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Hydraulic problem on MMM

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sbruse
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2002-02-21          35783


Hi all. I recently purchased a Cub Cadet 7275 (1995) with FEL and 72 in. MMM. The tractor has about 590 hrs. on it and is in reasonably good condition. I am having a problem with the MMM though. If I raise it up to full height, it drops back down in about 15 minutes to its lowest point. Also, the relief valve (I think) screams the whole time I'm raising it. Problem is, the screaming seems to come from the loader joystick area, and the service manual doesn't say anything about a relief valve here. The front end loader and 3pt stay up fine, and don't cause a screaming relief valve. Any thoughts before I attempt to fix the problem. Thanks in advance!!

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Steve in Buffalo NY
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2002-02-21          35787


My loader valve makes a lot of noise on my 7265 when I use the 3 pt hitch. On those occasions where I have removed the loader and looped the loader hose back to the bypass block the 3 pt is quiet as a mouse. I have the cub 476 loader (which I suspect is really a woods). I had been meaning to ask my dealer about it but keep forgetting.... ....

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Roger L.
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2002-02-21          35788


I don't know about that joystick, but lots of control valves have relief valves built into them. Not uncommon at all. It sounds like your MMM lift mechanism is binding. ....

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TomG
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2002-02-22          35794


I wonder how the MMM is hooked into the hydraulics. I don't know much about them, but I believe that some use the 3ph for lifting. It sounds like this one has it's own hydraulics, and it would be good to know how it's taped into the system. For example, does it have it's own SCV that runs off a loader SCV power beyond? Is the loader SCV a power beyond type, which would have one inlet and two return lines?

There are a number of possibilities, but more information would be good to help sort it out.

....

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Murf
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2002-02-22          35795


The screaming you refer to is actually the relief valve opening and closing at an exteremly high rate of speed, something it is NOT designed to do very often, or for very long. If it does this (or has done this) for long the valve will develop (or already has) an internal leak, since you say the MMM will not stay up I suspect this is the case. The diagnosis is a quick easy one, put a pressure gauge in the lift side of the system and lift the MMM to it's maximum hieght and try to keep going, if the gauge doesn't reach at least 1500 psi, or jumps erratically the valve is bad. The culprit is likely just a broken $0.05 spring. Unfortunately the valve needs to be overhauled now, which will cost a little more than $0.05, but not a lot, any hydraulic shop will do it for you. Best of luck. ....

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sbruse
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2002-02-22          35799


Thanks for your prompt replies guys. Unfortunately it will be about a week before I have a chance to work on it. I haven't looked at how it is tied in to the hydraulics, but it does run off of its own aux. hydraulics. I don't know much about hydraulics, though I'm sure I'll learn now. Murf, when you say the valve needs to be reconditioned, you mean the relief valve I assume. Is this a relief valve that is added when the aux. hydraulics were added, or does it come with the tractor hydraulic system? Basically, where is it and what does it look like? Thanks again for your help. I'll try to get out soon to look at the tractor and provide more detailed info, but the relief valve sure sounds like the place to start. ....

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Ted @ Abbeywoods Lan
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2002-02-22          35800


The FEL on your tractor is in fact made by Woods, that is a good thing. The loader control valve is made for Woods by Danfoss Hydraulics and is not re-buildable, it has an integral pressure relief vale. These valves have been a plague on an otherwise excellent tractor. If you remove the control lever knob, boot, and the sheet metal housing on the side closest to the hood, you'll find the adjuster for the relief valve. Remove the adjustment cap nut, look inside, you'll see an Allen hex head screw. Turn clockwise to increse relief pressure, counter-clockwise to reduce pressure. YOU MUST FOLLOW THE MANUFACTURER"S TEST PROCEDURE TO AVOID INJURY! I don't think this is the full fix, as was previously mentioned, you may also have a binding condition in the rock shaft assembly that lifts the mower, check for this before making any hydraulic adjustments. You will also find a pressure relief valve in the single lever valve that controls the mower lift cylinder. This valve is a royal pain to access without removing the inner fender and seat well sheet metal. Adjustment for this valve is the same as above, as it is for all of the Wood's implements sold for the CC line. For best results, use the pressure test valve as Murph described, your pressure should be 2100 psi, +/- 5 % at normal operating conditions with RPM at 2500. This test valve MUST BE connected on the line that flows from the main hydraulic block to the loader "in" port. Also reference your owner's manual to ensure that the hydraulic block diverter lever is in the proper position, locked with the cap screw, and not just loosely set in place. The cost for a new loader control valve is around $375.00. This job should take an experienced mechanic about three to four hours. Good luck. ....

