Brakes won’t release on 770 John Deere grader

[Da newfie]

His brakes are internal, oil bathed.

The park brake is electric over hydraulic.

To set the brake hydraulic pressure is released. This is logical so it doesn't slowly release after the machine is parked.

To release the brake hydraulic pressure is applied. This is accomplished with an electronic actuated solenoid.

I'm guessing you have lost electric power to the solenoid. Or the solenoid has failed.

Find the solenoid and check the circuit for power when the "key" is on. If no power, search for a fuse?

If the circuit powers up when the key is turned on then the problem is more than likely the solenoid.

Report back with your findings. Hope it's a simple fuse.

I've ran JD graders since 1989. Now running a JD 672G.

Welcome to TBN.

Thanks for the reply’s.
yes it’s hydraulic brakes and you are probably right on the solenoid, but do you know where the solenoid for the brakes is at? I saw about 5 in one spot. But I’m not sure if either of those are for the brakes. Thanks again for your reply.

 

[ovrszd]

Thanks for the reply’s.
yes it’s hydraulic brakes and you are probably right on the solenoid, but do you know where the solenoid for the brakes is at? I saw about 5 in one spot. But I’m not sure if either of those are for the brakes. Thanks again for your reply.

Can you tell us the year of manufacture, model designation and S/N?

 

[Da newfie]

Can you tell us the year of manufacture, model designation and S/N?

Hi there, I’m back with my findings on why my brakes would not release. I checked out the things you mentioned when the brakes didn’t release, So I was reading about solenoid’s and how they work on the brake system but didn’t quite figure out their location so I started at the pedal and followed lines and wires eventually ended up at the back of the rear ends saw a couple of solenoids behind what looked like the
transmission. They are really rusted so I tapped as hard as I could without damaging them and I could hear a difference in the sound of the hydraulic system (had the blade down into the ground as a precaution). Got up to see the parking brake light gone out. So now we can drive it, got good brakes but no parking brake until we get the solenoid’s replaced. So thanks for all your help and advice and thanks to this John Deere family forum for everything hope this can help someone else in the future.

 

[ovrszd]

Thank you very much for the report!!!! Often we never hear the end result!!! Deere.com has a pretty good online parts search site. You'll need the S/N to get accuracy. It should even give you the part numbers you need to replace the solenoids. When I'm using that site for guidance I print the page with the diagram and parts numbers. I take that with me to the dealership so there's no mistake about what I'm talking about. I've also used those diagrams to visit with mechanics to clarify what I need to do to replace parts.

I always lower my blade when parking the Grader. So the park brake simply becomes an extra safety measure. On the newer JD graders the park brake is activated when the machine is shut down. Fortunately yours doesn't do that!!!!