Bobcat Clark 720 - My new (old) toy broke - No Movement?

SteamNSteer · Feb 3, 2014

Hey everyone, I finally purchased an old barn find, a Clark Bobcat 720 with a little 4 cylinder gas engine. It took a while to pull it out of the mud, but i got it cleaned up and running well. Its not pretty, but worked great around the house for my little projects all summer. Well, as I jumped off the cat to get something, it made a horrible noise, i ran over and cut it off. Seeing nothing, I cranked it up, and again, real bad noise. I don't think its the motor, I now have no movement in the wheels or the arms/bucket. I am thinking maybe the hydraulic pump quit on me, and after lifting the cage, I think i see it, but before unhooking untold number of hoses, I wanted to check with you guys to see if you had any suggestions. Thanks, I really appreciate any help.

OldMachinist · Feb 3, 2014

U-joints in the coupling between the engine and pumps broke would be my guess. Don't run the engine any more till you're sure that's not the problem. It can do some serious damage if pieces of the u-joints or coupling start flying about.

SteamNSteer · Feb 3, 2014

OldMachinist said:
U-joints in the coupling between the engine and pumps broke would be my guess. Don't run the engine any more till you're sure that's not the problem. It can do some serious damage if pieces of the u-joints or coupling start flying about.

Well, Once i figured how to move all the stuff out of the way, I seen the Universal joint. Now, I see something in the bottom of the cowling that looks like a belt, all twisted up. Wondered why a belt would be in there, oh well, I reach down there and pulled out the "Belt". I jumped, fell backwards on the ice, and a dang big ol blacksnake fell on my chest. I threw it off, and got back up. I walked over and and kicked it. It spun around on the ice, and didn't move. I then realized, that I was having a fit with a dead black snake, but non the less, highly unexpected. Wife is still laughing. Dang snakes, I don't mind them if I see them, but when they are sneeky, thats a whole other story.

Now, back to the Cat. With the fluid cooler out of the way, the u-joint is flimsy. I touch they key, and the motor and joint spins, but what it is hooked to doesn't. It's like when you don't get a u joint hooked up to a 3 point attachment all the way, just flops around. Haven't quite figured what to remove to get a better look, but that explains why I lost all my power. Do these just slip on somehow, or better off getting a new one, or rebuilding this one. Thanks again!

OldMachinist · Feb 3, 2014

SteamNSteer said:
Well, Once i figured how to move all the stuff out of the way, I seen the Universal joint. Now, I see something in the bottom of the cowling that looks like a belt, all twisted up. Wondered why a belt would be in there, oh well, I reach down there and pulled out the "Belt". I jumped, fell backwards on the ice, and a dang big ol blacksnake fell on my chest. I threw it off, and got back up. I walked over and and kicked it. It spun around on the ice, and didn't move. I then realized, that I was having a fit with a dead black snake, but non the less, highly unexpected. Wife is still laughing. Dang snakes, I don't mind them if I see them, but when they are sneeky, thats a whole other story. Now, back to the Cat. With the fluid cooler out of the way, the u-joint is flimsy. I touch they key, and the motor and joint spins, but what it is hooked to doesn't. It's like when you don't get a u joint hooked up to a 3 point attachment all the way, just flops around. Haven't quite figured what to remove to get a better look, but that explains why I lost all my power. Do these just slip on somehow, or better off getting a new one, or rebuilding this one. Thanks again!

Engine needs to come out to service the coupling.

antfarmer2 · Feb 3, 2014

OldMachinist said:
Engine needs to come out to service the coupling.

You can get the ujoints from loadersorceparts for 97 bucks same as my 743 I just did but be careful I had to get four shorter bolts the ones they sent four were the wrong size (to long) and would put the ujoints in a bind easy to miss and would gusse that your spline might be bad hope not the shaft too

antfarmer2 · Feb 3, 2014

antfarmer2 said:
You can get the ujoints from loadersorceparts for 97 bucks same as my 743 I just did but be careful I had to get four shorter bolts the ones they sent four were the wrong size (to long) and would put the ujoints in a bind easy to miss and would gusse that your spline might be bad hope not the shaft too

Also make sure you use blue locktight I went a about 22 lb tourqe with the lube from the blue could never find the right tourqe evan the dealer could not tell me good time to clean the cooler and the rad and look at the seals

SteamNSteer · Feb 3, 2014

antfarmer2 said:
Also make sure you use blue locktight I went a about 22 lb tourqe with the lube from the blue could never find the right tourqe evan the dealer could not tell me good time to clean the cooler and the rad and look at the seals