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MarkS
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2002-02-22          35807


My experience with the CUbs 72" MMM was a very painful one. I didn't have the Aux hydraulics, mine was raised by the 3pt., but I do know the majority of the mechanisms are the same. If you plan on mowing aneven terrain much plan on purchasing tons of replacemt parts. The linkages were simply underdesigned. From doing some basic strass calculations it appeared to me CUB was only looking at Static loading on the linkage and not Dynamic. my 2c worth. I know it doesn't answer your hydraulic problem though. ....

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Murf
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2002-02-22          35808


I hate to contradict anyone, especially someone so obviously familiar with this product as Ted is, but, I have had many "Non-rebuildable" items rebuilt, and usually quite succesfully and affordably. That's why I suggested a good hydraulic shop. As an Engineer I can tell you ahydraulic valve is NOT complicated, it is a series of 'O' ringed pistons sliding in chambers which in turns routes fluid into different passages. The usual culprits in the case of failure are 'O' rings and springs. Neither are hard to get, expensive parts. Best of luck. ....

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Murf
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2002-02-22          35809


Oh, and I forgot, if the MMM is lowering it self the adjustment of the valve will do nothing to cure this problem. ....

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TomG
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2002-02-23          35820


I'm not sure debating hydraulic valve construction add much to fixing the sbruce's problem. It does help me learn about such things though.

As far as I know, some spooling valves have o-rings and are rebuildable to some extent. I believe other types have the spools lapped into the valve cylinders and donít use o-rings in these locations. If the problem is the spooling valves themselves, the ability to rebuild these type valves may be limited. I think that some types of relief valves use o-rings and others are ball check types. A ball check probably can't be rebuilt if the seat becomes worn from frequent rapid operations.

True enough, if a faulty check valve seat causes a leak down, adjusting the valve might fix it if it's an o-ring seal. However, increasing the spring pressure to seal a leaky valve also might create abnormally high relief pressures.

Guess what's right depends on construction of the particular valve, and that I don't know. Well, I think I got most of this stuff is right and somebody will tell me if I don't. Must have learned something along the way somehow.
....

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Ted @ Abbeywoods Lan
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2002-02-25          35862


Yes, to be sure many "non-rebuildable" components can be rebuilt as Murph has pointed out. Furthermore, being an engineer in the aerospace business for over twenty years I recognise Murph as one of this forum's most innovative contributors, so never worry about contradictions, Murph, that's how we (I) learn. In the case of this loader valve, if it is in fact this valve, the manufacturer has used the "en-bloc" method. That is one piece of metal, two spool bores in a solid body, with no replacement bore liner such as found on many of Prince's more expensive designs. The most frequent problem with this DanFoss valve is the piston scoring the soft(porous)bore when the "O" ring fails. An ambitious mechanic may want to try lapping the bore to remove the scoring, find an oversive "O" ring, and try it. But most just follow the factory's suggestion and replace the unit. Still, if one has the time and tools it may be worth the effort. I forgot to mention that a good Cub dealer can diagnose the entire system in about 3/4 hour, this will save a lot of guess work and is well worth the money. ....

