Case 350 - hydraulics drop from full height in less than 1 minute

[J_J]

There are two things that would let yur loader arms fall.

Cyl seals are worn.

Valve spool is not blocking fluid.

Cyl seals can be checked by applying pressure after the cyl is fully retracted, by removing the rod end hose and see if fluid is flowing out the cyl as you move the lever to retract.

To check the valve for leakage, install a needle valve in both the OUT port and the PB port if you have that feature. If the lift cyl's check good, then the fluid is flowing past the spools into the OUT port or PB port. If you block those ports using the needle valve, then the fluid has no where to go and the lift arms should stay up.

The rear rippers are probably on a separate valve and you may have worn spools on that valve also.

Is this hyd problem something that happen recently of has it been doing this for a while?

 

[Godhungry777]

I removed and disassembled the control unit and found that the main relief valve is completely missing the 'poppet'. That'd do it

I'll replace all the orings and backup rings while I've got it apart but am thankful that it's a simple fix and can't wait to get on it with it working properly.

Thanks again for all your help. I wouldn't have had the confidence to have a look if it hadn't been for your responses on this forum.

 

[Willl]

With a drop that quick, it could ONLY be a valve problem.

Heck, you could remove the seals totally on the lift cylinder pistons and as long as the return lines are closed, they will NOT fall.

((Edit; Need to rephrase that a bit, BOTH lines need to be closed.))

 

[boggen]

glad to hear you found problem. hope it all goes back together and works. (not reading back through post) if you have shop manual, double check the "torque" you need when putting it back together.

 

[Godhungry777]

Looks like Case Australia is needing to order the poppet in from the US. I'm wondering if it might be cheaper and quicker for me to just order from the US directly myself. Anywhere you'd suggest I look to buy Case parts online?

 

[Godhungry777]

UPDATE:
I replaced the poppet and all orings and reassembled (with workshop manual and an experienced Caterpillar tech overseeing). I lifted the bucket once and put it down pushing it into the ground and lifted the front of the tracks a few centimetres. I haven't been able to move anything since. I can't lift or make anything happen. As soon as you activate any lever the motor strains severely but nothing moves.
We pulled everything down again but couldn't find anything out of order. Reassembled and still the same problem.
I gave it a bit more rev and tried again. Blew the main hose coming from the pump. It would seem the pump is not the problem
Replaced the hose. Checked and cleaned the return filter and filter bypass. Still no improvement.
So my conclusions are:
- It seems to be a blockage in an area common to all spools but not in the main line (There is no problem or strain until you activate any of the levers in any direction)
- The fault does not seem to make any sense. I'm an electronics technician by trade and it's been my experience that when a fault defies logic and the usual order of things, it is usually technician induced.

I've been chasing this around for nearly two months and need a fresh perspective. Any suggestions?

 

[Leejohn]

Are you sure the out port and the PB port lines are hooked up right and not crossed? That is if you have a PB port.

 

[Godhungry777]

Are you sure the out port and the PB port lines are hooked up right and not crossed? That is if you have a PB port.

Thanks Leejohn. Yeah it's pretty much impossible to cross most of them. The in & out are much larger than any of the work ports. Not sure what a PB port is.

I was looking through the manual again and about the only thing I can see that I haven't checked is the secondary relief valves and the check valves (which may be the same thing) but I think that would only effect individual circuits.

 

[J_J]

I think I would recheck all the QD's.

Put a pressure gage on the hyd system, and take some readings.

You definitely have some leakage in the cyl seals or the valve spool.

Does the valve relief activate?

 

[Leejohn]

Is your system open or closed? It's sounding like it's closed. I wouldn't think you can be 100% sure if something like a relief to be working by looking at it. But I would clean them and try. That secondary relief valves and the check valves is that for all spools?