Mustang Mtl25 hydraulic problems

[DJZ001]

I have a mustang mtl25 and when you lift the boom at full speed everything is fine but when you ease off the joystick to slow the lift speed the boom wants bleed down when joystick is back to neutral position it stops and holds. I have pulled control valve apart checked spools in that valve and load check and everything is fine and smooth. The valve that operates the boom raise and lower has actually been replace with a new one. I have swapped relief valves from other functions and still the same result. I did discover aux hydraulic valve spool spring and bolt had backed all the way out and was laying in pilot cover but only gained operating speed but still the bleeding down remains. I am going to check cylinders today but at this point I’m lost any help would be appreciated. It is a nishina valve

 

[DJZ001]

I have swapped hoses on pilot control and problem remained but I have not checked the pressure of the pilot system yet

 

[stourpaine]

do a base line of all the pressures first ie pilot and main relief and line reliefs you may have switched line reliefs .as the valve has been replaced both the main relief valve and line reliefs should be all set up. You don't want pump pressure going over a line relief they are not designed to flow large amounts of oil. also can you perform a flow test of the main pump if the machine has auxiliary hydraulic couplers plug in there between them set to high idle then load up and see what you got. Compare all results to spec.....you will need to turn up all the line reliefs in order to set your main relief

 

[DJZ001]

I haven’t put a gauge on anything previous mechanic said he thinks it’s line reliefs but I’ve replaced them with one of the 5 others and set the screw all the way in and no change it’s only on that valve I can adjust relics on curl valve and get a change I did check cylinders and they are fine but I haven’t checked pressures yet

 

[stourpaine]

a base line should always be done on hydraulic trouble shooting a machine its the first thing to do it will help you then based on what you see go from there

 

[DJZ001]

are you familiar with mustang skid steers? What do I check first I don’t have gauges or anything but I will get them everything is British standard so fairly common I was just about to delete the self leveling valve and see if that was the problem but yes your right I’m basically guessing at this point

 

[stourpaine]

no I am not a mustang guy just a old guy thats done a bit of testing over the years! first thing to check would be charge pressure.....then pilot pressure then main system pressure then line reliefs. then a flow test You MAY be onto something with the the self level. you clearly are loosing oil in the circuit somewhere. does the boom spool have a nick in it? does the boom spool slide under its own weight in the valve? does the boom valve have a broken spring? does the valve use the same springs? and are the boom/bucket spools the same? maybe they are not and got mixed up.why did the valve get changed in the beginning?.....if it was for this problem then maybe you should look else where how is the pump that supply's the boom driven? is there a screen in the suction side? when you switched the pilot lines you tested the pilot system operation that moves the spool for the boom. basically you reversed the boom and bucket handle function operation so on that side of things if there were no change and the bucket operated normally it is not likely on the pilot side of things

 

[DJZ001]

So I pulled the spool and got my hands on the original they do match. the new spool was a little sticky and I was able to get it moving freely I did discover aux spool sticking and freed it up as well but did not help the bleeding off when booming up at about half way back on the joy stick. I am going to get fitting for pressure gauge and also fittings to delete self level in the morning original guy still preaching relief valves but I don’t think so. The filters are original but idk if changing them would solve my issue as every other function is strong

 

[stourpaine]

keep at it you will get there!! a hyd schematic would help too. plug off the leveler I think you may have some thing there. If the bucket was loaded and off the ground would it leak down with controls in neutral? the reason for a base line is to know the health of the hydraulic system and that all the settings for the different circuits are set to the factory specs....write them all down and be sure to do it with machine at running temp you may be required to do 2 sets of tests one at low idle one at hi idle. so a COMPLETE new valve body was installed?

 

[DJZ001]

Just the stack that controls the boom up and down I don’t think there was anything wrong with the old one myself but oh well I still have a suspicion that one of the cylinders is bad just because he bent one so severely he had to buy a complete new cylinder he said the problems arose after the new cylinder was installed but I bottomed them both out pulled hose off empty side and loaded the barrel and I got no blow by out of the open port so I think piston seals are good I’ll try plugging the self leveler and get back with you

 

[stourpaine]

do the symptoms happen at heights of the boom or just one particular place?

 

[bmd1987]

Approx. What year is your mtl25?
Does this seem to happen just when your control lever is in about the same position?
Almost 20 yrs. Ago the place i worked had some mtl25s and I remembered replacing atleast one of the pilot/ joysticks. Again, many years ago so i couldnt tell you what the symptoms were but i know that fixed the issue it was having.

 

[DJZ001]

I believe it’s an 05 it doesn’t say on the tag if the self level delete doesn’t work I’m going to lean on the pilot control I changed main hydraulic filter but did not change pilot filter so I think I need to try that as well

 

[DJZ001]

So I deleted the self leveling valve and no change. I noticed I hear a lot of flow coming from the valve when I get the pilot control in that position where the boom bleeds down I found the main relief on the stack that has the inlet from the pump and the return that goes to filter gets warm first I pulled it and it seems fine but I’m going to get new o rings for it in the morning

 

[DJZ001]

The symptoms happen wherever the boom is stourpain

 

[stourpaine]

ok assuming you have took the self level out the picture and had NO change time to move on! tee into the pilot line for the boom circuit watch the gauge and see what it does when acting up. i dont know the pilot spec but ball park 400-500 psi this should rule out the joy stick if nothing goes on with the pilot pressure when boom starts going down. after that tee into the head end of the boom cylinder...again dont know boom pressures ball park 2500psi-3000 you wont see full pressure untill cylinder is dead headed in either direction but with the bucket full you will see some pressure logic would say when it acts up pressure will suddenly drop. but while you have this hooked up you can dead head and see your boob circuit pressures both head and rod end. yes you will need a couple gauges and a few fittings etc but gotta have them

 

[DJZ001]

Yes sir I just picked up pilot filter and about to get the necessary fitting for gauges I will let you know what I find out thank you for the help and guidance

 

[stourpaine]

np yes let me know how it goes ....good luck!

 

[DJZ001]

So I changed pilot filter and put gauges on pilots going to boom valve and head side of rams as I pull back on pilot control at half speed I have 200psi and around 800 psi on cylinder. Pilot control all the way I get around 450 and around 1000 on cylinder. When I peg cylinder out I get around 2800 psi on cylinder. Ao when I find the sweet spot for boom to start bleeding down it’s a matter of at most 50psi drop in pressure. I also discovered all spools were in on wrong side of valve basically they weren’t completely centered in valve after corrected bleed off did get better but is still present.

 

[stourpaine]

good you have made progress! pilot sounds in the ball park boom sounds in the ball park too. Having the spools in wrong would mean they wouldn't be centered definitely would cause .problems. look carefully at BOTH boom cylinders look at the tubes for possible damage in one area.it wont take much to mess things up. got no damage.......time to pull both cylinders ONE at a time and pull out the rod and piston for a closer look inside the tubes .don't have to take them completely off. leave the bottom pinned with the boom supported SAFELY. remove the rod end pin.
loosen the cylinder nut with peg wrench or big pipe grips pull out the piston and rod it will be a mess get a bucket! to catch the oil. look for damage inside the tube possible damage, or loose piston nut .after doing that insert the assembly and screw the cylinder back together. with both hoses off move the rod thru its motion to see how it feels. After you have done both of them and reassemble make sure you set your line reliefs for the boom as you mentioned you had screwed them hard in....... if you have done all the things we talked about and you still have a problem then with out being there and seeing it I would have to say im stumped