Bobcat 643 disconnect u-joint and buying manuals

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mdj

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Hi everyone

I wont to by the service and parts manual on eBay, for my bobcat 643, but I am not sure if I should buy the operators manual, is it any good?

I have to chance my u-joint, how do I disconnect it, the easy way? (if there is anyJ)

/Mdj
 

Tazza

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Honestly the operators manual isn't worth it. Its really just common sense and service information. If you have the service manual you really don't need the operators one.
Removing the U-Joints are easy (well kinda).
Remove all hoses/fuel lines/wiring from the engine. Including the inlet and exhaust hoses/pipes. Remove the 4 bolts holding the engine down to the chassis. Use a block and tackle or some sort of hoist to a chain connecting to the 2 lifting points on the side if the head. Lift it up and pull the engine back and out. With the engine out you can replace the u-joints. Ensure you grease them up before re-installing the engine.
Installing it is the opposite but you need 2 ppl for this one. Lif the engine and sit it in the engine bay but not all the way back, you need to let the front sit on the lip of the chassis as you need to line the spine and drive up on the pump. Lay on the pump and push your hand through the blower housing and hold the joint up in-line with the spline on the pump, do NOT have any fingers or any part of your hand between the spline and joint, if the engone slips forward too fast you could loose a finger!. Get your helper to SLOWLY bar the engine forward till its just engaged. If it doesn't quite line up turn the engine slightly, i found holding the fan belt works for small movements. Push the engine forward till you can line the mounting bolts up. Re-connect everything, re-prime the fuel system and you are done!
Honestly it is easier than it sounds, but a helper is really a plus! Keep all your fuel hoses clean, plug them and the air intake. You don't want to damage anything. I pulled the engine on my 743 (same basic setup as the 643) worked on the joints and re-installed it in just over 2 hours. Thats from running to running. Take your time and you will be fine. Any questions just yell
 
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mdj

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Honestly the operators manual isn't worth it. Its really just common sense and service information. If you have the service manual you really don't need the operators one.
Removing the U-Joints are easy (well kinda).
Remove all hoses/fuel lines/wiring from the engine. Including the inlet and exhaust hoses/pipes. Remove the 4 bolts holding the engine down to the chassis. Use a block and tackle or some sort of hoist to a chain connecting to the 2 lifting points on the side if the head. Lift it up and pull the engine back and out. With the engine out you can replace the u-joints. Ensure you grease them up before re-installing the engine.
Installing it is the opposite but you need 2 ppl for this one. Lif the engine and sit it in the engine bay but not all the way back, you need to let the front sit on the lip of the chassis as you need to line the spine and drive up on the pump. Lay on the pump and push your hand through the blower housing and hold the joint up in-line with the spline on the pump, do NOT have any fingers or any part of your hand between the spline and joint, if the engone slips forward too fast you could loose a finger!. Get your helper to SLOWLY bar the engine forward till its just engaged. If it doesn't quite line up turn the engine slightly, i found holding the fan belt works for small movements. Push the engine forward till you can line the mounting bolts up. Re-connect everything, re-prime the fuel system and you are done!
Honestly it is easier than it sounds, but a helper is really a plus! Keep all your fuel hoses clean, plug them and the air intake. You don't want to damage anything. I pulled the engine on my 743 (same basic setup as the 643) worked on the joints and re-installed it in just over 2 hours. Thats from running to running. Take your time and you will be fine. Any questions just yell
Hi Tazza

Thanks for you reply, I have look ad it, and it looks quit easy.

But I have another problem, I get air I the hydraulic system, does anyone have and idea
where it can come from?

And another problem, there is a loud noise coming from the back of the hydrostat in the right side looking from the bucket, when I use the left stick, any idea?

/mdj
 

Tazza

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Hi Tazza

Thanks for you reply, I have look ad it, and it looks quit easy.

But I have another problem, I get air I the hydraulic system, does anyone have and idea
where it can come from?

And another problem, there is a loud noise coming from the back of the hydrostat in the right side looking from the bucket, when I use the left stick, any idea?

/mdj
Have you done any work on it at all? The air could be whats causing the noise. Air generally doesn't get into the system on its own, but if you repair say a ram it will get in that way but running the machine will get the air out over time. If you have done no work, it could be a seal problem in a drive motor, it can draw in air that way.
 
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mdj

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Have you done any work on it at all? The air could be whats causing the noise. Air generally doesn't get into the system on its own, but if you repair say a ram it will get in that way but running the machine will get the air out over time. If you have done no work, it could be a seal problem in a drive motor, it can draw in air that way.
No, I haven't done any work on it yet, I will fine that leak before I change the u-drive, but the previous owner has replaces the left drive motor, but not recently I think.
If the machine has stand still a few days it get worse and the bucket arm hack when I lift them.
I got an oil leak, it seems to come from the middle of the bottom on the hydrostat, could it be there the air comes in? Or can it come in the system without there leaking oil out?
 

