your grapple bucket and install a pressure gauge, 3,500 PSI should be enough. Run the machine at idle and operate the aux hydraulics to that line, see what the gauge reads, i should be in the high 2,000 PSI range. Throttle up and see if it changes. If it does, it seems like it could be the pump. You need more speed to get the pressure up if there is wear in the pump.
Its somewhere to start.
If the pressure does not change, its more likely its trash in the relief valve.
Oh My.... Thanks Tazza for your reply. Can u lead me to where pumps are sold? Would this be the main hydraulic pump or something else? thanks kerry
the pump which controlls the bucket , lift , charge pressure and aux is the gear pump which is bolted to the end of the sunstrand tansmission pump , with out high flow or a attachment hydraulic release it would have two hoses going to it , one supply and one pressure , looking at the machine with the cab up it would be on the left side , they go for about 800 from the dealer , some models cost more , I have seen a site on line that sells them a little cheaper but have never dealt with them , it is not a very hard job to do , maybe 2 hours max to change out a pump if all goes well --------------if you took it off and opened it up you would look for a wear line inside the housing and or a groove cut into the end plate under wear the gears rotate on the plate , either spot will cause a loss of pressure and or cavation ------------does you oil get foamy ? -------it doesn't always get foamy when the pump is going out but sometimes it does
Thanks for your reply Fishfiles. Ok, I'm looking from the bucket and I see a smaller looking somewhat square looking housing attached to the left end of the big pump. This housing has a large diameter hose coming from the hydraulic tank that bolts to the back of the small pump. On the front of the pump is high pressure hose that leads to other parts of the hydraulic system. Is that what I'm looking for? If so do I ask for a Gear Pump? I have not seen foamy fluid anywhere. Another question, my machines serial number placard is gone, is there anywhere else I can find the serial number? Thanks for your time and excellent advice. kerry
yes that is the gear pump and thats is a good name to call it -serial number maybe stamped into a couple of different places on that machine , I clean up and look above the chain case fill plug , on the side around the drain motor covers , also possible that is was written in marks a lot inside the machine on the wall on either side the motor ----------the easiest way would be to have a dealer hook a computer to it and pull the serial number out of it
As Fishfiles said, thats the pump. It wouldn't be a bad idea to remove it and inspect if for wear (scratches in the alloy housing) and the bearings where the gears run. If you have wear in any of these points, you need a new pump. New bearings will fix nothing as the housing would have worn because the gears are allowed to move further out and wear the housing.
OK guys, I'm in the process of cleaning up the beast. Lots of grease and dirt. Still looking for the serial number. I'm told i'll need the correct SN to order parts. After a good cleaning i'm gonna remove the pump and look inside. I'll let u know what i find. thanks, kerry
Hello Yall, well after cleaning for several hours I got down to taking that pump off. I'll try to explain what I did... 1. Raise the cab. Remove [2] 3/4 nuts from front of cab and raise, allowing cab to rest on a latch that prevents it from falling back down. 2. Drain hydraulic fluid from hydraulic tank. Remove 1 high pressure hose from tank and drain into several buckets. Very messy. 3. Pump is the square looking aluminum part [about the size of 2 fists] bolted to the left side of the big pump, near the left frame. It has a high pressure large hose on the front and a low pressure large hose on the back that attaches to the hydraulic tank. 4. Gain access to the pump so you can take out the [2] 5/16 allen bolts that retain the pump. The front high pressure hose is attached with an 1 1/4 inch nut. Take the hose loose 1st, then with the same wrench unscrew the small housing that the hose attaches to from the pump. Now you can access the front 5/16 allen bolt. 5. Next go to the back of the machine. With the door open, look to the right where the hydraulic filter is located. Take out the filter. Next take loose the large hose that is attached to the filter housing on the right side of the housing. This will give you more room to access the pump housing from the rear. You will see what appears to be a part with relays and many wires attached to it, I thing it has 3 or maybe 2 bolts. Unbolt it and hang it out the way with some wire. 6. Now you need some light. Looking from the back through the hole you just created you'll see the back of the pump and the