Hello everyone. This is my first post. A few weeks ago, I bought a bobcat 753c. 1996 model I believe? So far I've had minor issues with it. Tilt ram seal went out, alternator belt went out, cooling belt tensioner went out. No big deal on those things. I will point out first, that I do have a fluid leak. But my leak is from the aux hose to the left of the battery facing the engine. Talked to a few friends and they think that leak may be causing my issue? The bobcat runs like a champ. Sounds great, operates smooth as butter. Until It's used for moving dirt after an hour. I'll get an hour of flawless operation and like a switch, all controls get very slow. Seconds after slow controls, the loud whine comes from the pump. This has happened every time I use it. When the problem starts, I'll pull the engine rpm down to about 50% and let it run about 5 min or so. All controls come back to life and I'll use it another 15min, then the problem occurs again. I originally thought it was a overheating problem. So I flushed the system with new fluid. No improvements. So today, it happened again as usual. Cooling fan blowing good and hard. No restriction through the radiator or hydro cooler. When the hydraulics acted up on me today, I immediately started grabbing lines to try to feel the temperature. I was able to touch every hose and line on the machine without burning myself. Engine coolant Guage never shows it running hot. The overheat lights have never come on when this happens. The lights do illuminate when key is in the on position/engine off. So I know bulb isn't blown. I do have good mechanical background. I'm an auto mechanic for a living. So I have somewhat of a good understanding of how MOST parts work on the machine. But right now, I have no idea where to start diagnosing? As a guestimation, I'd say the pump is going out. But before I go dropping $2k on a pump, I'm hoping someone here could point me in a direction that may have similar symptoms? I also have no idea how to pull codes on this thing. To tell the truth, I don't think you even can. I read online about "753 code...ect". I haven't found info on how to pull the codes.
Welcome to HEF BigEasy374. :drinkup First, you don't really get diagnostic codes on a C series Bobcat. About the closest you get to what could be considered a code is if one of the LED lights on the BICS controller is flashing, even then that's a very basic code, sort of just points you in a direction, no real specific "code" information, imagine it compares to the old OBDI system on vehicles in the '80's. Second, you're loss of power with the functions and the squeal, pretty much a 99% probability that the drive belt is the problem, that belt has to be really tight. Possibly a worn out drive belt or tensioner not putting enough tension on the drive belt.
If it's not the belt it could be the pump getting week or even a pressure regulator bleeding off pressure when it gets hot? A new aux pump shouldn't be anywhere near $2k, should be closer to $5/600. It tales some special tools & fittings to check the pressure properly, may be worth a trip to the dealer.
I'll check the belt after work today. Hopefully it's that simple! I don't think it's the aux pump. I was thinking the drive pump was going bad.
if you were having pump issues, the problem wouldnt magically go away. drive belt has a spring loaded tensioner. if the belt is loose, 2 things will happen hydraulics and hydrostatics will get weak or slow down, belts will start making noise. :drinkup
Belt is good and tight. Today I finally had a chance to run the machine after it was acting up. Checked the fluid level first and it was over full. Which is odd because I checked the fluid level before I run it every time. Fired it up and it was groaning very loudly. Slow movements. Continued to cycle the arms bucket and drive. Within 1min if cycling, it was back to normal. Shut the engine down (about 3 min of runtime- engine still cold) checked the fluid again. Fluid level back to normal but it was extremely airated. Thousands of bubbles I can see through the fill cap. So looks like I definitely have air entering the system somewhere. The bobcat has done this since I bought it. When I flushed the system, I used ohreilly brand aw-32 with anti foam additives. Which was recommended by a friend that runs it in his bobcat. I'm not sure what brand fluid was in it when I bought it. I guess it's possible it's had the wrong fluid in it, but I think it's a little unlikely at the moment. Especially considering I'm not the only one running ohreilly brand fluid. Snooping around I haven't found any loose fittings or signs of entering air in the system besides the small aux line leak I have.
