763 leaves black tire marks everywhere

Help Support SkidSteer Forum:

m610

Well-known member
Joined
Apr 1, 2006
Messages
173
I was told about a 763 used to maintain an employee park at an insurance group. The problem is that they don't know why it leaves black tire tracks all over their concrete surfaces, It's used to smooth the baseball field clay and around the wooded area to remove debris thrown from the highway and for clearing out weeds from around the lake. Machine starts with difficulty then runs fine, doesn't seem to pull to one side or the other, but tires wear out every few months and the black marks are very noticeable. I tried it out myself and all seems normal but going in a straight line with a load of dirt it leaves black tire tracks on the concrete. Of course all around the grounds there's torn up grass too, but I think it's from their young and crazy operators. What could cause a machine to wear down tires when going straight, when everything on the Bobcat looks normal, and the chains seem normal and not stretched? The machine ls also quite rusty and scratched for a 1994 model. It sits outside behind the storage building. I was thinking of making an offer for this thing. Any ideas?
 

skidsteer.ca

Well-known member
Joined
Jan 20, 2006
Messages
3,853
Are both the tires on each side of the machine vary close to the same size? have the same air pressure? The 2 tires for the right are linked soilid mechaincally to each other as are the 2 on the left. Both front and rear tires are forced to turn the same rpm.
Other then that no reason I can thik of
Ken
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
Are both the tires on each side of the machine vary close to the same size? have the same air pressure? The 2 tires for the right are linked soilid mechaincally to each other as are the 2 on the left. Both front and rear tires are forced to turn the same rpm.
Other then that no reason I can thik of
Ken
As ken said, all i could think of is tyre size front and rear. Thats why the manual tells you when you replace tyres do one side, never just front or back. For example if they are worn on the front and new on the back they will turn at different speeds and wear out leaving black marks even going in a straight line.
 

m610

Well-known member
Joined
Apr 1, 2006
Messages
173
As ken said, all i could think of is tyre size front and rear. Thats why the manual tells you when you replace tyres do one side, never just front or back. For example if they are worn on the front and new on the back they will turn at different speeds and wear out leaving black marks even going in a straight line.
OK I went back there after work to look at the Bobcat. I had recommended that they swap front and rear tires and measure the circumference of each. The front tires are a bit larger as the rear tires wear faster. So I asked them to put the larger tires on the left side and the smaller on the right. Of course it tends to turn to the right now. Strangely it still leaves black marks, but more distinct on the left now. I put tape on the wheels in the up position on both sides, then got in the Bobcat and went straight. The wheels are not turning at the same rate as the rear wheel seems to turn faster than the front. It's the rear tires leaving the marks, but there's more odd behavior to note. The kid who runs the Bobcat failed to mention that it has strange steering behavior. At low speed it works fine, but at higher speeds there's a pulsation in the reverse position on each side. if you steer left or right it has a delay before turning, from a standstill it delays then kicks in suddenly, jerking the machine to one side. When going backwards on both sides it does it so hard the machine falls forward on it's bucket. I checked the fluid level and it's normal but after running the machine it seems a bit more aerated than normal. There's a lot of oil and grease in the engine area, not sure if it's just poor maintenance or a leak but it's ugly. I lifted up the front of the machine with the bucket and rotated the wheels, there's about an inch of play, nothing too excessive I think. Did the same wih the rear wheels by sticking the bucket under a forklift and the rear wheels have the same free play. Axles don't seem to have a wobble like if the bearings are bad. The company wants to purchase a new machine, they were thinking of one of those new fancy all wheel steer loaders. I want to buy the old one, and the trick is to see what this thing is worth. The hour meter is rusted out with 3,2XX on it. The engine seems to be worn out as it has difficulty starting. There's rust all over the machine, but it is a 1994 model. It was bought used from the Bobcat dealer in 1996. According to what I heard the problems may have been related to when the machine was driven into the mud by the lake and it sunk in. That was a few years ago.
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
OK I went back there after work to look at the Bobcat. I had recommended that they swap front and rear tires and measure the circumference of each. The front tires are a bit larger as the rear tires wear faster. So I asked them to put the larger tires on the left side and the smaller on the right. Of course it tends to turn to the right now. Strangely it still leaves black marks, but more distinct on the left now. I put tape on the wheels in the up position on both sides, then got in the Bobcat and went straight. The wheels are not turning at the same rate as the rear wheel seems to turn faster than the front. It's the rear tires leaving the marks, but there's more odd behavior to note. The kid who runs the Bobcat failed to mention that it has strange steering behavior. At low speed it works fine, but at higher speeds there's a pulsation in the reverse position on each side. if you steer left or right it has a delay before turning, from a standstill it delays then kicks in suddenly, jerking the machine to one side. When going backwards on both sides it does it so hard the machine falls forward on it's bucket. I checked the fluid level and it's normal but after running the machine it seems a bit more aerated than normal. There's a lot of oil and grease in the engine area, not sure if it's just poor maintenance or a leak but it's ugly. I lifted up the front of the machine with the bucket and rotated the wheels, there's about an inch of play, nothing too excessive I think. Did the same wih the rear wheels by sticking the bucket under a forklift and the rear wheels have the same free play. Axles don't seem to have a wobble like if the bearings are bad. The company wants to purchase a new machine, they were thinking of one of those new fancy all wheel steer loaders. I want to buy the old one, and the trick is to see what this thing is worth. The hour meter is rusted out with 3,2XX on it. The engine seems to be worn out as it has difficulty starting. There's rust all over the machine, but it is a 1994 model. It was bought used from the Bobcat dealer in 1996. According to what I heard the problems may have been related to when the machine was driven into the mud by the lake and it sunk in. That was a few years ago.
Thats pretty odd.....
I was thinking possibly chains or sprockets but you said the wheels have about the same amount of play (which is normal). The shuddering, does it do it when going from revers to forward too? if so it could be a broken tooth or chain problem. If it still has plenty of power i would say its not hydrostatics but i could be wrong.
On my 743, and i believe most other machines are the same i have 2 chains per side. One runs from the rear sprocket attached to the axle to a central double sprocket attached to the gearbox that attaches to the hydrostatic motor. The other chain runs from the central sprocket to the front sprocket attached to the axle. From that, there is no logical reason that the front spins differently to the rear unless there is a sprocket or chain problem. If there was slack or a missing tooth it will buck but it will do this all the time at the same spot, not just when taking off.
You could see what they are offered for a trade and pay them that if you think its worth the price.
With 3,200+ Hours up i would say you will be up for an engine rebuild, thats about a normal life span for a diesel engine. They get hard to start, but when warm they work well, so if you can live with the hard starting you can put the engine off a bit longer.
Let us know how it all goes!
 

