hydraulics

[Ack]

I have a 753 Bobcat with Boss. When I was doing some light work when it stopped moving forward or backwards. Further the bucket would not work. That said if I tried to move the levers to go forward or back there is incredible pressure pushing the levers back to the neutral position. When pushing the levers you can hear the pump scream. Any suggestions?

 

[skidsteer.ca]

What year is it? or is it a C, F or G series?
Sounds like the boss sytem has a malfunction and the safety locks are staying on. There the parking brake/solinoid is not releasing the drives, and the bics valve is not unlocking the lift and tilt fuctions.
Could be seat bar sensor malfunction, or a seat sensor malfunction (if equiped) Bobcat eliminated the seat sensor on later models and installed a “push to operate” green button. Or a wiring or blown fuse problem.
Download a manual from the online manual thread and start reading up.
Ken

 

[Tazza]

What year is it? or is it a C, F or G series?
Sounds like the boss sytem has a malfunction and the safety locks are staying on. There the parking brake/solinoid is not releasing the drives, and the bics valve is not unlocking the lift and tilt fuctions.
Could be seat bar sensor malfunction, or a seat sensor malfunction (if equiped) Bobcat eliminated the seat sensor on later models and installed a “push to operate” green button. Or a wiring or blown fuse problem.
Download a manual from the online manual thread and start reading up.
Ken

The scream could even be a slipping drive belt. Check it for tension and condition. But as you said its fighting you, i'd also suspect the park brake/safety interlock system.
Do you get any codes on the screen?
Check the seat bar and seat sensor.

 

[skidsteer.ca]

The scream could even be a slipping drive belt. Check it for tension and condition. But as you said its fighting you, i'd also suspect the park brake/safety interlock system.
Do you get any codes on the screen?
Check the seat bar and seat sensor.

I think if it was a loose belt the steering lever would not be heavy to push.
Ken

 

[Ack]

What year is it? or is it a C, F or G series?
Sounds like the boss sytem has a malfunction and the safety locks are staying on. There the parking brake/solinoid is not releasing the drives, and the bics valve is not unlocking the lift and tilt fuctions.
Could be seat bar sensor malfunction, or a seat sensor malfunction (if equiped) Bobcat eliminated the seat sensor on later models and installed a “push to operate” green button. Or a wiring or blown fuse problem.
Download a manual from the online manual thread and start reading up.
Ken

Thank you for your suggestions. I should have explained everything the first time, I am sorry I didn’t. Without question the locking break is pulled out all the way. I have confirmed that it is not the problem. When this happened I was on a decline. As I was rolling forward I tried to pull back on the controls and they would only move less than an inch. But as I applied some pressure I could feel the arms being pushed back by the hydraulics while still rolling forward. I am convinced that nothing is getting to the drive motors. I cannot remember if I had any control over the bucket lift/tilt. Before this happened I always had some play with the drive controls. Now when the engine is running it feels like they are welded in one position. Again when I try to push forward or backwards (less than an inch) there is an incredible amount of resistance pushing the arms back and the pump just screams. I am very good at changing the oil and filter but when this happened I did change the oil and filter again thinking it could be plugged. If there is more than one filter then I have messed up and that could be the problem. To me it feels like all the oil pressure is being built up in the control arm area and it is unable to pass through to the drives. It is just what it seems like to me. Again thanks for your help and suggestions

 

[skidsteer.ca]

Thank you for your suggestions. I should have explained everything the first time, I am sorry I didn’t. Without question the locking break is pulled out all the way. I have confirmed that it is not the problem. When this happened I was on a decline. As I was rolling forward I tried to pull back on the controls and they would only move less than an inch. But as I applied some pressure I could feel the arms being pushed back by the hydraulics while still rolling forward. I am convinced that nothing is getting to the drive motors. I cannot remember if I had any control over the bucket lift/tilt. Before this happened I always had some play with the drive controls. Now when the engine is running it feels like they are welded in one position. Again when I try to push forward or backwards (less than an inch) there is an incredible amount of resistance pushing the arms back and the pump just screams. I am very good at changing the oil and filter but when this happened I did change the oil and filter again thinking it could be plugged. If there is more than one filter then I have messed up and that could be the problem. To me it feels like all the oil pressure is being built up in the control arm area and it is unable to pass through to the drives. It is just what it seems like to me. Again thanks for your help and suggestions

When the motor is off you can push the sticks all the way back and forth?
If its extra siff when running only, then the pumps can't push the oil throgh the wheel motors.
Seen as it is 2 separate (for the most part) sytems it is unlikely that both sides of the machine would lock up at once, unless it is the parking brake. Is you parking brake the electric type that lets out a loud snap when it releases or the earlier 1993 and older type that just had a foot pedal/
Ken

 

[Ack]