i'd suggest you fix the leak for starters. foaming oil is usually caused by air getting into the system on the suction side of the pump. raise the cab, check the clamps on the large hose at the bottom of the hyd tank that goes to the hyd pump. the hoses get old, harden up and will "shrink" to the point where the clamps are loose... :drinkup
5 hours run tine today. Ran flawless. Until 5 min ago. Just checked the clamp and they both are tight. Didn't find any tears in the hose either. But today, when I shut it down I could clear hear the reservoir gurgling. Very very similar to a boil sound. Took the fill cap off and I had air bubbles as usual. This time, the fluid was slightly steaming. Almost seems like a cooling issue now? Although the temp light still did not illuminate. Possible I have a internal restriction to the oil cooler? The radiator is not stopped up as well as the oil cooler. Fantastic air flow exiting both sides of the bobcat.
check the airflow through the top of the hyd cooler/radiator, just because you have airflow out the sides, means you have airflow through the cooler. typically if you have an airflow restriction through the cooler the engine will be running warm as well.... :drinkup
Yes it has good air flow. Radiator doesn't have any dirt packed in it. I can even feel air pulling past my hand when it's running and my hand placed on the cooler. As for the engine, it has not overheated or some close to running hot. Stays very consistent. Thank you for the ideas here, I hope I solve it soon
You might consider checking the hyd tank real good. I know it's not the same machine, but hydraulics are similar in working no matter what machine it is, but I once worked on a Komatsu D41P-6 dozer that kept blowing the work equipment pump. I thought it was a pressure problem, kept approaching it from that perspective, until it blew a third pump, aerated oil and oil getting hot. I told my helper "we're gonna take every single piece of the hydraulic system on this thing apart until I find what's causing the problem". That being the case, the first place I started was drain the hydraulic tank and remove it. Immediately upon removal I found the problem. The suction pipe coming out of the tank was a 90 degree bend, I saw a stick, yes, a tree stick lodged in the elbow effectively blocking flow. This caused the pump to cavitate and destroy itself. You might consider taking the tank off of that thing as well as the rubber suction hose that delivers oil from the tank to the pump and see if there's something in there.
Great though Willie, as pulling a vacuum on pretty much any fluid will cause it to foam up. Also, most Bobcat machines run motor oil in the hydraulics not hyro fluid. Not sure if this could cause you problem but who knows...
Yeah, I'm not saying with any assurance that's his problem, I just know that Komatsu about drove me bat **** crazy until I pulled that tank off and found that stick blocking flow. And there's one thing for certain that a gear pump will do and that's suck. If it can't suck fluid in the suction line, it will suck it's own self apart, but it will suck. :yup
Well, I have been very busy with work lately. 90* weather, working in a 105* shop all day, I don't feel like running the bobcat. But the problem is still here. Yesterday I got the bobcat to dig up a rock in my yard that I keep hitting with my mower. It started acting up again. Now, a few days after my last post, I noticed my right side drive being weaker than the left. I didn't pay too much attention to it because it was very min or. Actually had to run on asphalt in a straight line just to notice. But it quickly got worse. Got to the point of spongy right side controls and a harse jerk when almost full drive applied. Wide open drive(full fwd or rvs) it will drive just fine. But variable drive speed on the right side, it's not looking good. Internet surfing is telling me to swap left and right drives and see if the problem moves to the left side. Makes 100% since to me. So I'll be doing that soon. Went and looked at the drive motors to see how big the job I was in for, doesn't look too bad. But I noticed a good bit of fluid under the right drive motor. Interesting I haven't noticed before. What would my odds be that this drive motor is causing all this chaos? My luck, throwing 1 stone never hits 2 birds.
Took out my right drive motor. I can spin the gear with my hand very easily. Literally spin it. Clearly, it's bad. Unfortunately I have the 6657024 motor and it's not easily available. Since my geroler is wore out, loader parts source is telling me it's basically not rebuildable. Leaving me with finding a used motor, or reman. Has anyone used a motor from another model and made it work? Just from looking at pictures, it seems the difference is the fluid line locations are offset vs in line like mine are. If I could make the offset fittings work, would it still drive the same or is it a lot more difficult than that? Sorry for the stupid questions, this bobcat is the first piece of equipment I've ever worked on.
