336F Slow Bucket

Good day, I’m currently having hydraulic issues with a 336F (S/N RKB10057) (10,000hrs on unit) and I’m looking for some advice. Customer complaint was slow bucket function and when tracking, all functions are slow. Arrived at unit and checked all the basics, fluid level, condition, etc. No active codes. Checked pump pressures and found that pump #1 (which controls bucket and left travel motor) was not coming up when bucket or left travel is actuated. The pressure will reach relief pressure when bucket cylinder is at the end of its stroke. Cut filters open, found them to be clean and they had not been recently replaced. Swapped pump controllers and issue stayed with bucket circuit. Swapped main pump feed lines at the control valve and issue stayed within bucket circuit. My question is: why is the bucket not causing the pump to stroke up? I should add that when moving the boom or stick both pumps are stroking up properly.

Maybe see if you can swap the neg control sensors on the main control valve and see if the problem swap sides, i.e. problem changes to slow right track and possibly slow slewing function? If it is still the same try swapping just the neg control electrical connectors to the sensors and try tracking straight and see if the left track picks up speed. See attached diagram for location of the sensors. Item 16 should be Pump 1 Neg control sensor and item 17 is Pump 2 neg control sensor. Best regards

The bucket sensor, as said above, is suspect. Retrieve the fault codes from the display monitor.

No active codes. Swapped neg flow control sensors and bucket cylinder pressure sensors with no change

Buenos días, puede intentar revisar la válvula de sobrecarga del cucharón. Una junta tórica rota, un resorte dañado, un atasco de material en el cono de la válvula o una calibración incorrecta provocan un movimiento lento.

Welcome Eduard. To comply with forum rules please post in English.

CRR said: No active codes. Swapped neg flow control sensors and bucket cylinder pressure sensors with no change Click to expand... If possible try getting a high pressure gauge connected to pressure tap connection "DD" on the pump to confirm that the pump is being commanded hydraulically to increase its displacement when the left travel or bucket function is operated. If you can get information on reading the pump stroke position sensors from the display monitor then this would also confirm that the pump is increasing its displacement without the need for connecting a pressure gauge.

Thanks Kobe, I snapped a 5000psi gauge on DD and when curling the bucket in, it comes up to about 750psi. When the bucket goes over relief it comes up to about 1500psi. Watching the pump displacement while curling in with the bucket, it’s reading 184cc/rev even when the bucket “gravity drops” and holds in that position for a second or two, and then kicks in and keeps moving. That tells me the pump is stroking up and that my issue may be on the control valve side of things. I’ve been over the pilot system a few times checking pressures so I don’t think it’s that. I pulled the bucket spool and inspected, no damage or broken springs. I swapped line reliefs with no change. What else do I check? Are there any check valves/orifices?

Maybe try looking into the straight travel valve which is electrically operated. Try and see if you can plug "P2" port connection on the pilot manifold and leave the "pST" port vented to atmosphere for the test. See diagrams attached. For additional testing of the pump to be ruled out, when swapping main pump lines at the control valve you would also need to swap the neg control pressure switch electrical connections and the pump solenoid and position sensor electrical connections so that the correct pump strokes up when using the bucket function or left travel. I was not sure if you had already done this or if you had just swapped the pump lines at the control valve.

Have you tried doing a track speed test with each track off the ground? Does it track straight when not using any other functions?

CRR said: Thanks Kobe, I snapped a 5000psi gauge on DD and when curling the bucket in, it comes up to about 750psi. When the bucket goes over relief it comes up to about 1500psi. Watching the pump displacement while curling in with the bucket, it’s reading 184cc/rev even when the bucket “gravity drops” and holds in that position for a second or two, and then kicks in and keeps moving. That tells me the pump is stroking up and that my issue may be on the control valve side of things. I’ve been over the pilot system a few times checking pressures so I don’t think it’s that. I pulled the bucket spool and inspected, no damage or broken springs. I swapped line reliefs with no change. What else do I check? Are there any check valves/orifices? Click to expand... Hi CRR, I’m having very similar issue with a 336F. Bucket gravity drops holds for a second then catches itself and curls in. The problem only occurs on the bucket curl in circuit. What did yours end up being?