Bobcat 753 C Series Machine. Close friend passed away recently and left me his 1994 753 bobcat. Going through the machine to do routine service. Removed the chain case CHECK PLUG and 12 gallons of excess oil puked out before it drained down to the proper fill level. I would guess this ends up with me pulling the side access covers and groping around blindly for a drive motor leak issues. Don't have any experience with drive motor issues and would greatly appreciate some in sight into what I should be looking for in the belly of this beast. Would also like to know a few of the the most common sources for leaks resulting in chain case overfill? Any pointers would be greatly appreciated. Willie59, I would be particularly grateful for your input here.
only one thing causes the chaincase to overfill... gearbox seals. you'll have to remove the drive motors to get to the seals. you'll definitely need your SN for that machine do both sides while you're in there. :drinkup
Welcome to HEF KyDirt. :drinkup Yes, that's typically caused by either a failed bearing carrier seal (drive motor mounting) or by a failed drive motor that has put hydraulic pressure on the carrier seal and blown it out. In most cases, but not all, when a drive motor craps out it will produce metal debris along with excessive case drain pressure, that pressure is what will blow a carrier seal. But at the same time it will send that metal debris to the case drain filter. I would start by removing, disassemble, and inspecting the case drain filter looking for debris. If they're clean, probably just a failed carrier seal. If you has debris in it, that will tell you which drive motor is bad.
Ha, crewchief beat me to a response.
ya gotta be quick !!:notworthy i'd be willing to bet it has the original gearbox seals in it. our shop had a run on them last year, one every 7-10 days, starting in the spring through early fall.. were seeing a LOT of 25-35 year old machines coming out of the woodwork.... sadly many of the "proud new owners" dont have the money to shell out for repairs :drinkup
Yep, likely has a leaky control valve as well. :yup
Crew & Willie thanks for the quick response. I didn't see the case drain filters anywhere under the cab when I was nosing around earlier today looking for them. Only a single in-line filter hanging off the hydro reservoir. I don't have a shop manual for this machine. Anybody know where the chain case filters are located? Possible related issue; pull back slowly on the left steering lever at low idle and machine doesn't move. slightly move the right steering lever at the same time and the left side will suddenly engage and lunge in the direction of travel. Can't tell there's an issue at mid throttle going straight forward or backward but start make turns and you can tell the left side is erratic in response. If your used to a bobcat it's an insufferable issue when trying to make fine adjustments while steering. Do these symptoms present like a drive motor issue?
First, I don't have a manual for a 753 C series so I don't know how they arranged the case drain filters. Some of the older C series machines only had one case drain filter at the hydraulic reservoir, later models had a case drain filter at each drive motor. To make it simple, each drive motor has three hose connections to it; 2 larger hose connections for drive, and one smaller hose connection, that would be the case drain for that motor. Follow that smaller hose backward as it returns to tank, if there's a case drain filter you'll find it inline between that motor and the tank. It will be a cylindrical aluminum housing with a large hex one one end. Second, to say your symptoms sound like a drive motor issue, well, yes, the left side does sound suspect, but without being there in the seat it's still hard for me to say, could still be a problem with a pintle arm connection to the pump control shaft on the left side, but does sound like a possible drive motor issue. See if you can find the case drain filter for the left drive motor and confirm.
if it does have case drains for each motor they will be close to the motor in the case drain hose. i recall some models they were screwed directly onto the fittings in the motor. from what you describe it sounds like you have a drive motor going out. some early drive motors are NLA from bobcat, not sure about parts availability either :beatsme a word of warning, if you have to replace a drive motor, you will likely have a machine that does not track straight, due to the other motor having wear, and not being efficent enough to keep up with the new motor. if you have the type of motor that is NLA it's recommended that they be replaced in pairs. :drinkup
Dealer says motor is NLA. They may be able to get a used one. I think I can work my way through putting a seal kit in on my own if that's the only problem. If the damage is more extensive, can it be sent off and remanufactured cost effectively? I understand this is a lot of hypotheticals considering I havnt even checked the filter yet. Just trying decide at what point I disable my only peice of loader equipment. If a repair costs me more than $500.00 I'll need to continue running it until I can generate enough cash to cover the parts.
i'd be willing to bet that a motor seal kit, fitting orings, and gearbox seals would be less than your $500 limit if you are doing all the work. i think what i'd do is drain the chaincase down to level, top off your hyd oil and run it for a while. then recheck your chaincase & hyd levels to see how much oil is leaking. thats typically what we do for an older machine, and a customer with a very limited budget. that amount of oil could be from YEARS of not checking, and reilling the hyd tank, or a little as a few hours of run time, depending on how bad the seals are. :drinkup
That sounds like a solid plan. I think I'll take that advise and run with it. Thanks for the input and direction.
