Cat 306 Pilot Valve

1. #1Nige2025-09-19 18:05

   No, but if you start with a machine Serial Number some might be forthcoming. I see a dozen different flavours of 306.

2. #2pittedmess2025-09-19 20:27

   MXH00488

3. #3Deimos2025-09-20 05:23

   Since the pilot valve is leaking, it's highly likely that its internal surfaces or seals are damaged. This means that at low control signal (when you're trying to move the travel motor gently), the valve can't smoothly (metered) open the fluid channel. Fluid leaks, pressure fluctuates, and the travel motor jerks. At full flow, leaks are less critical, and the system operates. It's probably worth repairing the pilot valve.

4. #4Nige2025-09-20 05:51

   The "was" implies that it is not leaking now, or am I misunderstanding you.? Has the pilot valve been disassembled recently.?

5. #5pittedmess2025-09-20 09:10

   When I replaced the seals, the spring tension was different between the 2. The jerking was prevalent before anything was done to repair the leak. Must be an aftermarket valve. The Cats parts were different from what I had.

6. #6Nige2025-09-20 11:20

   You mean the parts list I posted above does not correspond to what you actually have in your valve.? Are there any Cat part numbers on your valve, maybe on the body.?

7. #7pittedmess2025-09-20 13:11

   Will check

8. #8pittedmess2025-09-20 15:26

   Parts list is perfect Same one I use from my Cat Account. Valve is aftermarket The travel motors work fine in reverse The left side unlocks at last moment moving forward to create a jerk. Trys to move before it unlocks. Going to replace the valve. Seems to be leading to this.

9. #9Deimos2025-09-20 16:19

   Now we have a more detailed description of the problem. If the left side doesn't release immediately and with a jerk, this indicates that the hydraulic motor is not releasing the brake immediately. Presumably, the problem could be in the Counterbalance Valve of the left hydraulic motor. There could be other causes, but first, of course, we need to check the hydraulic motors. To rule out the main pump as a possible problem, I would swap the travel motor hoses in the swivel, thus swapping the pumps with the motors. This test will 100% determine whether the problem lies in the hydraulic motor or the pump.

10. #10Deimos2025-09-20 16:39

    You can also try swapping the Counter Balance Valves, or inspecting all components of the left Counter Balance Valve.

11. #11pittedmess2025-09-20 16:41

    But it works fine in reverse

12. #12Deimos2025-09-20 16:47

    The Counter Balance Valve works in both directions. It may work fine in one direction, but stick in the other. In addition to this valve, you can also check the crossover relief valves on the left hydraulic motor and swap them.

13. #13pittedmess2025-09-20 17:41

    I will check. Also going to reverse pilot valve connections to eliminate that. I can’t seem to get away from the pilot valve. The movement is so much different from the right side valve operation

14. #14pittedmess2025-09-21 10:13

    Interesting to note The travel motor is a Doosan 2302-9277B On left. Cat 330-7517 on right. MESS

15. #15pittedmess2025-10-09 18:58

    Update. Replaced the pilot valve for the travel motors No more jerking. Runs perfect. Thanks all