825 Hydraulic Drive Issue

[2003rubiblue]

I recently purchased an old Bobcat 825 the guys I bought it from said the drive motors were "tired". I changed out all 27 gallons of oil and replaced all three hydraulic filters. It is a little better but when I first start it sometimes the charge pressure light stays illuminated for a few minutes and the bucket hydraulics will be jerky and slow during the first minute or two. Also after running the machine hard for 30 - 45 minutes the drive motors will slow down and the hydraulic screeching noise will increase while turning sharply. The machine will still have some power but it decreases after she gets hot. Is this most likely a drive motor issue. I have read a lot about the vickers pumps and motors in these machines and since I can't really put a lot of money into it I think I should just run it as it is as long as possible does that make sense. From what I understand from the previous owner it was run in this condition for many years. Also does anyone know if there is a port block filter in these 825's my manual does not mention one but my symptoms sound similar to machines with a restricted port filter. I only use this machine around my property and for my private road maintenance and snow removal, she has a pretty easy life. Thanks, Brian

 

[Tazza]

Some of the older machines had a hidden filter that causes this issue. On different models, it was located in the port block that was on top of the hydraulic pump. Middle hose on the left hand side fitting.
If there is no filter, it could be pump wear. On some pumps, you can remove the wear with a sheet of glass and wet and dry sand paper. The parts that mark are the wear plates that the rotating groups run on, if you can feel a score with a finger nail, it's too deep.

 

[2003rubiblue]

Some of the older machines had a hidden filter that causes this issue. On different models, it was located in the port block that was on top of the hydraulic pump. Middle hose on the left hand side fitting.
If there is no filter, it could be pump wear. On some pumps, you can remove the wear with a sheet of glass and wet and dry sand paper. The parts that mark are the wear plates that the rotating groups run on, if you can feel a score with a finger nail, it's too deep.

Taz - Others, I am going to try to fix this myself in the spring. My plan right now is to pull all the reliefs, and also see if there are any hidden case drain filters. If that doesn't work I am going to pull the pumps. Does that sound like a reasonable plan. Also do the drive motors wear in the same manner as the pump, should I pull them as well.

 

[Tazza]

Taz - Others, I am going to try to fix this myself in the spring. My plan right now is to pull all the reliefs, and also see if there are any hidden case drain filters. If that doesn't work I am going to pull the pumps. Does that sound like a reasonable plan. Also do the drive motors wear in the same manner as the pump, should I pull them as well.

That's a good plan. Another one is to cap the lines to the drive motors and try and slowly move the steering lever for each side back and forth. You should feel the sticks being pushed back and the engine will bog down. This is essnetially loading the pumps down.
The drive motors will wear over time, but "generally" the pumps will wear before the drive motors do. Or at least wear enough to be a real issue. They will wear over time giving reduced power, but the pumps are more noticeable when they wear as it can happen quite fast if something gets past a filter.

 

[2003rubiblue]

That's a good plan. Another one is to cap the lines to the drive motors and try and slowly move the steering lever for each side back and forth. You should feel the sticks being pushed back and the engine will bog down. This is essnetially loading the pumps down.
The drive motors will wear over time, but "generally" the pumps will wear before the drive motors do. Or at least wear enough to be a real issue. They will wear over time giving reduced power, but the pumps are more noticeable when they wear as it can happen quite fast if something gets past a filter.

Just wanted to give an update. I have received a rather large and expensive package by freight. I got a good deal on a rebuilt hydrostatic pump assembly. So if the weather ever warms up and the snow melts I will be replacing my pumps. All of my diagnostic work has lead me to low pump pressure / low charge pressure. SO wish me luck. I will update again when done. Brian

 

[Tazza]

Just wanted to give an update. I have received a rather large and expensive package by freight. I got a good deal on a rebuilt hydrostatic pump assembly. So if the weather ever warms up and the snow melts I will be replacing my pumps. All of my diagnostic work has lead me to low pump pressure / low charge pressure. SO wish me luck. I will update again when done. Brian

Lets hope the machine will run like new after the transplant!

 

[2003rubiblue]

Lets hope the machine will run like new after the transplant!

