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770G that locked up drive wheels

Public Works Bob ยท 2021-12-02 15:57

We have a 2012 770G that was travelling in 8 to the next job and out of nowhere the back 4 locked up tight and quick. We checked the fluids and a few fuses but everything looks good. Has anyone had a similar issue? We only have 5500 hrs on the unit. Thanks

Replies11
  1. #1BigWrench552021-12-02 16:03

    Broken chains or park brake failure

  2. #2mg23612021-12-03 04:24

    Welcome to HEF Bob ! Ditto on what Paul ^^^^said. Any codes? Post a serial number as well.

  3. #3Public Works Bob2021-12-03 09:05

    Thanks Mate glad to join the forum. Only code was PCU 522398. Ser# 1DW770GXPCD642539

  4. #4ovrszd2021-12-03 09:42

    Hopefully NIGE will see this and post. He's our resident code decoder. I'm guessing park brake failure. It is held open by oil pressure. Release the pressure and the trans locks up. A tandem chain failure would only lock one side, unless you were roading with the diff lock engaged. Surprising that it slid to a stop. I'd have expected a brief sliding of the tandems then chaos and exploded parts. Anxious to hear what you find so keep us posted.

  5. #5John C.2021-12-03 11:40

    Just to clear any misunderstandings, I assume a 770G is a John Deere product.

  6. #6ovrszd2021-12-03 12:00

    Yep. G Model has been on the market for 11 or 12 years.

  7. #7mg23612021-12-03 12:01

    This code is for the park brake. PCU 522398.12 "Park brake pressure switch (B21) is not functioning properly or transmission pump slow to build park brake release pressure".

  8. #8ovrszd2021-12-03 12:05

    Linking a thread here on HEF in regards to the code you listed. It's on a backhoe. Park Brake solenoid failure. HeavyEquipmentForums

  9. #9ovrszd2021-12-03 12:05

    You beat me to it. I googled it.

  10. #10dieseldoctordan2021-12-15 00:46

    We currently run a pair of 770G s. Have had a similar problem on one of them. It would not only lock up the drive train, but would kill the engine as well. We had to replace the solenoid that releases and applies the park brake. It's kind of in an ugly spot to get at. You need to drop the rear crankcase guard to access the park brake, and the solenoid is at the lower RH side of the brake assembly. Our problem was a short in the solenoid. When checked with an ohm meter, it still showed continuity, but was about 2 to 3 ohms out of spec. That was just enough for it to drop the park brake pressure and apply the brake. Hope this helps DDD

  11. #11ovrszd2021-12-15 09:48

    Man that's gotta be hard on the powertrain!!!! It's a testimony to how strong the park brake assembly is. You'd think it would simply grenade!!!!