Repairing Bobcat 773

[willie59]

Our Bobcat 773 G Series has 3,100 hrs on it and the drive chains were getting loose. You could hear them slapping around while driving machine. Bought machine new, it has moved many truckloads of attachments. It's about ready for a new coupler, 3rd one. It's been a dang good machine. Figured it's time to rebuild the drive system. For any of you Bobcat owners that wonders what's down in there, here's a few pics.

Get the old girl on stands. Have to pull the axles to remove drive chain sprockets.



After removing axle sprockts and drive chains, here's a pic of the drive motor. You have a motor that's mounted on a motor carrier that's bolted to side of chain case. The motor carrier houses the shaft that sticks into chain case and has the drive sprockets on it.



Here's one of the removed drive motors. Seal is distorted, going to replace it.



Here's a disassembled motor carrier. You have to pluck that big seal out of the inside, then you can access the large snap ring that retains the shaft on the bearings. It all comes apart fairly easily. Biggest PITA...the motor carrier will not come out the access hole in the side of the Bobcat, you have to remove enough components to lift it straight up out of the belly of the machine.



Total parts from Bobcat; new chains, axle seals, motor carrier seals, and related gaskets, about $617.00. Decided to replace all the bearings in axles and motor carriers while I was in there, that's another $390.00 for Timken Bearings from bearing supplier. A little over $1,000 dollars in parts.

 

[AndyGrevis]

Hi Atco,
As i am in similar process of disassembly of my 863 to eliminate a few issues so might as well do chains also as one drive axle seal is leaking, a few questions pop up, how much is too much stretch in chains? does anyone have had them snap? Are there aftermarket chains available or BC only?
Do you have to remove motor carrier to remove chains?
Thanks!

 

[trukfan]

Pretty cool. We had the rear axle bearings replaced in our 763G in Aug. I went to replace the seals, since they were leaking, and lo and behold, the outer bearings's cages were broke. If it had been front the front, I would've tried the repair myself, but there's too much stuff over the rear for me to try, even with the service manual. Have you guys had any problems with the computer in your's? Ours went out in spring, kept flashing athe trouble code telling us there was an alternator/charging system problem. New alt. didn't fix it:Banghead, but the $800 computer did. Our machine has 5300 hrs. on it, and besides those headaches, it's been a good machine. I'd love a counterweight kit for the back, as some of our round bales get a little heavy for it, but such is the life for a skidloader.

 

[willie59]

Hi Atco,
As i am in similar process of disassembly of my 863 to eliminate a few issues so might as well do chains also as one drive axle seal is leaking, a few questions pop up, how much is too much stretch in chains? does anyone have had them snap? Are there aftermarket chains available or BC only?
Do you have to remove motor carrier to remove chains?
Thanks!

Hey Andy, haven't actually seen one pop, but i'd imagine things would get ugly if one did. Repaired one broke on a Mustang once, did quite a bit of damage in there, and we figure replacing chains is cheaper the replacing busted chains and all the carnage that follows. I would think someone could find a alternative replacement, not sure what the chain spec is though. The are Diamond brand chains. And I'm replacing with the continuous link chains, no master. The originals have lasted 3,000 hrs, and the bulk of that is the machine driving. If you have continuous links, you either have to cut the chain to remove, or remove the motor carrier to remove chains as left and right drive sprokets are practically against each other. If I get to continue assembly tommorow, I'll snap some pics of chains and sprockets installed.

Pretty cool. We had the rear axle bearings replaced in our 763G in Aug. I went to replace the seals, since they were leaking, and lo and behold, the outer bearings's cages were broke. If it had been front the front, I would've tried the repair myself, but there's too much stuff over the rear for me to try, even with the service manual. Have you guys had any problems with the computer in your's? Ours went out in spring, kept flashing athe trouble code telling us there was an alternator/charging system problem. New alt. didn't fix it:Banghead, but the $800 computer did. Our machine has 5300 hrs. on it, and besides those headaches, it's been a good machine. I'd love a counterweight kit for the back, as some of our round bales get a little heavy for it, but such is the life for a skidloader.

Hey trukfan. This has been a really good/reliable machine. Haven't had computer or BICS problems. The only recurring problem we have is it occasionally, for nor appearant reason, fries parking brake solenoid. It did it once while one of our workers was going full tilt forward. Talk about a sudden stop! Now that would stretch chains. As for our bearings, they weren't really bad, I could just see signs of scuffing on the cups. I told the boss, "nows the time to do them, your basically rebuilding the whole underdrive". Shouldn't have any problems for the rest of the life of this machine, and no problems is a good thing. The rear axle counterweights are almost necessary for us. Once of the attachments we handle with this unit is a big brush cutter, and it allows handling them with ease. :cool2

 

[trukfan]

Atco, good to here it's been a good machine for you. We're on our 3rd Bobcat, if you count the old 610 with the air cooled Wisconsin V-4, plus 2 763's. On our old one, I was going forward at a pretty good clip, hit pothole in the yard and somehow made the BICS think the seatbar became disengaged. I darn near bounced my head off the door of the cab. Does Bobcat offer a counterweight kit, or is your's an aftermarket type? I've never seen a Bobcat w/ counterweights, I've only seen them on the New Hollands I used to run at my old job. Perhaps a Interweb search is in order:beatsme

 

[willie59]

Atco, good to here it's been a good machine for you. We're on our 3rd Bobcat, if you count the old 610 with the air cooled Wisconsin V-4, plus 2 763's. On our old one, I was going forward at a pretty good clip, hit pothole in the yard and somehow made the BICS think the seatbar became disengaged. I darn near bounced my head off the door of the cab. Does Bobcat offer a counterweight kit, or is your's an aftermarket type? I've never seen a Bobcat w/ counterweights, I've only seen them on the New Hollands I used to run at my old job. Perhaps a Interweb search is in order:beatsme

I'll ask the boss where he got the axle counterweights for our machine. They're nice to have for heavy attachments, like a backhoe unit. Yep, it's fun when that brake comes on. Another thing I think we've all done at least once is be driving and reach to the control panel above door to operate Power Bobtach while driving, and instead hit the parking brake switch! The bull will buck ya then! :yup

 

[barklee]

Never had to take one of these apart. Do you have a pic of the chains? Sounds like a stupid question but what makes them become loose, do they stretch?