Thank all of you guys! I am very glad I joined this forum! I'll get the motor out, but weatherman is calling 5-13" of snow tomorrow (Nice range huh?) , so I guess I have to wait a few days (Broke down in my side yard). Anyway, what keeps that universal joint hooked onto the pump, is there some type of sheer pin or bolt that keeps it on there. Its just floppy where it hooks onto the pump. Im trying to figure out how it came off the pump Cheers, -John

antfarmer2 · Feb 3, 2014

SteamNSteer said:
Thank all of you guys! I am very glad I joined this forum! I'll get the motor out, but weatherman is calling 5-13" of snow tomorrow (Nice range huh?) , so I guess I have to wait a few days (Broke down in my side yard). Anyway, what keeps that universal joint hooked onto the pump, is there some type of sheer pin or bolt that keeps it on there. Its just floppy where it hooks onto the pump. Im trying to figure out how it came off the pump Cheers, -John

There is a spline with a key on the hydro shaft on mine I had the rad and the cooler off to slide it back togther when you put the engine in

OldMachinist · Feb 4, 2014

antfarmer2 said:
There is a spline with a key on the hydro shaft on mine I had the rad and the cooler off to slide it back togther when you put the engine in

The coupling is bolted to the engine flywheel and just slides on the splined pump shaft so if it's flopping around something is broken.

jerry · Feb 4, 2014

OldMachinist said:
The coupling is bolted to the engine flywheel and just slides on the splined pump shaft so if it's flopping around something is broken.

When you get around to buying the u joints be sure to get the ones that grease from the end of the cross. If you get the ones that grease from the center of the cross it will be much harder to grease.

SteamNSteer · Feb 4, 2014

OldMachinist said:
The coupling is bolted to the engine flywheel and just slides on the splined pump shaft so if it's flopping around something is broken.

Ahh, i understand now. Well, I'll give it a go. Is there other things I should do while the engine is out? I do want to check the gas tank, im sure its full of crud. Also the parking brake doesn't do anything. I finally got a service manual, and seen the 10 micron filter, I think i'll change it out as well. Trying to think of things to do to the machine since it had been abandoned so long. Looks like I won't be able to do anything until the weekend, hopefully the snow will move on out. Thanks again guys

antfarmer2 · Feb 4, 2014

SteamNSteer said:
Ahh, i understand now. Well, I'll give it a go. Is there other things I should do while the engine is out? I do want to check the gas tank, im sure its full of crud. Also the parking brake doesn't do anything. I finally got a service manual, and seen the 10 micron filter, I think i'll change it out as well. Trying to think of things to do to the machine since it had been abandoned so long. Looks like I won't be able to do anything until the weekend, hopefully the snow will move on out. Thanks again guys

The ones from loadersorcesparts are the ones jerry likes just like the ones on my 743 but whatch the bolts also look at the steal lines my two bottom ones where they cross failed

OldMachinist · Feb 4, 2014

antfarmer2 said:
The ones from loadersorcesparts are the ones jerry likes just like the ones on my 743 but whatch the bolts also look at the steal lines my two bottom ones where they cross failed

While you have the engine out remove all the tin shrouds and clean the cooling fins. After it sat so long I'd expect there to be all kinds of critter nests in there. The Wisconsin engine doesn't like running overheated they tend to vapor lock easy also it can warp heads and blow head gaskets.

antfarmer2 · Feb 4, 2014

OldMachinist said:
While you have the engine out remove all the tin shrouds and clean the cooling fins. After it sat so long I'd expect there to be all kinds of critter nests in there. The Wisconsin engine doesn't like running overheated they tend to vapor lock easy also it can warp heads and blow head gaskets.

Good idea then put your snake back lmao

Tazza · Feb 5, 2014

antfarmer2 said:
Good idea then put your snake back lmao

hehe i loved the story of the snake and laughing wife

HanSolo · Feb 11, 2014

SteamNSteer said:
Ahh, i understand now. Well, I'll give it a go. Is there other things I should do while the engine is out? I do want to check the gas tank, im sure its full of crud. Also the parking brake doesn't do anything. I finally got a service manual, and seen the 10 micron filter, I think i'll change it out as well. Trying to think of things to do to the machine since it had been abandoned so long. Looks like I won't be able to do anything until the weekend, hopefully the snow will move on out. Thanks again guys

Agree with Old Machinist. The M700 I bought had pieces of carpet, walnut shells and all other manner of mice nesting under the engine tins. When I first got it running there was a couple of small engine fires started by that junk. Before that, when I first went to look at it, there was a copper head snake skin draped across the seat. The PO said he had a problem with those on his property and I was mindful of that digging into the belly pan later.

SteamNSteer · Feb 15, 2014

HanSolo said:
Agree with Old Machinist. The M700 I bought had pieces of carpet, walnut shells and all other manner of mice nesting under the engine tins. When I first got it running there was a couple of small engine fires started by that junk. Before that, when I first went to look at it, there was a copper head snake skin draped across the seat. The PO said he had a problem with those on his property and I was mindful of that digging into the belly pan later.

