bobcat 643 hydrastatic pump

[liteman]

after replacing several lines and thoroughly bleeding my system I am still having trouble getting it to move forward or back. My bucket for lift and tilt works great. When I first start it, it tries to motivate a little, but once warm it quits. Any suggestions would be appreciated. Also if anyone has a manual for a 643 let me know.

 

[jerry]

Did you change or clean the bronze filter in the port block on top of the hyd pump? 632 had one and I think most 743 do so chances are 643 does. It is a square block attached on the top of the pump with 3 large hoses entering from the right side. filter is in the center hole you will see it when you take the hose off. lots of threads here on it.

 

[jerry]

Did you change or clean the bronze filter in the port block on top of the hyd pump? 632 had one and I think most 743 do so chances are 643 does. It is a square block attached on the top of the pump with 3 large hoses entering from the right side. filter is in the center hole you will see it when you take the hose off. lots of threads here on it.

This is from one of Tazza's posts on this subject. You would assume the problem would get better when the fluid warms up, but unfortunatly it doesn't seem to do that... My old 731 has a port block filter and it worked great for say 10-15 mins. then it would howl when i tried to move. After alot of calls to bobcat they told me to change the filter, i did and it works 100% now. It can be changed with no special tools and you don't have to drain your oil. Its located on the left side when looking from the bucket, there should be 3 hoses on the left side, its the middle one. Remove the front hose and put a bung in it. Then remove the middle one and un-screw the large fitting from the port block. There is a spring and a bronze filter behind it. The fitting should have a larger nut size than the other 2 fittings on that side. Let us know how it works out.

 

[liteman]

Did you change or clean the bronze filter in the port block on top of the hyd pump? 632 had one and I think most 743 do so chances are 643 does. It is a square block attached on the top of the pump with 3 large hoses entering from the right side. filter is in the center hole you will see it when you take the hose off. lots of threads here on it.

Thanks Jerry. Icleaned out the bronze filter and it worked! I think I might have to fill up with fuel and run it a while. It started to loose power after it warmed up, then it got better. I'll just have to play with it and see what happens.

 

[liteman]

Thanks Jerry. Icleaned out the bronze filter and it worked! I think I might have to fill up with fuel and run it a while. It started to loose power after it warmed up, then it got better. I'll just have to play with it and see what happens.

Hi everyone! Well I've been running around the yard and I'm still loosing power on the right stick. Also going up hill, even when it's warmed up. Any thoughts?

 

[jerry]

Hi everyone! Well I've been running around the yard and I'm still loosing power on the right stick. Also going up hill, even when it's warmed up. Any thoughts?

on the front of the port block where the bronze filter is there should be two sensors, one is for the charge pressure, I don't remember which, take it out and put a gauge in to check the charge pressure. Should be around 100 lbs, leave it in so you can see if it drops a lot as the machine warms up if it does you may have a weak vane pump. For more in depth instructions Tazza will be along soon.

 

[Tazza]

on the front of the port block where the bronze filter is there should be two sensors, one is for the charge pressure, I don't remember which, take it out and put a gauge in to check the charge pressure. Should be around 100 lbs, leave it in so you can see if it drops a lot as the machine warms up if it does you may have a weak vane pump. For more in depth instructions Tazza will be along soon.

Its possible its wear in your wear/valve plates in the pump. If its worn badly, it could cause issues like this too. If you have time and patience, you can use a sheet of glass and wet and dry sand paper to flatten the valve plates. I have done it before, as has a few other memebers, with excellent results.
It could had a leaking seal in the lazy drive motor as you said it loses power.
Checking the charge pressure is a good idea too. As you have cleaned the bronze filter, there is nothing else i can really think of to check.

 

[jerry]

Its possible its wear in your wear/valve plates in the pump. If its worn badly, it could cause issues like this too. If you have time and patience, you can use a sheet of glass and wet and dry sand paper to flatten the valve plates. I have done it before, as has a few other memebers, with excellent results.
It could had a leaking seal in the lazy drive motor as you said it loses power.
Checking the charge pressure is a good idea too. As you have cleaned the bronze filter, there is nothing else i can really think of to check.

You could also take the fill plug out of the front of the chain case and if oil of any amount comes out you probably have a leaky drive motor as the chain case is only filled to the plug level.

 

[R & R Yard Design]

You could also take the fill plug out of the front of the chain case and if oil of any amount comes out you probably have a leaky drive motor as the chain case is only filled to the plug level.

Guys i am having the same type of problem on my 643, what really is the port block. I would like to change it or clean it if i can

 

[Tazza]

Guys i am having the same type of problem on my 643, what really is the port block. I would like to change it or clean it if i can

Only the early machines have this block and filter. Lift the cab, look at the hydraulic pump. IF there is a square block on top of the pump, its the middle line you want, remove it and the fitting that screws into the vlock to un-cover the bronze filter.
Yours may be the newer style that does not have this filter though.

 

[liteman]

Still having a problem!!! Lost wheels and bucket, hydrostic pump re-built. From the start bucket always worked. Rebuilder says Control Valve on side block stuck. Stops everything from working?? true or false, if so he said to loosen???