 

[willie59]

Never had to take one of these apart. Do you have a pic of the chains? Sounds like a stupid question but what makes them become loose, do they stretch?

Yep, they stretch over time as well as wear at every pin joint. A slight bit of wear at every pin joint with that many links is going to amount to some slack in the chains. And since Bobcat doesn't use adjusters, you get slack. I plan on taking some pics of everything during reassembly.

 

[willie59]

One thing about working in the chain case of Bobcats is there is no drain plug for the oil, just a fill level plug. If you have a small pump, it helps emptying the oil from chain case. You will find some metal debris in there from the brake plates as well as who knows where these metalic flakes come from! I had the machine on stands with it low on the front so oil would flow to the front of chain case. Washed the chain case first with diesel, then finished off with mineral spirits so it would evaporate and leave a nice clean chain case. To remove the diesel and mineral spirits, that's a perfect job for the "suck bucket". I've posted this before, but it's a good place to show the suck bucket again. Take a 5 gal bucket with lid. Put a hole in lid opposite pour spout. Make the hole so a piece of vinyl tubing fits snug in hole. Now you stick the hose of a shop vac over pour spout of bucket, and use vinyl tubing to suck up liquid or metal fragments. All the liquid and debris goes into the suck bucket, shop vac stays nice and dry. Got the chain case nice and clean using the suck bucket.

 

[trukfan]

Posted by ATCOEQUIP:

One thing about working in the chain case of Bobcats is there is no drain plug for the oil...

The 773 doesn't have a drain plug in the back, near the engine bay? On our 763, there's a removable skidplate under, and a little ahead of the engine, that you remove and gain access to the drain plug.

 

[willie59]

Yep, I saw the drain plug you mentioned in the back of the chain case. Didn't get to work on machine today, so I didn't check if there's a cover plate under machine to access drain plug. In our case, I simply used a small electric oil pump to transfer oil from chain case into 5 gal buckets. Finished clean up with suck bucket.

 

[td25c]

Cool thread ATCO,well done and informative.Love the "suck bucket" idea,I'l keep that in mind.

 

[willie59]

Cool thread ATCO,well done and informative.Love the "suck bucket" idea,I'l keep that in mind.

Well, just thought some Bobcat owners would like to see what's inside their machine 25c. The thing is, I was off on vacation last week, our truck driver (my occasional helper) took it apart. LoL, he's been sick with flu this week, so you know who gets to put it back together. :tong I'll take some more pics as I get components installed.

And the suck bucket is handy for a number of tasks. I've used it to remove water from the bottom of fuel tanks that had stuck or no drain valves. Take a short piece of steel hyd tubing that is just the right size to fit vinyl tubing inside steel tubing. This gives the vinyl tubing some weight at the end and allows you to drop it to bottom of tank. Then as you apply vacuum to bucket, you just watch the water go through clear vinyl tubing until it changes to the color of fuel, and your shop vac is nice and dry inside. :yup

 

[willie59]

Got to do a little more work on it today. Reinstalled the motor carriers after rebuilding, new bearings and seals. Be sure and put chains in place before installing both carriers, you can see they ain't gonna fit between the shaft sprockets.



Installed parking brake plates. You have to have a heavy snap ring plier with 90 degree tips. It's tight in there.

 

[willie59]

Then slide axle in housing with outer bearing installed on axle. Place inner bearing on axle splines, fit chain on sprocket, and fit sprocket on splined shaft of axle.



Inner bearing slides easily on axle splines, but will encounter machined surface that bearing is press fit. At this point, you can install sprocket retainer bolt and washer, start tightening bolt with wrench to press inner bearing in place. Bad part is, a ratchet won't fit in here, it's wrench all the way.



Got everything installed.



Time to fit the outer axle seals. An old excavator pin bushing fit perfect for knocking tool.



Pour the oil in one of the access cover holes until it reaches fill level plug on front of chain case. Lot easier to pour in holes than through that little hole up front. Now just install covers with new gaskets and finish things up.

 

[Dufoman]

very good pics

I have just redone the axle bearings and seals on a 753...wish I had seen your excellent pics first...I enjoy your posts...Keep them coming...

 

[willie59]

I have just redone the axle bearings and seals on a 753...wish I had seen your excellent pics first...I enjoy your posts...Keep them coming...

Welcome to the forum Dufoman. :usa

Sounds like you had a pretty good little project with your 753.

 

[trouble007]

damm i which i would have seen this earlier we just spent all day trying to remove that plug that was rusted and striped this just made my day

 

[willie59]

damm i which i would have seen this earlier we just spent all day trying to remove that plug that was rusted and striped this just made my day

Yep, that's enough to bang your head over. :Banghead

Welcome to the forum trouble007. :usa

 

[trouble007]

ya, i hope after this little problem my boss will get it through his head how important proper maintenance is this could probably been avoided if the plug had been opened every 250 hours like the manual suggests. o well, another lesson learned the hard way.