large low pressure hose. Hose is attached with 5/16 hose clamp. Take the clamp off. You'll see the part that the hose attaches to is screwed into the pump housing, much like the front was. However, the nut is bigger than 1 1/4 inches. Maybe 1 3/8 inches. I used a dead blow mallet and taped the elbow end to the left gently. It came loose easily and I unscrewed it. Now you can access the remaining 5/16 allen bolt. 7. It's loose now, but be carefull. Take a screw driver back around front of the machine and slide it between the pump housing the the large pump housing. Gently pry the pump slightly away from the big pump. NOW inside the pump housing where you just took out the 2 allen bolts is a adapter that will fall into the belly of your bobcat, never to be seen again. Sooo with this in mind slowly slide the pump away from the big pump and grab the adaptor before it falls. 8. You can now thread the pump out from the installed location and take it in to you shop and look it over. 9. This took me about 4 hours from beginning to end. 10. The most painfull part is that bobcat charges you $1070, including tax and freight for something weighing less than a bag of sugar. Hope this helps someone as you have helped me. Thanks, kerry
bobbie-g
Well-known member
- Joined
- Mar 15, 2004
- Messages
- 577
Wow, what a beautiful description! Very nice! Glad you're sharing your info with the rest of us. That's what makes this site so useful. BTW, I had to replace the injector pump on my 751, almost $1400, sounds like it's the same size as your hydro pump. I think mine was machined out of a solid block of titanium, with platinum parts added.....
---RCHow the the inards fo the pump look?Wow, what a beautiful description! Very nice! Glad you're sharing your info with the rest of us. That's what makes this site so useful. BTW, I had to replace the injector pump on my 751, almost $1400, sounds like it's the same size as your hydro pump. I think mine was machined out of a solid block of titanium, with platinum parts added.....
They sure can be a pain to get access, thankfully i have not yet needed to do that.
In the past i have removed the pump and motor as one unit, not sure if its faster or easier though. It does allow for much better access though and an excuse to get the pressure washer in there and clean behind the pump and motor.
You're spot on with the coupling, its one thing to make sure you don't forget to re-install when you put the new pump in too
OK, here goes. I installed the new pump today, still have'nt cranked my beast. I'm walking round and round making sure every hose is back in its proper place. Have to replace filter hose and filter. Then I'll crank. I was told by bobcat that I should let it idle only a few seconds then shut it down, repeating this 5 or 6 times to allow the hydraulic oil to fill all hoses and pump. As far as the old pump, I've taken the end plates off it and there are rubber o rings that are broken. They are not really round, more like a kidney and a winding circle. Several peaces are missing and theres something blue [maybe plastic] that looks like the pump might have eaten something undesirable. I have'nt takine the propelers out yet to see how the bearing look. Will update soon. Thanks, kerryHow the the inards fo the pump look?
They sure can be a pain to get access, thankfully i have not yet needed to do that.
In the past i have removed the pump and motor as one unit, not sure if its faster or easier though. It does allow for much better access though and an excuse to get the pressure washer in there and clean behind the pump and motor.
You're spot on with the coupling, its one thing to make sure you don't forget to re-install when you put the new pump in too
Its not a bad iidea to start it then shut down. I just wonder if you can use a jack under the bucket to lift the arms and operate the lift, this will draw oil through the pump. The only issue is you need to get them un-locked. If you turn the key on, sit in the seat and have the seat bar down, your hydraulics should un-lock and let the arms lift when the jack is raised.... The only thing that may be a problem is there is a sensor that detects if the engine is running, not sure if it will lock you out or not....
I have primed a few pumps this way, operating the hydraulics and pulling a ram stick out to move oil through the pump, it works a treat, no dry starts.
As for the seal, that sounds about right, they are a W shape, its weird but its how the made it...
I worked for Bobcat of Orlando for many years and have been working for myself for the past two plus years. Your problem is one of two things. Either when you had the hose made they crimped the end on to tight and not allowing enough fluid to pass through it or unfortunately the gear pump on the end of the hydrostatic pumpset is wore out and must be rebuilt or replaced.