 

[Tazza]

Still having a problem!!! Lost wheels and bucket, hydrostic pump re-built. From the start bucket always worked. Rebuilder says Control Valve on side block stuck. Stops everything from working?? true or false, if so he said to loosen???

Not sure about that. Its worth cracking open the port block, you are talking about the block on the side of the machine that the large hose joins to from the hydraulic pump?
I personally can't see that being the issue, but you never know.
Did you get the drive motors checked out too?

 

[liteman]

Not sure about that. Its worth cracking open the port block, you are talking about the block on the side of the machine that the large hose joins to from the hydraulic pump?
I personally can't see that being the issue, but you never know.
Did you get the drive motors checked out too?

I pulled the pump off & took it back to the re-build guy. I left the port block on it and he said he'd check it all out. Also suggested me to move the control valve on top of side block to bucket control. Tried it and nothing changed. I appreciate the response. Will keep you posted. Thanks

 

[Tazza]

I pulled the pump off & took it back to the re-build guy. I left the port block on it and he said he'd check it all out. Also suggested me to move the control valve on top of side block to bucket control. Tried it and nothing changed. I appreciate the response. Will keep you posted. Thanks

The control valve wouldn't do anything to the drive. It only controls the lift/tilt and aux hydraulic functions. Even if something was stuck, it would just be confined to the hydraulic system, not your hydrostatic drive. It has to be pump/motor related
Do let us know what they find out.

 

[7LBSSMALLIE]

The control valve wouldn't do anything to the drive. It only controls the lift/tilt and aux hydraulic functions. Even if something was stuck, it would just be confined to the hydraulic system, not your hydrostatic drive. It has to be pump/motor related
Do let us know what they find out.

ok guys i try to keep my hands off this 25 yr old stuff. but tips and tricks, you are probally dealing with a suction leak here it should show its face by foamy oil.(air in sys cant get out) there is proucdure to remove air by putting hose in from where to where i dont recall would have to look up. it sounds crazy but if looking for suction leak put shavining cream on all suctiong hoses .(supply) if dimpled there is youre leak. it works thats old school at its best sound a little nuts i know, but so did using lemon joy to free up rings that are so carboned up you cant get them off .

 

[liteman]

The control valve wouldn't do anything to the drive. It only controls the lift/tilt and aux hydraulic functions. Even if something was stuck, it would just be confined to the hydraulic system, not your hydrostatic drive. It has to be pump/motor related
Do let us know what they find out.

While running, no fluid to filter in port block, no fluid to charge pump in front, no fluid to wheel lines. When the motor is not running, the front charge pump, fluid comes out. While running i disconnected wheel lines and got air sound, like it's starving for fluid. I checked out port block-clear, no blockage. Fluid path is from tank to port block to charger and pump also line on left then to oil filter and then back to system. It appears that the pressure just isn't there. Could it be sucking away from charger? Before all this started bucket worked, i understand seperate system, so something is not letting fluid charge the system?????

 

[Tazza]

While running, no fluid to filter in port block, no fluid to charge pump in front, no fluid to wheel lines. When the motor is not running, the front charge pump, fluid comes out. While running i disconnected wheel lines and got air sound, like it's starving for fluid. I checked out port block-clear, no blockage. Fluid path is from tank to port block to charger and pump also line on left then to oil filter and then back to system. It appears that the pressure just isn't there. Could it be sucking away from charger? Before all this started bucket worked, i understand seperate system, so something is not letting fluid charge the system?????

Just what lines did you replace? Could something have gone on wrong? or could you have had a plug in the line and accidentally put the hose on with it in there still? It has happened before.
It just doesn't make any sense why changine the lines made your drive system stop.

 

[liteman]

Just what lines did you replace? Could something have gone on wrong? or could you have had a plug in the line and accidentally put the hose on with it in there still? It has happened before.
It just doesn't make any sense why changine the lines made your drive system stop.

I'm sorry, I guess I didn't explain that very well. I replaced the line from the port block to the rear filter becausse the coupler was broken, but that was before I had the pump repaired.Before I had the pump repaired the bucket worked. I had the pump repaired thinking that would fix the motivation problem I was having, which at that time was my only problem. After I put the pump back in I had no wheels and no bucket. When it's running there's no fluid to the front pump, I disconnected the line and no fluid. Then I disconnected the wheel lines and could hear air or suction? Then I turned it off, took the line off again and fluid came out of the front pump. It appears the pump is functioning backwards? Is that possible??The center shaft rotates clockwise if you're sitting in the bobcat.

 

[Tazza]

I'm sorry, I guess I didn't explain that very well. I replaced the line from the port block to the rear filter becausse the coupler was broken, but that was before I had the pump repaired.Before I had the pump repaired the bucket worked. I had the pump repaired thinking that would fix the motivation problem I was having, which at that time was my only problem. After I put the pump back in I had no wheels and no bucket. When it's running there's no fluid to the front pump, I disconnected the line and no fluid. Then I disconnected the wheel lines and could hear air or suction? Then I turned it off, took the line off again and fluid came out of the front pump. It appears the pump is functioning backwards? Is that possible??The center shaft rotates clockwise if you're sitting in the bobcat.

I wonder if its possible when you got the pump done, it was done backwards?