CAT 303CR Slow Swing

New to me Cat 303CR the swing function is incredibly slow. If I bump the boom control down the swing will operate at full speed as long as you are swinging. If you stop for more than a second or two the swing goes back to being slow.

Any one have any experience with this issue?


SN- DMA02366

I also can not get the boom to lower if the machine is off. Even with the key on and left armrest down. Possible issue with the accumulator?

There is no accumulator on these at least on the one I have there is not. Your swing problem is most likely in the control valve. It is not giving the pump command to pump but when you move the other control who gets flow from that pump it gets it going. Revolvers maybe I'm not 100 percent knowledgeable on these valves

Serial number ?

DEMLONE70 said:

Serial number ?

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It was under the video, should have put it before, sorry.

SN- DMA02366

Tyler d4c said:

There is no accumulator on these at least on the one I have there is not. Your swing problem is most likely in the control valve. It is not giving the pump command to pump but when you move the other control who gets flow from that pump it gets it going. Revolvers maybe I'm not 100 percent knowledgeable on these valves

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I can feel the supply hoses to the swing motor getting oil when moving the joystick. Is the swing brake hydraulic?

Hi John, since this post is related...
https://www.heavyequipmentforums.com/threads/303-cr-hydraulic-line-locations.92414/#post-1016942
I'll reply here...

Yes the swing brake is within the swing motor and is hydraulically released, spring applied. The spring motor has its own gear pump piggybacked onto the main pump. As for the swing brake dragging, what's your gut instinct tell you?... if the engine feels like it lugs slightly more when the swing slows, and RPMs drop slightly, then yes go down the path of troubleshooting the swing brake.

I'm not sure how easy that control valve spool is going to be to remove and inspect for debri/wear. If you don't want to start pulling things apart and playing guess work I thing you're going to need some pressure testing gear if you don't already have.

If I was working on it I'd want to first confirm that pilot pressure was dropping during the "slow swing" event. That would tell me whether it's a pilot or main hydraulic system issue.

Gut says swing brake.

You can feel the engine lug slightly when you try to swing. When you try to swing and simultaneously lower the boom the brake releases and the swing works as normal. So seems like the boom down is giving correct pilot pressure to the brake.

This is how the pilot lines for the brake are plumed:


I have access to pressure testing gear. Do I need to T into the P or the R lines on the brake?

The only reliable way to verify correct hydraulic hose routing is to use parts pictures out of a parts manual in conjunction with the schematic. Might be worth buying one if you have doubts. If there's no way of knowing the machine history who knows what they've done.

Does the blade and boom swing have the same fault by any chance? If not, hold off checking pump pressures for now. They all share the same pump.

The rectangle you've drawn next to the swing motor is the swing brake control valve. In physical form it should be a little housing bolted onto the swing motor somewhere with those two lines running off it. If you could somehow tee into them both and check pressures it would help, but I'm not sure you're going to have the room down there. Jam your bucket into the ground, load it up and try to swing, check pressure. Then bump the boom down to "fix" it, check pressure again. Both hoses should stay somewhere near 500psi. If this is the case, you've proven the swing brake is getting the correct pressure/signal to release, and you've proven the pilot section of the main control valve is doing it's job. Might then be worth pulling that control valve off the swing motor and inspecting, as well as the two relief (shock) valves on the upper section.

If the pressure in one of those hoses changes significantly, time to dig into the main control valve (hyd schematic does show a screen in there that could be blocked - diamond shape near PP2) and check swing pump main pressures. If everything checks out ok, and it's still faulting, time to replace the swing motor IMHO.

PM'd you some docs.

History is questionable, previous owner had the boom and bucket hoses swapped on the main valves, after fixing a leak. That's why I'd like to confirm hose locations.

The blade and boom swing work perfectly.

If I can get teed into the lines on the swing brake control valve, I should see 500psi when trying to swing?

Would the screen be inside the main valve?

John David Boreing said:

If I can get teed into the lines on the swing brake control valve, I should see 500psi when trying to swing?

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You should see close to it on both, and one hose may take longer to ramp up pressure then the other, that's ok.. the important thing is you're looking for a significant difference as to when its faulting and when it's not faulting. Should be done with hydraulics warm at high idle. You can jam the bucket into the ground like I said or slew against an immovable object.

John David Boreing said:

Would the screen be inside the main valve?

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You're guess is as good as mine. The schematic shows it there, the disassembly/assembly instructions make no mention of it.

As you know, these checks are only really valid if the hose routing is correct. If you could at least verify the machine worked properly once with the hoses as they are now, that would go a long way.

Have it at the mechanic, he is saying pilot and supply pressures are correct. Does the Attachment and Boom Convergence Valve (20) change positions when trying to swing? Could that be blocking the return line from the Swing Control Valve (21)? But when you bump the boom down it is operating the bm2 into 20 and opening the return oil flow?