skidsteer.ca

Well-known member
Joined
Jan 20, 2006
Messages
3,853
Thats pretty odd.....
I was thinking possibly chains or sprockets but you said the wheels have about the same amount of play (which is normal). The shuddering, does it do it when going from revers to forward too? if so it could be a broken tooth or chain problem. If it still has plenty of power i would say its not hydrostatics but i could be wrong.
On my 743, and i believe most other machines are the same i have 2 chains per side. One runs from the rear sprocket attached to the axle to a central double sprocket attached to the gearbox that attaches to the hydrostatic motor. The other chain runs from the central sprocket to the front sprocket attached to the axle. From that, there is no logical reason that the front spins differently to the rear unless there is a sprocket or chain problem. If there was slack or a missing tooth it will buck but it will do this all the time at the same spot, not just when taking off.
You could see what they are offered for a trade and pay them that if you think its worth the price.
With 3,200+ Hours up i would say you will be up for an engine rebuild, thats about a normal life span for a diesel engine. They get hard to start, but when warm they work well, so if you can live with the hard starting you can put the engine off a bit longer.
Let us know how it all goes!
Do the glow plugs work? You should see the volt meter dip a volt or 2 when you hit the switch.
What is the ambient temp where you are? It starts ok after it has run a minute or 2 or always hard starting? How much blowby does the engine have? Did they say it was using anly oil. Is there any play in the bobtach pins?
With your tape idea do both left tires make exactly one revolution at the same time? How about the right side?
If it is a 94 it shuld have the electric park brake/pin and a BICS controler on the right side of the seat beside the backrest. (A black box with 5 green lights on it)
Ken
 