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sbruse
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2002-02-25          35876


I appreciate all the advice I've been given, and I think I'll take Ted's advice to take it to the dealer. I tried
to figure out the hydraulic connections to provide more detail on this post and it was pretty much
overwhelmingly confusing. I don't understand hydraulics!! I do suspect that a bad loader relief valve is the
culprit though.
Here is what I do know---1. The loader relief valve screams when I raise the MMM and the 3-point, but
not the loader. 2. Leakdown occurs on the MMM only, and occurs much more slowly if I don't use the loader or 3-point. 3. I don't see any obvious signs of binding on the MMM, but something is not right with the
set up. The hydraulic hose that goes to the main lift cylinder on the MMM is what stops the MMM's
upward motion. The metal connector where it screws in near the lift cylider hits the underside of the
tractor if I raise the deck as high as possible. This can't be how it's designed, can it? Also, there is a
manual "arm" used to lock the MMM in a raised position, and I don't see how this works.
I think I'll let the mechanics diagnose it, and maybe they can give me a quick lesson
in hydraulics. Thanks again for the help.
....

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TomG
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2002-02-26          35884


Sbruce: There are some hydraulics primer type discussions here in the archives--mostly about open centered systems, which is almost certainly what you have. Pretty good discussions, but some of the reading is a little ponderous since I wrote a fair number of the comments.

I guess the problem was present when you got the tractor and there's not recourse to a dealer or warranty. It does sound like the installation may be wanting. Having it sorted out by a mechanic isn't a bad idea, but get back to the board if the results aren't satisfactory. We most likely can sort it out.

I'm guessing that Ted is a heavy contributor to this board back with a new name following the format changes etc: If so, good to see you around.
....

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Murf
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2002-02-26          35893


After reading over some of the new information that you have posted my suspicions about the problem have changed. If the loader vale screams when you raise the MMM then I'm going to say that it is more likely that there are some hydraulic lines connected wrong. It sounds a lot like the excess fluid from the MMM mechanism is being routed back into to loader valve instead of either a power-beyond circuit or the reservoir depending on how your system is setup. It is a simple diagnosis if you have the hydraulic schematics for all the components. Hydraulics (like electricity) are baffling to most people because they are things that you can't watch do their thing, so it's hard to comprehend them. think of it in this basic model, it might help. The fluid gets pumped into a maze, with many possible routes, when pressure finds it's way to a piston, it moves, period. The trick is in controlling the pistion's motion. This is done by opening and closing doors (valves) within the maze. Your problem sounds like a particular door leads to the wrong place, in other words, there is a line (or two) in the wrong spot. If two systems are related wrong your exact problem is a common result. There are few other explanations of your circumstances, especially your comment about the leak-down & squeal combination. I would try a hydraulic specialty shop first, dealers (the mechanics actually) don't see enough of hydraulics to get really good at it, besides, if they made the error in the first place it's unlikely they'll spot it later either, or not until the spend lots of time (and your money). Best of luck. ....

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sbruse
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2002-02-26          35897


After a little further inspection I need to clarify a few points. In my last post I said the hydraulic hose connection to the MMM lift cylinder was binding or hitting the metal above it when I raised the MMM deck. This is not true, I just didn't look at it carefully enough. The lift cylinder doesn't really move up and down with the deck, it is mounted to the tractor and is stationary. So, I see no obvious signs of binding on the deck as it rises.
Also, I looked at the leakdown a little more rigorously and discovered that if I raise the loader, 3-point, and MMM and shut the tractor off they all leak down at about the same rate (2-3 inches per hour, roughly). The MMM, if the tractor is running and I'm using the 3-point or loader, leaks down much faster than this.
Again, the loader relief valve does not blow when using the loader, but screams like crazy when using the MMM and screeches to a lesser extent when using the 3-point. I think I'll open look directly at this relief valve tomorrow and see if there is an obvious defect in the valve. ....

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TomG
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2002-02-27          35906


I seem to be in the buz of agreeing with Murf today. Hydraulics appears more complicated then they are. Getting a mechanic to sort out the problem probably would be good. However, I imagine you're asking questions here because you want to know how this stuff works. Persist with a little reading, and the basics can be gained without much difficulty.