I'm hoping. Anyone have any ideas on anything else I should look at or replace while I have it apart? I'm going in as soon as spring arrives. I'm a little nervous about removing all the hoses from the pump, any advice, or should I just go at it with a wrench. Are they usually super tight?

 

[Tazza]

I'm hoping. Anyone have any ideas on anything else I should look at or replace while I have it apart? I'm going in as soon as spring arrives. I'm a little nervous about removing all the hoses from the pump, any advice, or should I just go at it with a wrench. Are they usually super tight?

Use a wrench, mark the hoses. I used a centre punch so i knew what went where. I'd advise using plugs and not rags for the hoses. Rags can be forgotten and sucked into the system.
While the pump is out, you may want to check for any wear that you can access easier with the pump out.

 

[Tazza]

Use a wrench, mark the hoses. I used a centre punch so i knew what went where. I'd advise using plugs and not rags for the hoses. Rags can be forgotten and sucked into the system.
While the pump is out, you may want to check for any wear that you can access easier with the pump out.

Oh, you may need to hit the fittings with a hammer and drift to crack them. I used bars on the spanners, even had to use a chisel to crack one.
Hopefully it's not as bad as you may think, just take pictures and mark the hoses as they come off so they don't get messed up.

 

[2003rubiblue]

Oh, you may need to hit the fittings with a hammer and drift to crack them. I used bars on the spanners, even had to use a chisel to crack one.
Hopefully it's not as bad as you may think, just take pictures and mark the hoses as they come off so they don't get messed up.

Just an update. It took three days but I replaced the hydrostatic pumps and got to fire her up today. She has never had this much power or speed the whole time i've owned her. The high pitched growling from the pumps is also gone. It wasn't easy though I found a 1/2'' hydraulic hose on the bottom of the chain case that fed the hydrostatic pump inlet filter had been installed wrong at some point and got in a fight with the front sprocket. Needless to say it needed to be replaced, may also explain some of my low charge pump pressure. Got that done, then promptly dropped a wrench down into the bottom of the chain case, a couple of hours of fishing with magnets and hooks later I got that back, had a great time adjusting the pintle levers to get neutral on the new pumps. It was a project but I am happy. I swear everything in these older bobcats is hard to get to, my hands are cut, bruised, and scraped!! Thanks everyone. Brian

 

[Tazza]

Just an update. It took three days but I replaced the hydrostatic pumps and got to fire her up today. She has never had this much power or speed the whole time i've owned her. The high pitched growling from the pumps is also gone. It wasn't easy though I found a 1/2'' hydraulic hose on the bottom of the chain case that fed the hydrostatic pump inlet filter had been installed wrong at some point and got in a fight with the front sprocket. Needless to say it needed to be replaced, may also explain some of my low charge pump pressure. Got that done, then promptly dropped a wrench down into the bottom of the chain case, a couple of hours of fishing with magnets and hooks later I got that back, had a great time adjusting the pintle levers to get neutral on the new pumps. It was a project but I am happy. I swear everything in these older bobcats is hard to get to, my hands are cut, bruised, and scraped!! Thanks everyone. Brian

Great news, i feel your pain trying to fish a lost item out. The sprockets in the chain case can be like razor blades.
It's nice when a plan actually works as you had hoped. There sure is a difference between a tired and nice new shiny pump, the power difference sure is different.

 

[2003rubiblue]

Great news, i feel your pain trying to fish a lost item out. The sprockets in the chain case can be like razor blades.
It's nice when a plan actually works as you had hoped. There sure is a difference between a tired and nice new shiny pump, the power difference sure is different.

Pain literally...Lol!!! There is a whole new hell for me and it is the bottom of my 825's chain gallery. You know the power difference is amazing!!!! One thing that I forgot to mention was I removed the four large hoses at the hydrostatic pumps, two for each motor. When I removed the two for the right side hydro motor they felt loose of the motor side. I opened the access panel under the operators feet to access the lower gallery and found the two fittings on the motor literally finger tight!!! No one has been in that lower gallery in a very long time, there is a filter under there that looked like it had never been changed. Do you think they could have vibrated loose or was the last person to work on it, which was a bobcat dealer, careless?? Doesn't matter now but it makes you wonder. I don't like other people working on my stuff. Brian