Cat 336el hydraulic problems

[Kelson Turner]

Hi guys. have a 336el with a bzy prefix.

Anyways having some issues with the hydraulics. The swing function is very weak until you multi function. Right track is the same it’s very weak till you multi function. But the weird part is when you use right travel pedal it strokes up both pumps. Any help on this would be appreciated.

thanks

 

[Nige]

Sounds like classic symptoms of a resolver (shuttle valve) issue.
Don't ask me which one though .......... it seems like there are dozens of them on that machine including the pilot manifold. Every one of those plugs has a ball behind it.

 

[John C.]

You will need to check for codes before you do anything else. Unfortunately I don't have a video that shows how to get access to the diagnostics in the monitor panel for the E series machines.

 

[Kelson Turner]

I checked codes as I have cat et. No codes related to the issue.

 

[Per Eriksson]

Can you clarify, you wrote that the right track is weak but then you write when you use the right travel pedal it works ok?

 

[Kelson Turner]

Sorry the right track is weak. When you are multi functioning the power in the right track comes back.

 

[92U 3406]

I think Nige is on the right track. I'd pull the hydraulic schematic out, map out the resolver network and then operate the swing function and each function 1 at a time to see which function(s) bring the swing power up and which don't. Then repeat with the track and note the results.

If you then follow the oil flow on the schematic through the resolver network you should be able to narrow it down to which resolver could be the culprit based on what the machine is/isn't doing.

 

[92U 3406]

The resolver network typically takes the highest pressure from any of the functions and routes it back to the pump, signalling it to stroke up. If a resolver is jammed up or bypassing, the pump won't see the correct pressure to signal it to stroke up for increased flow demands. When you run a 2nd function that requires higher pressure than swing or right track, that pressure is now the one signalling the pump to upstroke. That's why you're seeing the speed pick up during multifunctions.

 

[Nige]

If you want a copy of the Hydraulic Schematic just ask. I’ll send you a copy.

 

[Per Eriksson]

Ok, I think I know what your problem is.
Inside the main valve there's check valves that can fail and then let's pump 2 oil bypass through the stick spool causing low flow/pressure to right track and swing unless the stick is active at the same time.

Pull them and check, in your case I'm leaning towards the top one being the issue.

 

[Per Eriksson]

Remove manifold on the rear of the main valve to access it.

 

[rmllarue91]

Did you cut filters ?

 

[Per Eriksson]

Any news, gonna leave us hanging?

 

[Kelson Turner]

Hi guys. We have recently checked all shuttle valves and everything looks fine. And we have checked the check valves in the main valve. We have ruled out everything and had the support from our local dealer and haven’t found the issue.

they are sending a dealer mechanic out on Monday and started a dsn so hopefully they will find something.

thanks for all the help

 

[Kelson Turner]

NFC2 relief broke and pounded out the seat in the valve. But its the relief on the bottom of the valve not the top

 

[Per Eriksson]

Interesting, never seen that before.
But the nfc valves are in the top section, the checkvalves for pump pressures to the main relief are located in the bottom section however and looking on the schematics I think you can have the same kind of symptoms if one of those is broken.

 

[NathanG1995]

Hey having a similar problem and found this forum, I have checked the NFC reliefs on top but where is the NFC on bottom I have checked over the schematic a dozen times! Also the check valves that are noted what are these check valves for?

 

[Per Eriksson]

Check valves in the bottom is for letting flow from each pump go to the main relief but not cross over to the other pump and vice versa

What's your serial and symptoms?

 

[NathanG1995]

336F RKB Serial - Will not track on right side and very weak on swing until you stick in and both track and swing work as it should!

 

[Per Eriksson]

Take a look at the check valves I highlighted in post#10, most likely the upper has failed but change both while your in there.