I think the most important idea in hydraulics is that pumps don't develop pressure, they develop flow. Loads develop pressure. Relief valves provide protection against excess pressure due to excess loads. A screaming relief valve is a sign of excess load, and the fact it screams is a pretty good indication that it's working more or less OK. Tractors shouldn't be operated for prolonged periods with open relief valves, because it's an extra load on the engine and it also overheats the oil. An open relief valve when there is no apparent load usually is a sign of a line obstruction. Basically, loads only develop enough pressure to move a load, but an obstructed line is a load that doesn't move.

The basic idea of an open centred hydraulic system is that the pump flows oil continuously when no hydraulics are operated. Oil goes from the pump through the high pressure and return lines back to the sump. The only load is the line resistance and only low-pressure results. Operating a valve blocks the line and opens passages to a cylinder. Oil is diverted to a cylinder, and the pump develops enough pressure to move the load or to open the relief valve.

Another basic idea is that control valves are placed in the high-pressure line in series. Except for several complexities, operating one valve prevents a valve further down the line from developing pressure, because it doesn't get any flow--the line is blocked ahead of it. In many hook ups, loader valves and any other auxiliary system valves are ahead of the 3ph. Generally, operating a loader prevents the 3ph from simultaneously lifting.

There are some other complexities such as power-beyond valves, and the difference between double acting loader cylinders and a single acting cylinder that is probably on the MMM. But, the basic idea is that oil circulates continuously and it always must have a path back to the sump. In fact relief valves do just that--provide paths back to the sump during times of excessive loads.

Hope this helps some. Answers to a few specific questions about the plumbing are needed before much more can be said.
....

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nimscharrer
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2002-02-27          35932


I have had a similar problem with my 7260. The Loader raises and lowers just fine but when I add a grader blade the 3pt makes the same high pitched noise. However, in summer when the loader is removed, the 3pt handles a 6ft brush hog without any difficulty or strange noise. Could this be an overload valve problem ? Do the fixes mentioned also apply to this model of Cub. ....

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TomG
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2002-02-28          35941


I'm starting to wonder if Cubs might have some specialty hydraulics on them. I'm assuming that they are open centred systems with conventional control valves and hook ups. I'm also assuming that this noise is only heard when either the 3ph or loader is operated and not when everything is neutral.

I'm also wondering if there's certainty that the noise actually is a relief valve. Hydraulic systems working under high loads do make more noise than under light loads due to the higher pressures. A test might be to run the loader to the limit of its curl travel and hold the valve for a few seconds. A relief valve should be heard, and I wonder if that's the same sound mentioned? Power steering also makes a similar noise, but the source of the noise would be different than described and would occur only when steering.

Since I'm full of wonder today, I'll continue to wonder if this noise is heard while the 3ph and loader are being operated simultaneously, individually or both?

Generally speaking, the operation of a control valve or loads on cylinders does not affect other parts of the system, except that downstream valves are shut off by operation of upstream valves. Most SCV's as well as 3ph's have relief valves that protect cylinders and lines from load shocks while controls valve is centred. Without these valves the cylinders would be isolated from the rest of the system when their control valves are centred. As far as I know, some auxiliary SCV's also have system relief valves and some don't.

Anyway there are a bunch of things here that could be going on--all the way from normal operation to bad or misadjusted relief valves to incorrect hookups. I'm thinking that the possibilities need to be narrowed a bit. I'm also thinking that it would be a mistake to interpret my comments as coming from any particular expertise, but I do have to get these comments shorter.
....

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sbruse
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2002-02-28          35949


Well I finally did what Ted first suggested, which was to turn up the pressure on the Danfoss loader valve, and I think it fixed the problem. I increased it by about 125 psi and sure enough the squeal and leakdown are gone! All the hydraulics worked great, no problems that I can see. I am very happy that it worked and would like to thank everyone who gave me advice. Thanks to this forum I didn't pay the Cub Dealer $50 an hour (at who knows how many hours) to fix the problem. Again thank you. ....

