2018 Toolcat 5600 2100 hours charge pressure dropping when warming up !

[RichardV-Quebec]

In January I had a front motor hose brake , left the machine there for 1 month in the snow, then patched up the hose with a screw-in connector. In May, we retighten the connector as it had lost all the oil. I then added Mobil oil and restarted the machine. Moving sand for about one hour, it started to hardly move forward or reverse. (if you want, see other long posts I made about this) As someone suggested I jacked up the TC and noticed the front wheels were not turning but the rear wheels were. We removed the front transaxle and capped the brakes lines (one with a pressure gauge) and capped the motor case drain and 2 speed hoses and connected together the 2 big motor hoses with a T connector and a pressure gauge so I could move the TC somewhere else with a lift. I checked the charge pressure port under the TC with a gauge before and it went to 360 psi or so when cold (at 2,000 rpm) but noticed it would drop to 120-140 psi at 1280 rpm. Warmed up at 2,000 RPM, charge port pressure drops to 200 or so psi. 100 psi at 1300 rpm. It looks/feels like the brakes are not releasing at low idle, upping the rpm kind of makes the TC move but then eventually the brake pressure gauge drops to 100 or less PSI so does the pressure gauge on the T connector on the front drive hoses. So.... immense charge pressure drop or at least brake pressure drop. We used to run the TC at low idle with no problems. Front equipement (up and down) and steering work fine. I was thinking of checking the fluid level on the rear transaxle to see if it is over the check plug but also wonder if I should pressure test the 2nd brake hose. Any ideas anyone ?

 

[oldnslo]

Where you losing charge pressure with the front motor disconnected (hoses looped) or with motor actively in the circuit?

I suspect motors connected and if so sounds like you a pump or motor leaking excessively causing loss of charge pressure when system warms up.

 

[RichardV-Quebec]

Where you losing charge pressure with the front motor disconnected (hoses looped) or with motor actively in the circuit?

I suspect motors connected and if so sounds like you a pump or motor leaking excessively causing loss of charge pressure when system warms up.

Front motor is hoses looped. I don't know where I am loosing the charge pressure. I suppose I could hose loop the rear motor and see what happens ?

 

[RichardV-Quebec]

Sorry I reread your comment and yes I was loosing pressure with the motor hoses connected too.

 

[oldnslo]

Sorry I reread your comment and yes I was loosing pressure with the motor hoses connected too.

Not familiar with tool cat circuit, do they run separate pump for rear motor and front motor?

If yes then would point towards a leak in front pump or front pump charge circuit.

Do you have the hydraulic schematic for this machine. If yes can you attach it to this post so we can view it.

 

[oldnslo]

Richard
Thanks for posting that schematic.

Per schematic the charge pump is common for both front and rear drive pumps so you should be losing charge to both front and rear circuits.

Both axle drive motors have flushing valve built in so to diagnose bad motor you have to check motor case flow at no load and then see how much it varies under load. If I understood your previous post charge pressure dropped with out front axle motor connected so that would point towards problem in rear axle drive.

To test the pump you might have to cap the work ports to the motors and then try to drive and watch charge pressure. If it drops it is the pump leaking.

Unfortunate reality is that when a motor or pump goes bad in an HST circuit it usually destroys both the pump and motor and requires carefully cleaning all the lines or hoses between pump and motor before installing any new components.

Do you have make and or model code for pump and motor? Being Bobcat might just have their p/n on them which is of little value to you and I.

 

[RichardV-Quebec]

Richard
Thanks for posting that schematic.

Per schematic the charge pump is common for both front and rear drive pumps so you should be losing charge to both front and rear circuits.

Both axle drive motors have flushing valve built in so to diagnose bad motor you have to check motor case flow at no load and then see how much it varies under load. If I understood your previous post charge pressure dropped with out front axle motor connected so that would point towards problem in rear axle drive.

To test the pump you might have to cap the work ports to the motors and then try to drive and watch charge pressure. If it drops it is the pump leaking.

Unfortunate reality is that when a motor or pump goes bad in an HST circuit it usually destroys both the pump and motor and requires carefully cleaning all the lines or hoses between pump and motor before installing any new components.

Do you have make and or model code for pump and motor? Being Bobcat might just have their p/n on them which is of little value to you and I.

This is what I recorded, the gauge on the left is attached to one of the front brake hose and the one on the right is on the looped motor hose. Lifting the cab to get to the pump is not an option at this time...

 

[RichardV-Quebec]

This is what I recorded, the gauge on the left is attached to one of the front brake hose and the one on the right is on the looped motor hose. Lifting the cab to get to the pump is not an option at this time...

The 50-13 error code is because I don't have the front speed sensor connected.

 

[oldnslo]

No charge pressure in the front pump circuit with the motor hoses looped when no movement is being requested points towards a bad HST pump. In neutral you should see full charge pressure in loop.

 

[RichardV-Quebec]

No charge pressure in the front pump circuit with the motor hoses looped when no movement is being requested points towards a bad HST pump. In neutral you should see full charge pressure in loop.