I don't know of a source for used Bobcat motors, not to say there isn't one, just not aware of one. Besides, I wager it would be a roll of dice to go with a used motor anyway, even if you could find one, might find yourself right back to square one. Did Loader Parts Source have a new replacement available?
Yes, they have the updated version that's $1,500 each. Recommended to replace both of them. These motors are crazy expensive!
I wager they're more than that from Bobcat. :yup
Heh, I feel the pain, but Willie, tell him what that would be in Komatsu dollars!
Amen to that bro, like $24,000 for a final drive for a CD110R-1.
Haha. I'd wager you are correct! Hard to drop that kinda money into a machine I paid 6500 for. It's a part of the game. Gotta pay to play. So looks like an easy $3000 is about to drop in the 753. So as you all are more experienced than me, which route would you go with a personal owned-around the land bobcat? Go for the heavy $3000 repair with both new motors, or $1500 now, get it rolling again, and get the other motor a few months from now? Reason being, I can financially swing 1 motor now. But doing both of them puts me in a tight spot. I'd rather have them both, but at the same time I don't want my bobcat sitting another month or 2 useless. Or, replace my bad motor and send my other good one in for a rebuild at $700. Putting the repair at $2200-ish?
WOW!!!! I don't feel so bad about my little $1500 motor now haha
It's a gamble, there is no correct answer aside from replacing both and thereby minimizing the gamble. However, the reality is that sometimes the wallet is on a starvation diet, or might as well be as thin as it is. If your other drive motor seems to be operating properly, and assuming your model 753 has a case drain filter for each drive motor (some only used one case drain filter for both motors), check the case drain filter of the (we hope) still good drive motor. If it's clean inside, not full of debris/fragments, then yes, you may get a few more miles out of that motor before you have to drop the coin and replace it. On the other hand, if the case drain filter has debris in it, well, looks like your going to be ordering the double cheeseburger instead of the single.
Ok thanks! I'll have a look at the filter tomorrow and see how it looks
It's possible the reason they suggest changing out both motors is that the new ones are a slightly different displacement than the originals and may run faster or slower for a given control position. If that's true you'll just have to compensate a bit with the controls to keep it going straight if you only change one side. It's annoying but we do it to a degree with every hydrostat we run even new they're never perfectly matched, it's the nature of the beast.
with one old motor and one new motor you'll probably notice quite a difference in speed from side to side. but if it's something you can live with, then do just one..... if it was MY bobcat for around the house/farm ect, and i was dong the work myself, i'd just do one. if it was for a paying customer, he'd be buying 2 motors.... :drinkup
Well, had a look at the filter and yes my bobcat only has one. Meaning both drives have seen the same debris. So I bit the bullet and bought both drive motors. Since i got both new motors, i will definitely replace the filter at the reservoir and the filter at the engine and flush out all the fluid. Any thing else i should do while im doing the repair? I plan on putting the bobcat on jack stands and purging the air out of the lines while there is no load on the machine. I assume this is the best way to do it. Maybe not?
I should have listened to you sooner. As I was beating my head against the wall trying to resolve the issue, I decided to shine a flashlight in the reservoir. As the tank was gurgling I noticed a tube surface and fall back down. Turned out, a 1ft long 3/4" nylon clear tube was in my reservoir and had made its way to the upright position, in the feed hose. On level ground, the fluid level was above the tube, making it unnoticeable, but as soon as I had the bobcat at an angle, it would suck air through the tube. I assume this used to be at the end of a jug or something to help when filling with fluid and must have fallen off and no one noticed. I fished the tub out with a coat hanger, ran the bobcat 3 hours straight without a hiccup. I guess since the tube was clear, I was never able to notice it before. The black tank didn't help either. But I am thrilled to say this was my issue the whole time. Thanks for the suggestions everyone!
Never EVER would have thought of that! Well done! :drinkup
well, i've seen some strange things happen over the past 30 years, but thats a new one :crazy :drinkup
Are there case drain filters on all 753 models?