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TomG
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2002-03-01          35960


Sbruce: That's a good result. I'm curious if the 125 extra pounds was measured by a gauge or estimated by the number of turns of an adjusting screw. It is possible to adjust a relief valve for too high a pressure, but 125 pounds should be within any safety margin. ....

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sbruse
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2002-03-01          35970


TomG-it was estimated by turning the screw, according to the numbers I was given by the Cub mechanic (75 lbs. per 1/4 turn). It does concern me to not know the actual psi in the line but I too assumed I was problably within the margin of safety. I hope I'm right. ....

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nimscharrer
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2002-03-01          35979


Tom G. THe noise I hear on my 7260 is only when the 3pt is raised and the FEL is on the tractor. The loader never makes the noise, just the 3pt. However, the 3pt is quiet when I have the brush hog hooked up(I leave the loader off of the tractor for cutting ) I double checked the hydraulic hook ups, they appear to be correct. Thanks for the info. ....

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TomG
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2002-03-02          35989


Nims: There should be a system relief valve somewhere on the tractor. On my 1710, it is in the hydraulic block on the lower side of the engine, but it could be located near the 3ph on some tractors. There also should be a relief valve in the 3ph that protects against load shocks when the hitch is in neutral.

Ordinarily the 3ph relief is set to considerably higher pressure than the system valve. So a relief squeal that is heard when the 3ph is lifting should be the system valve. When the lift and other hydraulics are in neutral, line pressures are around 100 lbs.. The system valve shouldn't be opening and the 3ph valve is isolated from the system. The 3ph valve may open due to a high 3ph load, but I doubt they squeal under those conditions.

One possibility here is that the relief squeal is heard only when the 3ph is fully raised. An out of adjustment hitch may not go out of lift mode at the top of its travel. In such a case the 3ph would remain in lift mode and the relief valve would open.
....

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nimscharrer
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2002-03-03          36024


Thanks for the info. From what you're saying, it looks like it is the system relief valve. The noise from raising the 3pt starts well before it reaches it's highest point. The relief valve is on the side of trator. I'll try some slight adjustments. Thanks again! ....

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TomG
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2002-03-04          36045


Nims: I still can't think through why a relief should open when the loader is on and not when it is off. However, there are some possibilities if the loader and 3ph are operated simultaneously and other possibilities if a loader valve with power beyond capabilities is used. I'll carry on with this type of thinking if you're interested. I might become more focussed and even succinct. ....

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Ted@Abbeywoods Lands
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2002-03-04          36062


Some footnotes regarding the CC 7000 line, including the 7260. All hydraulic attachments sold under the CC name have pressure relief valves, especially those made by Woods. The 7000 hydraulic system is an open center system; if any relief valve in the circuit is weak, the entire system suffers. If the loader's relief valve is weak, poor 3pt hitch cylinder operation usually shows up with the loader valve screeching- remove the loader, the 3pt will work fine. All of the cylinders, lines, and connectors are fully capable of two to three hundred psi over-pressure without failure, the danger comes when the implement's lift ability exceeds designed load specifications and exceeds the tractor's balance and steering capability. The 417 loader, with relief valve over adjusted to max, can lift just about a ton to near full height. THIS IS SUICIDE! Especially on a machine that is so light in weight, even with a counter balance. There is also a danger of twisting the loader frame, and if the upright (towers) aren't torqued properly, the loader will probably fall over to one side or the other wrecking a lot more than just the loader. The Mitsubishi engineers have worked out a system to keep the main pump charge from developing too much pressure. Under the cap of the main tractor hydraulic relief valve is a space for adding shims. Shimming this valve only raises the maximum pressure available to any component by (off the top of my head, didn't look at spec.'s lately) 25psi per shim. Each little shim costs a fortune, and with the maximum allowed shims you won't get the entire system much over 100 to 125psi. Even so, add this to a maxed out relief valve and some very serious accidents could happen faster than anyone might predict. Never exceed the design spec.'s unless you have a death wish. ....

