Komatsu PC75uu-2 house rotation while traveling

[Batkom]

Finally got the beast out of the shop yesterday.
after 3 months of doing maintenance,replaced all the stick/bucket end pins n bushings. Replaced all the pump side intake and pressure hoses, fuel lines, radiator hoses, a lot of cleaning and electrical details and painted it. Fixed everything that I could see.
Still have a hydraulic leak/weep between the main pump and the gear pump thats on the end of it.
But to the question.
Ran about 5 hours yesterday doing various things, plowing snow, digging a big burn pit, digging n moving snow piles.
Problem -
I noticed every time I started to travel that after a little bit the house would be rotated the operators right a little, correct it and pretty soon it would again be rotated again.

The travel seems up to speed, surprisingly fast feeling for not having a high speed travel.
But all the other functions feel slow to me, especially the main boom lift. My last machine was a 2014 john deere 60G that I bought new. So I am not sure if its just my perception of having run the newer machine hundreds of hours and the old machines are just inherently slower.
Will have to do some of the Timed tests in the services manual when I get a chance.

Seems I ran across this house rotation problem on here but I cant find it now.
Whats the likely cause?

 

[John C.]

The only thing I can think of right now is maybe the plate on top of the quad valve joy stick controller might be a little tight. It's possible that you have a compensator leaking internally.

 

[Batkom]

John
Thanks, had not considered that, but I did adjust it down to take out most of the play.
I will watch it while I am moving next time.
Excuse my ignorance, what does a compensator do, and where Are they located in the hydraulic system.
How many years have you been working on these machines, your depth of knowledge is incredible!

 

[John C.]

You need a little bit of play so the plate doesn't put any pressure on one of the valve poppets.

I'm not sure if your machine is an open center system or a closed center system. A photo of the pump or the valve bank would tell me. The closed center machines have a single mono block valve. Normally all have what is called a load check valve that hold oil in the cylinders until pressure from the pump overcomes that pressure and the valve opens. This prevents an implement from falling down slightly when the directional valve spool opens and pump pressure is still low. The open center systems have a regular load check. The closed center systems have a pressure compensated load check generally known as the compensator valve. It is a load check valve that has a passage from all the other functions plumbed into a port in the top of the check. What it does is ensure all the implements feel the function with the highest pressure. If it wasn't there and you were raising the boom and opening the bucket at the same time, the bucket being a lower resistance to flow would get most of the oil and the boom would stop being raised until the bucket pressure was the same as what was needed to raise the boom. That oil is also sensed by the hydraulic pump which is governed to keep the pressure in the system at least 300 PSI higher than needed to operate a function.

If a compensator is leaking the oil is dropped in pressure that the pump sees so the output is reduced to only supply what is needed. The speed of all the functions then is slower. The quick cycle time to check is boom up. If you have a book it will show you how to run that test. Generally boom up at max engine speed and highest operating mode should be around 4 seconds or less. Anything around 5 seconds indicates something is a little off.

 

[Batkom]

Thanks for the explanation!
A couple other things I noticed yesterday that may or may not have any influence on the slightly swinging house.
The swing brake is not working. Testing the solenoid it's pretty much dead. One more thing to tear apart n fix.
Also noticed that at some point the hoses on the boom appeared to have been switched-so that the one for the up was on the down and the down on the up.
Traced it on the hydraulic diagram and it had been switched, changed it back the way it's supposed to be.
Only problem with that is the stick forward raised the boom instead of lowering it. So i took the joystick console apart and swapped the hoses on that valve that the joystick operates - the one the disc pushes on the poppets.
Fired it up for Just a couple minutes in the shop to verify operation.
wow what a difference!
The boom lowereing had been jerky and you could not ease it down. Now its smooth as silk and you can lower it really controlled.
I tell you the previous owners really screwed things up on this one!
Been an adventure trying to figure out what they did!

 

[Batkom]

So ran it a couple hours this morning since swapping the hoses to there correct positions.
What a difference, digs with authority now, boom speed feels normal. timed it with my 36 in heavy duty esco dig bucket on it, Ground level to fully up in 3.5 seconds.
Checked rotation speed of house, doing 8.25 rev per minute - spec is 8.5.
I don't think the compensator valve i an issue, and I did not notice the house rotating today
!

 

[John C.]

Sound like you have all the issues nailed down.

Now go run it, make some money and have some fun.