Bobcat T740 brake problem.

[JYM654]

So I had a crazy experience. I was running my T740 along the hillside and knew it was getting lower on fuel, but it suddenly shut off and then I rolled backwards down the hill. It appears that the brakes would not hold without the engine running. Luckily it rolled a short distance and it flattened out, and I never hit anything. From what I can tell the brakes work fine when it's running, but don't hold if it is not running. Any ideas on what could cause this?

 

[fortworth-cowboy]

So I had a crazy experience. I was running my T740 along the hillside and knew it was getting lower on fuel, but it suddenly shut off and then I rolled backwards down the hill. It appears that the brakes would not hold without the engine running. Luckily it rolled a short distance and it flattened out, and I never hit anything. From what I can tell the brakes work fine when it's running, but don't hold if it is not running. Any ideas on what could cause this?

So the Engine was turned off?
What do you have Joysticks or Manual Steering?
Test the Brake:
Manual Steering-- Unlock and operate machine--apply brake via brake switch or lift seat bar-- apply pressure with manual controls to hydrostatic pump and see if you move either on one side back or forward or even on both sides--if you almost stall out the engine your brakes are good--if you can drive, even slowly and it makes a squalling noise, your brake is bad one at least one side

Joystick machine: unlock and operate machine--switch to H-Pattern--apply brake via switch ONLY--drive each side forward or backwards and check if the machine drive in either direction--if yes one or more brakes are bad

if either test reveals that the brake drives for a moment and then holds the machine, you popped valve in the control valve could be bad, but I would have to tell you to perform a other test

 

[JYM654]

So the Engine was turned off?
What do you have Joysticks or Manual Steering?
Test the Brake:
Manual Steering-- Unlock and operate machine--apply brake via brake switch or lift seat bar-- apply pressure with manual controls to hydrostatic pump and see if you move either on one side back or forward or even on both sides--if you almost stall out the engine your brakes are good--if you can drive, even slowly and it makes a squalling noise, your brake is bad one at least one side

Joystick machine: unlock and operate machine--switch to H-Pattern--apply brake via switch ONLY--drive each side forward or backwards and check if the machine drive in either direction--if yes one or more brakes are bad

if either test reveals that the brake drives for a moment and then holds the machine, you popped valve in the control valve could be bad, but I would have to tell you to perform a other testo

So the Engine was turned off?
What do you have Joysticks or Manual Steering?
Test the Brake:
Manual Steering-- Unlock and operate machine--apply brake via brake switch or lift seat bar-- apply pressure with manual controls to hydrostatic pump and see if you move either on one side back or forward or even on both sides--if you almost stall out the engine your brakes are good--if you can drive, even slowly and it makes a squalling noise, your brake is bad one at least one side

Joystick machine: unlock and operate machine--switch to H-Pattern--apply brake via switch ONLY--drive each side forward or backwards and check if the machine drive in either direction--if yes one or more brakes are bad

if either test reveals that the brake drives for a moment and then holds the machine, you popped valve in the control valve could be bad, but I would have to tell you to perform a other test

It is a scpa machine. With electric joystick steering and mechanical pedals for lift tilt. I will try to parking brake test. As far as I know it works normally as it has never rolled when turned off. This time it stalled out due to low fuel. Maybe that kept the brake from applying because it was still key on and green interlock light on??

 

[fortworth-cowboy]

It is a scpa machine. With electric joystick steering and mechanical pedals for lift tilt. I will try to parking brake test. As far as I know it works normally as it has never rolled when turned off. This time it stalled out due to low fuel. Maybe that kept the brake from applying because it was still key on and green interlock light on??

No, as soon the Gear Pump is not producing any pressure anymore the brake will apply. It is by design like that, concept of an Airbrake by a Truck just with hydraulic pressure and plates etc.

 

[JYM654]

I believe I have found the problem. After checking it every way I know, the brake works when it is first started

 

[JYM654]

Sorry I entered too early. LOL The brake works when first started most of the time- a few times it seemed like it was weak. After starting and releasing the brake, it would not hold no matter what position the switch was in or even after I shut he machine off. I lifted the cab and found the lines going to the motors from the brake solenoid block. I loosened the hose from the solenoid to the motor connection and it had pressure on it. I restarted the machine and retested the brake. It worked, held strong. I released the brake and it released, then it would not hold again. I again cracked the hose to the brake and it had pressure. I conclude that the solenoid it not releasing- draining the pressure off the brake after it is charged. I ordered a new solenoid and will update when I install and retest it. I also left the hose off the solenoid block and ran the engine to see if perhaps pressure was bleeding from the drive motor to the brake circuit and it does not appear to.

 

[fortworth-cowboy]

Sorry I entered too early. LOL The brake works when first started most of the time- a few times it seemed like it was weak. After starting and releasing the brake, it would not hold no matter what position the switch was in or even after I shut he machine off. I lifted the cab and found the lines going to the motors from the brake solenoid block. I loosened the hose from the solenoid to the motor connection and it had pressure on it. I restarted the machine and retested the brake. It worked, held strong. I released the brake and it released, then it would not hold again. I again cracked the hose to the brake and it had pressure. I conclude that the solenoid it not releasing- draining the pressure off the brake after it is charged. I ordered a new solenoid and will update when I install and retest it. I also left the hose off the solenoid block and ran the engine to see if perhaps pressure was bleeding from the drive motor to the brake circuit and it does not appear to.

There is also a poppet valve in the control valve, if that popped valve is damaged you will have break issues as well.
Remove 43, it is connected to a tube line, you should find pieces of a spring (if not use a pick and look inside the tube line, and a worn poppet.
Disregard the poppet valve and the spring, look into your piece #43. Does it have a Screen? If yes punch it out, if it is already destroyed make sure to take the rest off. And then install it back.
OR by an updated fitting by bobcat which replaces #43.

 

[JYM654]

There is also a poppet valve in the control valve, if that popped valve is damaged you will have break issues as well.
Remove 43, it is connected to a tube line, you should find pieces of a spring (if not use a pick and look inside the tube line, and a worn poppet.
Disregard the poppet valve and the spring, look into your piece #43. Does it have a Screen? If yes punch it out, if it is already destroyed make sure to take the rest off. And then install it back.
OR by an updated fitting by bobcat which replaces #43.

Thank you very much. I will check that ASAP.