Thank you for your suggestions. I should have explained everything the first time, I am sorry I didn’t. Without question the locking break is pulled out all the way. I have confirmed that it is not the problem. When this happened I was on a decline. As I was rolling forward I tried to pull back on the controls and they would only move less than an inch. But as I applied some pressure I could feel the arms being pushed back by the hydraulics while still rolling forward. I am convinced that nothing is getting to the drive motors. I cannot remember if I had any control over the bucket lift/tilt. Before this happened I always had some play with the drive controls. Now when the engine is running it feels like they are welded in one position. Again when I try to push forward or backwards (less than an inch) there is an incredible amount of resistance pushing the arms back and the pump just screams. I am very good at changing the oil and filter but when this happened I did change the oil and filter again thinking it could be plugged. If there is more than one filter then I have messed up and that could be the problem. To me it feels like all the oil pressure is being built up in the control arm area and it is unable to pass through to the drives. It is just what it seems like to me. Again thanks for your help and suggestions

After giving this more thought I have had something like this happen before. Several times when I started to move forward the arms would kick back and the pump would scream. It would only do it once then it would work fine. I would only do this once in a while. I may have done this about 4 times. Now it won’t move and the controls are locked all the time when the engine is running

 

[Ack]

After giving this more thought I have had something like this happen before. Several times when I started to move forward the arms would kick back and the pump would scream. It would only do it once then it would work fine. I would only do this once in a while. I may have done this about 4 times. Now it won’t move and the controls are locked all the time when the engine is running

I have physically removed the break from the solenoid and the problem is on both control arms

 

[Ack]

I have physically removed the break from the solenoid and the problem is on both control arms

Yes when the motor is off I can move the controls the normal (full) distance

 

[skidsteer.ca]

I have physically removed the break from the solenoid and the problem is on both control arms

After you removed the solinoid you pulled the rod in the center of it up and retained it or completely removed the park gear from the chain case? coreect? So no more parking brake and same trouble.
If you jack it up can you roll all 4 wheels a bit to be sure the chains are not broken or a wheel bearing jambed. (still unlikely it would affect both sides) You could remove the chain case cover and take a look there also.
If that all looks good then you are down to a hydraulic problem
Ken

 

[Ack]

After you removed the solinoid you pulled the rod in the center of it up and retained it or completely removed the park gear from the chain case? coreect? So no more parking brake and same trouble.
If you jack it up can you roll all 4 wheels a bit to be sure the chains are not broken or a wheel bearing jambed. (still unlikely it would affect both sides) You could remove the chain case cover and take a look there also.
If that all looks good then you are down to a hydraulic problem
Ken

That is correct I pulled the rod out and replaced just the solenoid so there is no parking brake. I have not jacked it up to check the chain. Nor have I removed the chain cover. When this happened it did continue to roll freely for about 20 feet (felt like no fluid in the drive motors). The next day I went to move it and the wheels would not turn. I will jack it up and try the suggested test. I would think if there was something in the chain case prohibiting movement I should be able to slightly rock the machine? Again there is too much hydraulic pressure on the arms to try this. Ron

 

[Tazza]

That is correct I pulled the rod out and replaced just the solenoid so there is no parking brake. I have not jacked it up to check the chain. Nor have I removed the chain cover. When this happened it did continue to roll freely for about 20 feet (felt like no fluid in the drive motors). The next day I went to move it and the wheels would not turn. I will jack it up and try the suggested test. I would think if there was something in the chain case prohibiting movement I should be able to slightly rock the machine? Again there is too much hydraulic pressure on the arms to try this. Ron

That seems really odd. If it was a chaincase issue i'd have expected it to not roll 20' as you stated. The pumps are connected to the motors, so any excess pressure/oil should make the motors turn if they are not locked up.
Your description of the arms fighting you means the oil is not moving. Its the feeling you have when the brake is locked on. It will scream and fight you every time you move the levers, back or forth.
There are no other filters that you could have missed.
I'm really not sure what else there is that you can ckeck. You could always try and slide the drive motors out of the carriers and see if they turn when you move the sticks. It will be messy as the case drains will be open, oil will be lost.

 

[skidsteer.ca]

That seems really odd. If it was a chaincase issue i'd have expected it to not roll 20' as you stated. The pumps are connected to the motors, so any excess pressure/oil should make the motors turn if they are not locked up.
Your description of the arms fighting you means the oil is not moving. Its the feeling you have when the brake is locked on. It will scream and fight you every time you move the levers, back or forth.
There are no other filters that you could have missed.
I'm really not sure what else there is that you can ckeck. You could always try and slide the drive motors out of the carriers and see if they turn when you move the sticks. It will be messy as the case drains will be open, oil will be lost.

I would suggest starting to look what could affect the hydrostatic pumps on both sides simultaneously. Unlikely both drive motors acting up at once.
Is there a hydrostatic test section in our online manuals?
Ken

 

[Tazza]

I would suggest starting to look what could affect the hydrostatic pumps on both sides simultaneously. Unlikely both drive motors acting up at once.
Is there a hydrostatic test section in our online manuals?
Ken

I don't think there was.... There is for the hydraulics/cylinders but not specifically the pumps.
I like your idea to check one side at a time.