Tazza

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No, I haven't done any work on it yet, I will fine that leak before I change the u-drive, but the previous owner has replaces the left drive motor, but not recently I think.
If the machine has stand still a few days it get worse and the bucket arm hack when I lift them.
I got an oil leak, it seems to come from the middle of the bottom on the hydrostat, could it be there the air comes in? Or can it come in the system without there leaking oil out?
Hopefully that is where the air is coming from. Are you sure its coming from the middle of the pump? Its really hard to see under the pump to know 100% where the oil is coming from. Its unusual for it to leak between sections but i guess anything is possible. Most pump leaks are from the seal where the pump connects to the motor.
So you mention that using the hydraulics is all jumpy too? not just the hydrostats? For it to have that sor tof problem you have a lot of air coming in. Usually a pluged filter will cause airation of the oil but it will only be a problem with the drive not the hydraulics.
I would start with the oil leak and work from there. Sometimes the hose that twists from the port block to the bottom of the control block (return line) is a problem, it may be an idea to check that hose too. There is also a small hose that runs under the pump from the motors, this could have worn through causing a leak?
If the machine is dirty give it a real good clean with de-greaser and a pressure washer goes well here too (steam is even better). This will help you find out just where the leak(s) are coming from.
 
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mdj

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Hopefully that is where the air is coming from. Are you sure its coming from the middle of the pump? Its really hard to see under the pump to know 100% where the oil is coming from. Its unusual for it to leak between sections but i guess anything is possible. Most pump leaks are from the seal where the pump connects to the motor.
So you mention that using the hydraulics is all jumpy too? not just the hydrostats? For it to have that sor tof problem you have a lot of air coming in. Usually a pluged filter will cause airation of the oil but it will only be a problem with the drive not the hydraulics.
I would start with the oil leak and work from there. Sometimes the hose that twists from the port block to the bottom of the control block (return line) is a problem, it may be an idea to check that hose too. There is also a small hose that runs under the pump from the motors, this could have worn through causing a leak?
If the machine is dirty give it a real good clean with de-greaser and a pressure washer goes well here too (steam is even better). This will help you find out just where the leak(s) are coming from.
Well you right, it hard to se where it comes from, I will give it a good cleaning.
It doesn't seem to be jumpy when I use hydrostats, just very noisy especially when I use the left stick (looking form the behind).
The other day when I drive it, suddenly I couldn't turn it around; I turn it of, waited a few moments and started again, and it woes ok again, could it be air too?
 

Tazza

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Well you right, it hard to se where it comes from, I will give it a good cleaning.
It doesn't seem to be jumpy when I use hydrostats, just very noisy especially when I use the left stick (looking form the behind).
The other day when I drive it, suddenly I couldn't turn it around; I turn it of, waited a few moments and started again, and it woes ok again, could it be air too?
That could indeed be air.... But as it seems to be worse on the left side, so it really could be a problem with the hydro pump too. The hydro pump can be worked on by anyone with patience and common sense. If its just the swash plate that is worn you can use sand paper and a piece of glass to make it flat again. But this usually just causes low power and not airation of the oil. It really sounds like a filter issue but as it only seems to be a real problem on one side which sounds like the pump may need attention, its hard to say exactly what it is..... Its hard to say its the pump or motor or even a filter without fiddling more. You could try swapping motors over but it depends in your machine is a simple spline fit or if its the older style that has a bolt through it making it a pest to remove.
Sorry i can't be of more use than that, its really hard to say what it is without actually seeing it and trying a few things.
One last thing, is there a square block on top of the hydraulic pump with a 3 hoses going in to it from the left side (looking from the bucket at the pump)? The older machines ran a suction line filter behind the centre hose, behind the fitting in the block (the fitting that looks larger than the other 2). When it gets clogged it causes problems EXACTLY like what you are having. If you have that style, pull the hose and fitting out and replace or give the filter a good clean with diesel and compressed air.
 
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mdj

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That could indeed be air.... But as it seems to be worse on the left side, so it really could be a problem with the hydro pump too. The hydro pump can be worked on by anyone with patience and common sense. If its just the swash plate that is worn you can use sand paper and a piece of glass to make it flat again. But this usually just causes low power and not airation of the oil. It really sounds like a filter issue but as it only seems to be a real problem on one side which sounds like the pump may need attention, its hard to say exactly what it is..... Its hard to say its the pump or motor or even a filter without fiddling more. You could try swapping motors over but it depends in your machine is a simple spline fit or if its the older style that has a bolt through it making it a pest to remove.
Sorry i can't be of more use than that, its really hard to say what it is without actually seeing it and trying a few things.
One last thing, is there a square block on top of the hydraulic pump with a 3 hoses going in to it from the left side (looking from the bucket at the pump)? The older machines ran a suction line filter behind the centre hose, behind the fitting in the block (the fitting that looks larger than the other 2). When it gets clogged it causes problems EXACTLY like what you are having. If you have that style, pull the hose and fitting out and replace or give the filter a good clean with diesel and compressed air.
I ´am not sure what you mean with "square block on top" I have seen it other places on the forum, I have uploaded some picture of my hydrostat under "mdj bobcat 643, maybe you could see them and explain from the picture?
Is it the "old" one?
 