Well team, I got the motor out, and no more snakes. Lots of Dirt, sticks, oil and mess. The actual uJoint looks good except for where it mates with the pump. That part looks wallered out. Also on the pump, it looks a little worn. When I took the motor off, I seen what I am going to call the motor pan, a big piece of metal the motor bolted to. It was just flopping around. I have no idea how a human is supposed to put nuts and bolts into that, as i couldn't fit. But I was able to simply lift it up. I guess the nuts vibrated off, and I am suspecting there is some type of rubber piece that fits in the wholes, although there are just tiny reminders of it. My guess is that these bushings or mounts wore down over 30 years, and allowed the motor pan to slide forward enough to allow slipping and wallering out. So, I'll pick up the new u-joint yall talked about, but looking at the picture do you think i need the piece that goes on the pump as well? Also need to find the little bushings/rubber mounts, and while im at it, I think i will replace the alternator belt, as it looks easy to do now rather than later. Lastly, I seen a huge white filter(i think) directly below the pump, Im guessing that should probably be replaced as well. Thanks guys, highly appreciated!!!.
http://imageshack.com/a/img812/4199/9u7u.jpg

http://imageshack.com/a/img833/821/5g7k.jpg

Mikefromcny · Feb 15, 2014

SteamNSteer said:
Well team, I got the motor out, and no more snakes. Lots of Dirt, sticks, oil and mess. The actual uJoint looks good except for where it mates with the pump. That part looks wallered out. Also on the pump, it looks a little worn. When I took the motor off, I seen what I am going to call the motor pan, a big piece of metal the motor bolted to. It was just flopping around. I have no idea how a human is supposed to put nuts and bolts into that, as i couldn't fit. But I was able to simply lift it up. I guess the nuts vibrated off, and I am suspecting there is some type of rubber piece that fits in the wholes, although there are just tiny reminders of it. My guess is that these bushings or mounts wore down over 30 years, and allowed the motor pan to slide forward enough to allow slipping and wallering out. So, I'll pick up the new u-joint yall talked about, but looking at the picture do you think i need the piece that goes on the pump as well? Also need to find the little bushings/rubber mounts, and while im at it, I think i will replace the alternator belt, as it looks easy to do now rather than later. Lastly, I seen a huge white filter(i think) directly below the pump, Im guessing that should probably be replaced as well. Thanks guys, highly appreciated!!!.
http://imageshack.com/a/img812/4199/9u7u.jpg

http://imageshack.com/a/img833/821/5g7k.jpg

Looks like the coupling gave out. Since you already have the u joint, I'd replace both sides of the coupler and you should be back in business.

HanSolo · Feb 16, 2014

SteamNSteer said:
Well team, I got the motor out, and no more snakes. Lots of Dirt, sticks, oil and mess. The actual uJoint looks good except for where it mates with the pump. That part looks wallered out. Also on the pump, it looks a little worn. When I took the motor off, I seen what I am going to call the motor pan, a big piece of metal the motor bolted to. It was just flopping around. I have no idea how a human is supposed to put nuts and bolts into that, as i couldn't fit. But I was able to simply lift it up. I guess the nuts vibrated off, and I am suspecting there is some type of rubber piece that fits in the wholes, although there are just tiny reminders of it. My guess is that these bushings or mounts wore down over 30 years, and allowed the motor pan to slide forward enough to allow slipping and wallering out. So, I'll pick up the new u-joint yall talked about, but looking at the picture do you think i need the piece that goes on the pump as well? Also need to find the little bushings/rubber mounts, and while im at it, I think i will replace the alternator belt, as it looks easy to do now rather than later. Lastly, I seen a huge white filter(i think) directly below the pump, Im guessing that should probably be replaced as well. Thanks guys, highly appreciated!!!.
http://imageshack.com/a/img812/4199/9u7u.jpg

http://imageshack.com/a/img833/821/5g7k.jpg

The splines on the shaft and the coupler look pretty worn to me. I'd replace both of those (if you can get them new) and the u-joint. The motor plate mounts you see remains of are rubber pads with large washers. If those aren't available new, you might be able to fabricate them from chucks of old tires. If I remember right correctly, those were about 3/4" thick on my M700. They are tricky to position when you slide the motor mounted on the plate back into the machine. I think I ended up sliding mine back in without those in place, then I used a short pry-bar to lift each side and insert the mounts. There were some hard lines on the right side that made that procedure even more difficult. And then tightening the bolts without a helper was a whole 'nother challenge

Bobcat Clark 720 - My new (old) toy broke - No Movement?

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