753 New pumps, no hydraulics

[KyMadMan]

Installed a new hydro-static and hydraulic drive pump. Rebuilt the control valve. Got everything back together and I can move the unit but I get nothing on the arm lift or bucket tilt up. From all indications the hydraulic drive pump is working as it should. Since the entire system was drained and refilled after the new pumps and control valve were installed I'm wondering if there is a bleeding process or some other step I need to perform to purge any and all air from the arm and bucket system? When I engage the foot controls for the arms and or bucket I don't really hear any change in engine speed or even the "click" of the valves engaging and disengaging. Open for any suggestions as I am at a loss. Thank you in advance guys. KMM

 

[Tazza]

I'm wondering if it's your BICS system preventing the lift/tilt from working. Do all your lights light up on your dash or the BICS box?

 

[KyMadMan]

I'm wondering if it's your BICS system preventing the lift/tilt from working. Do all your lights light up on your dash or the BICS box?

Thanks Mr. Tazz! I don't believe I have that system on this machine. It is a 1994 753F according to Bobcat. It does have the BOSS control box, but the only electrical connections on the control valve are for the 2 solenoids on the top portion of the valve. It appears I am getting 12V feeding them when the machine is on / running.

 

[Tazza]

Thanks Mr. Tazz! I don't believe I have that system on this machine. It is a 1994 753F according to Bobcat. It does have the BOSS control box, but the only electrical connections on the control valve are for the 2 solenoids on the top portion of the valve. It appears I am getting 12V feeding them when the machine is on / running.

Can you try enabling your aux hydraulics when the machine is running at idle and seeing if the machine boggs down? I'm wondering if your pump could not be working just right, this is a different circuit, and hopefully will confirm if it's working or not.

 

[farmshop]

Can you try enabling your aux hydraulics when the machine is running at idle and seeing if the machine boggs down? I'm wondering if your pump could not be working just right, this is a different circuit, and hopefully will confirm if it's working or not.

Did you replace the charge pump and the hydrostatic pump or the hydrostatic pump and the drive motor for travel? Just trying to clarify so we are talking about the same thing. There is no real bleeding as the gear pump is lower than the tank. You might get some chatter as the air works through the system

 

[KyMadMan]

Did you replace the charge pump and the hydrostatic pump or the hydrostatic pump and the drive motor for travel? Just trying to clarify so we are talking about the same thing. There is no real bleeding as the gear pump is lower than the tank. You might get some chatter as the air works through the system

Replaced both the hydrostatic (tandum) pump and the hydraulic drive pump which mounts onto the tandum pump.

 

[KyMadMan]

Can you try enabling your aux hydraulics when the machine is running at idle and seeing if the machine boggs down? I'm wondering if your pump could not be working just right, this is a different circuit, and hopefully will confirm if it's working or not.

The switches for the aux hydraulics have never worked since I've owned this machine. I know there is some kind of pressure adjustment on the control valve, but haven't figured out how to adjust that with no aux hydraulics. I now have the tilt control moving, it has to be 1/2 throttle and moves almost as slow as a snail and there is no bucket attached presently. I'm guessing if the bucket were on there would be no movement at all. Too many irons in the fire here lately hence my long overdue response.

 

[SkidRoe]

The switches for the aux hydraulics have never worked since I've owned this machine. I know there is some kind of pressure adjustment on the control valve, but haven't figured out how to adjust that with no aux hydraulics. I now have the tilt control moving, it has to be 1/2 throttle and moves almost as slow as a snail and there is no bucket attached presently. I'm guessing if the bucket were on there would be no movement at all. Too many irons in the fire here lately hence my long overdue response.

Even if you have a BOSS machine, you still have BICS. There is a box behind the seat on the right that should have a row of lights on it. That sounds like the source of your issue, especially if your BOSS display is not throwing a code.
Also, for the aux controls to work, you need to press the aux enable button, below the BOSS display.
Hope this helps - SR

 

[KyMadMan]

Even if you have a BOSS machine, you still have BICS. There is a box behind the seat on the right that should have a row of lights on it. That sounds like the source of your issue, especially if your BOSS display is not throwing a code.
Also, for the aux controls to work, you need to press the aux enable button, below the BOSS display.
Hope this helps - SR

I realize you need to turn the Aux on. The switches themselves are no good. The switch below the display functions as it should, at least the last time I tried it. Where is this row of lights? The box looks like a sealed unit and didn't notice any lights. I'll look again, but I had that removed when I pulled the engine and didn't see them. Thanks Skid