Checked case drain filter and found no metal or unusual contamination. Filter was in severe need of replacement. After running the machine now for about 16 hrs the fluid doesn't seem to be hemorrhaging into the chain case unusually quick. (thanks crewchief888) it must have been long term accumulation. Now that I have a better feel for the machine I have noticed some particulars to my problem. The unresponsiveness of the left drive motor drastically increases the longer the machine is operated. The problem is sufferable for about an hour and then after that the motor will engage and fade, engage and fade, as I back up. It jerks every time it engages. The problem seems to be much more drastic in reverse. I don't seem to notice as much going forward. If you pull back equally on both steering levers after its run for an hour or so, the machine would eventually back in a complete circle if you had about a 200ft radius, with the left motor engaging and slacking off the entire time. The problem gets so debilitating I seldom run the machine for more than a couple hours at a time. Does the increase in severity after an hour use and the noticeable difference in reverse as opposed to forward narrow down the possibilities for what might be the root cause of this issue?
I have a 753C and had exactly the same problem/symptoms on the left side ( would steer to the left, pull back straight with a little more power, but not equal....and would jerk forward every now and then when left drive motor engaged). I ended up buying a rebuilt drive motor ( with core exchange). It was a pretty straight forward repair.
These motors are one of the few that can eat seals without blowing up, we have re-sealed many many of these that showed no metal wear, the blown seals can allow "bypassing" which sounds an awful lot like what you describe. It can do this without necessarily leaking oil into the chaincase. When bypassing, the oil goes through the motor without turning it, lots of travel lever - more flow, and she takes off with a jerk?
Exactly.
Got one motor out of the machine and onto the bench tonight. Shaft flops around in the housing. I can easily spin it by hand and it has almost an inch of free travel when pulled in and out of the housing. Is this a hopeless chunk of scrap metal?
Yes
i'm having a brain fart... can you post a pic of the motor? :drinkup
The shaft moving "in and out" is not a problem it kind of floats around in there, the rotating group looks fine as best as I can tell from the picture, Is there a reason new seals can't be installed and results tested?
New seals...good to go.
The plan all along has been to pull the motors, install seal kit, and get back to work. The following statement from Loader Parts Source page is what has me suddenly asking "are my motors junk". If your geroler is worn we will be unable to rebuild your motor. The geroler is the center drive section and if you can turn the shaft by hand it is badly worn. We are unable to rebuild 80% of these motors due to this common failure and a new motor is the only option if they are available. I can spin both motor shafts by hand. Internally I see nothing that indicates a severely worn motor. Actually I was quite surprised to see such good looking internals on a piece of equipment this age. So what's the general consensus, is free spinning motor really a lost cause like they claim?
Surging, Bucking, Jerking Hey guys, long timer reader, but first time posting. hope this is not hijacking this post since I initially added too much fluid and hope this is the answer to my problem. I have been able to work on my own equipment for years now since the repair shop made the comment " its not how much you pay for the equipment that hurts. its how much it cost to work on it to keep it running". I have not been to the repair shop since 2007. I have been searching posts for the bucking and jerking problems and have not been able to find anything to help me understand what I need to do. So I went back to the moment before the problem occurred and this past weekend after delivering my Bobcat T-190 to my property in NC. I added about 2 1/2 gallons of hydro fluid because I had a small leak on top of the hydro pump at the square post for the pintals. ( thanks to Willie59 for the in depth post on how to do this with ease) Once I replaced the o rings and seals I did the adjustment for neutral, then added maybe a bit to much fluid. anyhow I was able to work several hours on Friday evening and about 4 hrs on Saturday am when I had a problem with the entire machine bucking wildly. I have been working on moving a hill side and stock piling the dirt for future use. All I could think of is that I may have over filled and cause something to break loose and cause a blockage. I may be incorrect on this since I later noticed that the extra is just coming out of the vent tube. I was wondering if it allowed some air to be introduced and cause cavitation. No foam that I can see in the fluid. it is time for the filter to be replaced and I have one ready, but was waiting to see if I need to do more before I changed all the fluid and filter. I have been operating this machine for around ten years and the reaction that I get is similar to when I drive on asphalt the same jerking motion. when it starts I just completely let go of both sticks and it stops. I again placed the entire machine on blocks and re adjusted the neutral blocks and while I had it running off the ground I decided to go thru the process to see if it was jerking without a load. sure enough it ran flawless and fast in forward, backward, zero turn in both directions no jerking of the stick and no hold back pressure on the stick. what I mean by the hold back pressure,,, before I raised the machine again I tried to do several tests at different rpms so I ran it full force in forward and as it was trying to buck and jump I could feel the resistance of both sticks trying to force it backwards. almost like a pulsating action back and forth after about 8 seconds it is so wild it will literally give you whip lash. Needless to say I hope it is a simple filter change and fluid. thanks for any help in figuring this problem out. I have a 2003 T-190 with 2200 hrs. no major work ever except sprockets and a rear idler the rest is just filters, new muffler and new tracks. oil changes done regular, along with the filters for all fluids.