Tazza

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I ´am not sure what you mean with "square block on top" I have seen it other places on the forum, I have uploaded some picture of my hydrostat under "mdj bobcat 643, maybe you could see them and explain from the picture?
Is it the "old" one?
That is the new style.
I would give it a real good clean and see if you can spot the leak(s). The big hose at the top in picture 1 that is held with hose clamps, this is your main scution line. It appears you have a leak here that could be pulling air in! it could be as simple as tightning the hose clamps up.
Now, the other oil leak at the sender, i had a sender that did leak on me, it was only a dribble but it sure made a mess!!!. If its the sender thats leaking throw a new one at it to stop the leak. You will not draw in air from here though, this is under constant pressure, 90PSI or higher.
Start with that, and give it a real good clean! then you can spot where the oil is coming from if you have more leaks. If you can't get a sender straight away, you can plug this hole. I ran my machine for 2 years without the sender being even hooked up...... Not what i should have done, but it worked all the same.
As for the noise, its very common for the hydrostats to make noise when they are full of air, even a small amount will cause noise.
See how you go with that and let me know.
 
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mdj

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That is the new style.
I would give it a real good clean and see if you can spot the leak(s). The big hose at the top in picture 1 that is held with hose clamps, this is your main scution line. It appears you have a leak here that could be pulling air in! it could be as simple as tightning the hose clamps up.
Now, the other oil leak at the sender, i had a sender that did leak on me, it was only a dribble but it sure made a mess!!!. If its the sender thats leaking throw a new one at it to stop the leak. You will not draw in air from here though, this is under constant pressure, 90PSI or higher.
Start with that, and give it a real good clean! then you can spot where the oil is coming from if you have more leaks. If you can't get a sender straight away, you can plug this hole. I ran my machine for 2 years without the sender being even hooked up...... Not what i should have done, but it worked all the same.
As for the noise, its very common for the hydrostats to make noise when they are full of air, even a small amount will cause noise.
See how you go with that and let me know.
Thanks Tazza, I will do that
Is there anyway to see what year the macine is from?
 

Tazza

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Thanks Tazza, I will do that
Is there anyway to see what year the macine is from?
If your serial number plate is still attached you can quote it to your dealer and they can look it up for you. From what i see, it is the later style as it has the plastic oil tank and the port block is not on top of the pump. The older ones have a metal oil tank with a dip stick and the port block sits on top of the pump. The dash is also a good indicator of the year. If its one piece its slightly older but if its in 3 pieces (triangular panels on the left and right sides) its the later style.
If that makes any sense!
 
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mdj

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If your serial number plate is still attached you can quote it to your dealer and they can look it up for you. From what i see, it is the later style as it has the plastic oil tank and the port block is not on top of the pump. The older ones have a metal oil tank with a dip stick and the port block sits on top of the pump. The dash is also a good indicator of the year. If its one piece its slightly older but if its in 3 pieces (triangular panels on the left and right sides) its the later style.
If that makes any sense!
Today I have clean everythink.
When I should drive it in, it could turn again, I turn it of, when there was silent, there was some think bobbled, I tjek the temp. that was ok, I started it up again and drive it around for a bit, stop it, and the bobble was there again, I took the prop of the hydraulic tank, and it was full of bobbles.
I drived it in, stop it, open up to the hydraulic pump, but I cant find any leak.
When it is started, and run with little throttle, it don't seems to come air in the tank, but if I idled it up to half throttle and let it be there for a minute or to, there comes a lot of air in the tank.
Everything look dry, I have I little leak with a sensor and a little one with the bucket hydraulic.

Where can all that air come from? Is there any specific to look for, or how can I find the problem?

Any ides?
 

Tazza

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Today I have clean everythink.
When I should drive it in, it could turn again, I turn it of, when there was silent, there was some think bobbled, I tjek the temp. that was ok, I started it up again and drive it around for a bit, stop it, and the bobble was there again, I took the prop of the hydraulic tank, and it was full of bobbles.
I drived it in, stop it, open up to the hydraulic pump, but I cant find any leak.
When it is started, and run with little throttle, it don't seems to come air in the tank, but if I idled it up to half throttle and let it be there for a minute or to, there comes a lot of air in the tank.
Everything look dry, I have I little leak with a sensor and a little one with the bucket hydraulic.

