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Brazos Valley | Trying to get the park brake fixed on a 520-50 telehandler. So far what I’ve come up with is the dash switch is good, I am getting power to the solenoid on the front of the transfer switch and the solenoid is reacting.
I could not find my hydraulic pressure gauge to confirm pressure at the solenoid. So I did what any good redneck would do and that is I tore the brake open.
What I found is that all of the friction plates are like new and don’t seem to be worn or installed incorrectly. What I did find concerning was that the “piston” (part #77) had a very tight fit in the housing (#81). It was so tight that I had to get a small punch and hammer it out. I saw no visible signs of scaring or metal wear which brings me to my hypothesis.
Is it possible the incorrect oring was installed on that piston and bound it up to the point the hydraulic pressure from the park brake solenoid wouldn’t move it? I have the OEM oring I ordered several months ago about the same time I thought I’d get around to rebuilding that hay cutter I listed for sale lol.
But if I’m being completely honest I don’t quite comprehend how this park brake even works. It appears as though when you activate the dash switch it opens a solenoid forcing hydraulic fluid behind the piston that then compresses all of the friction plates to form a brake. What I don’t understand is how does it remain engaged when power is off and what opens the friction plates to disengage.
I wish we had a JCB dealer nearby but the closest one is 120 miles away.
Thanks
Caleb
Edited by AgAcGuy 3/18/2026 20:44
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Any JCB mechanics on here?