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Murf
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2002-03-04          36065


As a follw up to Ted's excellent comments. Most people forget one small but undeniably important factor about compacts with loaders. Unlike skidsteers, the front axle on a compact pivots in the center to allow it to follow uneven terrain without flexing the chassis, creating undue stress on the machine. When raising the loader it goes up 90 degrees (side to side) to the surface on which the machine is setting. If that is a 10 degree side slope then the loader goes up at 80 degrees to the pull of gravity, when the load exceeds the C. of G. (center of gravity) the front axle will pivot and the machine will fall over, PERIOD. Best of luck. ....

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TomG
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2002-03-05          36093


Yes, pretty good comments here. Iím thankful for comments from Ted and Murf. A couple of things I'm not clear about though. I thought the relief sound was coming from the 3ph area rather than the loader valve. I'm also not clear if the loader valve remains in place when the loader is removed.

A nice simple explanation would be that the loader SCV has a relief valve that the high pressure line sees and that valve is set lower than the tractor's system relief pressure. In that case as Ted noted, high load on the 3ph during lift would create high pressure. Both the loader and system valves would see the pressure and the one with the lowest pressure setting would open. The condition would only happen during 3ph lifts of heavy loads when the loader valve is in the system and the diveter valve in the auxiliary system position. The high-pressure line should see an open centre pressure around 100 lbs. when the 3ph is in neutral or lower irrespective of weight on the hitch.

The description is still a mystery to me if the relief sound comes from the 3ph area. If the above condition is the case, a simple fix might be to reason that the system valve is set correctly and the loader valve is low. With a heavy load on the 3ph, the loader SCV relief valve setting could be increased until the system relief opens rather than the loader relief. In this type hookup, a relief in the loader SCV would be redundant. At least I think that would be a fairly safe approach.
....

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PJDrew
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2002-03-06          36149


I saw this thread after everything appears fixed, but it would appear you need the service manual on your tractor. I have a 7275 and when I bought it it had no manuals. Owners manual was 8.00 and Factory Service manual(its huge and covers everything) was only 30.00. I was frankly shocked how cheap these were through my IH dealer. I'd highly reccomend you get them, should help you with alot of questions. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-03-07          36158


Yes, the owner's manual gets me by for servicing routines. For everything else, I find myself looking in the repair manual. It was a good investment.

After several years of going cross-eyed looking at repair manual diagrams, I recently got a parts manual. They are even bigger, cover more tractors and cost a bunch more. It's a good investment too. The manual will solve a couple of problems I had receiving wrong minor parts when ordering by phone. Ordinarily I don't actually need parts numbers because the dealer can look them up. I really got the parts manual for its detailed exploded diagrams. You can really see how things are put together; right down to the last washer and widget. ....

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section8
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2002-03-08          36198


In Nov of 2001 I added a 417 loader to my 1996 cub 7275.
There was squealing whenever I dumped a load or lowered the lift arms (with or without a load). If left in a mid level raised position the bucket would be on the ground in about 35 minutes. This was unacceptable to me. The dealer came out two times to replace this that and the other thing but still the problem remained. I told him I wanted some other solution to be attempted before the one year warrenty ran out. Finally in Jan of 2002 Cub authorized a replacement. He replaced the "cub" control valve with a Woods control valve. What a difference. No squealing whatsoever and if I leave it in a mid level position it dosent move a millimeter (at least in two days). It just feels sturdier and better constructed. Its too bad they just dont use these on all their loaders. It would certainly eliminate a lot of problems and dis satisfaction. ....

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jfortune06
Join Date: Feb 2016
Posts: 10 Texas
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2016-02-16          194538


I have a cub 7300 with this exact issue as well. I did adjust the relief valve in the loader control block just enough to stop the squealing when using the 3 point lift. I didn't have a gauge to measure the pressure but will do this later before using the loader for anything heavy. One thing I don't get is, why does the 3 point lift seem to put so much pressure on the system when lifting almost no weight. I currently only have a trailer mover on there which weighs maybe 50 lbs. It seems that the pressure increases greatly the closer to the top that the lift gets. Is this normal? I can see the loader hydraulic lines tighten up every time I lift the 3 point. ....

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