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Caterpillar hydraulics system noise and vibration

viper

Titanium
Joined
May 18, 2007
Location
nowhereville
We are still working on an older caterpillar machine. We have most things repaired and looking into a hydraulics noise. Before I start, I will mention that hydro oils is gray, known to have water in it, and hydro oil level is very low. We have not added oil simply because we are getting ready to change the oil due to all the contamination.

When cycling a cylinder when cold, machine sounds just fine. If cycled multiple times with higher rpm, machine will not make noise until an implement is operated, then will exhibit a growl along with vibration in the entire machine and implement but implement will still function fine other than slight jitter when operating at very slow speeds.

pumps are variable displacement axial piston pumps. I really think that the low level in the tank coupled with faster cylinder cycles pulled air in the system and cause all the noise and vibration but curious of other's experiences? We really do not want to change over 100gal of of hydro fluid if a pump is really bad but pressures and volume performance indicate otherwise at this time. even after experiencing the noisy hydro system. After allowed to sit all night, the system is still quiet next day at low rpm/demand situations. We are unwilling to exercise it much more until we change fluid.
 
... We really do not want to change over 100gal of of hydro fluid if a pump is really bad but pressures and volume performance indicate otherwise at this time. ....

No getting around it. The water in the fluid will cause the surging. It can also cause cavitation in the pump and problems with some valves. Change the fluid, then, If you end up doing more work just drain, filter and reuse the new fluid.
 
As they say...you can pay me now or you can pay me later.

1. If you do not dump the oil now, you will need to when you have to replace the pump or keep the oil and keep buying pumps. Pure and simple.

2. You have phase separation, bacteria formation, entrained air, dissolved air and God knows what else. If you wish to do a torture test of the pump continue as you are doing now.

3. This is penny wise and pound foolish.

4. Cavitation will emmit a high pitched squeal and subsequently the pump will fail.

5. Sucking air somewhere on the intake will sound like a bad bearing, give erratic banging and popping noises.

Drain the system, purge the system, fill with proper viscosity, replace the filters, flood the pump and IF you haven't ruined the pump already you should be fine. I see no quick fixes or remedies.
 
I second what Fran said about the pump and the fluid. Cut open the filter cartridge. If there is no metal in the filter, and the pump makes good pressure, you may have dodged the bullet. Drain the system as dry as you can get it, even if you have to crack a few fittings, change the filters. Add hydraulic oil to a minimum level for operation. Cycle the cylinders, but do not uncover the intake and introduce air into the system. Get the system up to operating temperature, then look at the oil. If it looks OK, and the system works correctly, change the filters again and fill to the full line. Good Luck. PS- Oil and filters are MUCH cheaper than pumps. Regards, Clark
 
After allowed to sit all night, the system is still quiet next day at low rpm/demand situations.


I'm surprised that you haven't toasted the pump already. :rolleyes5:

Get the existing crap out of the system, flush with a minimum fill and new filters, drain and refill with fresh fluid and new filters. As mentioned, open the filters for inspection, and cross yer fingers.

Was this rig in a flood, or just badly abused?


Rex
 
The chances that you don't have internal damage are slight, but sometimes you get lucky. Drain and clean system right away, flush with fresh oil and redo filters again. cut open old filters and the flush filters and check for metal. Now you can safely go trouble shooting from there. Good luck, sounds like you may need some.:codger:
 
I'm surprised that you haven't toasted the pump already. :rolleyes5:

Yeah, me too...

Get the existing crap out of the system, flush with a minimum fill and new filters, drain and refill with fresh fluid and new filters. As mentioned, open the filters for inspection, and cross yer fingers.

Based on my experience, if the existing oil is as contaminated as it sounds you'll probably need to do the flush, fill thing at least twice. Hydraulic oil needs to be clean! Flush/purge the system once, fill it, using enough oil that you can run the machine and get it hot so it flows freely and picks up as much crud as possible. Check the filters if you want but I suspect that they're going to be full of crud. Flush it again and repeat the cycle till you get clean--or very nearly so--filters after you've run the machine for a while...
 
I worked on a large 1960's Clark forklift that had slow hydraulics. I found that it had a large fine screen in the tank at the pump pick up. The screen was sucked into a tight knot from being stopped up. I cleaned and straightened the screen and it acted like a new forklift!
You might need to change that oil more than once if it has a lot of water.
 
All the above and are you feeling lucky?
First, work out how much the machine is worth and is it insured?
Then get a price on a pump, 2-4 times the total oil capacity and a box of filters.
Compare the 2 figures + labour.
If you don't burn it, just make sure the pump dos'nt run dry and keep changing oil and filters. Opperate all systems until hot then change the oil and filters. When you think you've got the oil cleen, take a sample and after 50 hours take another sample. Repeat as necessary. Make sure your sitting down when you get the price on a new pump!

Russell
 
OEM Cat hydraulic pumps are pricey, but until Viper comes back and mentions what he is working on there's no telling what kind of $$ would be involved.


Rex
 
Machine is an excavator.

Pump configuration:

(2) variable displacement axial piston, 9 barrel, 2.5-9.0 ci/rev, operating rpm 1800, 3600psi main relief

(1) gear type constant displacement, 25gpm at 2200 rpm, 2400psi main relief

All pumps a components are available and rebuildable. New pumps are not an option. By the time we get done replacing everything that is recommended, we might as well buy a new machine. Pumps are about 10K each, plus 20 oil changes, lines, etc. Due to age, this one will likely be driven into the ground before we go to that expense.
 
Pumps are about 10K each...

??? I would believe it for the bent axis piston pump, not for a gear pump. The gear pump shouldn't put you back more than 1K. Not sure what the mounting flange and port sizes are but based on your flow and pressure a P257 Permco with 1.25" gear section (#12) would give you what you need in terms of a gear pump. If you're getting quoted $10K for a gear pump I'd be interested in knowing what's so unique about it.

If it was only that easy though, you still have the piston pumps to deal with. Sounds like a tough situation, hope something works out for you.
 
Yup already almost worn out..

Without clean oil an excavator is worthless, with clean oil, it is worth a drum of clean oil.

If something is going south in a pump, the chunks of pump get spread through system.. Cut/open a filter and look..

Sure the parts may be available, but you will likely need ALL of them...

The one piston pump (with broken input shaft) on 225 at mine, had been rebuilt at least once already (rebuild plate)

Any machine that weighs say over 60000 lbs, is going to cost to operate.

If you can't afford to change the oil, get rid of it..

These are not toy machines, they require $$$$ service and repair, even if just lightly used..

There is no magic to working on one.. Take it apart until you find what is broken or worn, repair, repeat. Only a couple hours to pull all 3 pumps and assy drive.. The piston pumps are at least 3 or 4 hours each to open up, clean and reassemble.. Service/Parts manuals with correct serial number for machine are vital..
 
If it works well at low rpm's and noisy at high rev's go to the intake strainer in or near the tank. Most all hyd filters are on the return side of the system, not on the suction side. Hydraulic is a non detergent oil, so crap gathers in the bottom of the tank, rather than continusly run through the system, add some water and the rust/scale will plug the strainer. Drain the tank and make something to scrape the bottom of the Hyd tank and see what you find, likely a black mud of stuff growing away.
 
remove return line,dump into barrel.cork return line inlet on tank.clean tank and fill with fresh oil.
with fresh oil in tank,old dirty stuff draining into barrel,cycle hydraulics at idle,replaces old oil with new,follow up with new filters.
no matter how you look at it,oil is the cheapest way to clean the system
 








 
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