 

[TriHonu]

I realize you need to turn the Aux on. The switches themselves are no good. The switch below the display functions as it should, at least the last time I tried it. Where is this row of lights? The box looks like a sealed unit and didn't notice any lights. I'll look again, but I had that removed when I pulled the engine and didn't see them. Thanks Skid

&nbsp
The Bobcat Interlock Control System (BICS) controller is mounted inside the cab, on the back wall, at the operators right shoulder when seated.
Its purpose is to lock out functions if the operator is not sitting in the seat, with the seat bar lowered. It is a separate system and is not part of the Bobcat Operation Sensing System (BOSS).
The BICS controller is pictured below. The 5 circles on the left side of the label are LED's. If you are seated with the safety bar down and loader is running, the LED's should be lighted green.

 

[KyMadMan]

&nbsp
The Bobcat Interlock Control System (BICS) controller is mounted inside the cab, on the back wall, at the operators right shoulder when seated.
Its purpose is to lock out functions if the operator is not sitting in the seat, with the seat bar lowered. It is a separate system and is not part of the Bobcat Operation Sensing System (BOSS).
The BICS controller is pictured below. The 5 circles on the left side of the label are LED's. If you are seated with the safety bar down and loader is running, the LED's should be lighted green.

Sorry TriHonu there is no such device on this machine. It's a 1994 and there is no BICS on it.

 

[TriHonu]

Sorry TriHonu there is no such device on this machine. It's a 1994 and there is no BICS on it.

&nbsp
If your 753 was made in early 1994, it is not an F series.
In late 1994 Bobcat released the C series for the 753, 763, 773 and 853. Later in the 90's the F series loaders were released.
I know the BOSS system was released in 1990.
To the best of my knowledge, if your data plate states it is an F series, it was made in the late 1990's and should have BICS as a standard feature.
Whomever you spoke to at Bobcat must have mis-spoke. It appears you have an early 1994 753 made before the C series release.
All that aside, what sealed box did you remove? Where was it located?

 

[KyMadMan]

&nbsp
If your 753 was made in early 1994, it is not an F series.
In late 1994 Bobcat released the C series for the 753, 763, 773 and 853. Later in the 90's the F series loaders were released.
I know the BOSS system was released in 1990.
To the best of my knowledge, if your data plate states it is an F series, it was made in the late 1990's and should have BICS as a standard feature.
Whomever you spoke to at Bobcat must have mis-spoke. It appears you have an early 1994 753 made before the C series release.
All that aside, what sealed box did you remove? Where was it located?

Not sure what you mean by sealed box? I pull the engine to replace the tandem pump. In the process I removed the BOSS from the "firewall" behind the seat cage. The control valve was removed and new seals and such installed. The only "BICS" system this has is the mechanical foot control lockout that engages once the seat bar is pulled down into the operating position.

 

[KyMadMan]

Not sure what you mean by sealed box? I pull the engine to replace the tandem pump. In the process I removed the BOSS from the "firewall" behind the seat cage. The control valve was removed and new seals and such installed. The only "BICS" system this has is the mechanical foot control lockout that engages once the seat bar is pulled down into the operating position.

Well, I have a bit of movement. with the throttle just past 1/2 way I can get the tilt to operate very slowly up and about normal in the down position. If I run it all the way down and try to operate the arm lift the arms lift as far as the tach plate can push it. The arms will stay in that position but will not raise. I can lower them with no problem. This tells me that my control valve is working properly... right? I did notice I have tiny bubbles on the level check stick after running the unit and going through this procedure. Is this an indication of air still in the cylinders that may work out or of an air leak at the pump mounting location? Thanks all

 

[SkidRoe]

Well, I have a bit of movement. with the throttle just past 1/2 way I can get the tilt to operate very slowly up and about normal in the down position. If I run it all the way down and try to operate the arm lift the arms lift as far as the tach plate can push it. The arms will stay in that position but will not raise. I can lower them with no problem. This tells me that my control valve is working properly... right? I did notice I have tiny bubbles on the level check stick after running the unit and going through this procedure. Is this an indication of air still in the cylinders that may work out or of an air leak at the pump mounting location? Thanks all

How much bubbling in the oil are we talking about? Is the oil foamy?
If you were drawing air in through the gear pump suction line, that could cause a foaming issue, and if it is drawing in enough air, could really slow down your hydraulics.
Cheers - SR

 

[KyMadMan]

How much bubbling in the oil are we talking about? Is the oil foamy?
If you were drawing air in through the gear pump suction line, that could cause a foaming issue, and if it is drawing in enough air, could really slow down your hydraulics.
Cheers - SR

Small amount of bubbles. Not foaming up. I've checked the hoses and they are as tight as they can be before they'd be loose again. I've contacted the supplier of the pump and they are working on a replacement as it appears it is a defective pump from all indications.