skidsteer.ca

Well-known member
Joined
Jan 20, 2006
Messages
3,853
Thats pretty odd.....
I was thinking possibly chains or sprockets but you said the wheels have about the same amount of play (which is normal). The shuddering, does it do it when going from revers to forward too? if so it could be a broken tooth or chain problem. If it still has plenty of power i would say its not hydrostatics but i could be wrong.
On my 743, and i believe most other machines are the same i have 2 chains per side. One runs from the rear sprocket attached to the axle to a central double sprocket attached to the gearbox that attaches to the hydrostatic motor. The other chain runs from the central sprocket to the front sprocket attached to the axle. From that, there is no logical reason that the front spins differently to the rear unless there is a sprocket or chain problem. If there was slack or a missing tooth it will buck but it will do this all the time at the same spot, not just when taking off.
You could see what they are offered for a trade and pay them that if you think its worth the price.
With 3,200+ Hours up i would say you will be up for an engine rebuild, thats about a normal life span for a diesel engine. They get hard to start, but when warm they work well, so if you can live with the hard starting you can put the engine off a bit longer.
Let us know how it all goes!
Mayby someone has put the wrong # of tooth sprockets on either the front or the rear.
If the back seems faster try this
Mark the top of both left tires, and drive ahead 5 full turns on the front tire, did the back one turn more then 5 turns? Howbout if you go ten full turns. If the sprockets are mismatched the back tire should now be twice as far ahead of the front as it was in the 5 turn test.
Ken
 

m610

Well-known member
Joined
Apr 1, 2006
Messages
173
Mayby someone has put the wrong # of tooth sprockets on either the front or the rear.
If the back seems faster try this
Mark the top of both left tires, and drive ahead 5 full turns on the front tire, did the back one turn more then 5 turns? Howbout if you go ten full turns. If the sprockets are mismatched the back tire should now be twice as far ahead of the front as it was in the 5 turn test.
Ken
The glow plugs seem to work as the voltmeter does drop when key is turned, then goes up when started. I went straight down the parking lot for at least 100 feetthen stopped with the front rire's tape up. The rear tire's tape was near the bottom, like it had rotated around more than 90 degrees from starting in top position. It was 80 degrees when I got there and started the engine. Pulling the oil filler does not show any blow by but I am sure it's being sucked in the ventilation system anyway. Radiator looks to be in exceptional shape but the hydraulic fluid looks too light colored unless newer machines use a different type than older ones. I did see the black box on the side of the seat but no visible lights just rust. The bobtach system looks completely unused, and the levers are quite rusty but the pins do have a lot of grease around the fittings. I was not aware that there are different sized sprockets that fit any given Bobcat. After work I am going to visit the machine again, is there anything I should look for? If it's not a basket case and the price is right I look forward to adding it to my collection.
 

Tazza

Administrator
Staff member
Admin
Joined
Dec 7, 2004
Messages
16,697
The glow plugs seem to work as the voltmeter does drop when key is turned, then goes up when started. I went straight down the parking lot for at least 100 feetthen stopped with the front rire's tape up. The rear tire's tape was near the bottom, like it had rotated around more than 90 degrees from starting in top position. It was 80 degrees when I got there and started the engine. Pulling the oil filler does not show any blow by but I am sure it's being sucked in the ventilation system anyway. Radiator looks to be in exceptional shape but the hydraulic fluid looks too light colored unless newer machines use a different type than older ones. I did see the black box on the side of the seat but no visible lights just rust. The bobtach system looks completely unused, and the levers are quite rusty but the pins do have a lot of grease around the fittings. I was not aware that there are different sized sprockets that fit any given Bobcat. After work I am going to visit the machine again, is there anything I should look for? If it's not a basket case and the price is right I look forward to adding it to my collection.
If it was me, i would take out a glow plug or 2 just to see if they are worn. They may be a little worn out, i had a set that tapered off to almost a point. When the got warm, they would glow at the back but not the tip making it a real pig to start!.
There has to be a sprocket problem!!! thats the only reason it would rotate that much more at the back than the front. But if they did this, the chain would be a different length....
 

skidsteer.ca

Well-known member
Joined
Jan 20, 2006
Messages
3,853
If it was me, i would take out a glow plug or 2 just to see if they are worn. They may be a little worn out, i had a set that tapered off to almost a point. When the got warm, they would glow at the back but not the tip making it a real pig to start!.
There has to be a sprocket problem!!! thats the only reason it would rotate that much more at the back than the front. But if they did this, the chain would be a different length....
M610
Did you ever solve the black mark mystery, or did ya just walk away?
Ken
 

m610

Well-known member
Joined
Apr 1, 2006
Messages
173
M610
Did you ever solve the black mark mystery, or did ya just walk away?
Ken
Actually I am still trying to get that machine. After doing a little research, I figured out who last serviced the machine, and it had come apart for axle bearing replacement. Evidently there was damage to sprockets from loose chains that distorted the teeth. Most likely he replacements were the wrong size. I am also looking at an 843 sitting in a backyard, but the owner thinks it's worth a fortune. One thing I have noticed is that all bobcats seem to wear tires on the right side more than the left. Guess people like to turn right more than left. Still looking for the right loader, can't wait to see if I get one.
 
Top