Where can all that air come from? Is there any specific to look for, or how can I find the problem?

Any ides?
Just running the machine will not remove any air, you need to work it. Drive it around, lift and tilt just make it work. If its simply air trapped this will get rid of it. If its getting drawn in somewhere this will simply not get rid of it.
I really don't know here else to look. The only other option could be a drive motor seal. I doubt the oil pressure sender could be the problem but it wouldn't hurt to change it. It needs to be done anyway to stop the leak.
 

sterlclan

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Just running the machine will not remove any air, you need to work it. Drive it around, lift and tilt just make it work. If its simply air trapped this will get rid of it. If its getting drawn in somewhere this will simply not get rid of it.
I really don't know here else to look. The only other option could be a drive motor seal. I doubt the oil pressure sender could be the problem but it wouldn't hurt to change it. It needs to be done anyway to stop the leak.
If the wear plates in the hystat are worn enough you get cavatation in the pumps it can cause bubbles in the oil............Jeff
 
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mdj

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If the wear plates in the hystat are worn enough you get cavatation in the pumps it can cause bubbles in the oil............Jeff
I seems to be worst when I use the arm, today I have driven it around turn left/right used the bucket to plan with for quit a wile, and there comes no ore very little bubble in the tank, and no air noise. But when I use the arm up and down a few times there comes air, and the arm lose pressure when I let it be, and will be on the ground in a few minutes, If I continue to use the arm, the air noise gets better but still bubble in the tank, when I turn it off, and let it be for a hour or so, the air and air noise is back, when I use the arm.

But it seems to get better, the only think I have done, is to tightening the clamps to the main suctions line (as you described earlier Tazza), but the hose is very hard and is these clamps org.? They seems a little thin to me for that job, even there is no pressure there.

Sterlclan:
I'm not sure what you mean, but last Thursday I order the service and part manual for it, I hope they come this week, when they arrived I hopeful better can understand what you mean.
 

sterlclan

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I seems to be worst when I use the arm, today I have driven it around turn left/right used the bucket to plan with for quit a wile, and there comes no ore very little bubble in the tank, and no air noise. But when I use the arm up and down a few times there comes air, and the arm lose pressure when I let it be, and will be on the ground in a few minutes, If I continue to use the arm, the air noise gets better but still bubble in the tank, when I turn it off, and let it be for a hour or so, the air and air noise is back, when I use the arm.

But it seems to get better, the only think I have done, is to tightening the clamps to the main suctions line (as you described earlier Tazza), but the hose is very hard and is these clamps org.? They seems a little thin to me for that job, even there is no pressure there.

Sterlclan:
I'm not sure what you mean, but last Thursday I order the service and part manual for it, I hope they come this week, when they arrived I hopeful better can understand what you mean.
if the bubbles get worse with arm movement it makes me think there may be some problem with the lift circuit are there any leaks at the spools or cylinders?
 

Tazza

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if the bubbles get worse with arm movement it makes me think there may be some problem with the lift circuit are there any leaks at the spools or cylinders?
I would try and tighten the 2 clams on the hose to the pump. There is no pressure there but there will be some vacuum that could pull air in.
You keep saying it gets worse when you operate the hydraulics, this is really odd. Operating the hydraulics helps get the air out of the system...... I was half thinking it could be the hydraulic pump that it shouldn't cause airation, just slow hydraulic opeartion.
 
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mdj

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I would try and tighten the 2 clams on the hose to the pump. There is no pressure there but there will be some vacuum that could pull air in.
You keep saying it gets worse when you operate the hydraulics, this is really odd. Operating the hydraulics helps get the air out of the system...... I was half thinking it could be the hydraulic pump that it shouldn't cause airation, just slow hydraulic opeartion.
Both of you, thanks for your reply

Sterlclan - Its my theory to, but the only leak I can find is the cylinder for my bucket it dripped a little bit and a little leak with my sender, I thought I have a leak somewhere with my hydrostatic, but after I clean it up, it has been dry.

It's a little mystery, I my head there will always come oil out if the comes air in, a least at some point, but I think I will try to raise the arm a meter or so over the ground a few times, maybe with some load on, turn of the machine, and let it go down to the ground as it self, and see if there comes any oil somewhere.

Is there anyway to test a hydraulic connection, ex. If I disconnect the connection to the arms, is it possible to connect any tools and get pressure on, like if a I work on a cooling system I have a tool to connect, there can put pressure on, an I can see, if the pressure fall, the most be a leak somewhere?

Tazza - I think I will replace the clams, I have tightening them, as most I can, I believe, is the hose special or can I use a hose from a cooling system, the one on it, is very stiff and hard?
About the air getting worse – When I work with the arms, the air noise getting more and more silent (= the air getting out of the system) but when the machine has stand still for ex. and hour, a day or so, and I start it up, the air is back in the system again.
 
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