 

[KyMadMan]

Small amount of bubbles. Not foaming up. I've checked the hoses and they are as tight as they can be before they'd be loose again. I've contacted the supplier of the pump and they are working on a replacement as it appears it is a defective pump from all indications.

Months have passed and I still have no pump. Have had 3 excuses for failure of the pump. The latest is "contamination" entered the pump and destroyed it. I believe this is BS, but I digress. Question: Once the pump starts turning, it pushes fluid into the control valve and follows a path determined by the arms and bucket pedals. The question I have is once the fluid has gone into and then back out of a cylinder, does it not travel the the oil cooler and then through the hydraulic filter before returning to the pump to start the process over? What about the fluid in the tandem pump? Once it runs through the drive motors doesn't it flow through the cooler and filter before returning to the system? I find it hard to believe "contamination" entered the system since most everything was replaced and I didn't have issues before I changed the pump. The only reason I changed this pump was ease of replacement since the engine needed to be pulled to replace the tandem pump that was still working, just noisy and old. Thoughts anyone?

 

[Tazza]

Months have passed and I still have no pump. Have had 3 excuses for failure of the pump. The latest is "contamination" entered the pump and destroyed it. I believe this is BS, but I digress. Question: Once the pump starts turning, it pushes fluid into the control valve and follows a path determined by the arms and bucket pedals. The question I have is once the fluid has gone into and then back out of a cylinder, does it not travel the the oil cooler and then through the hydraulic filter before returning to the pump to start the process over? What about the fluid in the tandem pump? Once it runs through the drive motors doesn't it flow through the cooler and filter before returning to the system? I find it hard to believe "contamination" entered the system since most everything was replaced and I didn't have issues before I changed the pump. The only reason I changed this pump was ease of replacement since the engine needed to be pulled to replace the tandem pump that was still working, just noisy and old. Thoughts anyone?

You are mostly right, the fluid goes from the hydraulic pump, through the control valve, to the cylinder(s), what is not used, goes through the oil cooler, then back to the tank or pump depending on fluid requirements.
The fluid to the motors goes from the piston pumps to the motors and back in a circle, but most motors have a case drain line, this is to return any internal leakage back to the tank that is replenished by the returning fluid from the oil cooler. I don't know how it doesn't over heat too, as there really isn't a whole lot of internal leakage to give it lots of cooled oil.
If something was wearing, i can see it eating up pump parts, but surely you'd know it when you have poor drive due to a failing motor that is eating its self up with trash.

 

[KyMadMan]

You are mostly right, the fluid goes from the hydraulic pump, through the control valve, to the cylinder(s), what is not used, goes through the oil cooler, then back to the tank or pump depending on fluid requirements.
The fluid to the motors goes from the piston pumps to the motors and back in a circle, but most motors have a case drain line, this is to return any internal leakage back to the tank that is replenished by the returning fluid from the oil cooler. I don't know how it doesn't over heat too, as there really isn't a whole lot of internal leakage to give it lots of cooled oil.
If something was wearing, i can see it eating up pump parts, but surely you'd know it when you have poor drive due to a failing motor that is eating its self up with trash.

Hey Mr. Tazz! I have seen many talk about "case drain filters" that are suppose to be on the drive motors. I haven't seen anything that looks like that on this unit. The drives have 2 large lines and one small. The small hose on one side goes back into the tandem pump and the other side goes back into the control valve (I believe, don't hold me to that as I haven't been inside it for some time now due to waiting on a 2 new pump, but I digress) I've wondered if you or anyone has a way to remove all (or almost all) the hydro fluid from the drive motors short of removing them from the unit? I was told the 1st pump (that never worked) first, nothing wrong with it, then it was the seals were blown due to me having the pressure relief valve set too high, to finally, it's trashed due to contaminates so no warranty. Myself and several other threw the brown flag of BS on this company and their "diagnosis". So, before I put in my new (2nd) pump, I'd like to make sure I'm in good shape. During this ordeal everything was drained except the drive motors and the tilt cylinder. I didn't find any "contaminates" in the original pump and the only reason I changed it was I figured since I had to yank the engine for the tandem I'd save time and headaches and replace both. THAT'S what I get for thinking!