Bobcat 753, with Hydro Pump Problem

Hi,

I am looking for some advice on a Bobcat 753 that I am considering buying. This loader is a bit of a project. The engine and pump assembly is currently removed. The owner seemed to take care organizing things so he could put it back together. He just got a quote today for $2000 to rebuild all 3 pumps; the loader pump and the 2 drive pumps. The two drive pumps are old, but were working before the loader pump gave up the ghost.

I am new to loaders so if this comes off as a newbie post, that's because it is. Anyways, with that disclaimer, I have done lots of engine work in the past, but I have limited experience with hydraulics.

So this Bobcat has a bad pump; the one that powers the bucket, lift arms, etc. The owner took the pump out, but the engine had to come out to get at it also.

So it needs a new pump, and the valve body is contaminated with pump guts. The guy wants about $2500 for it all torn apart. It has about 5500 hours. The rest of the loader is in good to fair condition.

My question, how bad of a repair is this? I know it is a loaded question, but if I tear down the valve body and get it clean, clean out the lines, etc., what are the chances that this will self destruct again in a short period of time? I don't know how well these machines filter in a bad pump scenario like this?

I figure a new pump, just the auxiliary one, not the two drive pumps could be replace for about $400 or so. Figure in a few buck for oil, etc. and I maybe could have this going for a little over $3000. Does that sound reasonable, or am I dreaming?

Regards,
Tim in Mass

As long as the drive/hydrostatic pumps are OK, you should be fine. I just replace the hydraulic pump (the one that controls the arms/bucket) on an 863 about a month ago. The customer bought the parts which included a new pump and an adapter fitting (because the new one was ported differently), and I think the parts total was somewhere areound $700.

As far as the system being contaminated, what happened to the old pump? Typlcally the pump body is made of aluminium, and they will wear internally until they don't work anymore. That said, unless it just flat out disentigrated, there's really nothing in the system to clean out, as any of the material that came from it would have been filtered out of it by the return oil filter. Even if it did disentigrate, there's not alot you can really do to 'clean' it out without taking every part of the system apart, and running something through each and every line to inure no particles of pump remain. That said since the pump does nothing but work the cylinders on the loader arms having it 110% 'squeaky clean' isn't as important as it would be if it ran a hydraulic motor, etc. (like the hydrostatic system). In other words the cylinders are usually going to do nothing but suck in any material and the force it right back out when they reverse direction, with no real harm caused.

As far as clean out goes, internally the valve is nothing but openings cast into the valve body and grooves in the spool to connect those openings to operate the machin/cylinders. Basically there really isn't much inside the valve body to flush out because, in most cases, any material in the oil stream would have gone on through the system, and been filtered out when the machine was running. There might be a little bit of material built up inside of the base of the cylinders, but the only way to really get all of that out would be to dissasemble the cylinders. Usually though it's going to do nothing but lay there until the force of the oil moving around it carries it back to the return oil filter, removing it from the system.

Ultimately, like I said, unless the old pump just completely disentigrated, there's really not alot you need to do to get the machine back in operation. Basically reassemble it with the new pump, run it for a day or so to flush out the system, and then change the filter, and you should be good to go.

Over the years I've changed out quite a few pumps that 'went bad' on everything from dozers to excavators. Unlike the dealerships who want to charge both arms and legs, and other parts of the anatomy, to do a complete system cleanout/flush, I have never had a customer put me in a position time, or money, wise to go to that extreem. To that end I've always done the best I could to insure the tank, etc was clean, and that the return filters were new/clean. I never worried about the valving or anything like that as going to that extrem would have, in most cases taken weeks to do. I have never had a problem out of any of the machines I have repaired caused by material from the damaged pump.

Good luck and if you run into any problems feel free to post again. Wayne

I think it would depend on what caused the pump to go bad. If it was run low on oil for example, the hydro's might be on their last legs too and they aren't cheap to fix.

Wayne and Stickwelding,

Thanks for the replies. Armed with this info I am going to ask the customer a few more questions. Specifically, I am going to ask about the oil level, and why he thinks the valve body is not 100%.

He did say that he was using the machine and lowered the boom, or bucket, and the pedal stuck. He gave the pedal a kick to free it up and then there was no boom/bucket control. Maybe there is nothing wrong with his pump at all and only his valve body is to blame?

I need to call him and discuss some more details.

Thanks again,
Tim

Not anything to worry about in the hydraulics but there is ONE big issue, which engine does it have. I bought a bobcat at auction about like your project. Assumed it had the KUBOTA as most do. Turns out it had a perkins. Had to go overseas to get engine parts turns out BobCat no longer supports this engine but it gets worse some have an another engine like an issu or something and parts are not there for that engine also , so check the engine and see what is in you machine.

JM,

The Bobcat has the 4 cylinder Kubota engine.

From the looks of it I don't think it has ever been overhauled. With 5000+ hours, what kind of service, or problems could I expect from this?

Tim

I don,t know. Been a KUBOTA dealer for 28 years and probably have seen more engine failures in bobcats than all other things combined. Bobcat chose to mount the radiator up high on some units and not unusual to see overheating issues in the bobcats. At 5000 hrs I would say you are certainly on the edge of use full engine life if it has not already been overhauled. The 753 is a real popular unit but you can also pick up used ones when they get older fairly cheap.

If he was lowering the boom and the peddle stuck he may have put the spool into the dentented, float, position. If he doesn't use that position very often it might have stuck in that position. I had one awhile back where that happened to a customer and he had absolutely no control of the boom with that peddle. I had to use a pry bar to get the spool untsuck, and then pull the detent mechanism and clean/free it up for him so it didn't happen again. That said if he kicked the peddle too hard he may have also broken, or bent, a part of the linkage causing the funtion not to work.

In any case, based on what your saying happened, I think the guy made an assumption on the problem and then began taking things apart without every doing any real troubleshooting (nothing uncommon in my experience). That being the case, I'd say the probility of the pump actually being bad are really slim. Good luck and hope it turn out to be a good machine if you wind up buying it.

I agree he could have kicked into float position. I would hazard a guess that over 50% of skid steer owners don't have a clue their machine has a float position and what it's used for. The other thing the poster said is the bucket didn't work either which would indicate another problem. Float would affect the lift arms but not the bucket.

Just thought of something else. If the aux. pedal was pushed forward and locked in would cause the hyd's. not to work. It would also make it labor when trying to start and heat the oil pretty good. It's easy to do and not something you'd think about, especially if you never used the aux. hyd's.

I had that thought in mind too, but the way he stated it was kind of ambiguious as to wether he had no boom or bucket control. I say this because he said the guy was lowering the boom or bucket, and then the peddle (singular) was stuck. Saying he was lowering (loader arms), and using the word peddle -vs- peddles lead me to believe the problem was related only to the loader arms and not the bucket roll. But I could be wrong........

I agree. My buddy experienced that problem with a rental machine awhile back. Granted the machine was a Case, not a Bobcat, but when the aux controls stuck in the ON position everything else stopped working, and it was nearly impossible for them to get it started to figure out what had happened. Never did hear what the actual cause of the problem was, since all he did was call the rental company to come get it, but that is definately another option.